Now that the preliminary report by the Aircraft Accident Investigation Bureau (AAIB) into the AI 171 accident that claimed 261 lives has been made public, all the speculated causes of the accident, including fuel contamination, configuration issues, flap position, all-up weight issues etc., have gone out the window.
What instead emerges are a few possibilities that need to be underlined.
Fuel starvation caused engines' shut down, but how did it happen?
The preliminary report by the AAIB, though subject to change, cites the reason for the accident as twin-engine failure due to fuel starvation.
But what led to the fuel starvation? It says that the fuel control switches that are primarily responsible for fuel supply to the engines were shifted to the cut off position from the run position during the critical phase of the flight.
The report further says that relight attempts by the pilots were not successful as the aircraft had not reached the height and speed needed for a safe twin-engine relight after failure. The engines stalled, leading to a loss of thrust and the crash landing of the aircraft in an inhabited area.
According to Rule 3 of Aircraft (Investigation of Accidents and Incidents), Rules 2017, the sole objective of the investigation of an Accident/Incident shall be the prevention of accidents and incidents and not to apportion blame or liability. My intention here is the same—to assess the preliminary report and not to jump to conclusions as to the causes and reasons.
The fuel control switch is the one that energises and de-energises a solenoid valve, which is an electrically actuated, mechanically activated valve, supplying fuel to the engine when energised and cuts off the fuel supply when de-energised. It acts like a gate.
The fuel control switches are designed with a detent mechanism that requires deliberate action to move them from the 'run' to 'cut off' position, preventing accidental activation. The switches are spring-loaded to remain in position.
To change from run to cut off, the pilot will have to pull it from its position and then move to the cut off or run position. Once the switch has reached the desired position, it is released and locked in position by the spring force.
Lesson from an Air Force plane crash
The report, though a preliminary one, clearly spells the fundamental cause of the accident as fuel starvation, leading to engine failure and caused by the fuel control switch being cut off.
I believe those who are waiting for the final report are only waiting to see who and what caused the engine control switch to move to the cut off position during the critical phase of the flight.
As a flight engineer in a military aircraft, it is my strong conviction that the switch requires human intervention to get activated.
There were only two pilots in the cockpit. From the AAIB report, the CVR recorded the pilot in control (PIC) asking the other pilot as to why he switched the fuel control switch off. The other pilot, who is co-piloting says, he did not do it.
That means both pilots were unaware of the switch getting into the cut off position. It is hard to believe that the pilots with such vast experience can indulge in such a suicidal attempt. Also, it is surprising that the report does not mention any other conversations from the cockpit.
I am very much sure that there were nonstop conversations in the cockpit till the end. And a lot more can be inferred from those last conversations.
I am reminded of a fatal accident of an AN 32 aircraft, which crashed immediately after takeoff from the Yelehanka Air Force station in the 90s
A trainee cadet's mistake had led to the tragedy in which four crew members lost their lives.
The last words of the captain were, "You……., you killed us." This helped us in knowing the actual reason behind the crashWhy the preliminary report into the Air Indian crash is not mentioning any other conversation inside the cockpit then is indeed strange.
It must be noted that the report does not say these were the only words captured in the CVR.
Accidentally switched off?
The other possibility is of an accidental human intervention.
But then as I mentioned already, these switches cannot get activated accidentally. They require deliberate human intervention. Further, they are guarded by brackets on both sides to deny inadvertent access.
Also, a strong spring-loaded locking mechanism holds it in position. So, any accidental operation of the switches is only the remotest of possibilities.
Could it have been a systems failure?
A third possibility is a design fault.
The report itself mentions the special airworthiness information bulletin (SAIB) issued by the Federal Aviation Administration (FAA) in 2018, regarding the POTENTIAL DISENGAGEMENT OF THE FUEL CONTROL SWITCH LOCKING FEATURE. Though it was issued based on the reports of the operators of Boeing 737 aircraft, the fuel control switch design, including the locking feature, is similar in various Boeing models including Boeing 787.
The report says that Air India did not conduct the suggested inspections as the bulletin was only advisory, not mandatory. This is definitely a lapse on the part of Air India. In aviation, flight safety is of paramount consideration. Bureaucratic lethargy is not acceptable.
This makes me look at another possibility.
Let us assume that while starting the engines on ground, pilot operated the fuel control switch by pulling it outward, and then pushed it to the run position. Now when the pilot releases the switch, it is supposed to get locked in the position under spring force. What if it didn't get locked?
During takeoff, while the aircraft achieves 180 knots, due to the force of inertia, the switches that were not locked in position earlier, overcome the spring force and come back to the cut off position, without the pilot knowing about this. The report substantiates this possibility.
It says that the switches transitioned to the cut off position at the speed of 180 knots. The operators, Air India, cannot deny this could have happened, as they did not carry out the advisory inspection and ruled out any issue with the locking mechanism.
The need for patience
But while discussing all this, as the aviation minister said on Saturday, let's not jump to conclusions. Let's wait for the final report to arrive. But till then, every probability is a possibility that cannot be completely ruled out.
"Justice needs to be served", as the minister emphasised. Here's hoping it will be.
(Wing Commander A Mahesh (Retd) was a flight engineer with IAF and is a keen follower of the latest developments in the aviation industry.)
