COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Pratt and Whitney Canada Turbine Engines - PT6A Series
AD/PT6A/28 Water Washing 2/99 DM
Applicability: All PT6A series engines installed in single engine aircraft:
- Carrying passengers for hire or reward in Civil Aviation Regulation (CAR) 206 commercial operations, and
2. Conducted in a salt laden environment.
Note 1: For the purpose of this directive, operating in a salt laden environment is defined as a take-off and landing within 10 nautical miles of the sea or, the flight route is within 10 nautical miles or over the sea and at an altitude of less than 10,000 feet .
Requirement: 1. In accordance with an inspection procedure and the criteria for acceptable damage detailed in the applicable Pratt and Whitney Canada maintenance manual, carry out a visual inspection of the compressor turbine blades for evidence of sulphidation, and
2. Carry out engine compressor and compressor turbine water washing in accordance with the procedure detailed in the applicable Pratt and Whitney Canada maintenance manual.
Note 2: The visual inspection may be carried out by either a boroscope inspection or a hot section inspection.
Compliance: 1. Unless the compressor turbine has been inspected within 200 hours time in service prior to the effective date of this directive, carry out the inspection within 10 hours time in service from the effective date of this directive.
2. In accordance with the “Wash Schedule Recommendations” table detailed in the applicable Pratt and Whitney Canada maintenance manual.
This Airworthiness Directive becomes effective on 30 December 1998.
Background: This Directive has been issued to require an inspection of the compressor turbine blades for evidence of sulphidation and, water washing of the compressor and compressor turbine. The requirement reflects concern for the airworthiness of single PT6A engine aircraft operated in a salt laden environment when water washing is not carried out at a frequency recommended by the manufacturer.
The concern results from the investigation of a recent PT6A in flight shut down event which has been attributed to compressor turbine blade fracture resulting from sulphidation. The level of sulphidation was consistent with inadequate water washing.