Boeing B727-200F Wiring Inspection

>> Tuesday, November 3, 2009

Boeing B727-200F Wiring Inspection


This report details the findings of the wiring visual inspection in the following areas based on Quality Inspection Card (QIC) issued by QA Department. Dated 1st Feb 2006, three (3) B727 acfts have been completed the inspection.

  1. From Nose to E&E Compartment
  2. Forward Lower Deck Cargo Compartment
  3. Aft Lower Deck Cargo Compartment 
  4. Main Wheel Well
  5. LH Wing (Port & Stbd)
  6. RH Wing (Port & Stbd)
  7. Flight Deck Upper (Overhead) to 9G Bulkhead
  8. 9G Bulkhead to Aft Entry Door (Nain Deck Cabin)
  9. LH & RH Aft Airstairs Area
  10. Tail Compartment (including vertical fin and stabilizer)
  11. Engine 1, 2 & 3 including pylon areas

The overview of the findings for each areas is provided below in para 1.1 to 1.9. However, the details of the findings are provided in the table.

A total of 4898 wires, 65 pressure seals and 752 connectors were visually inspected. It was observed that 21.9 percent of the wires suffered deterioration due to chaffing, kink, hardened and brittle insulation and unauthorised splicing. Also 16.0 percent of the connectors suffered from corrosion at the pin contacts or dialectic insulation and 53.8 percent of the pressure seals are damaged.

It should be emphasized here that wires that showed discoloration at the outer insulation jackets are not included as degraded wires. Similarly, connectors that have corrosion at the outer, shells are also not included in the percentages above.

1.1        Outer Leading Edge (LH and RH)

A total of 294 wires, 74 connectors and 16 pressure seals were inspected for the LH and RH leading edge wiring looms. 145 wires (49.3%) and 16 connectors (21.6%) were found to be degraded. Also 10 pressure seals (62.5%) were found to be deformed and hardened.

Connector found with corrosion at the pin contacts are mainly concentrated around the top of the horse collar in front of the firewall and at outer wing pressure break areas. Corrosion of connector pin contacts around this area is significant because most of the connectors have wiring from numerous system passing through it. It addition to corrosion at connectors' pin contacts, the wire's terminating end at the back of the subject connectors also shows sign of discoloration, which indicates that either overheating has occurred or chemical reaction has taken place between the rubberized grommet and bushing material with the wire's insulation, both of the which in time may affect the integrity of the wire's insulation.

The thermal damage may caused by the heat source coming from either the wire's core itself (as in the case of electrical overcurrent) or from external source. Either case may cause the wire's insulation to be gradually discolored and in time may carbonized the insulation material, which turns the insulation material into a conductor. The now conductive insulation may in time become short‑circuited with nearby wires, causing systems failure or in extreme case, an electrical fire. It should be noted that the discoloration found at this area are not due to cable clamps.

1.1.1                                Left Hand Outer Leading Edge

Of the 147 wires inspected its about 75 (51.0%) wires were found with discrepancies. 6 (16.2%) out of the 37 connectors were found at this area with corroded pin contacts and 5 (62.5%) of the pressure seals were damaged.

Other discrepancies detected on LH Leading Edge wiring includes corrosion at conduit connector (which is not easily observed unless the wiring installation is removed) and illegal splicing close (less than 12 inches) to the connector's end. The illegal splicing are probably due to maintenance insitu repair.

1.1.2                                RH Outer Leading Edge

Significantly more wires i.e. 70 (47.6%) out of the 147 wires inspected, are found to have discrepancies. However, only 10 (27.0%), out of the 37 connectors have corrosion at pin contacts and 5 out of the 8 (62.5%) pressure seals are damaged. The outer RH Leading Edge wiring displays the similar discrepancies as of the wiring on the LH Leading Edge. The condition shall not be considered lightly since the affected systems are vital to the aircraft's operation should the wiring interconnection fails due to corrosion and deterioration.

Discoloration of wire ends was also detected at the back of the RH Leading Edge connector's mounting bracket. Since the bracket is similar to the LH Leading Edge's, the affected systems that may be failed due to the discrepancies.

Other discrepancies found on the RH Leading Edge wiring includes deteriorated cable insulation and serious overheating effect that damaged wire's insulation. The overheating of the wires occurred at about 3 feet inboard from the No. 4 engine.

In both cases, should the insulation be exposed to similar effect for a prolonged time, it may cause the wiring to fail and the cores to be shortcircuited, leading to other more catastrophic damaged than just the particular system malfunction, such as electrical spark or even fire.

1.2           Inboard Leading Edge/Center Wing (LH and RH)

The center wing wiring looms runs from outer wing pressure breaks through the pressure seals at the armpit to splices at FS 245. There are a total of 490 wires, 28 pressure seals and 58 connectors in the wiring looms inspected. 115 wires (23.5%), 22 pressure seals (91.7%) and 9 connectors (15.5%) were found to be degraded upon visual inspection. The number of discrepancies found for the left hand and right hand areas are approximately the same. Also for both the left hand and right hand center wing. The connectors with corroded pin contacts were found at the firewall area near engine No. 2 and No. 3 and at the outer wing pressure break areas. This finding is similar so that on the outer leading edge looms. Most of the wiring discrepancies are found from the outer wing pressure break to the armpit pressure seal area i.e. the leading edge area.

1.2.1    Left Hand Center Wing

60 out of the 245 wires (24.5%) were found with discrepancies such as wiring insulation deteriorated (i.e. frayed, broken or brittle) illegal splicings, and dry solder joints. Illegal splicings are usually carried out as a result of temporary repair during line maintenance. The wiring with insulation deteriorated are from various system such as propeller ice control, oil pressure indicator, engine regulated fuel system control, oil quantity indicator, fuel flow indicator, engine fire warning, generator No. I and No. 2 power supply and thermocouple wires for turbine inlet temperature indicator 6 wires from generator No. I and No. 2 were found with dry solder joints. All four (4) connectors out of the 29 connectors found with corrosion at the pin/socket contacts are located at the LH outer wing pressure breaks.

1.2.2    Right Hand Center Wing

Again 55 out of the 245 (22.4%) of the wiring were found with discrepancies similar to that of the LH side. This would indicate that line maintenance repair of wiring were carried out. The wiring with deteriorated insulation were found to be from propeller ice control, propeller synchrophasing control, fuel flow indicating system generator No. 4 power supply and engine fire warning systems.

Of the 5 connectors found with corrosion at pin/socket contacts, two connectors are located at the outer wing pressure break and wiring from multiple system are terminated at these connectors. Wiring for up to 10 systems can be terminated at a connectors. The other two connector are from the emergency valves system for engine bleed air pressure regulation.

1.3       QEC

QEC wiring has been removed by RMAF before the aircraft hand over to AIROD for rewiring. Therfore the wiring inspection have not been carried out for QEC systems.

1.4       Trailing Edge (LH and RH)

Of the 336 wires inspected 138 (41.1%) of the wire were found to be degraded i.e. chaffed or insulation brittle (17.9%) or contiminated with oil (20.5%) and 7 out of the 82 connectors (7.3%) inspected have corrosion at the contacts/socket pins. The main problem with wiring is that the wiring insulation is found to be kinked, brittle or cracked. There is a difference in the number of wires on the RH trailing edge compared to the LH trailing edge because of differences in systems involved. Wiring loom from 17 sub‑systems were covered in each of the LH and RH trailing edge. The RH trailing edge has same number of connectors that are degraded as compared to the LH trailing edge.
1.4.1                LH Trailing Edge

65 (40.4%) out of the 161 wires inspected were found with either wiring insulation degradation. This affected 12 out of the 17 sub‑system wires located at the LH trailing edge. The systems affected are main the fuel system (Boost, Auxiliary Tank and External Tanks Pumps, Refueling, Crossfeed.

Dump and APU, Trim Tab Position Indicator and Control, formation lights, Engine Fire Extinguisher and paratroop air deflector control. A high percentage (60%) of the wires used in this area a belong to MIL‑W‑5086/2 which has been superseded by MIL‑W‑22759/34.

Degraded wires were mainly from MIL‑W‑5086/2 and MIL‑W‑25038/1 wire specifications. MIL‑W‑25038/1 wires are still valid for use. However 85% (30 out of 35) of this wires type are found to be brittle.

Of the 41 connectors inspected, 3 (7.3%) connectors from the fuel refueling system and paratroop air deflector control system were found with corroded pin/socket contacts. These connectors are also found to be degraded at the RH trailing edge. 21 out of the 41 connectors inspected are for connection to the fuel tank. None of these connectors which are located next to the fuel tanks are degraded. Similar findings were obtain for the fuel tank connector.

1.4.2     RH Trailing Edge

73 out of the 175 wires (41.7%) inspected were found with wiring insulation degradation i.e. insulation hardened, broken or brittle. This affected 12 of the 17 system wires located at the RH trailing edge. The subsystems with degraded wires are almost the same as that found in the LH trailing edge i.e. 9 of the 12 subsystem are the same.

The subsystem affected are the fuel system (Boost, Auxiliary,. Tank and External Tank Pumps, Refueling, Crossfeed, Dump and Pressure Indicator, Wing Flap control, Engine Fire Extinguisher, Fuel Quantity Indicator and Hydraulic pumps low pressure warning. Most of the wires used belong to the specifications MIL‑W‑5086/2 and MIL‑W‑25038/1. Similarly most of the degraded wires belong to these two wire types. 100% (33 out of 33) of all wires belonging to MIL‑W‑25038/1 wire specification has superseded to MIL‑W‑25038/3. Of the 41 connectors inspected 3 (7.3%) of the connectors were found with corrosion at pin/socket contacts.

Two of the subsystem affected, the fuel refueling and paratroop air deflector control, are the same as the findings on the LH trailing edge. The other subsystem with degraded connectors are the fuel system boost pump, formation lights, hydraulic pump low pressure warning and fuel system dump. As with the LH trailing edge 21 of the connectors inspected are coaxial enables and are mostly located next to the fuel tank. These connectors, were all found to be in good condition.

1.5    Dry Bay Wiring

The dry bay areas consists of No. 1, No. 2, No. 3 and No. 4 dry bays located behind the firewall of each engine and the center dry bay. The subsystem wiring looms are for the fuel system (dump, refueling, crossfeed, APU, Auxiliary and External Tank Pump, pressure indicator), hydraulic pump low pressure warning, engine fire extinguisher and emergency valves. These systems are similarly to that found on the trailing edge wiring. A total of 49 (34.3%) wires were found to be degraded with 13 wires found with brittle insulation, 15 wires with thermal damage and 21 wires were contiminated with oil. Wiring splices are probably due to insitu repair to one of the many fuel valves present in the dry bays. Again wire types are mainly of MIL‑W‑5086/2 and MIL‑W‑25038/1 (which are superseded by MIL‑W‑25038/3), 54% (19 out of 35) wire of MIL‑W‑5086/2 specification (which are superseded by MIL‑W‑22759/34 as per Lockheed design Standard No DS 5085, Rev. 5 dated 21 Mar 1990) were degraded. Similar to the findings of the trailing edges, it was determined that 56% (13 out of 23) of the MIL‑W‑25038/1 wire type which has been superseded by MIL‑W‑25038/3 inspected were degraded.

The number of degraded connectors i.e. connectors with corrosion at contact pins is 23 (51.1%) of the total 45 connectors inspected. This is very high percentage and it affects 8 out of the 10 subsystem in the dry bay areas. Since this is an unpressurized area, it is subjects to the cyclic environmental condition changes which may explain why we have a relative large number of degraded wires and connectors.

1.6      Fuel Tank

The wiring inside the fuel tanks were found to be in excellent condition. A total of 122 wires and 238 connectors from the wing outboard tanks, wing inboard tanks, auxiliary tanks and external tanks were inspected. 35 out of the 122 wires (28.7%) inspected were found with wiring insulation degradation i.e. insulation hardened, kinked, insulation cracks, contiminated with fluid or brittle. 5 (2.1%) out of 238 connectors were found corroded at outer shell.

1.7      Wheel Well and APU

A total of 195 wires, 31 connectors and 4 pressure seals were inspected. The wiring looms were from the nose landing gear/wheel well area, the main landing gear (LH and RH) areas and wiring leading to the APU located forward of the LH wheel well area. In general it was found that the wire sleevings were either deteriorated or hardened. 20 (10.3%) wires, 7 (22.6%) connectors were found to be degraded. Wiring around the APU area suffered relatively more degradation due to hardened/brittle insulation. The wires are mainly located between APU compartment fire wall and the APU which is a relative high temperature area.
Only 1 (11.1%) of the 9 connectors at the nose wheel well and the same number of connector for APU area suffered from corrosion of the pin contacts and outer shell. There is only 1 connectors in the LH main landing gear suffered from corrosion of the pin contacts. All pressure seals were found in good condition.

1.8     Empennage Area

Although the number of wires and connectors for this area were relative small for the wiring installation in the Empennage area, the percentage of discrepancies observed on the wiring looms were quite high. Of the 56 wires inspected, 33 (58.9%) of the wires were found to be degraded. The main defects found were chaffed insulation (27.3%), brittle insulation (36.4%), corrosion at terminal lug (15.2%), thermal damage (21.2%) and contiminated with fluid (6.1%). The insulation damage are possibly caused by mechanical vibration or movement at the wiring installation. Brittle insulation are mainly caused by wire type conforming to military specification MIL‑W5086/2. This is similar to the degradation found for wiring at the trailing edge and dry bay area which are also exposed to the cyclic environmental condition changes. Illegal splices were observed at wires from the main fuselage to the vertical and horizontal stabilizer. This is most likely due to insitu maintenance repair. 2 (18.2%) the connectors inspected were found degraded one with corroded pin contacts and another one with a cracked dielectric. 2 out of the 3 pressure seals inspected were found to be damaged/deformed.

1.9                   Cockpit

The cockpit wiring looms constitutes about 75 percent of the total wires (6543 wires) and about 33 percent of the total connectors inspected for the aircraft. A total of 3262 wires were inspected and it was determined that the communication/navigation systems have about one quarter of the total wires each while the electrical system make up the other half of the total wires in the cockpit. However, wires for electrical systems on this aircraft have not been removed and to be retained. The wires were grouped in this manner as it was found to be a convenient method of assessing the degradation of wiring looms. Furthermore the wiring in the cockpit runs from one end to the other. Communication/Navigation wiring generally runs from the receiver/transmitter at the underdeck shelf’s to the pedestal. Instrument system wiring generally runs from the main instrument panel/navigator panel to either the left hand underdeck rack or to the splices at FS 245. The engine instrumentation wiring runs from engine instrument panel to the FS 245. Based on the findings of the inspection, it was determined that only 538 (16.5%) of the wires in the cockpit were degraded with the more significant communication/navigation system (9%).

Of the 213 connectors inspected, 52 (24.4%) were found with corrosion at the pin contacts. The instrument system has 25.6% (32 out of 125) of its connectors degraded and the communication/navigation system has 22.7% (20 out of 88) of its connectors degraded.

1.9.1                Instrument System

 The instrument system is broadly categorized under the following systems/areas.

i)           Main Instrument Panel
ii)          C‑12 Compass
iii)         Autopilot and Flight Director
iv)         Oxygen System
v)          Air-condition
vi)         Fuel Quantity Indication
vii)        Hydraulic System
viii)        Engine Instrument

Significant degradation of wiring was found on the MIP, Autopilot/Flight Director and the Engine Instruments. Overall 398 (23.3%) out of the 1710 wires inspected were degraded. From the inspection the MIP and autopilot/flight director system also had higher percentage of degraded connectors. The other systems with degraded connectors are the oxygen, compass and engine instrument.             Main Instrument Panel (MIP)

For wiring on the MIP, 75 (33.3%) out of 225 wires inspected were found to be degraded some with multiple discrepancies from end to end. However all connectors of the MIP are in good condition.             Compass

The wiring of the compass system is generally in very good condition. Only 9 wires were found brittle. A total of 411 wires were inspected for the dual compass systems. 5 out of the 21 connector inspected were found with corroded pin contacts.             Autopilot/Flight Director

On the 624 wires 29 connectors inspected, 206 (33%) were found to be degraded ‑i.e. 119 wires with insulation found brittle and 23 wires terminating in dry solder joints. The wires were mainly of wire type MIL‑W‑81044/16 which is obsolete and superseded by MIL‑W‑22759/34 as indicated by US Navel Avionics Center. Dry joints are found at solder type connectors for the components such as Flight Computer No. 1, Yaw Damper Computer. Mode Coupler and Autopilot Amplifier. All equipment for the autopilot and flight director system is located in the underdeck rack under the cockpit floorboard and on the MIR The connectors with corrosion at the pin contacts were for the VG No. I and No. 2 and the rate of turn sensor. These components are located at the underdeck racks.             Oxygen System

Only 3 wires were found degraded with thermal damage. However the clear sleeving used for protection of the wiring were discolored and broken. One out of the 3 connector inspected were found with corroded pin contacts.             Air‑condition System

The air condition system wiring comprising of wires from the flight deck were in good condition. Overall 21 out of 136 wires and 2 (10%) out of 20 connectors were degraded. The rest of the wires and connectors inspected were in good condition.             Fuel Quantity Indicating

The FQI wiring in the cockpit consist of 43 wires and 35 wires (81.4%) were found to be degraded i.e. chaffed and insulation brittle (77.1%) or dry joints and corrosion at terminal lugs (22.9%). 6 (66.7%) out of the 9 connector inspected were found with corroded pin contacts and outer shell.             Hydraulic System

11 out of the 40 wires (27.5%) inspected were found with wiring insulation degradation i.e. insulation hardened, kinked and insulation cracks. 6 connectors were found corroded at outer shell.             Engine Instrument

222 wires and 32 connectors were inspected for the indicators at the engine instrument panels. 38 wires (17.1%) were found to be degraded. The main problem with the wiring looms was corrosion at the terminal lugs which occur for 15 of the 38 wires found degraded. These terminal lugs are located away from the engine instrument panel. The wires are from the torque, TIT oil quantity and tachometer indicating system. Only the engine tachometer has 1 (3.1%) connector which was corroded at the pin contacts.

1.9.2                Communications/Navigation System

Upon visual inspection on wiring looms for the communication and navigation systems, 140 (9%) of the 1552 wires inspected and 20 (22.7%) of the 88 connectors inspected were found to be degraded. The main discrepancies found on the wiring were chaffed, kinked and brittle insulation. About 50% of the connectors which had corrosion at the pin contacts were located at the center pedestal.             ADF System

The wiring for the ADF system suffered from dry solder joint terminations and deteriorated wire insulation. The wires that has damaged insulation were locate at the left hand wheel well area the wires found with dry joints were at the connectors to ADF No. 1 and No. 2 receiver units. The connectors to the No. 1 and No. 2 ADF control units at the pedestal corroded at the pin contacts. Weather Radar System

The wiring for the weather radar system suffered mainly from brittle insulation. Two coaxial cables were found terminated to the receiver transmitter with the ends soldered instead of being crimped to their respective crimp type contacts. All the connectors were in good condition.             HF System

As stated above, most of the HF wires which were found degraded were terminated in dry solder joints at the receiver transmitter. 2 out of 4 connectors inspected were found to be degraded.             TACAN System

14 out of the 210 wires (6.7%) inspected were found with wiring insulation degradation and 2 out of 14 connectors (14.3%) were found corroded at outer shell and pin contacts.             VHF System

7 out of the 92 wires (7.6%) inspected were found with wiring insulation degradation. Two connectors for the VHF control units at the pedestal were found to be degraded.             UHF System

One wire was found deteriorated insulations. 6 connectors were inspected and found in good condition.             UHF/DF (DF 301E) System

All the 20 wires and 1 connector inspected were in good condition.             Radio Altimeter

7 out of 54 wires (13%) were found brittle insulation and chaffed. Connectors inspected for the radio altimeter were in good condition.             VOR/ILS

Degradation of the wires inspected was mainly due to corrosion terminal lug and brittle insulation. 2 out of 16 connectors (12.5%) inspected were found to corrosion at outer shell and pin contacts.           ICS and Public Address

On the 473 wires 23 connectors inspected, 45 (9.5%) were found to be degraded i.e. 38 wires with insulation found brittle and cracked and 7 wires terminating in dry solder joints. 7 of the 23 connectors inspected were found to be badly soldered at the flight engineers headphone jack and corrosion at pin contacts.           ATC Transponder

None of the 38 wires and 2 connectors inspected were found to be degraded. 

1.9.3                Electrical System

Wires for electrical systems on this aircraft have not been removed and to be retained.


In section 1, it is stated that about 16 percent of all the connectors inspected were found to be corroded at the pin contacts or at the mating surface. The primary function of a connector is to make good connection and if the contact material is corroded, this most basic function cannot be achieved. The corroded contact will increase the contact resistance which is one of the critical parameters in a connector and typical measured value is in milliohms or a fraction of a milliohm.

Connectors with corrosion found at the mating surface also raises the possibilities that the insulation between the various pin contacts of a connector could be lower than the required value of 10 megaohms stated in CAAIP. It was determined that the dielectric insulation material separating the contacts of connectors are either ceramic or silicone based material.

A insulation resistance check was carried out on 100 connectors. Of the 100 connectors, 62 connectors were good conditions connector i.e. no corrosion were found on the connector mating surface. It was found that all the connector satisfied the requirement in CAMP i.e. insulation resistance between the contacts is greater than 10 megaohms. 29 of the connectors had silicone based insulation material while the other 33 connectors had ceramic based insulation material.

The other 38 connectors are degraded connectors i.e. the connector mating surface were found to be corroded. 30 of these connectors had silicone based insulation and 8 had ceramic based insulation. None of 8 ceramic based insulation showed a breakdown in the insulation connectors, 15 (50%) of the silicon based insulation connector showed an insulation breakdown with connectors having an insulation resistance of below I megaohm.

Apart from the fuel tank connectors, it is estimated that about fifty percent of all connector used in the aircraft are of silicone based insulation. The main concentrations of silicone based insulation are at the trailing edge, leading edge, dry bay, empennage and QEC. These areas also the SWAMP areas where the previous section on visual inspection showed greater degradation of wiring looms.

Table I: Result for the Insulation Resistance Check
Total No of
No of Silicone
Dielectric Degraded
Connector Inspected
No Of Connector
with Insulation
Trailing Edge
Leading Edge
Landing Gear
Instrument System Cockpit
Electrical System Cockpit
Radio Comm. System Cockpit
Instrument Panel Cockpit
Dry Bay

List of SB’s for B727 Wiring Inspection to be incorporated.

SB 727
Prevent personnel from being shocked by 115 volt AC when using the P13 fwd attendant's pnl or the P14 aft attendant's pnl. On P13 fwd attendant's pnl and P14 aft attendant's pnl, install a ground terminal lug over the shaft of the attendant's work light toggle switch so that it contacts the attendant's pnl aluminum faceplate. Install wire from the ground lug to the pnl connector and then to an existing AC groundstud.

Reroute air conditioning bay wire bundle to provide more clearance from the hot air duct and reduce the possibility of wire bundle overheat damage.   

Provides additional insulation for wire terminals to guard against loose metallic objects which can cause short circuit. 

Eliminates the possibility of damage to the power feeder by installing slotted head fasteners.

Prevent wetting of engine power lead wire bundle with engine oil from the oil tank drain by relocating the wire bundle further inboard. 

Improve short circuit protection for the APU generator and APU starter motor by installing separate ground power.  

Eliminate the possibility of damage for wire bundle routed with hot battery. Hot battery bus feeder wire will be isolated from the other wire bundle.  

Reduce the possibility of heat damage to wire bundles in the keel beam area.

Provide clearance between airplane structure and a wire bundle that supplies electrical power to the engine fuel pumps.  

Prevent the APU power feeder wire from contacting the E1-5 pnl door or structure which can result short circuit.

Provide instruction for performing inspection and clamping of wire bundle W116 in the E7E comp E1 rack. This is to prevent the wire bundle W116 from chaffing to the APU CB panel cover.  
TGA & TGB have been incorporated SB 727-24A0072. Recommended SB to be incorporated to all ex-UPS acft. 
Prevent damage to electrical wiring in the nose gear wheel well by installing the conduit to the existing wire routing.

To preclude failure of terminals on the flux valve wire bundle at the flux valve connection. Added clamp to support the wire bundle.

      R – Must be done 
      O – Optional
      C – SB’s have been incorporated by previous operator/Boeing        


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