Aircraft Maintenance Support

Navigation – Traffic Alert and Collision Avoidance System (TCAS) False Target due to improper suppression circuitry interface

>> Friday, January 8, 2010

Traffic Alert and Collision Avoidance System (TCAS) False Target due to improper suppression circuitry interface.

An operator reported a high rate of “false target” displayed on TCAS system. The “false target”, either a resolution advisory (RA) symbol or a traffic advisory (TA) symbol, would be displayed on the “nose” of the airplane symbol on the electronic horizontal situation indicator (EHSI).

Troubleshooting revealed that the suppression system coax cable contact in the rack connector had been recessed too far from the face of the connector to allow proper mating with the TCAS computer suppression jack. This allowed the TCAS computer to talk to its own ship transponder, resulting in the TCAS seeing itself as an intruder.

Investigation into the assembly of the connector revealed that the coax cable wire tripper would sometimes remove too much dielectric. This would prohibit proper insertion of the contact into the connector, causing some contacts to be too recessed and falling outside of the 0.192 inch requirement as measured from the front of the connector.

This condition has been corrected by reprogramming the wire stripper to ensure correct wire exposure. In addition, a method of verifying proper contact insertion was added to the Boeing assembly drawing D6-5456.

Weather Radar Radiation Absorber Material – B727

>> Thursday, January 7, 2010

Weather Radar Radiation Absorber Material – B727

Part Number: 65-26554-( ) (typical Boeing IPC 34-40-0-44, item 1)

The radiation absorber material is necessary for proper operation of the weather radar system on airplanes with radar antennas that scan 360 degrees.

The radiation absorber material provides protection for the radar receiver when the antenna is directed aft toward the pressure bulkhead. It also prevents false target that may otherwise be displayed due to reflections from the pressure bulkhead.

The purpose of the radiation absorber material is not for the protection of the flight crew.

New weather radar systems scan approximately 180 degrees in the forward direction only. Radiation absorber material is not required for airplanes equipped with radar antennas that do not scan 360 degrees, such as the new ARINC 708 weather radar system.

Splice repair of electrical cable in a flammable leakage zone for Boeing Aircraft

>> Monday, December 7, 2009

Splice repair of electrical cable in a flammable leakage zone for Boeing Aircraft.

Definition of a Flammable Leakage Zone: A flammable leakage zone is an area where leakage of flammable fluids or flammable vapors can occur as a result of:

1) One failure

2) Leakage during normal operation

SWPM 20-02-10 "AIRPLANE FLAMMABLE LEAKAGE ZONES" provides basic guidelines for fuel vapor areas.

There are additional safety precautions in SWPM 20-00-10.

Also, SWPM 20-30-00 Paragraph 4 provides information on sealing of electrical terminations in a flammable leakage zone.

All electrical connections in a flammable leakage zone should be sealed. In the case of a splice, sealed splices should be used.

SWPM 20-30-12 paragraphs 7.B or 7.C (for temperature A and B zones) or paragraphs 8.B or 8.C (for high temperature zones C and D) are the preferred methods. Although there are sealed splice kits with heat shrink sleeves, use of a heat gun in a flammable leakage zone is not recommended.

Tapes used in the previously mentioned SWPM tasks do use P-421, which is a temperature grade D tape and can be used for all temperature repairs.

References: Boeing Standard Wiring Practices Manual (SWPM) 20-02-10, 20-30-00 and 20-30-12