Posts by user "EDML" [Posts: 38 Total up-votes: 120 Pages: 2]

Originally Posted by sTeamTraen

SLF question... how difficult would it be to accidentally knock the fuel control switches to "Cutoff", say if your hand slipped from the throttle levers?

Originally Posted by The Ancient Geek

+
My personal theory FWIW is that the tank pumps never ran due to some fault and the aircraft made it to V2 on fuel in the system (possibly involving the centre tank).

Originally Posted by FrequentSLF

FLS here with engineering background, a simple question, how the TCMA software is coded, multiple designers, on different hardware and redundant? Can be a bug on that system definetevely impossible?

Originally Posted by sevenfive

Correct procedure after enginefailure is to tilt the wings about 3 degrees toward the engine that is still running.

Originally Posted by sevenfive

If - and I say if - they in this stressed situation managed to shot down the wrong engine following the engineout procedures the RAT would come out.

Originally Posted by JPI33600

Not an avionics specialist, but electronics / software engineer here, with extensive experience in hardware fault tracking, protocol monitoring and software debugging in embedded systems : mods, feel free to delete this post if I am completely out of track (and thank you for the huge amount of work you've done trying to keep this discussion clean).

After I have read the whole thread, I think most of the community agrees about a lack of engine thrust being the cause of the crash. Searching in that direction, I'm trying to "think out of the box", discarding the usual suspects (birds ingestion, TCMA, human mistake...), and to find a plausible single point of failure among the various subsystems involved. I was thinking of reversing the causality of the event, i.e. exploring a case where the engines would have behaved unexpectedly because of a major electrical failure, instead of the already explored case where both powerplants went AWOL first.

Therefore, I have a couple questions for tdracer / fdr / other informed contributors (BTW, fantastic contribution guys, please keep the good info coming):

1. From the scarce info available, is it reasonable to conclude that the engines were totally shut down? Could they have just been set to idle or reduced thrust instead?

2. In the second case, if (and that's a big IF) a major electrical failure happened first (which could have triggered RAT deployment), and considering this plane is a FBW aircraft, could there exist a case where the FADECs would command idle thrust -- or significant thrust reduction -- because they receive invalid input data from the throttle controls? Kind of a garbage in-garbage out case?

The associated scenario would be: major electrical fault (with subsequent RAT deployment) -> major protocol disturbance on ARINC/AFDX buses -> FADECs detect invalid data from the controls -> FADECS enter some kinf of safe mode and command reduced or idle thrust.

Does it make sense or is it pure fantasy?

Originally Posted by syseng68k

EDML: "No. The throttle position sensors (dual per engine) are part of the FADEC. The throttle position data is not transmitted through the ARINC busses of the aircraft".

To clarify, you are saying that the throttle position sensors are wired directly to the FADEC, and nothng else ?.

Originally Posted by compressor stall

I'd be interested in any history or understanding as to why Boeing went with the common tank approach on takeoff?

Originally Posted by artee

Surely that's not quite right? If the center tank has fuel, both engines will be fed from the center tank. Only once/if the center tank doesn't have fuel, will the engines be fed from their respective wing tanks.

Originally Posted by Cury Lamb

Here’s what went down:

CP as PF (hands on the thrust levers), accidentally retards thrust levers just after lift-off, due to low level turbulence (hot, dry, 40\xb0C).

FO as PM (being trigger happy) sees this as DUAL ENG failure, does memory items (at the speed of light), without confirmation from the PF.

The rest is history…

Originally Posted by ettore

I believe they're native speakers professional pilots on Pprune who might have read or could find the original piece. Could they help to clarify Aryan's statements in English?

Originally Posted by D Bru

Uncommanded high trust on (at least one of) the engines during the TO-roll, in particular past V1, resulting in a discrepancy with the actual (likely derated)thrust settings, could have triggered TMCA on or just before lift-off.

Originally Posted by Lead Balloon

I was struck by a comment in this or the earlier thread that I cannot now find. It was to the effect – I’m paraphrasing – that fuel shut off results in an almost immediate cessation of thrust. (Please correct my paraphrasing if I’m off track.) I was also struck by how quiet the aircraft was in the original video, except for the RAT. (Or was it a motorcycle? Sorry couldn’t resist. Just joking…)

Someone earlier asked how the aircraft could have kept climbing if both engines stopped very late in the take-off roll or shortly after take-off. My answer: Momentum.

Originally Posted by Someone Somewhere

I (and I think everyone else here) have been assuming that the FADEC does in fact have a dedicated permanent-magnet alternator, as is the case on the Airbuses (confirmed by FCOM) and surely the 737.

Originally Posted by Someone Somewhere

Yes. That is what I have read here, that is my assumption, that is how Airbus does it, that is what makes sense .

But I am being told elsewhere by someone with an A&P badge that that is not quite the whole story, and that the FADEC PMGs do double-duty as the flight control PMGs.

I am hoping for some documentation to confirm/refute that.

Originally Posted by mechpowi

There\x92s at least N2 overspeed protection that actually uses the same hardware as TCMA to stop the noise. There might exists crosstalk and inhibit for the N2 overspeed protection if the N2 overspeed protection has shut down the other engine. In fact it\x92s not confirmed that no such crosstalk exists in 787 TCMA system. It would complie with \x94no single fault should cause\x85\x94 certification requirements. Other than that I see no practical difference in the propability of TCMA and N2 overspeed protection to shut down both engine during take-off.

Originally Posted by Util BUS

Based on my previous speculation regarding a BTB short, I wonder how aircraft engines might react in a situation where initially a transient power fault is followed by only battery power being available? As I understand it, there are no longer cable connections to the engines, given no valid inputs from the.thrust levers, what thrust mode would the FADEC's revert to?

Originally Posted by Sailvi767

Correct. If the flights involved needed less than 128,000 lbs of fuel the center tank would not be used. There is a scavenge system to insure the center tank remains empty when burning from the wing tanks. On the flight in question 128,000 lbs of fuel would in fact likely be close to the fuel required. The center tank might have been empty or contained a small amount of fuel. It’s quite possible the aircraft could have been transitioning from center tank to wing tank fuel at liftoff. With the design of the fuel system I can’t really see how that could be significant but I am sure it will be looked at in the investigation.

Originally Posted by Squawk7700

I haven't read anywhere where the yaw to the right was noticed not that long after takeoff? I'm assuming this was due to the roll-back.

About 9 seconds after wheels-up it's clear that power is well and truly deminishing.
17 seconds after wheels-up, there's a defined yaw to the right.

It looks like the right engine power is lost, a yaw to the right occurs and immediately after, the aircraft pitches up, potentially due to elevator input and subsequently some left rudder. It gives some credit to the theory that one engine was lost.

I can only assume that the associated yaw from a lost engine would be significant, so on the face of it, it doesn't look severe enough, but it does look somewhat upset.

Originally Posted by Aerospace101

The evidence is the spoiler pair deflection behind the engines prior to impact. See earlier post . . That specific spoiler pairing is only controlled by electrical power (directly connected to pilot control column). We should see other flight control deflections if the RAT was powering hydraulics. In the final moments I would speculate the flight controls had only emergency electric power from the battery.