Attention:
Owners, operators and maintainers of Pratt & Whitney Canada CORP. (P&WC) model PT6B-37A engines, all serial numbers
| File Classification No.: | Z 5000-35 |
|---|---|
| RDIMS No.: | 20884556 |
| Document No.: | CASA 2025-07 |
| Issue No.: | 01 |
| Effective Date: | 2025-05-15 |
Purpose:
The purpose of this Civil Aviation Safety Alert (CASA) is to provide awareness of reported contamination of the Py lines and FCU on P&WC model PT6B-37A engines.
Background:
Following an engine overhaul, an event resulting in a momentary rotor speed drop during transition from takeoff and climb was reported. Troubleshooting of the issue identified a slow acceleration of the engine which could not be recovered with published maintenance procedures. Subsequent investigation revealed contaminants of sodium hydroxide in the rear Py line introduced from a cleaning procedure performed at engine overhaul, which migrated to the FCU.
Contamination at the FCU could lead to slow acceleration, slow deceleration, loss of power or uncontrolled acceleration.
Figure 1 and figure 2 show contamination of the rear Py line and at the FCU and front Py line connection, respectively.
Figure 1 - Contamination of the rear Py line.
Figure 2 – Contamination at the FCU and front Py line connection.
Figure 3 and figure 4 show acceptable condition of the rear Py line and at the FCU and front Py line connection, respectively.
Figure 3 – Acceptable condition of the rear Py line.
Figure 4 – Acceptable condition at the FCU and front Py line connection.
Recommended action:
Transport Canada recommends that owners, operators and maintainers perform acceleration checks and corrective actions in accordance with P&WC Service Bulletin (SB) A39125 Revision 1, dated 1 April 2025, or later revisions, for the PT6B-37A engines for which FCU and/or Py lines from affected engines listed in the SB were installed.
Within Canada, in accordance with the reporting requirement of Part V, subpart 21 (521) of the Canadian Aviation Regulation (CAR), owners, operators and maintainers should submit a Service Difficulty Report (SDR) to Transport Canada for the discovery of each reportable service difficulty. Please note that if contamination of the Py lines or the FCU is found, an SDR should be submitted. If the discovery of such condition is made by someone not required per the CAR to submit SDR, the condition should be reported to the design approval document holder (DADH) i.e. P&WC. Outside Canada, report any such occurrence in accordance with local reporting requirements.
Contact office:
For more information concerning this issue, contact a Transport Canada Centre; or contact Isabelle Hallé, Continuing Airworthiness in Ottawa, by telephone at 1-888-663-3639 or by e-mail at TC.CAWWEBFEEDBACK-retroactionWebMDLN.TC@tc.gc.ca.
Original signed by
Jenny Young
Chief, Continuing Airworthiness
National Aircraft Certification
PY Lines and fuel control unit (FCU) contamination
(PDF, 352 KB)
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.