Posts about: "Dual Engine Failure" [Posts: 270 Pages: 14]

If you wanted to an analyse this further:
1. You might mathematically start at TE=0 at start of takeoff-roll, and treat drag as minimal until rotation.
2. Typically rotation will be to say 15deg nose up, but flight path will be much less (5deg? for heavy hot 787). Once that rotation is complete, aircraft will stop accelerating. Therefore engine thrust (energy gain) equals gain in PE - drag x time.
3. This might give a better insight into where energy gain/loss became unusual?

Looking at the raw data in your post, and given the speeds are likely IAS based i.e. can be affected by wind, I don't see the IAS loss as equating to dual engine failure i.e. zero thrust - but could be wrong. Once a heavy airliner gets to lift off the acceleration is reduced (drag) and the decays to zero as PE gain kicks in.

Ditto a time / distance to the crash site might give some energy info? Looks like the crash site is 50' (?) below the airfield (Google Earth will give more).

I think you are doing an interesting study on the absence of other info

Firstly, I've read through this whole thread - thank you Admin & Mods for your considerable efforts to clean things up.

Secondly, as a (now ex) glider pilot who remains extremely interested in aviation in most of its forms, this discussion has been an education and thought-provoking, as it so frequently is whenever I lurk here (usually without logging in). Thank you all for sharing your knowledge, expertise and thoughts.

To my mind the above post (especially the sentence I highlighted) is amongst the best (and most succinct) summary of what the pilots likely faced, with little to no time to resolve the situation. I cannot imagine those last few seconds and my heart goes out to them, the passengers and the many loved ones left behind. If there is any good that can come of this, it is that the cause is found quickly, with no bias, and steps are taken to ensure the same holes in the cheese cannot happen again.

How long does it take for an engine to fail in terms of thrust output - what does thrust over time look like for various failure scenarios - e.g., no electrically powered fuel pumps, or contaminated fuel, or thrust set to idle or other issues?

The original mobile video (not the copy from someones phone screen) clearly sounds like a RAT but what does the engine itself sound like - is it idle or reduced in some way?

What is the minimum amount of thrust that would need to be lost to stop climbing and sink back down - it took 30 seconds from leaving the ground to impact from the CCTV and the first 15 was climbing.

I would look carefully at the fact that the PCU still has the technical ability to tell all AC generator control units to turn off via software, as proven in the documented and fixed 248-day software issue.

We agree that there was a lack of thrust. Possibly caused by a dual engine failure. But the sharpest frames in the video do NOT show the RAT and this is counter evidence to the RAT theory. If there were substantial technical failures who knows what sounds could be generated. I find the evidence weak at best. And we immediately get into a chicken-egg problem: did some power issue of unknown nature cause an engine failure or did a dual engine failure occur, resulting in a power loss? Both are extremely unlikely and need to be backed by quality evidence. The video is not it, in my opinion. I don't know the APU intake mechanism and whether it could open after the impact.

The investigators will certainly soon know, but how sure are you that they'll share that in public?

Nope, you may not have read the whole thread - the full set of conditions which can trigger the RAT have been posted multiple times before your reply

I'd phrase it differently: the frequency (and harmonics) of the noise are consistent with it being a RAT. If you then assume that it was a RAT and infer distance and speed curves from the Doppler variation, you get plausible values for an aircraft. But the two things are somewhat linked so you can't really treat the second thing as confirmation of the first. (FWIW, I'm personally quite satisfied that it was indeed a RAT on the audio.)

To simplify the chicken/egg:

Tdracer earlier confirmed that an airplane electrical power loss would allow engines to keep running , because 1) engines are fully-capable of suction feed operation in takeoff envelope (if boost pumps lost), and 2) the EECs are powered by their own PMAs when running and to substantially below idle (I recall roughly 10% N2). Airplane powers the EEC for ground starts, prior to PMA coming online, and as backup to the PMA after that.

Related:

Engine igniters are powered by the aircraft. So theoretical full loss of aircraft power would disable Autorelight upon a flameout. Ignitors typically don't make the cut for most-essential battery-only loads because it would also take an engine flameout, and the airplane past V1 in ground roll can fly fine on one engine that can achieve takeoff thrust.

Autorelight is relevant - if there was a single-engine failure post V1, autorelight will attempt to relight the engine, so there is no need for a pilot to try to cycle the fuel switch to reset the EEC (potentially grabbing the wrong one), or to otherwise intervene. In such a circumstance, they need to trust their training. I've heard accounts that the most likely pilot instinct in such a situation would be to push the throttle(s) forward.

Finally - there was talk earlier about accidentally cutting the fuel switches - and it was duly noted that they have to be pulled out over the detent, so very unlikely. The same cutoff effect could be achieved with the engine fire handle(s), right behind the fuel switches on the pedestal - though they are an upward pull, so also not subject to inadvertent or accidental engagement.

A loss of lift AND thrust at this critical juncture could have had caused this awful disaster. I think the data recorders have already revealed the cause but If it's this, then I don't think we will hear much anytime soon.

Ah, yes. Missed that. Thanks. But I have to assume (I know) that any responsible aviation engineers designing a system that can shut down both (all) engines simultaneously when the airplane is on the ground is going to want to make very sure that the airplane is on the ground.

But I'll check.

If decrease in thrust not by transition to climb thrust due to early inadvertent flap retraction and pilot action on fuel control switches from accomplishing dual engine failure memory items, then fuel cavitation /fuel fumes lock may be a cause. Just saying.

Yes. Thank you tdracer. All those postulating TCMA / FADEC faults please read and understand this clear explanation.

Then, ask yourselves which extraordinarily low probability bundle of previously unrevealed faults could spontaneously manifest themselves on both engines simultaneously.

Also ask yourselves why these faults manifested at that critical phase of flight and not during taxiing or take-off roll when some of the TCMA sensors would have been primed.

After reading tdracers informative post this morning, I too was musing: Why is all this attention being given to TCMA.

Of course, when the probable cause is profoundly unclear, our continuing distrust of latent technical systems comes to the fore .... as sadly, the shadow of MCAS still looms large in our imaginations

Having followed this thread since the beginning, it is clear to me that this discussion is tainted by the fact that many contributors have MCAS and Boeing quality issues at the front of their minds.

I perfectly understand that, so no judgement from me, but it no doubt causes confirmation bias with conclusions being made about extremely improbable outcomes (dual engine failure at the same time during rotation/take off).

The RAT being deployed does not prove a TCMA-failure on both engines nor does it prove that both engines failed (its still not disproved or proven if it was manually deployed).

It was posted but in a nutshell:

Airbus assumed their pilots would not spill their drinks but they did, and this resulted in an un-commanded dual engine shutdown. Now they have to use Sippy Cups!

Boeing assumed their pilots would spill their drinks so made the system robust enough to tolerate liquid spills without shutting down the engines.

My information differs to yours, We do know the EAFR was recovered on Saturday. Are you suggesting that it sat in a room for three days?

Wow you seriously think a professional crew would shutdown an engine below 400 feet?
​​​​​​​Is there any yaw or rudder deflection in any videos?

This doesn't make any sense. The plane was in the air for approximately 30 seconds, the plane stops climbing around 12 seconds after take off, and the noise of the RAT is heard 11 seconds before the plane crashes - even if we assume the RAT both deploys instantly and deployed the exact moment that video began recording, that only gives the pilots a 7 second window to perform an action that results in it being deployed.

There just isn't enough time for the RAT to be deployed as a result of any action by the crew, IMHO. And to demonstrate how long 7 seconds is - that's enough to say 20 words, assuming no interruptions .

If you read the thread, you would know:

The RAT was almost certainly deployed. 4 different sources.
The Flaps were not retracted. Visible at the accident site plus many other sources agreeing they were indeed down.
APU will autostart when all engine power is lost. Potentially explaining why the inlet door was open or partially open at the accident site. Mentioned in several previous posts
On a 787-8, the main bogies tilt as the 1st action of the gear retract sequence. As stated in previous posts. I don't think this happens unless gear is selected up. So the conclusion was, gear was selected up. One caveat, IIRC, there was some discussion around a failure could have caused the bogies to tilt without Gear up being selected but I don't recall the outcome.
As for the Air France remark, un-necessary IMHO. Let's respect the crews please.

Not 757 - it was a 767. Second time it happened in about 12 months.

Determined to be an ergonomics problem with the switch layout in the flightdeck.

Early 767s (JT9D and CF6-80A) had a supervisory "EEC" (Electronic Engine Control - Boeing still uses "EEC" to identify what most people call the FADEC on modern engines). The procedure if an EEC 'failed' was to switch both EECs off (to prevent excessive throttle stagger - unlike FADEC, the engine could operate just fine with a supervisory EEC failed).

Problem was that the EEC ON/OFF switch was located on the aisle stand - right above the fuel cutoff switches. Turned out 'muscle memory' was when the pilot reached down there, it was usually to turn the fuel ON or OFF - which is what they did. Fortunately realizing what he'd done wrong, the pilot quickly restored the switches to RUN and both engines recovered. And yes, they continued on to their destination (RAT was still deployed since there is no way to retract it in-flight).

Previous event was with JT9D engines (United IIRC). In that case, only one engine recovered (second engine went into an unrecoverable stall), they simply came back around and did a single engine landing.

Realizing the ergonomic issue, the EECs were relocated to the pilot's overhead (retrofit by AD).

To the best of my knowledge, there hasn't been a repeat of an inadvertent dual engine shutdown since the EEC switches were relocated. It's also very difficult to 'accidentally' move the switches as there is a locking detent - the switch must be pulled out slightly before it can be moved to CUTOFF.

Sorry but you are wrong. The RAT was basic on the 767 - every single 767 built has one. The Gimli glider deployed the RAT (1982), and the Delta dual engine shutdown out of LAX deployed the RAT.

Yes. Thank you tdracer. All those postulating TCMA / FADEC faults please read and understand this clear explanation.

Then, ask yourselves which extraordinarily low probability bundle of previously unrevealed faults could spontaneously manifest themselves on both engines simultaneously.

Also ask yourselves why these faults manifested at that critical phase of flight and not during taxiing or take-off roll when some of the TCMA sensors would have been primed.