Air India 171 Prelim Report – A CLOSE Look @ Those Switches
The prelim report for the Air India 171 crash highlights a 10 second delay the fuel control switches being changed. They question is why?
Recap – Air India 171 Preliminary Report
The prelim report said that there was a 10 second delay between engine one fuel control switch being changed from “Cutoff” to “Run”. In other words, the fuel control switch for engine one was in the “Cutoff” position for 10 seconds (switched to Cutoff about 3 seconds after takeoff).
And the fuel control switch for engine 2 was in the Cutoff position for 14 seconds (engine 2 switch was changed to Cutoff about 1 second after engine 1).
And additionally, there was a four second delay between the fuel control switch for engine one and engine two being switched back to run. Engine two switch was turned back to “Run” four seconds after engine one.
Questions
The obvious one first.
Why would the switches be turned to Cutoff at all in this stage of flight?
I do not believe there is any good reason. The risks of putting both valves to cutoff is probably higher than almost anything else that could happen to the airplane.
Is it possible for the flight computer to think the switches are set to cutoff when they aren’t?
I am not an expert by any measure on avionics so take my answer with a pinch of salt. I believe the flight computer on the 787 will monitor both poles on the switch and send the signals indicating each pole position to separate systems. For example one pole is active and one is not when switch is on. If there is a contradiction from the switch ie it shows both poles are active at the same time, which would mean switch is on and off at same time, a warning message will be displayed to the pilots saying discontinuity on the switch or something along those lines.
There is redundancy in the switch because it confirms the state of the switch using two signals. And there is redundancy in the computer as two separate systems receive a signal from the switch. The switches are probably ultra reliable and in the small chance a switch does develop a fault, the chance of it going unnoticed by two separate systems is also tiny, in short I think it’s highly unlikely for a switch to develop a fault and go unnoticed. For two switches to fail at the same time and for the failure of both switches to not be noticed by the planes systems, the chances seem infinitesimal.
Software Fault?
Is it possible that the software had an issue where it “read” switch positions that weren’t real?
It seems like there could be two different systems and therefore two different pieces of software reading switch position. For a fault not to be recorded would take the two pieces of software, reading phantom switch signals at the same time. But this wouldn’t be the first time software has been an issue on a plane.
Pilots Words
The prelim report says that one pilot asks the other “why did you cutoff?” and the other pilot responds “I did not”.
Without knowing how these words are said it is impossible to grasp what is going on in the cockpit.
If ChatGPT is correct, the cockpit would have been a world of chaos as soon as either of the fuel control switches were set to “Cutoff”
Sequence of Events and Warnings (Fact-Based)
Assume a takeoff is in progress, and within a few seconds after rotation, a pilot moves an engine’s fuel control switch to CUTOFF.
Here’s what happens and what the crew sees:
1. Engine Shutdown Occurs
- Fuel is cut immediately.
- Engine spools down; FADEC detects loss of combustion and command.
2. EICAS Alerts Triggered
The following messages are displayed on EICAS (FACT — confirmed via Boeing message logic):
ChatGPT
Message Type Meaning ENG FAIL L or R Caution Engine not producing commanded thrust. ENG SHUTDOWN L or R Caution/Status Engine has shut down. ENG CONTROL L or R (optional) Status or Advisory If disagreement or FADEC input issue occurs. FUEL CONTROL SWITCH L or R Advisory (depending on config) May appear if switch is off while expected to be on. From ChatGPT
ChatGPTSummary (All Fact-Based)
Event Confirmed? Source ENG FAIL Caution ✅ Boeing EICAS message list ENG SHUTDOWN Caution/Status ✅ Boeing FCOM & QRH Fuel cut causes engine shutdown ✅ FADEC logic Thrust asymmetry effects ✅ Boeing 787 flight control logic Autopilot/Autothrottle disengage ✅ (likely) Boeing control system logic
I think it’s correct to say there would be a visual and audio overload in the cockpit if the switches were turned to cutoff. Perhaps the report makes the cockpit sound calmer than it was.
What if it was calm?
The reply quoted in the report is “I did not”.
Maybe something is lost in translation but for a native english speaker, that would be read as a calm response of someone who perhaps does not understand what they are seeing.
The pilot who asked “why did you cutoff?”
Again, perhaps something is lost in translation but this does not strike me as the words of a pilot who has a cockpit with caution lights & chimes going off. And perhaps why even ask, just fix the problem.
Why the delay putting fuel control back to “Run”
I’ve said in the previous article, we don’t know when these words are spoken. For some reason the authors of the prelim report saw fit not to include a time stamp on these words. It’s possible the words were said as soon as fuel control was set to Cutoff but it’s also possible they were said when engine one switch was set back to “Run”
I think the only thing we can take away from the words is that perhaps the pilots were calm and perhaps also confused.
Why 4 Seconds Between Engine One and Two?
Engine two fuel control was put back to “Run” four seconds after engine one.
Again, I think this part of the report only increases the speculation. Perhaps the pilots did not want to overwhelm the electrical and hydraulic systems by trying to start two engines at the same time?
The RAT
Another event with no time stamp. In the video screenshot above, it’s presumed that the RAT was deployed as soon as engine one fuel control switch was set to cutoff.
If this is the case, it suggests manual activation in advance. I presume the flight computers would take at least a second or two to get the RAT down and deployed.
And as I’ve said before, manually deployed or automatically deployed, neither one jives with pilot suicide. I mean, why would they bother deploying it?
General Thoughts – Air India Flight 171 Prelim Report
I guess the prelim report smells a bit like politics to me.
They want to soften up people’s resistance to it being pilot error, so they include the pilot’s words (without time stamps…)
But at the same time they want to appear open minded, so they bring up the issue with the switches possibly not being spec’d the way they should.
If I’m reading between the lines they think it was pilot error, or they want to make people think it was pilot error, and they throw in the nothing burger switch to show impartiality.
Other Videos
And here is a rundown of the report by a YouTuber
