Singapore’s defence ministry has shed more light on the pitch rate gyroscope failure that resulted in the crash of a Lockheed Martin F-16 on 8 May.
In a final update on the crash, during which the aircraft was lost but the pilot ejected safely, the ministry revealed that wear and tear had degraded the inputs from two of the jet’s four pitch rate gyroscopes.
The probe into the accident was conducted by the Republic of Singapore Air Force (RSAF), the Transport Safety Investigation Bureau, and manufacturer Lockheed.
The gyroscopes measure the aircraft’s pitch, roll, and yaw, and provide input to the jet’s digital flight control computer. The other motion sensors that provide data to the computer are accelerometers and an angle of attack transmitter.
During the pre-flight check on 8 May no fault was discovered, with gyroscopes 1, 2, and 3 providing similar inputs, with gyroscope 4 serving as a back-up. While taking off, however, gyroscopes 2 and 3 gave erroneous but similar inputs.
The correct input from gyroscope 1 was rejected because it varied from that provided by the faulty gyroscopes 2 and 3. Gyroscope 4 activated, but its input was also rejected.
The aircraft thus took off with erroneous data from gyroscopes 2 and 3. This caused a flight control malfunction warning, with the aircraft “deemed uncontrollable by the pilot”, according to the probe.
“It is assessed that the two pitch rate gyroscopes had degraded due to wear and tear and failed during take-off,” says the probe.
“To reduce the chance of a reoccurrence, the RSAF has put in place an additional preventive maintenance procedure for the gyroscopes, under which RSAF engineers will periodically remove the F-16 gyroscope assemblies and test them using specialised equipment.”
Following checks on all F-16 gyroscopes, flights of RSAF F-16s resumed on 21 May.
