What happened
On 3 July 1998, a BAe ATP, registration G-MANU, was performing a scheduled public transport flight when the crew noticed irregularities during their descent through FL 70. The pilot reported that the right engine torque and propeller RPM began to fluctuate. The crew found that the engine stabilized once propeller synchronization was deselected. The flight continued to Manchester Airport, where the landing was completed without further engine issues. However, following two subsequent flight sectors, the crew noted that the de-icing system for the right propeller had become inoperative.
The investigation
An engineering inspection of the aircraft following the incident revealed significant damage to the right engine propeller assembly. All six blades and the spinner were damaged. Investigators found that the propeller spinner was missing a portion of its structure because bolts had been projected forward from the back plate mounting position. Specifically, all six bolts intended to secure the back plate to the propeller hub thread inserts were missing.
This loss of hardware caused the spinner to become insecure, which subsequently led to the disbonding of the propeller de-ice sliprings, explaining the failure of the de-icing system. The force of the ejected hardware was sufficient to damage the intake lip and penetrate the fuselage ice guard. One bolt struck a stringer, which prevented it from fully penetrating the fuselage skin into the cabin.
Findings
- The primary cause of the incident was the loss of all six bolts securing the propeller back plate.
- The missing bolts caused the propeller spinner to become unstable, leading to damage to the propeller blades and the failure of the de-ice system.
- The loss of hardware resulted in an ejected bolt striking the aircraft fuselage.
- A subsequent fleet-wide check by the operator identified other aircraft with loose propeller bolts.