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Investigations have concluded into the crash of a Republic of Singapore Air Force F-16 fighter jet, with the identification of a “rare” malfunction of aircraft gyroscopes.
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The RSAF F-16 crashed at Tengah Air Base in Singapore on 8 May following ejection by its pilot. The pilot was then transferred by RSAF RESCUE10 helicopter to the Singapore General Hospital, in line with established medical evacuation procedure.
Following the crash, an investigation was led by the RSAF, supported by Lockheed Martin and the Transport Safety Investigation Bureau. In addition, pilot and aircraft engineers were interviewed as well as study of maintenance records and procedures.
“During the investigation, data downloaded from the Flight Data Recorder and the Digital Flight Control Computer of the incident F-16 were reviewed,” according to a public statement published by the Ministry of Defense of Singapore.
“The pilot had experienced a malfunction of his F-16’s Digital Flight Control System during take-off. As a result, he was not able to safely control the aircraft.
“After correctly determining that it was unsafe to take the aircraft further, the pilot responded in accordance with emergency procedures, and ejected within Tengah Air Base.
“The root cause of the malfunction has been attributed to degraded pitch rate gyroscopes, which form part of the motion sensors feeding inputs to the digital flight control computer.
“Specifically, two out of four pitch rate gyroscopes in the F-16 gave erroneous but similar inputs to the digital flight control computer.
“This resulted in the flight control logic accepting the similar erroneous inputs as ‘correct’, and sequentially rejecting the inputs from each of the remaining functioning gyroscopes as ‘incorrect’.
“Consequently, the digital flight control computer manoeuvred the aircraft in response to the erroneous pitch rate feedback signal from the two degraded gyroscopes, making the F-16 uncontrollable by the pilot. According to Lockheed Martin, this is a rare occurrence and the first such failure reported to it since the F-16s first flew in 1974.
“The investigation also concluded that the F-16 aircraft was maintained in accordance with established protocols, and the RSAF had adhered to required maintenance inspections. The RSAF F-16’s gyroscopes are the same as those used by other F-16 operators around the world. Lockheed Martin does not stipulate any preventive maintenance for these gyroscopes. The gyroscopes are to be replaced when a fault is detected. The F-16’s pre-flight built-in test did not detect any fault with the functioning of the aircraft’s gyroscopes before take-off.”
Singaporean F-16 have four pitch rate gyroscopes with three in use during normal conditions and one as backup. Gyroscopes consist of a mechanical spinning rotor set within gimbals to help detect rotation rates. This is then converted to electrical signal readings, which are fed to the flight computer.
Investigation findings have been reviewed by the Republic of Singapore Air Force’s Inspector General Office. The External Review Panel on SAF safety has also been updated on the investigation findings. The panel concurred with the additional preventive procedure by the RSAF.
“Additional preventive measure going forward. It is assessed that the two pitch rate gyroscopes had degraded due to wear and tear and failed during take-off. To reduce the chance of a reoccurrence, the RSAF has put in place an additional preventive maintenance procedure for the gyroscopes, under which the RSAF engineers will periodically remove the F-16 gyroscope assemblies and test them using specialised equipment,” according to the statement.
“This will increase the likelihood for engineers to detect early signs of degradation and pre-emptively replace the gyroscopes, before the gyroscopes reach the stage of accelerated degradation leading to failure.
“This measure is over and above the prescribed aircraft manufacturer’s maintenance procedures. Before the RSAF resumed F-16 flights on 21 May 2024, each RSAF F-16 aircraft’s flight control gyroscopes had been checked and cleared.
“The RSAF will continue to ensure the highest standards of maintenance for the airworthiness of every aircraft. With approximately 3,100 F-16s operating in 25 countries and over 19 million flight hours, the Ministry of Defense and the RSAF remain confident in the operational capability and reliability of the F-16 to defend Singapore’s skies.”
