Posts about: "Fuel Cutoff" [Posts: 302 Pages: 16]

Originally Posted by AfricanSkies

Both of them? 1-2 seconds apart? That\x92s extremely unlikely.

Originally Posted by Flightrider

A question from an accepted standpoint of relative ignorance - neither a pilot nor hugely familiar with 787s although have spent a lot of time around both.

The accident report indicates that the aircraft had a STAB master caution warning on the previous sector. A maintenance action took place during the turnaround in AMD before the accident flight.

Noting that the two guarded stab cutoff switches are directly adjacent to the two guardedfuel run/cutoff switches at the base of the throttle quadrant, is there any condition that could have led a pilot to reach for the stab cutoff at the critical moment? Recurrence of the tech defect from the previous sector or switches being left in the wrong position but not noticed under the red guards ?

If that\x92s possible then accidental action of the fuel cutoff switches when the intent was some intervention with the stab switches seems more likely than a wilful pilot action to cut off fuel flow.

Is that remotely possible, given the defect history?

Originally Posted by Hedge36

Question:
What messages, if any, are displayed on-screen when the fuel cutoff switches are re-positioned (especially to OFF)? I'm wondering if the pilot who asked about the shutoff SAW the other pilot manipulate the switches or if he was alerted by a message... or perhaps he looked down at rollback and realized they were in the OFF position.

Originally Posted by Propjet88

I don\x92t know if the FDR measures the switch position or the electrical signal. The latter is probably more likely, although there has been much discussion around potential scenarios involving accidental switch movement as well as possible causes of electrical glitches. Let\x92s assume that the switches were actually moved, and ignoring the \x93bad faith\x94 scenario, we need a situation that encompasses the switches being moved to Cutoff by one pilot, this action being queried by the other pilot and denied by the pilot who moved the switches.

For consideration, here is a possible scenario that hasn\x92t been mentioned yet and encompasses the frailty of human performance. The report mentions that the flight crew on the immediately prior flight had written up a "STAB POS XDCR" status message, and that troubleshooting was carried out. I wonder if the scenario could be that the accident crew received a Stabiliser EICAS message on or around take-off and the Capt (who was PM) decided to action the first checklist item immediately from memory, by intending to move the Stab switches to Cutoff but moving the fuel switches instead. As in all modern Boeings, the Stabiliser Cutoff switches are immediately next to the Fuel Cutoff switches and operate in the same sense (i.e. down for Cutoff). They are guarded and never normally moved but, with an intent to move the stab switches, \x93muscle memory\x94 (cerebellum activation if you prefer) may have taken the Captain\x92s hand to the Fuel switches, which are operated on every flight. The FO (who is PF) is manually flying at this stage sees and queries it. The Capt denies it, as he doesn\x92t realise what he has done (confirmation bias perhaps). After a few seconds, the terrible mistake is realised, and the fuel switches are moved back to run, but sadly too late and the Capt makes a Mayday call.

Perhaps a bit of a stretch but not as much of a stretch as many of the other scenarios in this thread. I think it is a real possibility. Sadly, the only other explanation that I can see is the deliberate \x93bad faith\x94 scenario, which we would all hope is incorrect.

Fly Safe
PJ88

Originally Posted by KSINGH

as per the report- at *most* 1s apart, particularly significant given that it has been mentioned the recording interval of the DFDR is 1s

also I don\x92t know if we\x92ve had an adequate answer to the fact of what data streams the DFDR records, was it only detecting the electrical signal of fuel cut off or the actual position of the toggles- I don\x92t believe it would be the latter which opens an entirely different rabbit hole

Originally Posted by Flightrider

The accident report indicates that the aircraft had a STAB master caution warning on the previous sector. A maintenance action took place during the turnaround in AMD before the accident flight.

Noting that the two guarded stab cutoff switches are directly adjacent to the two guardedfuel run/cutoff switches at the base of the throttle quadrant ,

Originally Posted by mexmike

Hi! Have you read my comment regarding the possibility of Cannon plugs under the switch module not being fully engaged ?

Originally Posted by tdracer

Since some posters seem focused on the theory that the fuel control switches didn't move - just the electric output did (and as I posted earlier, the FDR only knows electrical states, there is literally no other way for the FDR to monitor the switch position).

So I did a little thought experiment. Uncommanded engine shutdowns (for all causes) are already rare - a 10-6 event. Now, during my 40 year career, I can't remember ever encountering a case where the fuel shutoff was commanded without a corresponding movement of the fuel switch. However in this industry it's a good idea to 'never say never', so let's assume it's happened. It would take something like a hot short to cause it to happen ( moving the voltage from RUN to CUTOFF ) since an open circuit will simply leave the valves where they were. That would put its probability way out there - something like 10-8/hr.

Originally Posted by Engineless

Then other possibilites must be considered and we should therefore not default to assuming 'a hand was on the fuel cutoff switches'. Especially as neither of the pilots can defend themselves against such allegations.

Originally Posted by dsbery

Good question as the report says FAA advisory NM-18-33 (check for potential fuel cut-off switches fault) was not implemented by Air India.

Originally Posted by T28B

If you go down the no hand route, how did they turn them back on? I am not buying the loose canon plug gambit.
(The above posted as neither mod nor admin, to be clear).

Originally Posted by pampel

First, 10 seconds is not a long time. Second, I don't know where you are getting the idea that there was a 10 second gap between the pilots noticing or asking 'why did you cut off' and the switches being reset, because the report doesn't give a timestamp for either exclamation from the pilots. It may well have only been a couple of seconds between them noticing and resetting them, the report simply doesn't give that detail.

The truth will be in what was said after 'I didnt', but that's conspicuously absent from the report.

Originally Posted by T28B

If you go down the no hand route, how did they turn them back on? I am not buying the loose canon plug gambit.
(The above posted as neither mod nor admin, to be clear).

Originally Posted by Sailvi767

On the other hand pilots deciding to end their lives in a spectacular fashion is not inconceivable. In fact over the last 25 years it may be the single most numerous reason for a catastrophic loss of a transport category aircraft operated at a major airline.

Originally Posted by mh370rip

Tdracer has certainly explained that separation of cabling runs etc would have it very improbable that a single cable fault or short would impact both engines simultaneously in the same way. The CVR data is derived from local sensors with a dedicated battery backup, however all the FDR data and the fuel shut off commands are electrical signals which ultimately have a common source in the aircraft power buses. A water ingress into the EE bay at rotate which momentarily shorted all the low voltage buses to higher AC voltage is unlikely but is it unlikely to the same extent.

Originally Posted by dsbery

Good question as the report says FAA advisory NM-18-33 (check for potential fuel cut-off switches fault) was not implemented by Air India.

Originally Posted by verticallimit

Just a thought \x97 the fire extinguisher handles perform the same function as the fuel cut-off.
Could there have been a strap /booklet or something else that accidentally got under the fire handles and activated them when one of the pilots pulled on the item?
The fire handles are not particularly well protected against something getting underneath them
Is there any information on whether the fuel cutoff switches and fire handles register as separate events on the flight data recorder, or if both are logged under a common indication, such as 'fuel switch cut off'?

Originally Posted by DTA

It is worth remembering that each switch has 4 poles. Think of a pole as a section of the switch. Each section controls a different function - reporting switch position to FDR, fuel cut off and so on. The chances of anything other than real physical switch movement (whether it be spilt liquid, wiring damage, loose canon plug or whatever) changing the status of all 4 sections is impossibly small. Then you have two switches.