What is RAT and how does it work? The emergency system at the centre of Air India crash probe | WION Decodes

The Federation of Indian Pilots (FIP) has written to the Aircraft Accident Investigation Bureau (AAIB), flagging discrepancies in the preliminary report on the Air India Flight AI171 crash. Highlighting that the deployment of the Ram Air Turbine (RAT) may not be linked to the fuel interruption and raising doubts on the timeline, the FIP has called for fresh simulator tests to verify the sequence of events. The issue has drawn attention to a little-known aircraft safety system, which may provide investigators with clues on what led to the deadly crash that claimed the lives of 260 people onboard and on the ground, leaving just one surviving passenger.

What is a Ram Air Turbine (RAT)?

A Ram Air Turbine (RAT) is an emergency backup power system installed on several commercial aircraft, including the Boeing 787 Dreamliner, which was involved in the crash in Ahmedabad last year. The RAT, which is a small wind-driven turbine, is connected to a hydraulic pump or an electric generator. It is deployed automatically if a plane experiences a major loss of electrical power, hydraulic power, or engine-generated power.

Once deployed, the RAT can provide enough power to operate critical flight controls, instruments, communication systems and other essential functions needed for pilots to maintain control of the aircraft and attempt a landing.

When is RAT deployed?

RAT can be deployed automatically if both engines of an aircraft suffer a failure. It can also be deployed in case of a complete loss of power or if severe hydraulic failures are detected. The RAT can also be deployed manually by the pilots in case of an emergency.

As RAT is linked to major failures of an aircraft, its deployment on flight AI171 may give investigators crucial clues on the sequence of events that led to the deadly crash.

What are the doubts raised by pilots’ bodies?

The pilots’ body raised concerns about whether Boeing 787 simulator results align with the timeline outlined in the AAIB’s preliminary findings, which stated that the aircraft’s emergency RAT was deployed after the fuel control switch movement. The FIB suggested that the RAT deployment may have occurred due to an electrical fault or other existing issue, adding that it may have deployed before the fuel switch movement.

The FIP also cited flight simulator data indicating that the RAT typically begins generating power roughly 18 seconds after a fuel interruption. On this basis, it argued that the RAT deployment might not be directly linked to fuel switch movement.

“While the report indicates RAT power generation approximately 4-5 seconds after fuel interruption, simulator testing reportedly indicates approximately 18 seconds. The letter therefore suggests that RAT deployment may have occurred before fuel control switch movement and may indicate an earlier system or electrical fault requiring further investigation,” the letter read.

Referring to CCTV footage from Ahmedabad airport, the letter noted that the RAT appeared to already be deployed while the aircraft was still on the runway before rotation. This, it said, further strengthens the possibility of an earlier system anomaly rather than a fuel-control-triggered event.

The letter additionally highlighted a series of events leading up to the crash, including a loud explosion-like sound, a noticeable dimming of cabin lights, and multiple ACARS maintenance messages sent before takeoff. It suggested that these elements, along with damage patterns seen in the aft flight recorder imagery, should be analysed together to reconstruct a clear and consistent timeline and to assess whether an electrical failure played a role.

The association urged the investigating agency to independently verify the acceleration data in the preliminary report and to closely examine the relationship between RAT deployment, hydraulic power generation, and fuel control switch movement. The FIP recommended that these aspects be fully addressed in the final investigation report.

Ahmedabad plane crash

On June 12, Air India flight Boeing Dreamliner 787-8, carrying 242 people onboard, crashed moments after taking off from the Sardar Vallabhbhai Patel International Airport in Ahmedabad in the afternoon. The deadly incident resulted in the death of 241 people on board, leaving only one survivor. Other casualties were also reported on the ground at the site of the crash, bringing the total death toll from the incident to 260.

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