Air India B787 crash Ahmedabad

[jenib]

There is some interest online about this section of the report (Section 4)

""The FAA issued Special Airworthiness Information Bulletin (SAIB) No. NM-18-33 on December 17, 2018, regarding the potential disengagement of the fuel control switch locking feature. This SAIB was issued based on reports from operators of Model 737 airplanes that the fuel control switches were installed with the locking feature disengaged. The airworthiness concern was not considered an unsafe condition that would warrant airworthiness directive (AD) by the FAA. The fuel control switch design, including the locking feature, is similar on various Boeing airplane models including part number 4TL837-3D which is fitted in B787-8 aircraft VT-ANB. As per the information from Air India, the suggested inspections were not carried out as the SAIB was advisory and not mandatory. The scrutiny of maintenance records revealed that the throttle control module was replaced on VT-ANB in 2019 and 2023. However, the reason for the replacement was not linked to the fuel control switch. There has been no defect reported pertaining to the fuel control switch since 2023 on VT-ANB."

 

[Duffa]

I’m sure they’re looking, but I’d be interested in knowing more about whatever wiring is under the switches. Is there a circuit board that they activate, in which case a board fault could be taken as a switch throw?

Maybe. I think you’d see the hand movement, but perhaps not.

The reported conversation is strange as well.

A pilot issue is something that will be leapt upon with relief from some quarters, but as we saw with MCAS, issues can lie deeper below the obvious cause. In the interim, I think I’ll keep clear of both 787s and Air India.

Thanks, JB.
Boarding a 787 in about 4 hours.
In light of such information I shall probably accept the pre-takeoff champagne.

 

[jb747]

Interesting it takes 4 seconds to move both fuel switches from CUTOFF to RUN but less than 1 second to move both the other way.

It’s exactly the same action, so I’d have thought it would take about the same time. I’d really like to see the exact time line. I don’t think I could move them both in either direction in under a couple of seconds.

 

[jb747]

Thanks, JB.
Boarding a 787 in about 4 hours.
In light of such information I shall probably accept the pre-takeoff champagne.

Ask to keep the bottle.

 

[RooFlyer]

It’s exactly the same action, so I’d have thought it would take about the same time. I’d really like to see the exact time line. I don’t think I could move them both in either direction in under a couple of seconds.

I know you'll read for yourself, JB, but for discussion, I think the report says

8:8:42 both switches to cut-of within a second
Question asked why that was done - denied
RAT deployed
8:8:52 switch 1 moved to RUN
8:8:56 switch 2 moved to RUN

Both engines re-lit automatically, Engine 1 started to produce thrust (in layman's terms) not engine 2 before data cut-off.

 

[jb747]

8:8:42 both switches to cut-of within a second

The only way that I think I could move them in that time frame would be to use both hands, one for each switch. And even then I think it would take longer. Of course, I'm assuming the locking mechanism is functioning as I'm used to...

Question asked why that was done - denied

Interesting. If you've just done something as obvious as that, why would you deny it?

RAT deployed

Expected.

8:8:52 switch 1 moved to RUN
8:8:56 switch 2 moved to RUN

That's more the sort of time I'd expect.

Both engines re-lit automatically, Engine 1 started to produce thrust (in layman's terms) not engine 2 before data cut-off.

This is some of the text from the Boeing bulletin about the switches:
The Boeing Company (Boeing) received reports from operators of Model 737 airplanes that the fuel control switches were installed with the locking feature disengaged. The fuel control switches (or engine start switches) are installed on the control stand in the flight deck and used by the pilot to supply or cutoff fuel to the engines. The fuel control switch has a locking feature to prevent inadvertent operation that could result in unintended switch movement between the fuel supply and fuel cutoff positions. In order to move the switch from one position to the other under the condition where the locking feature is engaged, it is necessary for the pilot to lift the switch up while transitioning the switch position. If the locking feature is disengaged, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation. Inadvertent operation of the switch could result in an unintended consequence, such as an in-flight engine shutdown.

It's difficult to understand how this could possibly have not been considered a mandatory safety of flight issue.

 

[serfty]

Interesting. If you've just done something as obvious as that, why would you deny it?

Poor CRM?

 

[Must...Fly!]

Interesting. If you've just done something as obvious as that, why would you deny it?

I'd respond to that with, why when experiencing a sudden lack of thrust would you ask your counterpart why they'd cutoff the engines? It seems like an odd conclusion to immediately (and I mean, immediately) jump to.

 

[lovestotravel]

This seems fishy to me....

 

[offshore171]

When I was flying the 767, back around the mid ‘90s I found a repeatable bug in the FMC programming, that would allow the aircraft to descend through the MCP selected altitude. At that time it had been in service for around 10 years, and that sort of FMC had been in use across multiple types, so thousands in daily service.

Appreciate the insights. There's a first time for every failure mode.

I guess I'd add further on the probability side of things, that it would be remarkable for the first occurrence of a double switch failure to occur at the exact moment of seconds after departure.

Has there been any inflight occurrences of exactly this failure? At altitude the dual relights would allow the plane to recover, but I imagine we'd see RAT deployments each time?

 

[Saab34]

I guess the recorder will pickup a slight ‘click’ sounds if they had been moved to OFF. If they don’t, well, who knows where this will head next.

 

[jb747]

I'd respond to that with, why when experiencing a sudden lack of thrust would you ask your counterpart why they'd cutoff the engines? It seems like an odd conclusion to immediately (and I mean, immediately) jump to.

No, you wouldn't assume that. But the switches are easy to see, so I'd guess that he'd looked.

Appreciate the insights. There's a first time for every failure mode.

Exactly.

I guess I'd add further on the probability side of things, that it would be remarkable for the first occurrence of a double switch failure to occur at the exact moment of seconds after departure.

Without knowing a lot more about the switch and its lock..... In flight, even in turbulence, things are quite smooth. On the ground, you've got vibration and bumps from the runway.

Has there been any inflight occurrences of exactly this failure? At altitude the dual relights would allow the plane to recover, but I imagine we'd see RAT deployments each time?

If it had happened there would have been multiple reports. But, perhaps it actually isn't as likely in flight vs on the runway. Even if relevant to this event, the issues with the lock are obviously extremely rare, though whether that should allow it to be dismissed is a different question entirely.

This is possibly one of the few events where I'd admit a video would be useful.

 

[flyer89]

I think we are probably over thinking it at this point. If we assume the aircraft systems didn’t turn demonic it’s either going to be gross incompetence or something nefarious. I assume it was the PIC who asked the question. One wonders whether he had the presence of mind to put it ‘on record’ for the CVR.

 

[Must...Fly!]

No, you wouldn't assume that. But the switches are easy to see, so I'd guess that he'd looked.

Agree, to me if you ask that question you have definitive reason to ask it, not a spurious/speculative query.

 

[AviatorInsight]

The fuel control switches are the same as the new 737s. That is, they’re mechanical. They’re hard wired to the EECs. So when you move the switch to cut off, it physically interrupts fuel flow by commanding the EEC (engine control) to shut off the fuel metering valve.

There is no dependency on software or FMC electrical busses.

This is actually a good thing because in the event of an electrical failure, you still have direct control of shutting an engine down (if you need to).

In layman’s terms…when you toggle a switch to CUTOFF, it bypasses most of the aircraft’s software infrastructure and goes straight to the engine control to stop fuel.

The switch itself it very quick to action because the lever is very small (similar to the 777). It has a locking mechanism and you need to pull out and down to get it out of the detent.

4 seconds to move the switch to cutoff? I don’t believe it.

 

[Duffa]

Great insights from everyone. Thank you.
Two hours now....

 

[Aussie_flyer]

I'd respond to that with, why when experiencing a sudden lack of thrust would you ask your counterpart why they'd cutoff the engines? It seems like an odd conclusion to immediately (and I mean, immediately) jump to.

Because it's the only plausible explanation at that point.

 

[Must...Fly!]

Because it's the only plausible explanation at that point.

No it isn't. It might be possible, it might be likely, but it's most certainly not the only plausible explanation.

Unless you've seen the other pilot do it, then it's the only plausible explanation.

 

[jb747]

The fuel control switches are the same as the new 737s. That is, they’re mechanical. They’re hard wired to the EECs. So when you move the switch to cut off, it physically interrupts fuel flow by commanding the EEC (engine control) to shut off the fuel metering valve.

Well, if they’re wired, there’s electricity involved. They aren’t soft touch software switches that the aircraft are so full of these days, but they are not a mechanical linkage to the EECs. They’re probably very simplistic, but there’s bound to be a small circuit board associated with them. Hopefully not one board for both.

4 seconds to move the switch to cutoff? I don’t believe it.

It’s the selection of both from run to cutoff in under a second that seems a tad rapid. Next time you do a flight, trying timing it.

 

[jb747]

Because it's the only plausible explanation at that point.

Unless I saw it happening, I don’t think I’d ever get to that conclusion. And if I did see him, it wouldn’t be followed by a question.