AD/AL 250/67 Amdt 1 Increased Labyrinth Seal Clearance Second Stage Turbine Nozzle Cancelled (Cth)

AIRWORTHINESS DIRECTIVE

On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive AD/AL 250/67 Amdt 1.

Allison Turbine Engines - 250 Series

AD/AL 250/67 Amdt 1 Increased Labyrinth Seal Clearance
Second Stage Turbine Nozzle 6/2009

Requirement:

CANCELLED.

This AD is cancelled on 4 June 2009.

Background:

This unique Australian AD raised in 1985 against Allison Commercial Engine Bulletin (CEB) 250-C28B, C28C CEB-A-72-2123 Rev.1 required a modification to the engine second stage turbine nozzle by increasing the interstage seal bore diameter to provide greater clearance with the seal knives on the first and second stage wheels to preclude the possibility of the labyrinth seal knives rubbing on the stationary member of the seal.

Compliance was:  In accordance with the requirement document.  The requirement document compliance was:  Comply at next time gasifier turbine assembly is disassembled at an overhaul facility.

This AD has been sufficiently promulgated for the affected engines to have been modified by now; therefore this AD is considered to be no longer required.

James Coyne
Delegate of the Civil Aviation Safety Authority

24 April 2009