Civil Aviation Safety Alert (CASA) No. 2013-07

ATTENTION:
OWNERS/OPERATORS AND MAINTAINERS OF PRATT & WHITNEY PT6A ENGINES

Issuing Office: National Aircraft
Certification Branch
Document
No.
:
CASA 2013-07
File Classification No.: Z 5000-35 Issue No.: 01
RDIMS No.: 7051974 Effective Date: 2013-10-29

IMPORTANCE OF COMPRESSOR AND TURBINE WASHES (ALL PT6A)

PURPOSE:

The purpose of this Civil Aviation Safety Alert is to reiterate to PT6A operators the importance of compressor and turbine washes in preventing corrosion and sulphidation.

BACKGROUND:

Operating experience has shown that corrosion and sulphidation affects the aerodynamic efficiency and fatigue life of compressor and turbine components. Corrosion can be caused by salt deposits (sodium) and other atmospheric pollutants. Sulphidation attacks the oxide protective coating of turbine blades and will eventually expose and attack the base metal. This will weaken the blade and can eventually lead to catastrophic failure.

Sulphidation is a chemical process between sodium and sulphur that occurs in the hot section environment of a gas turbine engine.

Most aviation turbine fuels contain sulphur in sufficient amounts for sulphidation to occur.

Routine compressor and turbine washes can help reduce the damage caused by atmospheric pollutants by removing them before they cause corrosion. Compressor washes provide the best results if performed after the last flight of the day before deposits have a chance to do any lasting damage. Since sulphidation is dependent on temperature, there is no advantage to performing the turbine wash at any particular time of day; however, since the compressor wash will transfer deposits onto the turbine, it is recommended to do a turbine wash immediately following the compressor wash.

RECOMMENDED ACTION:

Transport Canada Civil Aviation recommends that owners, operators and other responsible agencies be familiar with, and follow the instructions detailed in P&WC Service Information Letters (SIL) PT6A-144 R2 (Compressor and Turbine washes as an effective means of preventative maintenance) and (SIL) PT6A-146 (PT6A-114 and -114A Compressor Turbine Blade Maintenance).

Defects, malfunctions and failures occurring on aeronautical products are to be reported to Transport Canada, Continuing Airworthiness in accordance with CAR 521 mandatory Service Difficulty Reporting requirements.

CONTACT OFFICE:

For more information contact a Transport Canada Centre; or Dean Ciaschini, Continuing Airworthiness, Ottawa, at 613-952-4357, facsimile 613-996-9178, or e-mail CAWWEBFeedback@tc.gc.ca.

Note: 
For the electronic version of this document, please consult the following Web address
www.tc.gc.ca/civil-aviation-safety-alert

For the Director, National Aircraft Certification,

ORIGINAL SIGNED BY

Derek Ferguson
Chief, Continuing Airworthiness

The Transport Canada Civil Aviation Safety Alert (CASA) is used to convey important safety information and contains recommended action items. The CASA strives to assist the aviation industry's efforts to provide a service with the highest possible degree of safety. The information contained herein is often critical and must be conveyed to the appropriate office in a timely manner. The CASA may be changed or amended should new information become available.

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