AD/F50/101 Engine Controls Automatic Flight-Idle Stop Control Unit (Cth)

AIRWORTHINESS DIRECTIVE

For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.001(1) of CASR 1998.  The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.

Fokker F50 (F27 Mk 50) Series Aeroplanes

AD/F50/101 Engine Controls - Automatic
Flight-Idle Stop Control Unit 5/2009

Applicability:

F27 Mark 050, Mark 0502 and Mark 0604 aeroplanes, all serial numbers.

Requirement:

Unless accomplished previously, install an automatic flight-idle stop control unit and accomplish the associated modifications in accordance with the Accomplishment Instructions of Fokker Services Service Bulletin SBF50-76-017 dated 30 September 2008 or later revision approved by the European Aviation Safety Agency (EASA).

Note:  EASA AD 2009-0049 refers.

Compliance:

Within 24 calendar months after the effective date of this Directive.

This Airworthiness Directive becomes effective on 7 May 2009.

Background:

Detailed investigations of two accidents with Fokker 50 (F27 Mark 050) aeroplanes have identified as probable cause that the flight crew selected propeller reverse during flight while the protection from the automatic flight-idle stop system was temporarily not available.  This action is not in accordance with approved operating procedures.  In addition, it has become clear that in general, flight crews attempt to make power lever selections below flight-idle more frequently than anticipated.

This condition, if not corrected, could lead to further events of inadvertent propeller reverse selection during flight, resulting in loss of control of the aeroplane.  Even though the potential for this kind of event is primarily driven by operational (human) factors, corrective (AD) action is nevertheless considered justified.

A direct cause of possible temporary unavailability of the automatic flight-idle stop protection has been addressed by AD/F50/86 (CAA-NL AD 2003-091).

To improve the overall reliability of the flight-idle stop system, making the system less sensitive to intentional and inadvertent power lever selections below flight-idle, Fokker Services has developed a modification that meets the latest requirements.

This modification has been published as SBF50-76-017, which provides instructions to modify the flight-idle stop system and introduces additional monitoring and flight crew alerting which were not required during the original certification of the aeroplane.

For the reasons described above, this Directive requires the installation of an automatic flight-idle stop control unit and the accomplishment of associated modifications.

James Coyne
Delegate of the Civil Aviation Safety Authority

26 March 2009