What happened
On September 28, 1998, a Beechcraft 1900 D, registration F-GRPM, operated by Proteus Airlines, was performing a scheduled passenger flight from Saint Etienne to Bordeaux. While cruising at 19,000 feet, approximately five minutes after leveling off, the crew observed two distinct surges in torque on the right engine. The torque increased from a set 2,950 lb.ft to approximately 4,500 lb.ft before dropping sharply and stabilizing at a lower level of 2,000 lb.ft.
In response to the engine instability, the crew elected to shut down the right engine. The flight continued as a single-engine operation, and the aircraft returned to Saint Etienne, landing without further difficulty.
The investigation
The investigation focused on the technical history of the right engine, which had been removed and reinstalled on September 7, 1998, following a bird strike. While ground tests and a subsequent check flight had shown no anomalies, recent maintenance logs indicated intermittent issues with the propeller synchronizer.
Upon inspection of the aircraft following the incident, investigators discovered that the electrical connector for the propeller synchronizer had been swapped with the connector for the auto-feathering solenoid on the propeller governor. Because both connectors were identical and part of the same wiring harness, the error was physically possible during the engine reinstallation. This miswiring caused the observed torque fluctuations and, crucially, rendered the auto-feathering system inoperable.
Findings
- The primary cause was a maintenance error during the engine reinstallation on September 7, where two identical electrical connectors were inadvertently reversed.
- The aircraft's design allowed for this error because the connectors were identical and lacked distinct markings to prevent incorrect assembly.
- The error went undetected through several layers of oversight, including the post-maintenance ground test, the check flight, and routine line operations.
- The airline's maintenance oversight was also a factor, as the propeller synchronizer issue had been reported in the maintenance logs but had not been rectified within the required timeframe.
Safety action
The BEA recommended that the French civil aviation authority (DGAC) notify operators of Beechcraft 1900 C and D aircraft regarding the risk of connector permutation during maintenance. Additionally, the BEA requested that the FAA investigate a design modification to ensure such an error cannot recur.