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Wear and tear in pitch rate gyroscopes caused Singapore F-16 crash

June 26, 2024 (by Lieven Dewitte) - Singapore's Ministry of Defence (MINDEF) has attributed the crash of one of their F-16s on 8 May to “degraded” gyroscopes. The F-16 crashed shortly after take-off from Tengah Air Base.

RSAF F-16C block 52 #96-5028 from the 425th FS is parked on the tarmac at Luke AFB. The jet crashed on May 19th, 2004. [Janssens Ronny collection]

The probe into the accident was conducted by the Republic of Singapore Air Force (RSAF), the Transport Safety Investigation Bureau, and manufacturer Lockheed.

It appears that wear and tear degraded the inputs from two of the jet’s four pitch rate gyroscopes.

The gyroscopes measure the aircraft’s pitch, roll, and yaw, and provide input to the jet’s digital flight control computer (DFCC). 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.

Summary of events leading to F-16 crash at TAB.

Before Take-Off
  • Pilot conducted a pre-flight test; the Built-In Test did not detect any fault with the functioning of the aircraft's gyroscopes before take-off.

  • Pitch rate gyroscopes 1, 2, and 3 provided correct and similar inputs to the Digital Flight Control Computer, while pitch rate gyroscope 4 remained as a back-up

At Take-Off
  • Pitch rate gyroscopes 2 and 3 degraded erroneous but similar inputs.

  • As input from pitch rate gyroscope 1 was different from the other 2, it was rejected by the Digital Flight Control Computer

  • Pitch rate gyroscope 4 was activated but was also rejected

> The Flight Control Malfunction Warning was triggered

After Lift-Off
  • Pitch rate gyroscopes 2 and 3 continued to give erroneous but similar inputs

  • Aircraft took inputs from the erroneous pitch rate gyroscopes 2 and 3

> Aircraft was deemed uncontrollable by the pilot

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.

The DFCC manoeuvred the aircraft using erroneous pitch rate signals from the two degraded gyroscopes, making the F-16 uncontrollable by the pilot.

According to Lockheed Martin this is the first such failure reported to the company since F-16s first flew in 1974.

“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.

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