The Directorate General of Civil Aviation (DGCA) has launched a detailed investigation into the frequent “uncommanded” deployment of Ram Air Turbine (RAT) on Boeing 787s. The world’s largest aerospace company, Boeing, told DGCA that this pattern has been noticed in as many as 31 aircraft. These incidents happened within six months of maintenance that required the RAT to be manually stowed, Hindustan Times reported.
The recent incident happened on October 4, when RAT was deployed in the final approach of Air India’s Amritsar-Birmingham flight at around 1,600 feet. The plane, which landed safely, was grounded for further checks. The aircraft, VT-ANO, returned to Delhi the next day after checks and had undergone RAT maintenance in July, the report added.
The report further added that 29 out of the said number are not upgraded with a component that prevents the “uncommanded deployment”.
But what is the cause behind this?
The outlet further reported that Boeing points to a faulty locking mechanism behind the “uncommanded deployment” of RAT. The report mentions that if technicians try to stow the RAT while the hydraulic pressure is still high, the toggle assembly may fail to lock properly.
Additionally, vibrations from landing, movement of gear, or rough runways can shake it loose, causing the emergency power system to deploy unexpectedly.
To address this, Boeing introduced a better shuttle valve in 2014 that controls hydraulic pressure and helps the lock work properly. However, neither Boeing nor Collins Aerospace, the company that supplies parts, mandated airlines to install this fix through a service bulletin, HT reported.
In 2015, Boeing issued instructions telling technicians to keep the stow switch pressed until hydraulic pressure falls below 200 PSI, which usually takes about six seconds after stowing. For reference, normal system pressure is around 5,000 PSI.
India operates as many as 32 Boeing 787 aircraft, and 19 of them lack this. “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 was quoted by HT as saying.
About RAT
The RAT is a small turbine that gets activated from the aircraft’s fuselage to generate emergency power in critical situations. It can either be automatically or manually deployed by the pilot to keep the aircraft functioning when both engines fail or hydraulic pressure drops, the outlet further reported.
It further said that the system can also be activated if the cockpit instruments lose power or the electric motor pumps malfunction.