What happened
On August 10, 2010, at approximately 20:56 UTC, a Piper PA-28R-201, registration PT-OCQ, departed from Salgado Filho Airport (SBPA) in Porto Alegre, Brazil, for a local night instructional flight. The aircraft was operated by Aeroclube do Rio Grande do Sul with two pilots and one passenger on board.
After approximately fifty minutes of flight, while descending through 1,500 feet during the return to the airport, the engine began exhibiting fluctuations in oil pressure and manifold pressure. The engine power continued to decrease throughout the remainder of the flight. Despite the loss of power, the crew successfully landed the aircraft. Following the landing, the engine dropped to idle speed and the aircraft lacked sufficient power to taxi.
The investigation
The investigation conducted by CENIPA established that the aircraft was within its operational weight and balance limits and that all pre-flight checks had been performed according to the manual. The crew was properly qualified, and meteorological conditions were favorable for the flight.
Investigators determined that the power loss was caused by the rupture of the metal conduit through which the throttle control cable passes. This rupture split the housing into two parts, creating a gap. When the throttle lever was advanced, the control cable moved out of its original housing and into the space created by the break. This caused the cable to form an arc that physically limited the movement of the throttle lever, preventing the engine from reaching normal operating RPM.
Maintenance records showed no recent replacement of the throttle cable assembly. As the aircraft was manufactured in 1990, the components had been in service for approximately twenty years. The investigation noted that the manufacturer's maintenance manual did not require replacement of this specific component at 100, 500, or 1,000-hour intervals; instead, it was an "on-condition" part, with instructions limited to a visual inspection of its functional state.
Findings
- The engine power loss was caused by the mechanical failure of the throttle control cable conduit.
- The rupture of the conduit prevented the full travel of the throttle lever.
- The failure was likely due to natural wear and tear of the component after twenty years of operation.
- The maintenance manual only required a visual inspection of the component's condition rather than a scheduled replacement.