Posts by user "safetypee" [Posts: 6 Total up-votes: 0 Pages: 1]

Until weight-on-wheels logic fails in conjunction with thrust lever / reverse switch / sensors malfunction = double hush.
Not a new software weakness, but existing ones which come together with circumstance which overcome anticipated human mitigation; Boeing response to 'minor' malfunctions.

A lesson from this thread so far:

Beware acronyms which cite 'accommodation' or 'augmentation', particularly when they are not always explained or understood.

TCMA thrust control malfunction accommodation

MCAS manoeuvring characterises augmentation system

The lesson isn't avoiding failure. It's refusing to let failure define the outcome.

Depending on manufactures design principles, or certification standard, then the choice of switch may be determined by the result of normal operation; i.e. a reversible or irreversible outcome.

A 'unlocking' (guarded) switch, as per 787 fuel, is normally associated with normal use, but requiring a higher level of protection angainst inadvertent operation (two actions), but rarely, if at all, considers simultaneous dual operation - 2 switches.

Compare with covered / uncovered push button selections in other aircraft, and those requiring push button 'unlocking'.
A range of interchangeable words, meaning, interpretation; but the root principle is that form follows function.

Beware hindsight bias.

At this stage of the investigation, where the preliminary report is limited to facts and evidence , there may be insufficient knowledge to warrant urgent safety action.

However, some national regulators might choose to reiterate the FAA SAIB: NM-18-33, requiring that all switches must be checked i.e. not optional.
Additionally, and independently, pilots might check the switches preflight (nice to know): - note the range of different types of aircraft and variants which could be affected - fleet size, number of switches exposed to the condition.

Regulators might also enquire of the FAA how many 'non locking' switches were identified by the SAIB - what was reported; and 'non FAA' operators recheck their inspection results and action taken.
… and how many operators did not check.

If errant switches were identified, then was the original safety assessment reconsidered (FAA/Boeing), if so what arguments were made against inadvertent simultaneous operation.

https://static-gi.asianetnews.com/co...nm-18-33-1.pdf

From the CVR, the switch position was noticed, questioned, and with understanding selected to Run; the crew apparently had a quick understanding of what would be a very surprising situation - startle, mind numbing, thought restricting conditions.

It is reported that P2 was handling; in this case the Captain might guard the thrust levers until V1, moving his hands away, but not onto the control wheel - rearwards, … thence with cuffed sleeve …

A speculative scenario of inadvertent switch operation of 'unguarded' switches.

A combination of most unlikely - unbelievable factors, which came together at that time. Yet such rarities and combinations litter the wreckage of past accidents; and with hindsight they were 'normal'.
Normal SOP for P2 takeoff; errant switches escaped SAID checks - 'normal' for that aircraft.

If the switches were inadvertently moved, the realisation, even subconsciously, might support the apparent quick understanding and action.

… waiting for: a report on the condition of the cutoff switches condition wrt guarded operation …

Incorrect Locking
The spring function is still active, but due to the displaced locking ring, the tab does not engage with the detent.
The two conditions for the switch remain unaltered - Cutoff / Run, but the Run position is not gated, held in position.

Edit; "Can these switches be carelessly set in the on position but not fully locked? I am thinking whether it is possible for the switches to be electrically on, but not mechanically locked."
Yes