Plane crash

[Protagoras]

My reading is that the switch position is inferred from the electrical contact state, rather than e.g. video providing direct observation of the physical switch position.

This reading allows for the possibility that the connectors on the back of the switch may have made intermittent contact. So possibly the contact was disrupted when the plane was climbing, to be restored again when level / descending flight was reached.

I accept that this is perhaps less probable (given both switches) than human operation, but I don't think that the evidence made available allows for elimination of this possibility.

[willendure]

The switches have mechanical locks and require to be pulled out before they can be moved. They are a robust design that has been used for decades and it seems very unlikely they failed by themselves. Murder-suicide of some kind of absent minded mistake, I guess.

[DoctorStrangelove]

Considering that one of the pilots was about to retire, and from personal experience of such an age, ?some sort of brain fart?.

Whatever, it's an absolute tragedy.

Apparently one of the engines was spooling up, but too late, too late.

[Protagoras]

The switches have mechanical locks and require to be pulled out before they can be moved. They are a robust design that has been used for decades and it seems very unlikely they failed by themselves.

I was looking into these switches and their state detection. These switches are 4-pole devices and sensing electronics detect both states and are also able to detect invalid states which would indicate wiring faults. Assuming therefore that the mechanical integrity of the switches was not compromised, it seems that the physical operation is the most likely scenario.

[Paddy]

FAA
Aviation Safety
SPECIAL AIRWORTHINESS INFORMATION BULLETIN
SUBJ: Engine Fuel and Control
SAIB:
NM-18-33
Date:
December 17, 2018
This is information only. Recommendations aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin (SAIB) is to advise registered owners and operators of The Boeing Company Model 717-200 airplanes; Model 737-700, -700C, -800, and -900ER series airplanes; Model 737-8 and -9 airplanes; Model 747-400, -400D, -400F, -8, and -8F series airplanes; Model 757-200, -200CB, -200PF, and -300 series airplanes; Model 767-200, -300, -300F, -400ER, and -2C series airplanes; Model 787-8, -9, and -10 airplanes; Model MD-11 and MD-11F airplanes; and Model MD-90-30 airplanes of the potential for disengagement of the fuel control switch locking feature.
Based on an assessment utilizing the limited data currently available at this time, the airworthiness concern is not an unsafe condition that would warrant airworthiness directive (AD) action under Title 14 of the Code of Federal Regulations (14 CFR) part 39. The FAA will continue to monitor this issue.
Background
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.
Boeing informed the FAA that the fuel control switch design, including the locking feature, is similar on various Boeing airplane models. The table below identifies the affected airplane models and related part numbers (P/Ns) of the fuel control switch, which is manufactured by Honeywell.
2
Airplane Model
Honeywell P/N
717-200
3TL32-2-3D
737-700, -700C, -800, and -900ER
766AT613-3D
737-8 and -9
766AT613-3D
747-400, -400D, and -400F
3TL32-3D
747-400, -400D, -400F, -8, and -8F
4TL32-3D
757-200, -200CB, -200PF, and -300
3TL32-12A
767-200, -300, -300F, and -400ER
3TL32-3D
767-2C
50075622-001
787-8, -9, and -10
4TL837-3D
MD-11 and MD-11F
3TL32-1-3D
MD-90-30
3TL32-2-3D
Recommendations
The FAA recommends that all owners and operators of the affected airplanes incorporate the following actions at the earliest opportunity:
1) Inspect the locking feature of the fuel control switch to ensure its engagement. While the airplane is on the ground, check whether the fuel control switch can be moved between the two positions without lifting up the switch. If the switch can be moved without lifting it up, the locking feature has been disengaged and the switch should be replaced at the earliest opportunity.
2) For Boeing Model 737-700, -700C, -800, and -900ER series airplanes and Boeing Model 737-8 and -9 airplanes delivered with a fuel control switch having P/N 766AT613-3D: Replace the fuel control switch with a switch having P/N 766AT614-3D, which includes an improved locking feature.
We request that owners and operators report any failure of the locking feature of the fuel control switch to Boeing (see contact information provided below). The report should include the date the failure occurred, the fuel control switch P/N, airplane model, airplane serial number, and airplane registration number. Under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.), the Office of Management and Budget (OMB) has approved the information collection contained in this SAIB, and assigned OMB Control Number 2120-0731.
For Further Information Contact
Tak Kobayashi, Aerospace Engineer, Propulsion Section, FAA, Seattle ACO Branch, AIR-784, FAA, Seattle ACO Branch, 2200 South 216th Street, Des Moines, WA 98198; phone and fax: 206-231-3553; email: takahisa.kobayashi@faa.gov.
For Related Service Information Contact
Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; telephone 562-797-1717.

[WTFH]

Not that I don't trusty Paddy, but I decided to check, and yes, his post is genuine:
https://drs.faa.gov/browse/excelExte...dalOpened=true

[NotAllThere]

I do trust him and sent it to a journalist friend.

[vwdan]

Even on the off chance that the locking mechanism was faulty/missing/etc I can't imagine any turn of events where the switch movements weren't deliberate.

Not to say malicious, it really could have been the brain fart to end all brain farts or whatever, but deliberate for sure IMHO.

Tragically, unless some kind of smoking gun note is found, I don't think we'll ever truly know which pilot did it or why

[NigelJK]

Many carriers (including Indian) are now checking the the lock mechanism. The original warning did not have a mandatory check in place so many airlines (including Indian) didn't check if the mechanism was fitted.
Lots of officials are asking for video capture in cockpits as the pilots exchange regarding the cut offs in the black box didn't identify who did what.

[Paddy]

Even on the off chance that the locking mechanism was faulty/missing/etc I can't imagine any turn of events where the switch movements weren't deliberate.

Not to say malicious, it really could have been the brain fart to end all brain farts or whatever, but deliberate for sure IMHO.

Tragically, unless some kind of smoking gun note is found, I don't think we'll ever truly know which pilot did it or why

Have you ever seen what happens on a potholed bumpy runway?