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 repeals Airworthiness Directive (AD) AD/PT6A/28 and issues the following AD under subregulation 39.001 (1) of CASR 1998 and subsection 33 (3) of the Acts Interpretation Act 1901. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct an 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.
Pratt and Whitney Canada Turbine Engines - PT6A Series
AD/PT6A/28 Amdt 1
Water Washing
1/2015
 
Definitions:
In this AD:
an aircraft is operated in a salt laden environment if:
1.    it takes-off or lands within 10 nautical miles of the sea; or
2.    the flight route is within 10 nautical miles of, or over, the sea and at an altitude of less than 10 000 feet.
parachute training operation means an aircraft operation involving a descent by a student parachutist or a novice parachutist from the aircraft, and includes any aircraft operation involving a tandem descent by parachutists from the aircraft.

Applicability:
This AD applies to all PT6A series engines installed in single engine aircraft:
1.    carrying passengers in any of the following:
(a)     an operation for a commercial purpose prescribed by regulation 206 of the Civil Aviation Regulations 1988;
(b)     parachute training operations; and
2.    operated in a salt laden environment.

Requirement:
1.    A visual inspection of the compressor turbine blades for evidence of sulphidation must be carried out in accordance with an inspection procedure and the criteria for acceptable damage detailed in the applicable Pratt and Whitney Canada maintenance manual. A visual inspection carried out in accordance with AD/PT6A/28 is taken to be a visual inspection for this AD.
Note 1:  The inspection may be carried out by a borescope inspection.
Note 2:  The inspection may be carried out as part of a hot section inspection.
2.    Engine compressor and compressor turbine water washing must be carried out in accordance with the procedure detailed in the applicable Pratt and Whitney Canada maintenance manual. Water washing carried out in accordance with AD/PT6A/28 is taken to be water washing for this AD.

Compliance:
1.    Unless the compressor turbine was inspected within 200 hours time in service before 30 December 1998, the inspection in Requirement 1 must be carried out within 10 hours time in service from 30 December 1998.
2.    Requirement 2 must be carried out in accordance with the “Wash Schedule Recommendations” table detailed in the applicable Pratt and Whitney Canada maintenance manual.

 
The effective date of this AD is 30 January 2015.

Background:
AD/PT6A/28 was issued to require an inspection for evidence of sulphidation of the compressor turbine blades, and water washing of the compressor and compressor turbine, of PT6A series engines. The requirements reflect 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 resulted from the investigation of a PT6A engine in flight shut down event which was attributed to compressor turbine blade fracture resulting from sulphidation. The level of sulphidation was consistent with inadequate water washing.
AD/PT6A/28 Amdt 1 has been issued to clarify that the AD applies to aircraft engaged in parachute training operations. Those operations are regarded by CASA as private operations. However, the aircraft engaged in those operations must be maintained to charter aircraft standards to address the identified unsafe condition.

 
Mike Higgins
Delegate of the Civil Aviation Safety Authority
5 January 2015