What happened
On March 16, 2009, a Canadair CL-215, registration C-FTXB, operated by Buffalo Airways, was performing a ferry flight from Santa Maria Airport (LPAZ) in the Azores to Cascais, Portugal, as part of a delivery mission to Turkey. The aircraft was accompanied by another similar aircraft during the transit.
After climbing to 9,000 feet and stabilizing in cruise flight, the pilot reported an overspeed condition on the number one engine propeller. The crew attempted to follow recommended checklists to correct the pitch, but the propeller speed could not be controlled. To prevent potential engine damage, the pilot was forced to shut down the affected engine and feather the propeller. The aircraft subsequently returned to Santa Maria, performing a single-engine landing at 14:28 UTC without further incident.
The investigation
The GPIAAF investigation focused on the mechanical behavior of the propeller system and the condition of the engine components. Technical inspections of the removed propeller governor (s/n WH 9 and 780) were conducted by an external laboratory. The investigation examined the transition from climb to cruise power settings and how the propeller pitch responded to changes in engine load.
Findings
- The crew was properly qualified and followed all standard operating procedures and emergency checklists.
- The aircraft was airworthy with all necessary certificates valid at the time of the flight.
- The number one engine propeller entered an overspeed state that could not be corrected by the crew through pitch control procedures.
- Thick sludge and contamination were found inside the propeller governor body, which physically prevented the pilot valve from moving.
- A crack was also discovered in the governor body during overhaul.
- The accumulation of sludge, likely due to environmental exposure or inadequate maintenance, prevented the governor from directing oil pressure to increase blade pitch, which is necessary to counteract overspeed conditions.
Safety action
While the investigation initially considered a safety recommendation regarding the assessment of Buffalo Airways' maintenance procedures, this became unnecessary as Transport Canada had already initiated follow-up inspections and issued a Civil Aviation Daily Occurrence Report (CADOR) regarding the operator's maintenance practices.