Posts about: "Fuel Cutoff Switches" [Posts: 802 Pages: 41]

For those sky gods who confidently state they would reset the cutoff switches immediately I would say that 10 seconds is not a particularly unusual time for startle effect to impair cognition, especially for something as monumental and unexpected as a dual engine failure at rotation. One reference amongst many: https://www.icao.int/Meetings/LOCI/P...Strategies.pdf

And for those who scoff at the possibility of the PM inadvertently operating the cutoff switches (which is done as frequently as operating the gear lever), I\x92d remind you that more than one Airbus has landed with its parking brake on after the PM inadvertently set it rather than arming the spoilers.

From the report, there is no indicated time stamp identifying the point when one pilot asked the other "why did you cut off"
This could explain the the assumption that it took ten seconds to reverse the switch positions.
Cut off could have been noticed at any point later than 08:08:42 but before 08:08:52.

https://ad.easa.europa.eu/blob/NM-18...SIB_NM-18-33_1

That isn't the human factors question. All it does is tell us that one of the flight deck crew was unaware of the issue as it was initiated. It doesn't tell us which, and it doesn't tell us why.

So the switches either snapped back to cut off of their own accord…see warning…or they were moved deliberately, which is surely unlikely.

Well, it\x92s narrowed it down to 3 possibilities:

Action slip
SAIB NM-18-33
Intentional.

This is what's in the report:
It's not a verbatim quote, so we don't actually know what the exact words used were, nor at what point in time the question was asked (and responded to).

Like this? Actually, the middle switches should look like the port side ones IMHO. Properly guarded.

Fuel switches are NOT toggle switches precisely because aircraft designers mitigate against brain farts involving simple switching actions.

Anyone who has flown the 777/787 (imagine the 737 is similar) probably recognises that the movement of those switches has a very easily identifiable audio signature.

Given the sensitivity of the CVRs, I would imagine it would be a very simple task in the full report to compare that to the unlikely scenario of the switches being in some halfway house and slipping to cut-off to to rotation or g-forces etc

I would add a fourth, however unlikely it might be: some kind of electrical short which caused the "cutoff" signals to be sent without the physical switch moving.

Read the report. There is no evidence to support your contention that the question was asked as you have quoted.
The report simply says:

Even more serious incidents have occurred, such as the Luxair\x92s accidental retraction of the landing gear during takeoff rotation, leading to a failed liftoff:
https://avherald.com/h?article=48d1e3ae&opt=0

Those switches are lift to move. They were lifted to shut off and thrown back to start in the report. No CVR or FDR trace is going to explain why two switches were throw by error or by intention. Only a video would. PnF would have had his eyes outside or on instruments for the calls. As mentioned, other manufacturers put such switches out of harms way for general use. QRH is the only reason to go to them.

It looks to me like they already are. If you look at the photo of such a switch in isolation near the end of the last thread, you'll see that there are many wires shown - like in a ribbon cable - leaving the switch. But electrically, what you suggest doesn't really do it.

It's possible that a contact could "open" due to oxidation, vibration etc without any real switch movement (but extremely unlikely in aviation-grade equipment - apart from liquid spillages that occurred some time previously...). However, if it was a double-throw switch - which it may be - you'll have the chance to see one side open and depending on whether it's make-before break or the opposite (break-before-make seems more likely, but as I found out, when it doesn't behave consistently, the consequences can be dire), the other set of contacts will close, either before or after the first side opens. That's MUCH more difficult to have happen due to contact faults. I'd say impossible, except never say never!

Designing stuff like this is so difficult - do you eliminate one risky possibility only to create another?

For example, do you say, OK, to shutdown the engine, the Run contact must be Open and the Cutoff contact must be Closed before you can shut the engine down? Then, if someone tipped coffee into the switch a year ago, and the Cutoff contact is now insulated by a nice thick layer of dried, milky, sugary coffee and can't make contact, then the engine won't shut down. What do you do?

That said, I think the positions of those two, adjacent, low down Cutoff switches are simply accidents waiting to happen. (As has been said many times. When is the manufacturer going to act?)

Anyone willing to make an estimate of how long would be required to reach take-off thrust given the known movement of the cut-off switches? With engine 1 spooling up and engine 2 having relit but failing to accelerate, it sounds like they came oh so close to recovery.

I imagine that what happened with engine 2 ("able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery") will be a major part of the investigation.

it would have to be small enough to fit between the idle throttle position and guards on each side of the switches and weigh enough to push the switches over the detent, unless the SAIB cones into play.

The report proved that occams razor was right. Fuel switches acted which was the simplest explanation. And occams razor will not allow for a 15000h line check captain as PM to need over 10 seconds to reset fuel switches while both engines spooled down from TO thrust to sub idle within 5 seconds.

There is mention of fire damage or thermal damage to the centre pedestal, perhaps enough to identify the position of the switches but not to be able to determine their internal physical state relating to the detent mechanisms.

The Boeing 717 had a near identical Fuel Switch setup.

An Australian crew once had a Tech Log folder fall off top of the Instrument Shroud and land on a fuel switch which initiated a shutdown. This was at altitude so unlike this incident there was time to troubleshoot and recover the engine.

Australian registered B717s were then required to install a guard above the fuel switches to help prevent anything that falls on them from bumping them to the Off position.

Interestingly there was also a requirement to \x91jiggle\x92 the fuel switch after selecting it to ON after start to ensure it was seated correctly and wouldn\x92t accidentally flick to OFF due to it not being fully in the ON Position.