Emergency power, or RAT, deployed frequently on Boeing 787s, finds inquiry
Air India Flight 117's emergency power system deployed during landing, part of a global trend affecting 31 Boeing 787 aircraft due to a faulty mechanism.
When Air India Flight 117’s emergency power system deployed unexpectedly during a landing in Birmingham on October 4, it was part of a pattern affecting dozens of the aircraft – a Boeing 787-8 — worldwide, the aviation regulator has learnt.
As the Boeing Dreamliner jet approached the runway for landing, its emergency power turbine – the RAT, or ram air turbine – unexpectedly folded out of its fuselage when the jet was at 1,600 feet.
According to people aware of the matter, who asked not to be named, Boeing has told India’s aviation regulator that 31 similar incidents have occurred globally on 787 aircraft. Nearly all — 29 cases — involved planes without a modified component that prevents the malfunction.
The RAT is a small turbine that drops from the fuselage to generate emergency power if both engines or main electrical systems fail.
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Air India told the Directorate General of Civil Aviation that none of the conditions that should trigger deployment were present. The aircraft landed safely, and the plane returned to Delhi the next day after checks.
Boeing did not respond to requests for a comment.
The 31 incidents typically occurred within six months of maintenance requiring the RAT to be manually stowed, according to officials familiar with Boeing’s briefing. The Birmingham aircraft, VT-ANO, had undergone RAT maintenance in July.
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Boeing identified the cause as a faulty locking mechanism. When technicians stow the RAT while hydraulic pressure remains high, a toggle assembly may not lock properly. Vibrations from landing, gear operation or rough runways can then shake it loose, deploying the turbine.
The manufacturer introduced an improved shuttle valve in 2014 to regulate hydraulic pressure and ensure proper locking. But Boeing and parts supplier Collins Aerospace have not issued a service bulletin requiring airlines to install the upgrade, the official cited above said.
That means operators are not mandated to retrofit their fleets.
India operates 32 Boeing 787 aircraft. Nineteen still lack the modified shuttle valve.
After the Birmingham incident, Air India identified 16 aircraft that had undergone RAT maintenance in the past six months. The airline repeated the stowage procedure on 14 planes and scheduled the remaining two for checks during routine maintenance.
“RAT stowage was repeated for 14 aircraft, and the remaining two are scheduled for verification during ongoing base maintenance,” an official aware of the developments said.
Boeing published guidance in 2015 instructing technicians to hold the stow switch until hydraulic pressure drops below 200 PSI — about six seconds after stowing. Normal system pressure runs at 5,000 PSI.
