Posts about: "Fuel (All)" [Posts: 1005 Pages: 51]

Salvi, just spitballing here, a low alt capture is simple to rectify, but if you’re not expecting it ( perhaps a wrong MCP alt setting) coupled with a HUD , which focuses your attention on it, not the thrust levers, and add to the mix an inexperienced F/O. I can
also see in the final moments of desperation, reaching down and turning the Fuel Control Switches, OFF-THEN-ON, in the hope that an engine will come to life, if they believed that the engine was dead. This may be the reason the RAT extended? Just thinking out loud.

A case in point is the 2013 Boeing 787 battery fires. After two thermal runaways in 52 000 flight-hours, the root cause was still unknown; however, the FAA nevertheless issued Emergency AD 2013-02-51 grounding every 787 until a modification was available. IMHO a risk where the outcome is catastrophic, even very low probability, would trigger the FAA to issue an Emergency Airworthiness Directive as per their policy.

As I said in a previous post, every day that passes without a EAD suggest the cause was was specific to that aircraft (fuel contamination, maintenance failure, crew error - pick you own theory)

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.

I have been told elsewhere that this is not the case. A read of the draft FCOM available online for the 777 & 787 makes no mention of a FADEC generator, but then neither does the 737 manuals. Is this simply a case of "Boeing thinks you don't need to know"?

It has been proposed that the primary source of power for the FADECs is actually the flight control PMGs, mounted on the engine gearbox, but that this power goes to the avionics bay, has failover switching gear, and comes back to the EEC.

Can anyone shed concrete light on this (e.g. a source that clearly states there is both an EEC alternator and a flight control PMG on the accessory gearbox)?

Alternator and generator seem to be used interchangeably in this context.

It's not quite that, but there is a list of received channels for a GEnx 787 in the FDR report into one of the original battery fires . Unfortunately, it is only a list of parameters that they used and verified in the investigation - the only ones listed for the engines are N1 and cutoff switch. Other accident/incident FDR reports might be more focused on engines and include a similar table.

I don't think you'll find an actual wire list for it (or it won't be useful) as apparently most/all of the data is via an ARINC bus.

I attempted to PM this but your inbox is full.

[SLF with an electrical background and some exposure to ground-side critical facilities power]

Yes and no. As the investigating teams are not issuing running updates (and neither should they) we don\x92t know what stage of the process they have got to - the DFDRs might still be in a lab somewhere with a team of experts working out how to get the data out without compromising it. Or they could have the data but be none the wiser as to the cause(s) of the accident - Jeju comes to mind.

Given that there are >1,100 787s in service, you would be losing a significant part of the World\x92s air transport infrastructure if you grounded them. Also, if you\x92re still nowhere near understanding what caused it, how would you \x93unground\x94 the fleet if you don\x92t get answers for some time? It\x92s obviously something rare/unique, given the 14 years of operation without such an accident, so statistics should be on your side if you did nothing until you had more surety as to where the problem(s) lay?

Additionally, the lithium-ion batteries in the 787 design required compliance with "Special Conditions" in order to gain type certification. The addition of the Special Conditions at least strongly suggests that FAA's certification process brain-trust had maintained some vigilance with regard to the batteries once the type started operating, i.e., given their newness.

At this time, the fault or flaw at the root of this accident and how that fault or flaw worked through aircraft components and systems has not been identified publicly. It might not even have been identified .... I'm not convinced that separating "what" from "how and why" as a semantics exercise is enough to conclude the Annex 13 officials know the root cause yet. Maybe they do, maybe not.

And if they do not, then the contrast with the situation where FAA was, it seemed, keeping a close eye on battery issues in particular, is relevant.

I am a software engineer, I find it alarming that the power control unit had the ability to command all AC generator control units to effectively shut down - regardless of that being the side-effect of a bug, or an ability of the system to call on in appropriate scenarios.

Integer overflow is a specific type of issue common to many systems, but like you said - it is something that should be found with robust QA and analysis. The ability to shut down all generators at once from a single source seems like a risky design decision to me and I agree with your point about different software on 2 or more redundant sub systems.

My theory is that this was an accepted risk because the engine-driven fuel pumps would be more than enough in most phases of flight to keep the engines running, and you would still have 2 engines for redundancy. The APU would also restore AC power in lets say 30 seconds and you would then have electric fuel pumps as well.

I think there are several factors that could explain how loss of all AC power during takeoff could lead to a crash:

• The crash happened within 30 seconds - possibly too short for the APU to start, and the RAT doesn't power the AC electric fuel pumps
• The engine driven fuel pumps even if sufficient in level flight may have struggled during rotation - has Boeing tested an actual takeoff with only EDP feeding the engine while the fuel tanks are rotating and in extreme environments, or, have they only tested this statically?
• The takeoff was hot and heavy - combined with the landing gear stuck down and reduced thrust from loss of electric fuel pumps could this be enough?

Actually, according to tdracer , each channel of the FADEC gets just one throttle resolver input, as the two resolvers are on separate wiring looms. So, the FADEC is using the dual channel feature to handle erroneous throttle position inputs. However, according to the patent at least, each channel can trigger TCMA and cut the fuel supply independently. So now we're down to only needing only one erroneous throttle signal per engine. Or one wrong interpretation of a signal, e.g. value clipping where you shouldn't (shortcircuit -> idle), some integer overflow etc.

So, from my understanding, if there is an issue with some of the throttle position sensors, the FADECs will detect a disagreement and keep the high thrust -> assume safe is "fly", whereas one of the TCMA channels might read or misinterpret throttle position close to idle. As the thrust doesn't decrease, at some point the upper bound of the falling TCMA thrust contour will be breached and the engine will be shut down.

I didn't read that thread, but having flown the aircraft (challenger 600 type), I believe the consensus is that the Captain reaching underneath the thrust levers to actuate the flaps can (and has) resulted in the "triggers" on the back of the thrust levers being engaged- if this is done while the FO is bringing the thrust to idle, it can result in going below the idle stop to cutoff. In other words, the engines were inadvertently shut down.

But I agree that the complete, simultaneous loss of thrust on both engines has to be an astronomical probability, and the cause is going to be interesting to say the least.

I also agree that any one of us could be put in a horrible position within seconds that would be very hard to recover from- the older I get and the more hours I spend in the air, this starts to spend more time in one's consciousness, unfortunately.

BTW calling the crew " highly experienced" is a bit of a stretch IMO, the Captain certainly was, but 1100 hours isn't even enough for an ATP in most countries. For all we know it was not a factor, of course.

PS, what is an SLF??

@syseng68k
Consensus here is, that both engines where stopped by a closing fuel cut off valve, wich yields a fast loss of N2. The generators then shut down very quick as does the thrust in a few seconds. This is supported by the quick RAT extension which allowed the crew to control the flight. The APU did autostart too. A thrust changed with the thrust leaver to idle is much slower and would not result in the dramatic change in performance. Thrust set to idle will not engage the RAT since the electric generators would still work. So a thrust leaver changed to idle or any intervention by Autothrust (AT) would not yield to the RAT extension. Something or someone activated a fuel cut off. How and why that happened is the big question, the investigators have to answer.

A naive glider pilot question: if fuel cut off was (inconceivably) selected, would both fuel control levers have been flipped downwards from Run to Cutoff? And if they were then immediately flipped back to the Run position, how much time would have been needed to achieve enough thrust to maintain altitude?

The fuel cutoff switches can't be "flipped" in either direction; they have to be lifted over a detent and then moved, a very positive action.

The simplest answer: Lo Lvl Alt Cap; Thrust to Idle; Startle Factor; Inappropriate Memory Items : ( RAT deployed; insufficient time for Eng relight.

As an ex-tp, I would consider those cut-off switches a danger, and they should have guards either side of each.
Shirtsleeves/watches etc. can get caught, lift switch.
Very poor design. Would not pass `military-muster.`

They're guarded by the switch design/operation itself. To move one of them, the toggle handle has to first be pulled outward.

The 787-8 landing gear retraction is primarily hydraulic, using the center hydraulic system for the main operation. However, the alternate gear extension system utilizes a dedicated electric pump to pressurize fluid from the center hydraulic system for gear extension. Obviously due its size and weight and staged retraction, the effort required to raise and stow the gear greatly exceeds that required for extension.

The main gear retraction/extension is controlled by the center hydraulic system.

It is apparent that the hydraulics failed when the engines shut down after breaking the down-locks and leaving the Main Landing gear bogeys in the tilt position, ready for a next step internal stowage and door closure (that was now never to happen). It is therefore apparent that the dual engine failure and consequent automated RAT extension was precipitated by this gear selection or retraction cycle and thus likely to be either WoW micro-switch or 5G Radar altimeter-effect associated. Due to accumulator depletion, the electric pump load would have spiked to replenish it. This may have precipitated the dual engine shutdown due to an unfiltered electrical surge affecting the Ground/Air microswitches (or a local 5G transmission affecting the RADALT) and resetting the TCMA.

The RADALT? Another plausibility? Because of the furore over a spasticated frequency allocation by the US FCC, the US FAA had finally “bought in” and declared that individual nations and their airline operators were responsible for their own 5G frequency spectrum allocations and for taking essential steps to ensure mitigation of the interference effects upon aircraft automated landings and other critical systems caused by their own national approved 5G spectrum decisions. It was admittedly a situation calling for extensive modifications to (and shielding for) the three radar altimeters fitted for redundancy considerations to all modern airliners... for Category 3 ILS approach and landing in zero/zero visibility conditions. The RADALT also features in many air-ground sensing applications. (eg the 747-8).

This was an unusual FAA “passing of the buck” to manufacturers such as Honeywell etc. (to sort out with client operators). But then again, it was not the US FCC’s right to dictate the specific 5G frequencies internationally. These spectrum allocations now vary over the wide selection of 5G phones available (and also nationally). 5G Radar Altimeters constitute a part of the ground/Air sensing that changes the TCMA from ground mode (able to fuel-chop engines) to the air mode (inhibited from doing so)... Ground activation is acceptable ...where fuel chopping of uncommanded thrust can prevent runway sideways excursions or runway length overruns. The question now becomes: “Is it more (or less) safe having an automated fuel-chopping capability on BOTH your left and right, rather than leaving it to the pilot to react via his center console fuel cut-off switches... in the unlikely event of a runaway engine after landing (or during an abandoned take-off)?

5G Frequency Variations

The frequencies of 5G phones vary nationally based on the frequency bands allocated and used by different carriers in each country. In the United States, for example, carriers such as AT&T, Verizon, T-Mobile, and others use a combination of low-band, mid-band, and high-band 5G frequencies. Low-band 5G frequencies typically range from 600 MHz to 1 GHz, mid-band 5G frequencies range from 1.7 GHz to 2.5 GHz, and high-band 5G (mmWave) frequencies start at 24 GHz and go up to 40 GHz . These frequencies are allocated by regulatory bodies such as the Federal Communications Commission (FCC) and can vary between countries based on spectrum availability and regulatory decisions. In other countries, the specific frequency bands used for 5G may differ, leading to variations in the frequencies supported by 5G phones. Additionally, the deployment of 5G networks can also influence the frequencies used, with some countries focusing more on sub-6 GHz bands while others prioritize mmWave technology.

5G interference? It may be an avenue worth exploring?

Agree. The two most important controls in the aeroplane, sitting there in a wide-open, unprotected space. After an incident where a manual fell off the coaming (can't remember if a switch got bashed into the Off position), we put guards on our non-787 fuel switches:
Ours:

787:

Yes, and probably much to @Roo's disgust, we had an instance where an engine shut down all by itself in the cruise; it was concluded that the fuel switch hadn't been "locked" in the ON position and was just sitting on the edge. It was then highlighted to all of us that the FCOM stated "give it a good jiggle" to make doubly sure it was locked in ON.

The spec sheet says 100,000 cycles.
Switches fail sometimes. I have changed lots of lots of malfunctioning toggle switches in my day.
But both at the same time?
It has to be a common thing happening at the same time.
Someone slipping both switches into a worn middle detent is such a thing though, that is one habit that could be developed. A slight bump at takeoff and they both go to cutoff.
Or they are worn and theres an iphone behind the throttles, as someone mentioned.

The switches themselves are on-on 4 pole toggles, and doesn\x92t fail into one position over the other, and gravity would prefer the cutoff position in this design.

I mentioned I have used my share of switches, knobs and buttons. In much larger quantities than what you find in aircraft, but without the life and death factor, and thus no SOP.

Unexpected things happen, no one dies, but I myself brodcasted jolly sounding very inappropriate intro music over a very dark news report on the unravelling Joseph Frietzl case by dropping my phone on a switch. Several million viewers, a good chunk of which called to complain.

Grave errors can be banal.

Other than that, common connectors, the harness itself, I have seen a large amount of unexpected electronic things happen when those get bendt the wrong way.

This isn\xb4t quite right. They could both have had a malfunction without this being an issue until something or someone hit them at the same time (e.g. on rotation). It\xb4s just another theory which isn\xb4t less plausible than many others.

That is not a Boeing Fuel switch.