Boeing 767 Series AeroplanesBoeing 767 Series Aeroplanes

Boeing 767 Series Aeroplanes

AD/B767/144 (Continued)

Replacement of the WEU power supplies with new or modified power supplies having P/N 285T0035-202 Mod A, in accordance with SB 767-31-0106 Revision 1, is an acceptable means of compliance if carried out prior to the effective date of this Directive.

5. WEU power supply P/N 285T0035-201 may not be installed on any aeroplane as a replacement part.

Note 2: FAA AD 2001-11-08 Amdt 39-12250 refers.

Compliance: For Requirement 1 - Initially, within 15 days of the effective date of this Directive and thereafter in accordance with Requirements 2.a and 2.b.

For Requirement 2.a - Before each flight until either Requirement 3 or 4 is accomplished.

For Requirement 2.b - At intervals not to exceed every “A” check or 45 days, whichever occurs first until either Requirement 3 or 4 is accomplished.

For Requirement 3 - Before further flight. For Requirement 4 - Before 16 July 2002.

For Requirement 5 - As of the effective date of this Directive. This Airworthiness Directive becomes effective on 27 June 2001.

Background: The Federal Aviation Administration received a report advising that during a production test flight of a Model 747-400 series aeroplane the flight test crew noticed a power supply failure on the status page of the EICAS. Investigation revealed the automatic bench test procedure for the modular avionics warning electronic assembly (MAWEA) overstressed the 5.7 volt over-voltage clamp circuit which resulted in failure of the circuit to protect the warning cards in the MAWEA.

A slow failure of the MAWEA power supply could result in the gradual degradation of available visual, aural and tactile alerts, which could result in flight crew not being aware of and not taking immediate or appropriate action, in the event of an unsafe condition occurring.

The WEU power supply units on some Boeing 767-200 and -300 series aeroplanes are identical to those on the MAWEA on the affected Model 747-400 aeroplanes. Therefore, all of these aeroplanes may be subject to the same unsafe condition.