Repainting of Aircraft and Components

>> Friday, October 1, 2010

The purpose of this process specification is to provide a standard procedure for the repainting of aircraft and components.

This specification describes the requirements and procedures for the repainting of aircraft exterior, interior and components including cowlings, thrust reversers, wheels and brakes etc. The processes apply to primarily for aircraft with notes added for components where necessary.

a. CAA CAIP Part 2 Leaflet 2-7.
b. FAA AC65-15A Chapter 4
c. Airworthiness Notice No. 82.
d. Applicable Boeing Material Specifications.
e. Paint manufacturers’ Instructions, Processes and Standards
f. Component CMM/OHM.
g. Applicable aircraft exterior markings and colour scheme drawings.

Paints and chemicals listed in Appendix A are for reference; and are not exhaustive. Equivalent products may be used based on the specifications where stated since there are many such products in the market. Obtain the product technical data sheet for guidance prior to using it. Consult Technical Services as needed.


a) Carry out all work in adequately ventilated area.

b) Spray paint personnel MUST wear suitable respirators containing filter cartridges for organic vapours when applying epoxy and polyurethane finishes to prevent inhaling spray vapours. Wear rubber gloves, hoods and coveralls so that these materials do not come in contact with exposed skin

c) Where air circulation is insufficient, an air-supplied respirator is required.

d) Observe manufacturer’s safety instructions and precautions at all times.
Avoid prolonged or repeated contact of solvents or conversion coating material with skin. Use gloves, goggles and overalls to prevent contact with stripping material solvents or conversion coating materials.
Note: Do not allow paint stripper to contact skin.

e) Wash body skin or clothing with copious amount of water immediately after contact with any solvent, paint stripper or conversion coating material.

f) Should liquid curing solution or chemicals contacts the skin or eyes, wash skin with soap and water; flush eyes with large amounts of water and seek medical attention immediately.

g) Polyurethane and epoxy coatings are flammable materials, observe fire safety precautions at all times.

h) Ensure aircraft being painted is electrically grounded.


a) Water-Break-Free.
A water-break-free surface is one which maintain a continuous water film for a period of at least 30 seconds after having been sprayed or immersion rinsed in clean water at a temperature below 100ºF (38ºC).

b) A properly cleaned surface is essential to achieve a paint system of a high quality and a long lifetime. When a surface is not cleaned well, problems can occur, include adhesion problems, blisters and pinholes.
- Use clean lint-free cleaning cloths.
- Clean the surface using the “wipe-on-wipe-off” method (use two cloths, one soaked in cleaner to wipe on and the other, a clean, dry cloth to wipe off immediately)
- Do not let the cleaner dry on the substrate.
- Do not touch the degreased surfaces prior to painting (clean the aircraft as the last activity, after masking).
- Thoroughly check the surface for any faults after degreasing.
- Final clean just before painting.

c) Paintshop foreman is to ensure that painting task carried out is adequately defined by technical documents, drawings, data sheets, etc including PS003. Contact Technical Services if information is insufficient.

d) Painter shop foreman is to notify Planning and Maintenance of repainting schedules to plan any structural inspections scheduled including non-destructive inspections that could be better accomplished following paint removal.

e) All painted surface are to be tested/inspected as per para 18.
f) Any stencils/decals can be applied on painted surface after paint adhesion satisfies tape test per para 18.


a) Paints should be mixed, thinned and applied as required in accordance with manufacturers’ data sheets. Do not exceed dry film thickness recommended for best results.

b) Stirring of paints
Where a skin has formed in the paint, it should be removed before stirring. A flat-bladed non-ferrous stirrer should be used.

c) Mixing of paints
Before mixing, check to confirm the right products (base, hardener, and thinner) and that there is enough of each product available to complete the painting procedure. Check data sheet for the correct amount of hardener and thinner to be used.

d) Thinning of paints
The necessary degree of thinning depends on the type of spray equipment
- air pressure
- atmospheric conditions
- kind of paint

The viscosity range or thinning ratio is indicated on the data sheet of each product. Accurate thinning is important for optimum viscosity for best results. Use the correct viscosity cup to check the viscosity as needed.
Note; for tropical conditions, adjust to lower end of viscosity.

e) Straining of paints
All materials should be strained before use. Metal gauze (60 mesh) muslin or three layers of cheese cloth are suitable strainers.

f) Paint must be stored under the right conditions to guarantee the quality. Store the paint in the original unopened containers at a temperature between 5C and 25C. Before using the paint, it must be at the same temperature as the ambient.

g) Paint should be stirred, thinned and strained just before use. The lids of all containers should be wiped clean before opening. Containers should not be left open longer than absolutely necessary, otherwise excessive solvent losses will occur and hardeners may be affected by moisture.


a) Masking is to protect various areas from chemicals e.g. stripper and paint including over-spray. Adequate masking is a must around all openings that could admit paints and chemicals e.g. doors, seams, wheel wells.

b) Use aluminium tape to protect specific areas and seams from paint-stripper.

c) Use masking tape to mask paper (tape is not waterproof).

d) Use cello-tape to line out cheat lines and decorative lines.

e) Use kraft paper to protect large areas from over-spray during painting.

f) Use plastic coated paper or impregnated paper to protect from water and chemicals.

g) Use plastic sheet during stripping and spraying in order to mask bulk areas to avoid overspray but ensure that freshly painted surfaces are fully cured before draping with plastic (polythene). This is to avoid locking in of solvent vapour.

Note: Do not use plastic sheets along the border of area to be painted. This is to avoid dust in the wet paint caused by electrostatic charge of plastic sheets.

Keep the application and mixing equipment clean with solvent cleaner e.g C28/15 to avoid clogging of spray nozzle and depositing of foreign material on the coating surface.

If possible, air used for spray gun operation should be from a separate supply. If taken from a general supply line, install sufficient regulators and manifold to buffer abrupt changes or surges in the air pressure. Install sufficient oil and moisture separators in the air system and blow down the air hose at least twice daily (when in use).


a) If any flight control surface requires repainting LAE should determine if balancing is involved prior to painting. Such surfaces should be removed from the aircraft to allow re-balancing unless SRM permits re-balancing through calculation.

b) Typically flight control surfaces should be stripped of paint chemically (unless fiberglass/graphite/kevlar composite is involved) or mechanically. LAE is to ensure flight control surface is rebalanced per SRM requirement prior to reinstallation per applicable MM after repainting.

c) LAE is to note down the balancing data prior to repainting.

d) LAE is to coordinate with Technical Services to determine the basic weight and corresponding center of gravity position for flight controls as needed. See also Para 19

e) Fibreglass and graphite/kevlar composite surfaces are to be sanded down using grit 400 or finer abrasive paper or very fine Scotch Brite Pads to remove paint coating.

Note: Do not use paint stripper on fiberglass/graphite/kevlar surface or fiberglass repair patches on aluminum skinned composites

This paragraph applies also to repainting of aircraft components.

a. Ensure aircraft is located in a hangar that is relatively dust free. Electrically ground aircraft per applicable Maintenance Manual.

b. For components, ensure that parts are in relatively dust free area.

c. Spot check the adhesion of the paint as necessary with pressure sensitive adhesive tape 3M 600 or equivalent as per para 18. If the paint comes away with the tape, paint removal is recommended - proceed with para 10 or 13 as applicable. Otherwise go to para 9.
Note: Check at sufficient locations to confirm satisfactory adhesion.

d. Use appropriate tools to remove existing sealant and decals on the surface to avoid scribe marks/lines, particularly on aircraft fuselage lap and circumferential joints. Putty knives, razor blades or any sharp tools are prohibited to be used for sealant and decal removal. Refer to SB 737-53A1262 and AWC ref AWC/Boeing737/001(03) dated 6th May 2003


a. Remove any chipped paint around joints and fastener heads. Use aluminum oxide paper grade 280 or finer to feather edges.
Smooth out areas of built-up paint using aluminum oxide paper grade 280 or finer.
Note: Ensure all traces of cleaner are removed by flooding with water and scrubbing with Scotch Brite Pad.

b. Continue scrubbing until a water-break-free surface is attained.


a) When oil stains or other contaminants cannot be removed by the above means, use a clean cloth moistened with MEK or equivalent to wipe affected surface. Wipe area dry immediately with dry clean cloth.

b) Do not apply excessive amount of MEK which will soften the paint film. If a clean water break free surface cannot be obtained, the paint must be stripped as per para 10 or 13.

c. Allow treated area to dry for about two hours. Ensure no water is trapped at joints, seams, opening etc.

d. Mask as required using masking tape and kraft paper or plastic sheet.
Note: Where masking tape was used on areas to be subsequently painted, ensure all traces of tape adhesive are removed. A clean cloth moistened with MEK may be used. Do not allow any MEK to remain on the surface. Immediately wipe off with clean dry cloth.

e. Proceed to Para 14.


Note: Do not use paint stripper to remove paint on composite materials, fiberglass panels and fiberglass repair patches on aluminum skinned composites.
Use only Environmentally Friendly (EA) paint strippers that do not contain phenolics so as to allow easy disposal.

For aircraft this must be carried out meticulously to avoid stripper affecting certain material adversely; and stripper getting into crevices and gaps. For components mask areas that are not to be paint-stripped or where it is not desirable for strippers to be trapped.

a. Cabin and Cockpit Windows including window on Doors
Refer to para 10.2.

b Radome & De-icing Boot
Cover all exposed areas if radome and deicer boots if any are removed.

c Door and Openings
Cover all doors gaps and openings with tapes.

Vertical Fin
Cover exposed areas if rudder is removed. Cover fiberglass/composite panels and access openings.

d Wing & Horizontal Stabilizers
Cover wing-to-fuselage fairings and/or areas covered by these fairings; or cover areas exposed if such fairings are removed. Cover also between fuselage and horizontal stabilizer and fuselage-to-horizontal stabilizer attachment areas.

e Fuselage
Mask all cavities, sealed joints and static and pitot points.

f Landing Gear
Mask landing gear with aluminized kraft paper or plastic sheet and tape.

g Ground Support Equipment
Mask all ground support equipment in close proximity and likely to be affected by paint stripper with double layer aluminized paper and tape.

h Plastic or Fibreglass Structures (Including Composite Material)
Cover these surfaces if not removed from aircraft.

Majority of these windows are made from perspex and will be adversely affected by chemical stripper. Proper masking is therefore critical.

a. Cover all windows surface with aluminized kraft paper or plastic sheet and aluminum tape around the window gaps between fuselage skin and window frame with aluminum tape.

Note: Ensure aluminized kraft paper or plastic sheet is firmly pressed onto the base material by rubbing firmly with a rubber roller over the tape.

b. Cover window with a second layer of larger aluminized kraft paper or plastic sheet and aluminum tape. Ensure that the aluminized kraft paper or plastic sheet overlap is at least 1” over the first layer of aluminum tape before the second layer aluminum tape is applied.

c. Apply third protective screen over all passenger and cockpit windows using curtain of aluminized kraft paper or plastic sheet. This third protective screen is to span lengthwise the fuselage. Overlap where applicable.

Note: Ensure aluminized kraft paper or plastic sheet covers at least two inches above and below the windows.


a. Preparation
Washing is generally not required except for oily or greasy areas; but it is recommended so that all oils are removed to hasten the action of stripper.
Surfaces to be stripped must be dry and the temperature should be between 15 and 35C. Stripping should not be done in hot sun or rain.
The stripper should be thoroughly mixed in its container before use and it is advisable to keep the container closed when not in use. Keep paint strippers away from heat and sun and take care when opening a container (pressure).

b. Equipment for stripping aircraft
Pump: Use a standard 5:1 or 10:1 stainless steel barrel pump with teflon packing.
Use a stainless steel/teflon hose, fitted with a spray gun and swivel, stainless steel spray wand, and a non atomizing tip.
Test assembled equipment to ensure good working order, with no leaks.
Bristle brushes, squeegees, Scotch-Bright pads etc., normally used in stripping operations can be used with paint strippers.

c. Equipment for stripping components
same as (b) above except the pump.


a. Apply a full coat of paint stripper to the surface to be stripped, working from the bottom up and front to back for the fuselage.
If slippage occurs: apply a mist coat of paint stripper to the surface experiencing adhesion problems, let stand 10-15 minutes and re-apply a full coat.

b. Effect of temperature:
EA Paint Strippers are sensitive to temperature. For best results, the ambient temperature, the surface temperature of the aircraft, must be above 20° C, ideally 30° C rises in temperature are preferred. A 10° C rise in temperature will usually halve the stripping time.

c. Dwell time:
Depending on the stripper being used, paint system, film thickness, age of paint system, original surface treatment, temperature; recommended dwell time will vary from one to four hours. Do not agitate the stripper during dwelling. Do not allow the stripper to dry on the surface. Usually the paint will blister when loosened. Some paints do not blister and should be tested for looseness by scraping very gently with wooden or plastic scrapers. The stripper should be removed from the aircraft when it appears to dry or beads of water appear on the surface in large numbers.

a) Complete stripping of primer is not required provided remaining primer adhesion to metal can withstand scratching or pass the adhesion test per Para. 18.

b) If primer removal is required or if primer sticks stubbornly re-apply stripper and agitate such areas with white Scotch Brite Pads.

c) Never use steel wool or a steel brush or steel scrapers as tiny bits of steel will become embedded in the aluminium and this leads to corrosion.

d. Remove as much as possible stripper and loose paint residue using non-metallic scrappers and rags. Thoroughly rinse the reworked area with pressurized water hose and scrub. Use nylon brushes with white Scotch Brite Pads to remove residue.

e. For components, spray application may not be necessary but can also be used. Brush application of stripper can be used as alternative.


a. Agitate a workable area with a stiff polypropylene brush.
b. Squeegee off all loosened paint.
c. If stripping is not complete, re-apply stripper as necessary per para.

d. Hand work with Scotch Brite Pads to remove any residue.
Note: TURCO5948-DPM Cleaner can be used to help lubricate the surface for the Scotch Brite Pads.


a. To remove any remaining paint and/or paint stripper residues, thoroughly wash the entire aircraft or components with a 25% (vol) solution of TURCO 5948-DPM or equivalent, bottom to top, front to back for fuselage.

b. Rinse thoroughly with water, bottom to top and top to bottom, front to back.

c. Inspect bare surfaces for corrosion and other defects.

Note: for components, usually the entire components can be spray rinsed at one go.


a. Chemicals
Prepare the TURCO 5948-DPM solution by mixing 1 part TURCO 5948-DPM with 3 parts potable water (a 25% by volume solution)

b. Equipment
Same as 10.3 b


a. Apply the TURCO 5948-DPM solution from the keel of the aircraft upward to the top of the aircraft in approximately 20 feet long sections. The length of the section should be expanded or shortened based on manpower and equipment available.

b. After the TURCO 5948-DPM is allowed to dwell for a few minutes, use Scotch Brite Pads to thoroughly agitate, bottom to top, front to back for the fuselage, making sure that the entire surface is completely scrubbed.

c. As one section is being agitated, the TURCO 5948-DPM solution should be applied to the next section.

d. Once a section has been agitated, it should be thoroughly rinsed with high pressure, high volume water (warm is better than cold). The rinsing should begin at the bottom of the aircraft section and work up to the top, then back down again, repeating this sequence until all cleaner is rinsed from the surface. Pay particular attention to seams, door opening, etc., that could trap stripper residue.

e. While one section is being rinsed, the next section should be agitated.

f. This process should continue until the entire aircraft fuselage has been thoroughly cleaned and is water break-free.

Note: For components, spray application as above is usually not necessary. Brush apply TURCO 5948-DPM, agitate with white scotchbrite pads as necessary followed by thorough rinsing with water.

This step is optional, and may be omitted for aircraft. It is not necessary for components.

a. Chemicals
Prepare the TURCO METAL-GLO #6 solution by mixing 1 part TURCO METAL GLO #6 with up to 1 part potable water (a 50% by volume solution)

All High strength steel parts or fittings should be masked off with polyethylene sheeting or other water and acid resistant material using water proof tape.

b. Equipment
Same as 10.3 b


a. To help eliminate any tendency to splotch the surface, wet the aircraft surface with water prior to the application of the TURCO METAL GLO #6 etchant. Apply the TURCO METAL GLO #6 solution from the keel line upward to the top of the aircraft in approximately 20 feet long sections. The length of the section should be expanded or compressed depending on manpower and equipment available.

b. After the TURCO METAL GLO #6 has been allowed to dwell for 10-20 minutes, using Scotch Brite Pads, thoroughly agitate, bottom to top, front to back for fuselage, making sure the entire surface is completely scrubbed.

c. As a section has being scrubbed, the TURCO METAL GLO #6 solution should be applied to the next section.

d. Once the first section is agitated, it should be thoroughly rinsed with high pressure, high volume water (warm is better than cold). The rinsing should begin at the bottom of the aircraft section and work up to the top, then down again. Continue this rinsing pattern until the water sheets from the aircraft in a smooth, bubble free film. Pay particular attention to seams, door openings, etc., that could trap etchant residue. It is extremely important to follow this rinsing procedure – bottom to top – to avoid streaking the aircraft.

e. While one section is being rinsed, the next section should be agitated.

f. This procedure should continue in a smoothly flowing operation until the entire aircraft has been thoroughly etched and the aircraft has been thoroughly etched and the aircraft surface is completely water break-free.

LAE is to inspect for corrosion and for damaged sealant. Replace sealant as required. Inspect lap joints for scribe line damage per relevant documents.
Note: Inform Technical Services of any major corrosion findings.

Clean bare aluminum surface with 1:1 MEK/toluene mixture or equivalent, and check for water break-free. It may also be carried out for painted surfaces that have been rubbed down as necessary.


a) Apply chromate conversion coating Alodine 1200 or 1000 per SRM/MM 51 instructions to produce a coating that meets SRM/MM requirements.

b) Ensure water break free surface during rinsing after the alodine treatment.

c) Allow aircraft/component surface to dry. Wipe and blow seams/lap joints dry to help minimize entrapment of moisture and other contaminants in seams and lap joints.

d) Wipe all surfaces with Cleaner C28/15 or other approved solvent cleaner and clean with two rags, one wet/one dry (“wipe on/wipe off” method). Change often to avoid contamination.

e) Tack with tack cloth before primer application. It is now ready for primer application.

f) Remove all contaminated masking from the aircraft and clean the surrounding environment.

Note: The degreased surface should not be touched with bare hands (wear gloves) and should be protected from any contamination before paint application.
If surface has been allowed to collect dust or other contaminants, wipe with MEK or toluene or other suitable cleaning solvent using low lint cloth or rumple cloth.

g) If the time between cleaning and primer application exceeds 12 hours, solvent clean the aircraft/component surface using a blend of MEK and Toluene or other suitable cleaning solvent. Use clean low lint cotton cloth. Cloth should not be dipped into solvent cans as this will contaminate the clean solvent.
Either pour solvent onto the rag or, using an atomizing spray bottle, spray solvent directly onto the surface and wipe dry. Change cloth frequently.


a) Wash surface with an alkaline cleaner mixed as specified by the manufacturer.

b) Sand (rub down) painted surface per 13.1.

c) Sand areas that cannot be chemically stripped (i.e. composite areas); and also during paint rework (i.e. removing runs, orange peel, dust etc) or when the maximum re-coatable time has elapsed.

Note: Before sanding, the surface must be free of grease and other contaminants to avoid grease being sanded into the surface, which will cause bonding problems.


a. Always wear mask, gloves and goggles during sanding.

b. Electrically ground the surface before sanding to avoid frictional (static) electricity.

c. Use the right type of sandpaper for every paint system. The product to be applied determines the sanding grades to be used.

d. Decide on the successive sanding steps for each paint system remembering not to jump any more than 100 points finer at any time. i.e. from P.180 the finest you could go would be P.280 if you wanted to finish with P. 320. This is to avoid sanding marks in the topcoat.

e. When sanding with a sanding machine, avoid mushroom head rivets, seams and tapes or decals. These areas must be treated by hand, preferably using a Scotch Brite pad Type A (or very fine).

f. When sanding old paint systems, sand to the primer to avoid a building-up of too many layers. Too thick paint systems tend to lose their elasticity after a while, which lead to cracking and peeling-off.

g. With wet sanding (optional) the area has to be kept wet with water and sponge. Change the sanding water regularly. After wet sanding rinse the area thoroughly with clean water and dry off.

a. After wet sanding, ensure the surface is dry before painting. Wait at least 14 hours and use compressed air to remove water from seams and rivets (remove dirty kraft paper or plastic sheet and clean the areas before painting) and use tack-rags to remove the dust from the surfaces

After sanding, the areas and surfaces must be cleaned thoroughly to remove the sanding dust. Use compressed air for seams and other parts where dust can settle. Remove dirty kraft paper or plastic sheet and use tackrags on the surface.

a Remove mechanically the oxide film on paint surface all over and “key” the paint surface using aluminum oxide paper grade 280 or finer.

b Clean the surface using white Scotch Brite Pads and water to remove dust and all contaminants.

c Alkaline clean per Para 11 on reworked surfaces and rinse with water. Ensure water-break free surface. Follow para 12 drying and solvent cleaning method prior to paint application.



a) Conventional air spray
Atomizing air pressure: 60 to 70 psi
Pot pressure (if applicable): 5 to 20 psi

b) Air assist air-less electrostatic spray equipment
Fluid pressure: 850 - 1,000 psi
Atomizing air pressure: 65 – 75 psi
Tip size: 0.013 inches (0.33mm) or smaller, preferably .011 inch (0.28mm)

c) High pressure air-assist airless electrostatic spray equipment.
Fluid pressure: 2200 – 2500 psi
Atomizing air pressure: 60 – 75 psi
Tip size: 0.009 – 0.013 inch (0.23 – 0.28mm)

Observe General Notes.
Ensure surface is properly prepared and meets water break free test, fully dried and final tack solvent cleaned prior to painting. Apply one cross coat of primer.
Typical dry film thickness: 0.0005” to 0.0008”

Drying time: Re-coatable 1 hour (typical, see data sheet)
Dry to tape 4 hours. (typical, see data sheet)

After paint has dried check paint adhesion as per para 18.



As per para 14.1


Note: Observe General Notes.
Topcoat must be applied within 48 hours of primer application. If 48 hours is exceeded sanding of primer with scotchbrite pad (white) is necessary.
Apply one cross coat, or two coats of topcoat as required to achieve the desired finish.

Drying Time: Re-coatable 1 hour (typical, see data sheet)
Dry to tape 4 hours (typical, see data sheet)

After paint has dried check paint adhesion as per para 18.

Topcoat must be treated with Aerodur Clearcoat UVR within 4 to 48 hours of topcoat drying if Clearcoat is called out in the drawing.
Apply two cross coats of Aerodur Clearcoat UVR over the topcoat.
Drying Time: Dry to tape 10 to 12 hours.
After paint has dried check paint adhesion as per para 18.


a) In-process defects such as overspray, orange-peel, runs or sags occurring in the primers or in the topcoat which are considered excessive may be reworked by dry sanding with 240 grit or finer abrasive paper followed by wet or dry sanding with 380 - 400 grit or finer abrasive paper. (See para 13)

b) Sanding should not be attempted until the coating being reworked is sufficiently dry to permit sanding. This may take up to 8 hours depending on the weather.

c) After the sanding is completed, the surface has to be cleaned to remove the sanding dust. Use a cloth moistened with solvent cleaner and re-apply primer or topcoat, as required.

d) For some in-process defects such as overspray, runs or sags in finishing coats, it is possible to polish them away. Do not use ammonia-based polishes. Ammonia will destroy the gloss of most aircraft finishes. Only on high-gloss finishes, sags and runs can be removed by wet flatting with 1200 grit wet and dry paper and using clean water and soap. Use a non-ammonia polish with a fine cutting compound to remove the flatting scratches and a final cream polish to revitalize the gloss of the required area.

e) This operation can be done either by hand or polishing machine. When using a machine, a sponge head should be dampened down with water before applying the polish. This decreases the “burning” of painted surface.


Note: Tape adhesion test is to be carried after paint is fully dry. Refer to manufacturer data of specific paints used for “dry to tape” time.

a. Apply 1 inch wide 3M 600 Transparent Film Tape or equivalent to painted surface 1.5 inches long. Repeat this test with fresh tape on at least 3 locations some distances apart.

Note: Shelf life of tapes shall not be more than 6 months old from date of manufacture or as per manufacturer’s shelf life. Storage conditions at 70°F (21°C) and 40-50% relative humidity is recommended.

b. Press tape down firmly (5 pound minimum pressure)

c. Remove the tape within 5 minutes in one abrupt motion perpendicular to the paint surface.

d. Examine area for paint coating failure. Check tape for coating separation.

e. If there is an evidence of paint coating separation, determine extent of defective area and repeat para 8 when necessary.
This must be thoroughly carried out for all large surfaces to be repainted to ensure good paint adhesion. Utmost care is to be exercised not to contaminate areas and tested to be water-break-free.


a Inspect painted surface visually to confirm no defects e.g. orange peel, runs, sags, contamination

b Ensure all mandatory and maintenance markings are re-installed correctly.

c Painter and LAE are to inspect for any damages to transparencies, composites and sealants by solvent and paint removers due to inadequate protection and/or the retention of these products in crevices


Design Organization Approval (DOA)

>> Saturday, August 14, 2010

Design Organization Approval (DOA)

Part 1 – Obligation to the international requirements to ensure aviation safety


2) MCAR Regulation 27 - A certificate of airworthiness issued in respect of an aircraft shall cease to be in force if the aircraft, or such of its equipment as is necessary for the airworthiness of the aircraft, is overhauled, repaired or modified, or if any part of the aircraft or of such equipment is removed or is replaced otherwise than in a manner and with material of a type approved by the Director General either generally or in relation to a class of aircraft or to the particular aircraft.

Part 2 – Design Approval

1) Modification and Repair per ICAO Document 9760




• CAR 1996 Regulation 27 para 7 stated aircraft C of A become invalid, if the design change does not comply with the required airworthiness requirements.

2) Design Organization Approval (DOA)

• The local authority i.e. DCA / DGCA is not a Design Organization. Therefore DCA / DGCA cannot accept responsibility for the design.

• DOA is approval for an organization to provide reports and certify that the design of an acft, equipment or any part thereof or modification or repair schemes complies with DCA / DGCA requirements.

• JAR/EASA 21 – SUBPART J (DESIGN ORGANIZATIONS APPROVAL). The principles of both JAR/EASA and BCAR are similar. However, JAR/EASA has been developed more comprehensive than BCAR, i.e. Design Assurance System has been introduced in JAR/EASA.

• Benefit being approved as DOA is being granted privileges with responsibilities and may perform certification and airworthiness activities on behalf of DCA through the following granted privileges:

- Release certification documents without verification by DCA / DGCA
- Classify modifications and repairs
- Approve minor modifications and repairs
- DOA may issue information or instructions stating that the technical content is approved.
- For Modifications undertaken by organisations that are appropriately approved for the task and who have demonstrated a consistent and satisfactory level of competence for the type of work involved, then future similar Modifications may be classified as Minor by the DCA / DGCA.
- Efficient use of industry and DCA / DGCA time, resulting in lower costs.

• DOA shall be headed by an Accountable Manager (Chief Executive or Equivalent) and with full efficient coordination between their units/sections.

• Scope of work – The organization must have
– sufficient personnel with the right qualification, knowledge and experience.
– appropriate tools (Software), equipments (computer) and facility (i.e. office space, lab, flight test center)

3) Design Organization Manual (DOM)

• Policy/procedure of carrying out design activities and management of DOA
- Classification of Major/Minor
- Development of reports/drawings/Test Schedule
- Verification of Design Data
- Inservice difficulty reporting
- Correction action
- Internal Audit
- Retention of designs records
- Design Assurance systems (DAS)

4) Design Assurance System (DAS)

• A DOA shall demonstrate that it has established and is able to maintain a Design Assurance System (DAS) for the control and supervision of the design, and of design changes, of products, parts and appliances covered by the approval.

• The DAS shall be such as to enable the organization;
- To ensure the design of the products, parts and appliances or the design changes thereof, comply with the applicable type certification basis.
- Ensure that its responsibilities are properly discharged.
- Independently monitor the compliance with, and adequacy of, the documented procedures of the system (DOM). The monitoring shall include a feed back system to a person having the responsibilities to ensure corrective actions.

• DAS shall include an independent checking function of the showing of compliance on the basis of which the organization submits compliance statement and associated document to DCA / DGCA.

Part 3 – Certification of Modification/Repair

1) A modification or repair must meet two standards; the acft type certification rules and the performance rules.

2) Data Package is a set of documents required for the justification / accomplishment of the modification such as:

• Standard documents; i.e. Certification plan (for complex modification), Modification documents, SOC, CCD (if applicable) and Manuals amendments (if applicable)

• Type Design documents ; i.e. Drawings, Specifications, Information on dimensions, materials and processes, Airworthiness limitations and any other data necessary to describe the modification.

• Substantiating data; i.e. Test and analysis reports and Justification reports

3) Approved Data is a data which has been investigated and approved by an acceptable authority such as FAA, JAA and UK CAA and divided into two categories:- OEM data and Non OEM data.

• The data packages are only considered as an approved data provided the limitations, including applicability of an approved data are met.

4) FAA Form 8110-3 approved by FAA Designated Engineering Representatives (DER) i.e. OEM DER is accepted as approved data but require DCA installation approval. Consultants DER require review because it has similar status as the Non-OEM STCs.

5) Statement of Compliance (SOC) is a form used as the top-level document for the data package. SOC form shall be signed by a Design Approval signatory or authorized person.



>> Tuesday, June 15, 2010


This programme monitors aircraft delays, cancellations and significant events; giving alerts when adverse trends are identified. 



The Dispatch Reliability programme is meant to
a)      Provide performance measurement and monitoring for dispatch reliability and cancellations for the use of management.
b)Allow analysis of trends to identify and investigate technical problems for solutions.
c)      Permit analysis to spot problematic aircraft systems or components.
d)      Identify areas that require investigation and/or improvements in aircraft maintenance efficiency or effectiveness.
e)      Record significant events and their basic causes for preventive action, and for future reference.
Overall objective is to reduce delays, cancellations, and major disruptions caused by aircraft defects thereby reducing costs and improving customer service.  It helps the identification and elimination of deficiencies affecting aircraft operations. 



a)      Only delays, cancellations and significant events related to aircraft mechanical defects or failures shall be included for this programme.
b)      All revenue departures (at main base and line stations) which are delayed based on Scheduled Time of Departure (STD) arising from mechanical defects shall be captured.  Only delays exceeding 15 min. shall be counted for performance statistics.
c)      A revenue flight cancellation is considered as a delay.
d)      Significant events shall also be captured as part of this programme.  They
1.       Normally have significant impact to customer service e.g. prolonged AOG, unscheduled engine change, in flight shutdown, ground incidents;
2.       include events that require mandatory reporting by local authority e.g. In flight engine shutdown (IFSD), aborted take-off (ATO), excursion from runway, etc.  Particular attention shall be paid to engine related defects/events.
3.       May or may not cause delays/cancellations.



a)      Maintenance Control Centre (MCC) shall capture all necessary information for this programme in a database viz.
1.      Aircraft registration
2.      Flight number
3.      Date and station
4.      Length of delay
5.      Problem description
6.      Findings, in particular cause of defect if identified
7.      Corrective action taken
8.      Component replacement information
9.      Relevant contributing factors
10. ATA code/Incident code/Delay code
b)      Engineering shall obtain from Flight Operations and Technical Records the total number of revenue departures and operating statistics per month.
c)      MCC shall be responsible for ensuring good complete information for delays, cancellations and significant events are captured on timely basis.
d)      MCC shall capture the delay and cancellation data promptly in a computer database viz. AiMs (Aircraft Maintenance System).
e)      MCC supervisor shall vet through the information captured for completeness, and contact relevant person(s) for more information as required as promptly as possible.
f)       The root or most probable cause for each delay and cancellation shall be determined as far as possible and coded to allow easy analysis.
g)      Where the delay or cancellation is due to multiple defects, the defect that caused the longest delay shall be used as the main reason for that event.
h)      Urgent actions to prevent recurrence of defects or significant events shall be undertaken by respective departments, and reported during the monthly meeting.
i)        Approval holders reporting delays and cancellation shall use Delay Report Form.
j)        Approval holders reporting significant events shall use the same Delay Report Form for simplicity, but shall indicate “Prolonged grounding/Incident” on the form.
k)      MCC shall distribute to relevant parties monthly summaries of delays and cancellation produced by the database.



a)      The primary performance indicator used is dispatch reliability while cancellation rate per 1000 FH also provides indication of overall fleet performance.  Engineering shall calculate these on a monthly basis.  They may also be calculated by the computer system automatically once the system is verified to be reliable.
b)      The other information captured e.g. cancellations, major interruptions, ground incidents etc may be used qualitatively as necessary.
c)      Other indicators such as delays and cancellations per 1000 FH for specific aircraft registration may also be developed and used to compare aircraft performance.



a)      Dispatch reliability shall be calculated based on industry practices as described in WATOG (World Airline Technical Operations Glossary).
b)      Dispatch reliability is
(No. of revenue dep. for period – No. of rev. dep. delayed>15 min.) x 100%
(Number of revenue departures for the period)

c)      Flights that are delayed as a consequence of a delayed preceding flight shall not be counted.
d)      Flights that are retimed at least 4 hours in advance shall not be counted as delays.
e)      Cancellation rate per 1000 FH is
No of revenue flights cancelled in period x 1000
Fleet total flight hours for period

f)       Delays/cancellation used for calculating dispatch reliability/cancellation rate shall exclude those attributed to deficiencies other than aircraft itself e.g.
late arrival of flight or ground crew,
flight crew querying deferrable defect that was subsequently accepted,
adverse weather or air traffic problems,
loading delays,
spares late delivery from warehouse,
ground support equipment failure,
obvious failure of the human element,
deliberate engineering management decision to rectify deferrable defects.
g)      Delay codes used in the database categorise delay causes when the delay is not attributed to the aircraft failures. 


Non-Destructive Testing (NDT)

>> Friday, May 7, 2010

Nondestructive testing (NDT) are noninvasive techniques to determine the integrity of a material, component or structure or quantitatively measure some characteristic of an object. In contrast to destructive testing, NDT is an assessment without doing harm, stress or destroying the test object. The destruction of the test object usually makes destructive testing more costly and it is also inappropriate in many circumstances.

NDT is used in a wide range of industrial areas and is used at almost any stage in the production or life cycle of many components.
The mainstream applications are used in below:
1) aerospace,
2) power generation,
3) automotive, railway,
4) petrochemical and pipeline markets

NDT of welds is one of the most used applications. It is very difficult to weld or mold a solid object that has no risk of breaking in service, so testing at manufacture and during use is often essential.

Personnel Qualification
Personnel Qualification is an important aspect of non-destructive evaluation. NDT techniques rely heavily on human skill and knowledge for the correct assessment and interpretation of test results. Proper and adequate training and certification of NDT personnel is therefore a must to ensure that the capabilities of the techniques are fully exploited. There are a number of published international and regional standards covering the certification of competence of personnel. The EN 473 (Qualification and certification of NDT personnel - General Principles) was developed specifically for the European Union for which the SNT-TC-1A is the American equivalent.

NDT Methods

The main NDT methods are shown below:
1)Ultrasonic Testing (UT),
2)Radiographic Testing (RT),
3)Electromagnetic Testing (ET) in which Eddy Current Testing (ECT) is well know and
4)Acoustic Emission (AE or AET).

Besides the main NDT methods a lot of other NDT techniques are available, such as Shearography Holography, Microwave and many more and new methods are being constantly researched and developed.

NDT Applications in Commercial Aircraft Maintenance

During aircraft maintenance 'NONDESTRUCTWE TESTING' (NDT) is the most economical way of performing inspection and this is the only way of discovering defects. In simply we can say, NDT can detect cracks or any other irregularities in the airframe structure and engine components which are obviously not visible to the naked eye.

Structures & different assemblies of aircraft are made from various materials, such as aluminium alloy, steel, titanium and composite materials. To dismantle the aircraft in pieces and then examine each component would take a long time, so the NDT method and equipment selection must be fast and effective.
In the present trend of NDT application on aircraft 70-80% of NDT is performed on the airframe, structure, landing gears and the rest carried out on engine & related components.

In order to maintain the aircraft defects free and ensure a high degree of quality & reliability and as a part of inspection programme, usually following NDT methods are applied;

1) Liquid Penetrant
Liquid penetrant testing is one of the oldest of modern nondestructive testing methods & widely used in aircraft maintenance. Liquid penetrant testing can be defined as a physical & chemical nondestructive procedure designed to detect & expose surface connected discontinuities in 'nonporous' engineering materials.

Detection of surface detects or structural damage in all materials of aircraft. Fluorescent penetrants are used in critical areas for more sensitive evaluation.

2) Magnetic particle,
Magnetic particle testing is a sensetive method of nondestructive testing for surface breaking and some sub-surface discontinuation in 'ferro-magnetic' materials.
The testing method is based on the principle that magnetic flux in a magnetised object is locally distorted by the presence of discontinuity. This distortion causes some of the magnetic field to exit & re-enter the test object at the discontinuity. This phenomenon is called magnetic flux leakage. Flux leakage is capable of attracting finely divided particles of magnetic materials that in turn form an 'indication' of the discontinuity. Therefore, the test basically consists of three operations : a) Establish a suitable magnetic flux in the test object by circular or longitudinal magnetisation. b) Apply magnetic particles in dry powder of a liquid suspension; and c) Examine the test object under suitable lighting conditions for interpreting & evaluating the indications.

Fluorescent or black oxide particles in the aerosol cans are used during critical areas of aircraft structure/components inspection when using either permanent or electromagnets. Fluorescent particle inspection method is evaluated by black light (Black light consists of a 100 watt mercury vapour projection spot lamp equipped with a filter to transmit wave length between 3200 to 3800 Angstrom unit and absorb substantially all visible white light).

Simple in principle, easily portable. Fast and effective for surface & subsurface defects in ferromagnetic materials of any shape, removed from engines, pumps, landing gear, gear boxes, shafts, shock struts etc. Widely used for bolts inspection.

3) Eddy current
Eddy current tests are important test & widely used method within the broad field of Nondestructive materials & evaluation. This method is particularly well suited for the detection of service induced cracks usually caused either by fatigue or by stress corrosion. Eddy current inspection can be performed with a minimum of part preparation and a high degree of sensitivity.

Eddy current test is used to detect surface & subsurface defects, corrosion in aircraft structures, fastener holes and bolt holes. Surface detects and conductivity testing by high frequency and sub-surface detects by low frequency methods.

Routine eddy current inspection is carried out on aircraft under carriage wheel hubs for cracks also used to detect cracks in different tubes, tublar components of aircraft & engine.

4) Ultrasonic
Sound with a frequency above the limit of audibility is called 'ultrasonic'. It ranges with a frequency of 0.2 MHz to 800 MHz.
Ultrasonic inspection provides a sensitive method of nondestructive testing in most materials, metallic, nonmetallic, magnetic or nonmagnetic. It permits the detection of small flaws with only single surface accessibility and is capable of estimating location & size of the defect Providing both surfaces are parallel, ultrasonics may be used for thickness measurement, where only one surface is accessible. The effective result of an ultrasonic test is heavily dependent on subject surface condition, grain size & direction and acoustic impedance. Ultrasonic techniques are very widely used for the detection of internal defects in materials.

Ultrasonic inspection operates on the principle of 'transmitted' & 'reflected' sound wave. Sound has a constant velocity in a given substance; therefore, a change in the acoustical impedance of the material causes a change in the sound velocity at that point producing an echo. The distance of the acoustical impedance (flaw) can be determined if the velocity of the sound in the test material, and the time taken for the sound to reach & return from the flaw is known.

Used for detection of surface & subsurface detects in welds, forging, casting main structural fittings of landing gear legs & engine attachments. Bolts in critical areas, aircraft structure joints & pylon. Also checks adhesive bond quality of lap joints & composite structure. Used for thickness measurement after damage or corrosion removal

5) Radiography (x-ray/gama ray)
Radiography is one of the oldest and widely used nondestructive testing methods. A radiograph is a photographic record produced by the passage of electromagnetic radiation such as x-rays or gamma rays through an object onto a film. When film is exposed to x-rays, gamma rays or light an invisible change called a 'latent image' is produced in film emulsion. The areas so exposed become darker when the film is immersed in a developing solution. After development the film is rinsed to stop development. The film is next put into a fixing bath and then washed to remove the fixer. Finally dried so that it may handled for interpretation and record.

Considering the penetration and absorption capability of x-radiation, radiography is used to inspect a variety of nonmetallic parts; for porosity, water entrapment, crushed core, cracks and resin rich/straved conditions; and metallic products; such as welds, castings and forging as well as locating discontinuities in fabricated structural assemblies such as cracks, corrosion, inclusions, debris, loose fittings, rivets, out of round holes & thickness variations. Gamma ray radiography is usually used for detection of internal flaws of aircraft structure (steel & titanium) and engine components which require higher energy levels or other assemblies where access is difficult.

6) Visual/Optical
Visual inspection is probably the most widely used of all the nondestructive tests. It is simple, easy to apply, quickly carried out and usually low in cost. The basic principle used in visual inspection is to illuminate the test specimen with light and examine the specimen with the eye. In many instances aids are used to assist in the examination.

This method is mainly used i) to magnify defects which can not be detected by the unaided eye, ii) to assist in the inspection of defects and iii) to permit visual checks of areas not accessible to unaided eye.

Detection of surface defects or structural damage in all materials. Optical instruments are used for visual checks of internal areas and for deep holes and bores of aircraft structure, landing gears etc. Widely used to monitor engine components, such as, turbine wheels and nozzles, compressor vanes and blades combustion cans without opening the engine. 'Borescopes', 'fibrescopes' and 'video imagescopes' are most important optical aids in remote - visual inspection, which area is normally inaccessible.

7) Sonic/Resonance
Sonic and resonance testing methods are used primarily for the detection of separations between layers of laminated structures.
Sonic and Resonance testing is effective for detection of crushed core or debonds in adhesive bonded honeycomb, impact damage and delimitations in composite structures and exfoliation corrosion.

The tap test method has demonstrated the ability to detect cracks, corrosion, impact damage and debonding. The sonic testing instrument operate in the audio or near audio frequency range.

Resonance testing instruments may operate either or both the sonic or ultrasonic frequency range. Different methods of transmitting and receiving energy have been developed. Basically, each technique introduces a pressure wave into the specimen and then detects the resonant, transmitted or reflected wave.

To examine bonding exists between honeycomb, detect delaminations in composite laminates. Large structures such as, fairings, cowl and wing trailing edge, rudder, flaps, ailerons, elevators etc. are made from composites and honeycomb materials.
Tap testing is limited to detection of disbonds or voids between upperfacing sheet and adhesive. It will not detect disbond or voids at 2 nd or 3 rd layer bondlines, such as doubler areas. It is limited to the detection of delaminations, approximately 25 mm (1 inch) in dia or greater, located less than 1.3 mm (0.05 inch) below the surface being examined.

8) Infrared Thermography.
Infrared and thermal methods for nondestructive are based on the principle that heat flow in a material is altered by the presence of some types of anomalies. These changes in heat flow cause localized temperature differences in the material. The imaging or study of such thermal patterns is known as 'thermography'. The terms 'infrared' and 'thermal' are used interchangeably in some contexts. Thermal refers to the physical phenomenon of heat, involving the movement of molecules. Infrared (below the colour red) denotes radiation between the visible and microwave regions of the electromagnetic spectrum.

The intensity and frequency/wavelength of the radiation can be correlated closely with the heat of the radiator. it follows that radiation sensors can be used to tell us about the physical condition of the test object. This is the basis of the technology of 'thermography'.

Used to detect certain voids, inclusions, debonds, liquid ingress or contamination, foreign objects and damaged or broken structural assemblies. Infrared thermography also been chosen for quick operational use and the reliability of defection 'liquid contamination' in the composite sandwich in compared to x-ray method. Detection of
thermal overheating in electrical & hydraulic system.

Specially thermographic inspection on aircraft structures are carried out to detect following defects :
(i) Composite laminate parts - for delamination debonding or foreign objects
(ii) Composite sandwich parts - for debonding and liquid contamination.
(iii) Metallic bonded parts - for debonding of corrosion on.
(iv) Metallic sandwich parts - for liquid contamination, debonding of corrosion.


B727 & B737 Window Heat Controller

>> Sunday, May 2, 2010

A) Reason for the study

1)       B727/737 Window heat controller unit (WHCU) p/n 231-2 (alt p/n 65-52803-8, 83000-05602, 10-61833-2) was among the top 5 unscheduled component removal for 4 consequences months from Nov 2007 till Feb 2008.  These studies analyze common reasons of such failures from year 2005 till Nov 2007 to enhance its reliability.
2)       There are various P/Ns (various OEMs) of Window Heat Controller Unit (WHCU) installed on B727/B737. All P/Ns are fully interchangeable.
Boeing P/N
83000-05601 / -05602
BAE Systems
3)       There were 4 units of WHCU installed on 727 (and B737) airplane which for pilot and co-pilot No. 1 and No. 2 windows. The WHCU located at E5-1 electrical rack. It consists of temp controller which a solid state device that performs overheat control and temp control, overheat relay which direct 115V AC power from window heat CB to temp controller when energized and transformer which provide high voltage for heating window.



B) Data

1)       Repair and Findings Data from 1st Jan 2005 till 31st May 2008 were reviewed and has been classified into various types of common defect and shop findings; s/n and aircraft with repeated removals. Total 43 units were removed unscheduled with 30 DC and 13 DNC. None were scrapped or overhauled.

Defect Confirm
Defect Not Confirm
30 (69.8 %)
13 (30.2%)
2)       Unscheduled removals unit in 2005, 2006, 2007 and 2008 (till May) are shown below:
2008 (till May)
Removal Units
3)       MTBUR for B737 is 2935 hrs and for B727 is 4112 hrs. The average MTBUR is 3838 hrs. Design MTBUR for WHCU p/n 83000-05602 is 14046 hrs while MTBF is 29200 hrs.

C) Current Maintenance Program




Every ‘C’ chk (Card: C-102A-2)

Every ‘C’ chk            (Card: 72C1-E-2-4-016)

Inspect cabin control window anti-icing syst for components such as window heat power relay, anti-ice control panel, heat conductive coating, thermal switches and heat sensors for security, wiring condition and evidence of overheat.

Every ‘C’ chk (Card: C-103A-1)


Inspect window heat control unit (4 places) installed on the E3 rack for security of installation, condition of wiring, cleanliness and evidence of overheat / moisture.


D) OEM comments.

Email from Boeing and OEM are described below:

1)        Boeing via email dated April, 30 and May, 9 provided comments per below:

a)        Boeing has not received any reports from other operator similar to WHCU defects.
b)        Boeing provides current MTBF reported from Koito is 29200 hrs.
c)        Boeing has limited knowledge of the Astronics p/n 231-5 due to this is an STC mod and therefore the p/n is not reflected in Boeing IPC.
d)        There is no BAE p/n that equivalent to Boeing improved p/n 10-61833-6.
e)        Boeing recommends to upgrades WHCU to the newest Koito p/n 83000-05604 (Boeing p/n 10-61833-6). Boeing drawing provides data allowing this p/n to be installed to B727 airplane. The IPC rev July 2008 will reflect the p/n 83000-05604 usage on 727-200 airplanes.

2)    Comments from Astronics Advanced Eletronics Systems (previously known as General Dynamics or Olin or Pacific Electro Dynamics)

a)        OEM does not track the MTBUR and MTBF of Window heat controller unit p/n 231-2.
b)        231-5 is the latest WHCU p/n produce by Astronics. It is fully interchangeable with p/n 231-2 with an addition of BITE circuits.
c)        Suspect the latest mods (Mod L or M depending on the age of the unit) have not been  incorporated for serial number that have failures of parts in the output transistor section (Q26, 27, 28)
d)        Astronics has produced 16 SBs related to WHCU p/n 231-2. Refer attachment 7B for modification history from p/n 231-1 to 231-2 mod ‘M’.
e)        Astronics only do repair and re-certify origin WHCU p/n 231-x from astronics or all predecessor company names for astronics. 
f)          Astronics provide recommendation per below:
1.     Due to cooling air system accumulates dust and dirt which creates thermal stress on the unit, operator is recommended to review the maintenance chk task to inspect the cooling system and cleaning the dust and dirt in E&E compartment to keep dust from clogging the units.
2.     Operator to record mod level for each WHCU installed on the fleet.
3.     Any units had RV1-4 or F1 changed should have Q1 changed as well or there is risk of recurrence of the problem.

3)    Comments from Koito Mfg

a)        Design MTBUR for WHCU p/n 83000-05602 is 14046 hrs.

b)        Since most of the operators has already incorporated new WHCU p/n: 83000-05604, there is no news about p/n 83000-05602 recent few years.
c)        P/n 83000-05604 has a BITE function while -05602 has not. The other differences are the weight of unit. -05604 weight is 4.3 kg while -05602 is 3.7 kg.
d)        Koito recommended below:
1.     To upgrade p/n 83000-05602 to -05604 (Boeing pn 10-61833-6). Info: p/n 83000-05604 is interchangeable with -05602. P/n 83000-05602 is no longer produce by Koito.
2.     Send repair or overhaul’s WHCU to Koito repair station or Aviation Technical Services, Inc (formerly Goodrich ATS).
3.     All new purchase of Koito WHCU must be obtained from AAxico.

4)    Comments from Aero Technology

a)        No expected MTBUR and no recommended improved part number from repairer.
b)        Other operators do not have low time failure (LTF) for window heat controller p/n 231-2.
c)        Two units (S/n 478 & 6205) LTF was warranty denied.
1)        S/n 478 was repaired at 1st time visit.  Nil faults found for 2nd shop visit.  
2)        S/n 6205 found internal damaged due to excessive heat on Oct 07. 1 month later the unit was sent for repair and found different circuit board had failed. It appears that the second failure was also caused by an excessive heat.
d)        Unable to offer exchange with upgraded p/n due to no stock available.

E) Findings and Discussion.

1)       16 out of 43 WHCU unscheduled removals were caused by overheat. From the study, overheat will affect the window and cause the window to crack. 5 unscheduled removals due to CBs tripped can also cause window to overheat.  
Reason for Removals
Overheat / fail overheat test
Nil heating / inop
Nil control / nil indication / not regulating / not function
CB tripped
Window cracked / arching
Green light intermittent

2)       29 (67.4%) units were sent to Aero Tech for repair, 6 (14%) to Aero Instrument, Avborne 3, High Tech Avionic 1 and Aero Control Avionic and ST Aero 2 each. Most of units were sent to Aero Tech due to low flat rate compare to other vendor.

Aero Tech
Aero Instrument
Aero Control Avionic
ST Aero
High Tech Avionics
29 (67.4%)
6 (14%)
2 (4.65%)
3 (7%)
2 (4.65%)
1 (2.3%)

3)       Currently there were 57 units installed on the fleet which 47.4% was manufactured by Astronics, 33.3% by BAE system and 17.5% by Koito.
4)       The S/Ns show the repeated removals are 478 (4 removals), M01372 (3 removals), 662, 1607, 1634, 3718, 5126, 6205, 7142 and 7145 (2 removals each s/n).
5)       Most of the WHCU (47.4%) belongs to Astronic. However, Boeing has limited knowledge of the unit and cannot determine the replacement of part 231-2 with 231-5.
6)       All of Astronics p/n 231-2 was not upgraded to latest mod L or M.
7)       Koito unit is the most recommended p/n due to 50% of the unit is in good condition and only one was removed unscheduled for the last 1 year. Furthermore, Boeing only recognizes Koito p/n compared to Astronics or BAE p/n.
8)       BAE p/n 65-52803-8 had shown only 5 units removed unscheduled last year (2007). Compared to Astronics and Koito, BAE WHCU reported fewer problems. However, the OEM (BAE) is NOT contactable. 

F) Recommendations

1)       To advice repairer;  unit found with varistor (RV1-4) or fuse (F1) defect/damaged, transistor Q1 must be replaced to prevent from tripping and overheat shutdown
2)       To evaluate upgrading Koito WHCU p/n 83000-05602 to the newest p/n 83000-05604 (Boeing p/n 10-61833-6)
3)       S/n 7097, to incorporate mod K at next shop visit
4)       S/ns 662, 2749, 3486 and 7142 to incorporate latest mod L or M at next shop visit.
5)       Close monitoring for WHCU s/n: 478, 6205 and M01372 that have low time failure (LTF) last year. Scrapped or exchange for those s/n that have more than 3 LTF within 2 years (until June 2009).
6)       Should spares need to order extra WHCU, always purchase latest version pn: 83000-05604 alt pn: 10-61833-6 from Aaxico (Koito prefer seller).
7)       Inform the maint crew to follow the troubleshooting chart in AMM 30-41-02 figure 101 before make a decision to replace the WHCU due to failure. Ensure that the window temperatures are below 75°F and No. 2 windows are closed and latched before using the troubleshooting chart.
8)       Review maintenance task (‘C’ chk and ‘B’ chk) to inspect the cooling system and cleaning the E&E from dust and dirt.  

G) Conclusions

1)     Operator Window Heat Controller Unit (WHCU) MTBUR is 3838 hrs which is lower than the design MTBUR (14046 hrs).
2)     Aging is the main reason of the unscheduled removals.

Email from Aero Tech dated 22, 29 April, 28 May 2008
Email from Astronics dated 6 and 7 May 2008
Email from Boeing dated 30 April, 9 and 31 May 2008
Email from Koito dated 23 May 2008, 14 and 17 June 2008
Email from Aviation Technical Services dated 24 May 2008
Email from Aaxico dated 26 May 2008
ISAR No. 93-10 dated 30 September 1993
ISAR No. 90-11 dated 12 December 1990


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