Flanker Trouble: Did Fly-By-Wire Glitch Crash IAF Su-30?

It was unlikely an engine failure or flame-out that doomed the IAF Su-30 MKI that crashed on Tuesday near the Lohegaon air force station in Pune as had been conjectured over the last two days. An officer in Pune I spoke to today says it was highly likely a technical glitch in the fly-by-wire control. Two reports today (in the Indian Express and Pune Mirror) suggest the same thing, quoting IAF officials as saying the flight data recorder recovered from the aircraft appeared to render engine failure and pilot error unlikely.

A full-fledged crash inquiry is underway, and nothing is reasonably conclusive at this time. But prima facie indicators could be troubling if they are correct in identifying the principle trigger for the incident as an FBW breakdown.

In August 2012, then IAF chief Air Chief Marshal N.A.K. Browne had said, "We have identified a ‘fly-by-wire’ problem with the aircraft. It is a design issue and we have taken it up with the design agency." He was talking about type's third crash in Indian service in December 2011. This report quotes him more specifically as saying, "There was a problem with the aircraft's FBW controls and there is also an issue of design," indicating a problem with the FBW control system itself as well as the position of the switches.

In this report, former AOC-in-C Air Marshal (Retd.) Vinod Bhatia says two of the first three MKI crashes were put down by courts of inquiries (COI) to malfunctions in the the FBW system.

Bhatia explains, "The Su-30 MKI’s aerodynamic construction is an unstable longitudinal tri-plane that confers its unprecedented agility. Like most modern jet fighters, this highly unstable platform is manoeuvred by computer-controlled FBW system. Multi-layered backup systems are necessary as without the FBW, the aircraft cannot be manually controlled by the pilots. To ensure near-ultimate safety, the Su-30 MKI’s FBW system is endowed with quadruple redundancy. If one of the FBW channels becomes faulty, it automatically gets disconnected from the system, suitably warning the crew to take appropriate actions. A level-1 failure does not jeopardise the mission, while a level-2 failure would demand a diversion to the nearest suitable airfield. With so much in-built redundancy, a level-3 failure would normally be rarer than one in a million possibility which unless quickly rectified could lead to the loss of aircraft."

I'll say it again. Near nothing conclusive can ever be known about a crash just 48 hours later. But these are prima facie indicators that investigators are working with.

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