Posts by user "DTA" [Posts: 21 Total up-votes: 0 Pages: 2]

Originally Posted by Pilot DAR

Speculation on my part, the 787 has ceiling lights which change colour/colour can be changed? Could they produce "green flickering" if there were an airframe electrical problem? If the ceiling lights in the whole cabin "flickered green" it sure would be memorable!

Originally Posted by ATC Watcher

from the EASA statement yesterday :

​​​​​​​No mention of UK

Originally Posted by tdracer

On the 747, Weight on Wheels (WoW) depends on prox sensors on the landing gear (i.e. gear compression). I don't know how that's done on the 787.
The reason we used both Radio Alt and WoW is that both can give erroneous indications on certain conditions - RA can be 'fooled' by dense rain or even really dense fog (the signals bounce off the water and falsely indicate on-ground), the prox sensor system can subject to HIRF/Lightning interference.

TCMA acts quickly, but it does require some persistence, so an input glitch won't activate it (mainly N1, which is measured every 15 milliseconds).

What sort of 'confirmation' do you have in mind - the regulator mandate that resulted in TCMA basically says we can't take credit for the flight crew.

Originally Posted by Seamless

Has this been discussed already?

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


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Originally Posted by Europa01

I\x92ve had a look at the Honeywell spec sheet for TL type switches. They are a common type with many available configurations and are essentially a normal looking snap action switch. The locking feature is an add-on which can be specified. I have to say that from the diagrams, the locking mechanism doesn\x92t look that robust and I\x92d guess that it is subject to wear which was probably the basis of the SAIB. Given that this is a mechanical locking device seeing frequent use possibly with less than full mechanical sympathy it is possible to see how wear could occur. This does beg the question of how whether a check on the mechanism has made it into maintenance routines. ( Note - the locking mechanism appears to be the same for all TL switch types) . Those familiar with the switches - what do you think?

Originally Posted by Musician

How many cycles are they rated for?

Originally Posted by Kraftstoffvondesibel

Yes, seems like they also come in a on-off-on version, but the thing is what could happen when the mechanical function is worn, which is a thing with switches used over time in real world scenarios.

It seems the design, function and placement of these switches might have been \x93grandfathered\x94 over several generations of cockpit design.

Originally Posted by Seamless

I have read most of the thread (old and new). As a lawyer working in forensic investigations, I am constantly involved in problem-solving. My field of work also includes complex investigations related to insolvencies, which almost always require an analysis of the causes behind a specific, established outcome. In doing so, I naturally also have to deal with probabilities. However, it often turns out that the most likely or plausible explanation does not reflect what actually happened.

Many of the considerations I\x92ve read fail because the simultaneous failure of both engines is extremely unlikely, leading to a constant search for higher-order causes. It was suggested that an incorrect altitude setting led to an early thrust reduction. However, this would not explain the deployment of the RAT (Ram Air Turbine), especially since the thrust could have been readjusted. FADEC and TCAM are highly redundant systems, and TCAM failure is unlikely due to WOW (Weight on Wheels) logic, making a simultaneous engine failure after VR equally improbable.

With that said, and with regard to my question concerning the AD that relates to the fuel control switches (FCS), my thought\x97and it was nothing more than that\x97was that their activation becomes more probable if it can occur accidentally. That\x92s how I came across SAIB: NM-18-33.

Another user then brought up an iPhone. That notion would, of course, be dramatic\x97but how unlikely is it really that after approximately 10,000 actuations between December 2013 and June 2025, the two FCS no longer lock perfectly? Considering all of this, I find it quite conceivable that the A/T slightly reduced thrust in the first seconds after VR (e.g., if an incorrect target altitude had been entered) and that an object lying between the thrust levers and the FCS could have pushed the FCS into the \x93Off\x94 position. Due to the buttons on top of the switches, which provide some resistance, it\x92s even possible that the object both pulled and pushed them.

But all of this is speculation. The investigation report will bring clarity.

Even if my theory is not confirmed, I still believe that the positioning and mechanism of the FCS are suboptimal. Switches of such critical importance should be better protected, and movements in the area in front of the switches (like reducing thrust) should not follow the same direction as shutting off the fuel supply. A different switching direction alone would provide more safety\x97especially considering that the FCS are protected laterally by metal plates.

Originally Posted by AirScotia

Do the switches make an audible clicking sound, ie one that would be picked up by the cockpit recorders?

Originally Posted by PJ2

For info only - re-post of lever-lock fuel-switch design:




B787 Fuel Control Switches -

Originally Posted by Rarife

Is option 2 possible? It was my idea too but does the switch "connect" when it is not properly in its guarded possition?

Originally Posted by JPI33600

Well, speaking of fuel-cut switches, I read NM-18-33 SAIB with attention, and as a not-that-fluent english speaker, I stumbled on this sentence (my bold):



I could hardly figure what the "disengaged" word meant in this context, so I did a Google search for the switch part numbers (especially "766AT614-3D") to figure the difference between them, and a page from this chinese web site was part of the results.

And while I was painfully crawling the thread, I noticed the following picture about an "undesirable condition":

Incorrect lock tab position on fuel cut-off switch

If this incorrect mounting is actually possible, it would possibly remain unnoticed from the pilots (normal "pull-up then move" action is unaffected), but it would cancel the protective function of the so-called "locking tab", and even limit the travel of the switch handle in both directions, making it more vulnerable to an undesired change of state.

The photos above seem convincing enough, but I'd be very grateful for an informed opinion on this assembly mistake. Even if this is possible, the probability of both switches being unexpectedly snapped seems very remote to say the least, but not as remote as previously estimated.

Originally Posted by T28B

If you go down the no hand route, how did they turn them back on? I am not buying the loose canon plug gambit.
(The above posted as neither mod nor admin, to be clear).

Originally Posted by NSEU

I have a simplified 787 fuel control diagram showing 3 outputs from the fuel control levers. I suspect it represents poles. One signal goes to the EEC for "reset". One signal goes the fuel valves. Another signal goes to a Remote Data Concentrator where the signal is digitised and sent to innumerable devices (including the EEC and the FDR). That is not to say there are more. I don't see a line to the wing spar valve.

The 747 has 3 poles per switch. To send signals to all the systems it needs to, splices and multi-output relays are involved. On some aircraft there are even separate power sources going to some of these poles.

Originally Posted by Herc708

Does the EAFR record the electrical / physical contact of the RUN / CUTOFF switch or, does it record a software 'EVENT' which has the same 'signature' as the RUN / CUTOFF switch being toggled. My thoughts are that the RUN / CUTOFF switch never moved but, the underlying software / hardware system mal-functioned triggering a scenario similar to both RUN / CUTOFF switches being triggered

Some Boeing SB's describe circuit board failures triggering all sorts of unexpected / unpredictable failures

Originally Posted by barrymung

What about electrical wiring? If there's an intermittent wiring connection connection or the switch contacts were worn the circuit can indeed go off and come on again seemingly at random.