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

DTA
June 12, 2025, 11:55:00 GMT
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Post: 11899120
Sadly, the local police have just said that there appear to be no survivors from the aircraft. RIP.

Subjects: None

DTA
June 13, 2025, 09:08:00 GMT
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Post: 11900219
Quoting the Telegraph UK:

The Indian government is considering grounding Air India’s Boeing 787 fleet after one of its planes crashed, killing more than 240 people.

The country’s Ministry of Civil Aviation is mulling grounding all Boeing 787-8 Dreamliners as a precautionary measure while a safety review takes place, sources told Indian broadcaster NDTV.

Subjects: None

DTA
June 13, 2025, 10:42:00 GMT
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Post: 11900329
Reading the various reports about electrical problems on the prior and this flight, such as flickering lights reminded me of the BMI A321 incident discussed here 15 years ago:

https://www.pprune.org/archive/index.php/t-433616.html

A faulty generator caused all sorts of problems with control of the aircraft. It is a reminder that complete electrical failure is not the only failure mode. Shutting down the faulty generator on that aircraft recovered the situation, but they had time and altitude on their side.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Electrical Failure  Generators/Alternators

DTA
June 13, 2025, 10:56:00 GMT
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Post: 11900345
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!
A Google search for Dreamliner cabin lighting brings up some of the marketing from airlines when the aircraft came into service. There are a multitude of colours shown. I recall debate at the time whether it was cool or tacky.

Subjects: None

DTA
June 14, 2025, 17:15:00 GMT
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Post: 11901671
Originally Posted by ATC Watcher
from the EASA statement yesterday :

​​​​​​​No mention of UK
AAIB (UK) Update: Air India flight AI171

A team of four investigators from the UK Air Accidents Investigation Branch (AAIB) has arrived in India. They have expertise in aircraft operations, engineering and recorded data. Their role is to provide additional support and expertise to the safety investigation being led by India\x92s Aircraft Accident Investigation Bureau.

The UK AAIB has \x91Expert\x92 status in the Indian safety investigation. In accordance with international protocols, release of information on the investigation rests solely with the Indian authorities.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AAIB (All)  AAIB (UK)  AI171

DTA
June 16, 2025, 05:52:00 GMT
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Post: 11903115
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.
Where does the logic block that takes the WoW and other inputs to generate the singe air/ground indication live? Is it somewhere that would be affected by the aircraft power systems? Could a failure in the aircraft power cause a false ground indication to be sent to the FADECs?

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Weight on Wheels

DTA
June 19, 2025, 10:13:00 GMT
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Post: 11905888
Originally Posted by Seamless
Has this been discussed already?

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


​​​​​​​
Gated switches can fail such that the locking function no longer works. That failure can be the result of physical damage or wear so that the knob is stuck in the pulled position. It would not be obvious if you did not look closely. There are two switches of course and it would be disappointing if they were both in that state.

Subjects: None

DTA
June 19, 2025, 11:01:00 GMT
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Post: 11905926
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?
The generic version in your drawing has the centre position, whereas the version used on the 787 (4TL837-3D) has centre lockout. This photo shows the switch. You can see it is pretty easy to not place it in the locked positions. With this design of switch the cam on the toggle will eventually wear away.


Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Condolences  Honeywell  Special Airworthiness Information Bulletin

DTA
June 19, 2025, 11:47:00 GMT
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Post: 11905963
Originally Posted by Musician
How many cycles are they rated for?
They comply with a military standard that requires 40,000 cycles though the locking part is tested 20,000 times by just pulling to its full extent. Or something like that. How well that testing matches real world use is debatable.

Subjects: None

DTA
June 19, 2025, 13:08:00 GMT
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Post: 11906013
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.

When they get worn they become easier to force out of the lock position. But they still retain the normal switch type operation. Gravity will not be enough to cause a switch (off), you would still need to push it either way. The spring can fail on this type of switch, that is the spring that pulls the toggle part into the locked position. Again, it still functions as a switch but the locking is not good.

Subjects: None

DTA
June 19, 2025, 14:36:00 GMT
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Post: 11906073
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.
It is probable that the switches are becoming easier to move across the gate after 10,000 operations. Something falling on them would be a possibility to cause that. And there is certainly an argument to be had whether down=on is a safer way for them to operate.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Air Worthiness Directives  Engine Failure (All)  FADEC  Fuel (All)  Fuel Cutoff Switches  RAT (All)  RAT (Deployment)  SAIB NM-18-33  Special Airworthiness Information Bulletin  Weight on Wheels

DTA
July 09, 2025, 15:04:00 GMT
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Post: 11918446
Originally Posted by AirScotia
Do the switches make an audible clicking sound, ie one that would be picked up by the cockpit recorders?
Not really with this type of switch.

Subjects: None

DTA
July 09, 2025, 19:05:00 GMT
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Post: 11918581
Originally Posted by PJ2
For info only - re-post of lever-lock fuel-switch design:




B787 Fuel Control Switches -
A bit of a pedantic point, but the locking lever in the photo above is not the right action for the fuel cut off switches on the 787. The switch above has two locked positions and a biased further position. You could say ON-OFF-BIASSED. There are some photos earlier in the thread (assuming they are still there) of the correct Honeywell switch and its gate.

Edit: And here it is:


Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches  Honeywell

DTA
July 11, 2025, 20:56:00 GMT
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Post: 11919785
This part of the report shows how early the RAT was out.



Subjects (links are to this post in the relevant subject page so that this post can be seen in context): RAT (All)

DTA
July 11, 2025, 21:03:00 GMT
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Post: 11919796
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?
The switch state could be either on or off in that position. However, the CVR makes it pretty clear that the switches were moved deliberately to off. Just not why. Also, remember the report says one switch was moved then the other. Not together.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): CVR  Switch Guards

DTA
July 12, 2025, 10:26:00 GMT
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Post: 11920464
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 tab lock position on fuel cut-off switch
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.
NM-18-33 SAIB left me wondering the same thing. It give a procedure for detecting the defect but omits to explain the cause. I was thinking that the wrong switches had been supplied/fitted. Assuming the image from the Chinese web site is correct, it is disappointing that the actuator can get into that state. I did not see anything that said whether that was how the switch arrived from Honeywell or if there was a defect that allowed the actuator to turn.

One other useful thing from that web site is a partial schematic which shows the connection of the 4 poles in the switch. I believe this is from a 737NG but it should be the same idea.


Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches  Honeywell  SAIB NM-18-33  Special Airworthiness Information Bulletin

DTA
July 12, 2025, 21:20:00 GMT
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Post: 11920839
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).
It is worth remembering that each switch has 4 poles. Think of a pole as a section of the switch. Each section controls a different function - reporting switch position to FDR, fuel cut off and so on. The chances of anything other than real physical switch movement (whether it be spilt liquid, wiring damage, loose canon plug or whatever) changing the status of all 4 sections is impossibly small. Then you have two switches.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FDR  Fuel (All)  Fuel Cutoff  Fuel Cutoff Switches

DTA
July 13, 2025, 07:13:00 GMT
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Post: 11921074
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.
The actual switches on the 787 have 4 poles. Of course, that does not mean that all 4 poles are used. Alas the full 787 wiring diagram does not appear to be available online anywhere to confirm what each section is connected to.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): FDR  Spar Valves

DTA
July 13, 2025, 07:37:00 GMT
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Post: 11921088
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
An answer to this is just a few posts back. Each switch has 4 sections which control different functions. It is not a single switch with software behind it. Multiple simultaneous separate failures would be needed if the switch itself did not move.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): EAFR  RUN/CUTOFF

DTA
July 15, 2025, 12:44:00 GMT
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Post: 11922897
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.
You need to look back through the thread. Each switch has 4 independent circuits controlling different things. You would need multiple separate simultaneous faults for each switch.

Subjects: None