AD/F27/142 Amdt 1 - Main Landing Gear Actuating Ram (Cth)

COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES

Fokker F27 Series Aeroplanes

AD/F27/142 Amdt 1

Main Landing Gear Actuating Ram 5/98

Applicability: All Fokker F27 Mk 100 through Mk 700 series aircraft fitted with Dunlop main landing gear actuating ram, P/N AC67132, AC67134, AC67848 or AC67850.

Requirement: Modify the main landing gear actuating ram in accordance with Dunlop Equipment Division SB 32-1142 dated October 22, 1996, or Dunlop Aviation Australia (DAA) Service Bulletin 36-24 dated May 21, 1984.

Note: RLD AD BLA nr 1996-142(A) dated November 29, 1996, and Fokker SB F27/32-168 dated October 23, 1996, refers.

Compliance: Unless previously accomplished, at next repair or overhaul or within the next 4000 hours time in service or 24 calendar months, whichever occurs first.

This amendment becomes effective on 23 April 1998.

Background: Several operators have reported broken main landing gear lockstruts. Investigation by Fokker has confirmed failure of the lockstrut was due to loss of damping within the main landing gear actuating ram. To dampen the gear movement during extension the actuating ram is equipped with a damping chamber filled with silicon oil which is forced through a restrictor during ram extension. If a bobbin "O" ring seal fails then the silicon oil can leak past the seal and this may not be noticed during routine maintenance. Silicon oil loss usually leads to a gradual loss in damping which can be detected by an increase in landing gear extension speed or shaking of the aircraft at gear extension.

Dunlop Australia in 1984 developed a modification that also addresses the problem, however it changes the actuator ram seal configuration preventing fitment of the DED modification. This amendment reflects the suitability of the Dunlop Australia modification.