Posts about: "Fuel (All)" [Posts: 1005 Pages: 51]

Nothing in the report suggests that the engines began to run down before the fuel was selected to cutoff. The report states a sequence of events for power loss which begins with the switches being moved to cutoff. The maximum airspeed was immediately before the switches were moved, so there had not been a power rundown prior to that:

This is a preliminary report. It is quite detailed for a preliminary report.

Examining the before-takeoff checklists seems like it would be akin to examining the re-arrangement of the deckchairs before the titanic even hit the iceberg.

The engines were switched off. Unlike Embraer, B & A have no protections stopping you switching an engine off inadvertently. From everything in the report, everything operated exactly as designed. I am not certain of how long the relight window is without windmilling speed, but +- 10 seconds seems entirely reasonable.

The outstanding question that presumably requires much more in-depth investigation of the wreckage items and CVR audio is whether:

• the cutoff switches were operated deliberately (and by who)
• the cutoff switches were operated inadvertently (and by who)
• the cutoff switches were bumped (by what) and the guards failed or weren't installed
• some electrical failure perfectly mimicked both many-pole switches being operated, then being operated again (seems unlikely)

Interesting that the report mentions SAIB No. NM-18-33. Can you see a detent on the left switch base in the mishap photo on page 10., Fig. 13? Yes kind of blurry when blown up but maybe we have some photo gurus.

Transitioning from Off to Run do the control switches require a similar lift and move mechanism?

The Service Bulletin (link below) referenced on page 6 of the preliminary report describes just that...fuel control switches without detents or what the bulletin describes as a "locking feature" that can be "disengaged" and still allow the switch to function. It's somewhat of a glaring omission that the report did not state the status (detent or not) of the switches on this aircraft. Presumably if no-detent switches were found then an emergency AD would already have been issued.

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

Wouldn't they already know if the detents were missing in this case? They recovered the switches and told us what position they were in at impact.

Consider this post with a picture of the switches in question:


They must be lifted over the detent (if installed correctly) in each direction.

Far more than double pole - I think it's 4-8 ish. See the number of wires in the above picture. A previous post in one of the earlier thread indicated that it was essentially one pole per function - HPSOV, LPSOV, FADEC signal, generator etc. I'm not sure which one the EAFR reads. If it was a single contact failure, you would expect to see disagreement between the various systems controlled by the switch. I think that's very unlikely given both 'failed' in the same way near simultaneously and 'recovered' when switched.

For reference, it's pretty common for industrial emergency stop buttons to have 2-3 poles: redundant poles for the actual fault switching (legislative requirement above certain hazard levels), plus an additional pole for monitoring.

Depends on when they identified the SB and how obvious the lack of or incorrect fitting of detents is.

I haven\x92t seen this question asked and answered so apologies if I\x92ve missed it.

What observation(s) would or could have alerted either pilot to the fact that the fuel cutoff switches had been set to CUTOFF?

There is an EICAS message that comes up when an engine is shutdown (there is a small delay), which might prompt them to look at the switch - or just the sound the switch makes could prompt a quick glance down at the switch.

I think they know. Page 10 Fig. 13. It's telling that they referenced the SAIB in the report.

Both of the comments above imply that the 10 second wait to set the switches back to RUN is excessive and inexplicable for an "experienced" pilot.

Having read both previous threads, I recall there were easily a dozen or two comments that claimed that a pilot's hands should be nowhere near the thrust levers or fuel switches until 400' AGL, no matter if an engine is out or on fire. (This was in response to suspicions that one of the pilots has prematurely actioned the engine-out memory items.) A similar number of comments emphasized that the pilots should calmly verify any engine-related issues before taking any action that might affect thrust, and that their training emphasizes this.

You can't have it both ways. Either pilots are expected to react instantly (and cause mistakes like shutting off both engines by misreading the situation) or they're expected to take a moment to assess an unexpected failure before acting (in which case 10 seconds is still pretty darn fast).

I lean toward the latter of those.

I don’t 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’s assume that the switches were actually moved, and ignoring the “bad faith” 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’t 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, “muscle memory” (cerebellum activation if you prefer) may have taken the Captain’s 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’t 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 “bad faith” scenario, which we would all hope is incorrect.

Fly Safe
PJ88

Ever since the two 767 events in the mid 1980's where a pilot - thinking he was activating the supervisory Electronic Engine Control switches - set both engine fuel switches to CUTOFF (fortunately at ~3,000 ft. so the engines had time to relight and recover), the FAA has mandated something called a "Quick Windmill Relight" capability. Basically - with the engine at high power - the fuel switch is set to CUTOFF, then (IIRC) ten seconds later set back to RUN. The engine must recover and produce thrust within (again, IIRC) 90 seconds. It's a very challenging test for the FADEC s/w.
I assume the 10 second pause is based on how long it took the two 767 event pilots to realize their error and return the switches to RUN.

*sigh*

Let's take the sketchy CVR extract as a given for the moment.

So there's this hard working FO doing the takeoff. He wants to do a good job and impress favorably the Training Captain.

For (reasons that I cannot fathom) the training captain On Takeoff On A Revenue Flight chops the fuel before they get to 400 feet AGL.

Yes, that makes no freaking sense. None. Zero. Zip. Nada.

The natural response from PF to the PM (who is the training captain) is some version of "WTF with the fuel switches?"

And the response is "Uh, no, I didn't do that."

Think about this for a moment.

How many "WTF?" things erupt in your brain if that was the sequence of events?

Full Disclosure: I was in charge of the CRM training for the Navy (all of it) for a couple of years (and yes, that was a couple of decades ago). We got our CRM stuff, mostly, From The Commercial Airline Industry.

But, honestly, that reported back and forth between PF and PM has me smacking my forehead in disbelief... given the advanced state of CRM training in today's airline industry.

I confess to you all: I am more confused by this report than I was by the first two days of "data" eruption after the crash.

Not on the take-off roll. It was 3 seconds after liftoff.

This is pure speculation but I can envision the following sequence of events that would match the timeline and the little we know from the CVR and sequence of events.
- While PF is concentrated on flying the airplane, PNF moves the switches from RUN to CUTOFF in quick succession (for whatever reason).
- PF doesn't notice that the switches have been moved (again, he is concentrated on flying) but soon perceives the loss of thrust and sees a message on EICAS.
- PF looks down to check throttle position. It takes him a couple seconds to realize that the switches are in CUTOFF position.
- PF asks PNF (and his superior) "Why did you cut off the engines?" (or something similar). PNF anwers that he didn't (a lie, but we don't know if deliberate or just confusion / mental breakdown)
- PF realizes that PNF is in a wrong mental state, and attempts to restart the engines. It takes him a couple of seconds to move both switches because his other hand is on the yoke trying to stabilize the airplane.
- By then the airplane has lost too much energy for a successful recovery. One of the pilots calls MAYDAY because he knows that they are about to crash.
This sequence would match the timeline between the initial fuel cutoff, and when the switches were moved back to run position, and would actually indicate great presence of mind and quick decision from the PF.
Again, this is pure speculation but it would match well with the little information we have.

Unless defective. I only encountered one in a 30 plus year career where my Captain shutdown at block in and did not like the feel and checked that the detent was worn. Wrote it up. But Boeing installed some that did not have a detent and the FAA issued a SAIB, referenced in the Air India mishap report, to check for these switches because they could inadvertently be positioned to off. Whether they meant human or other inadvertent action was not clear.

Best theory I've seen so far.


I assume the unusual alarm cacophony that erupted after cutting the engines would have been overwhelming. Agree an error in good faith. If bad faith were involved, the switches wouldn't have returned to the run position, or at least they wouldn't have been allowed to remain there.

Yes - conflicting data issuing a warning when the system being controlled has no fault. That's a problem at considerable expense for a rare occurrence.

Literally covering all the bases with a video would not only show what the switch status was but also how it got there, if it has an immediate effect, which a second line would not do.

A plausible theory, however, if that were indeed the case wouldn't supporting FDR data be available/have been included in the initial report?