Air India B787 crash Ahmedabad

[DC3]

All currently speculative of course until the full report comes out.

 

[RSD]

I suspect that they weren’t testing for the lock’s presence, and were using the normal “lift and move” action, without realising that the “lift” wasn’t necessary.

Agreed. How it got through the manufacturing process and quality control is beyond me - the manufacturer would (or should) have had the parts that form the hurdle left over which should have instantly told them that the parts hadn't been installed - long before they were delivered to Boeing and assembled into planes.

 

[RSD]

The first (and in my opinion) the biggest reason is that it’s a design legacy. We know Boeing designs their coughpits to not over-automate pilot actions. They generally prefer giving pilots direct control, trusting them to manage switches appropriately.

During abnormal procedures (e.g. engine fire or severe damage), you don’t want to have to fumble with thrust lever position as a precondition to shutting off the engine. Time may be critical and if somehow the lever is not fully in the idle stop you won’t be able to shut it down.

For a Boeing design - definitely design legacy, and probably a bit of "if it works then why change it?".

As QF32 showed, when severe damage occurs sometimes the connection between the switch and the fuel valves can become inoperable and you are left with no way of shutting the engine down.

 

[RSD]

A little bit more information - the fuel control switches that Boeing uses are made by Honeywell. The problem with the switches that had been previously identified wasn't a missing part - it was that the locking system was disengaged - their words not mine - but I interpret that as being that the part wasn't installed in the switch correctly - it may have been installed upside down or something similar.

 

[RSD]

Some further on these switches.

The original problem that was discovered back in about 2018 was that some switches "were installed with the locking feature disengaged" - which to me seems like odd wording. My best guess is that the faulty switches had been assembled with the locking mechanism installed upside down - but it certainly could and should have been worded much more clearly IMO.

The FAA issued a SAIB with two recommended actions -
- inspect the switches on a wide range of Boeing aircraft to make sure that the locking feature is working correctly
- for Boeing Model 737-700, -700C, -800, and -900ER series airplanes and Boeing Model 737-8 and -9 airplanes it was recommended to check the part numbers and if the switches were of a particular part number then to replace them with a different part that has an improved locking mechanism.

Copy of the SAIB is attached.

 

[markis10]

Probably worth a note that the guards were recommended after a QFlink 717 had an incident on a very similar setup in 2006

 

[Quickstatus]

FAA SAIB NM-18-33

For some reason the above does not always link through:

Can search the FAA dynamic regulatory system and enter SAIB number "NM-18-33", then scroll down the page

..

The gear select lever was not raised, instead the fuel cutoff switches were moved to Cutoff.
Interested to know if "positive climb" was enunciated by the PM, then followed by PF saying "gear up"? prior to Fuel cutoff switch transition. Maybe they didnt get to "positive climb"

Software Glitch affecting 2 separate and unconnected fuel cutoff systems causing the same outcome within 1 second of each switch system?.