Airworthiness Bulletins

AWB 34-2 Issue 1, 8 May 2001
Ground proximity systems

Effectivity

Ground Proximity Warning Computers(GPWC) Sundstrand /Allied Signals / Honeywell, Part Numbers :

Background

A general information letter produced by Honeywell has highlighted recommended maintenance requirements for GPWC's. Periodic system ground checks, or computer bench tests should be made.
The letter further explains that although the computers have built-in test capabilities, the system is not 100% effective in detecting failures during normal operation or when performing a self-test in the aircraft. Some of these possible undetected failures may impair or reduce the warning capabilities of the system.

Recommendation

If the airframe manufacturers do not recommend the performance of dynamic system tests of the Ground Proximity Warning System at periodic intervals to simulate conditions that exercise all the warning modes, Honeywell highly recommends removal of the computer from the aircraft for a complete bench test.

If the airframe manufacturer recommends the performance of dynamic system tests of the Ground Proximity Warning System at periodic intervals, Honeywell highly recommends adherence to the airframe manufacture's schedule.

Honeywell highly recommends the following intervals for operational checks be applied where airframe manufacturers do not specify maintenance intervals.

For GPWC Part Numbers 965-0376-0XX;965-0411-010 ;965-0476-0XX at; 7,000 flight hour intervals

For GPWC Part Numbers at 965-0686-0XX at 5,000 flight hour intervals

Honeywell produces ground check out procedures and brake-out box drawings that allow the aircraft installation to be checked dynamically

Based on this information, CASA highly recommends that operators with the above part numbered equipment installed, review their aircraft maintenance programs to comply with the requirements of the following documents:

Honeywell General Information Letter GIL No GPWC - ALL-34-1 Rev 2 dated May 17/00

Honeywell Service Information Letter SIL No GPWC - Mk VI - 34 -1 Rev 1 dated Jan 12/94

Where GPWC's have been installed under an STC the Honeywell recommendations should be complied with unless the STC specifically addresses the continuing airworthiness aspects.