A recent inquiry has uncovered a concerning pattern of recurring activations of the Ram Air Turbine (RAT) on Boeing 787 aircraft. Air India Flight 117 experienced an unexpected deployment of its emergency power system during a landing in Birmingham on October 4th, an incident that has now been linked to a broader issue affecting numerous Boeing 787-8 models worldwide. Aviation authorities have been informed that 31 similar incidents have occurred globally, with 29 of these involving aircraft that have not yet received a critical modification to prevent this malfunction.
The RAT, a vital component that deploys from the aircraft’s fuselage to provide emergency power in the event of engine or main electrical system failure, deployed on the Air India flight as it approached the runway at 1,600 feet. Despite the unusual deployment, the aircraft landed safely and returned to Delhi the following day after undergoing necessary checks. Boeing has reportedly attributed the issue to a faulty locking mechanism. Specifically, when the RAT is stowed while hydraulic pressure is still high, a toggle assembly might not lock correctly. Subsequent vibrations, such as those from landing or rough runways, can then cause it to dislodge, leading to deployment.
While Boeing introduced an improved shuttle valve in 2014 to better regulate hydraulic pressure and ensure proper locking, a service bulletin mandating its installation across the fleet has not been issued. This means airlines are not currently required to retrofit their aircraft with this crucial upgrade. India, which operates 32 Boeing 787 aircraft, has 19 that still lack this modified shuttle valve. Following the Birmingham incident, Air India has initiated a review of its fleet, re-performing the RAT stowage procedure on 14 aircraft that had undergone maintenance in the six months prior, and scheduling checks for the remaining two.
Boeing had previously issued guidance in 2015 advising technicians to hold the stow switch for approximately six seconds after stowing the RAT, to allow hydraulic pressure to drop below 200 PSI (compared to the normal system pressure of 5,000 PSI), ensuring the locking mechanism engages correctly. The lack of a mandatory service bulletin, however, leaves a significant portion of the fleet potentially vulnerable.