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

I'm not sure if the engines would start , but once they were running, suction/gravity feed into the engine-driven high-pressure fuel pumps would keep the engine running, just like in an electrical failure.

Expect all the alarms, too.

The 320 starts even if you forget to turn on fuel pumps. Don't ask how I know.

In reply to you, I am solely stating that it's a thrust-side problem. I think I somewhat misinterpreted your post as it looks like you might have been saying that anyway.

In general, I think it's looking like dual engine failure/shutdown cutting electrics. I agree that why it occurred is very unclear. Outside chance of total electrical failure causing dual engine failure rather than the other way around, but that would perhaps be even more concerning a design failure.

Similar to Jeju, we also have what is looking increasingly like a loss of ADS-B data at the moment things went wrong, not just a loss of coverage.

That gives:

• Sound of RAT
• Visible RAT
• (edit: APU door open implies APU autostart)
• Loss of ADS-B out
• Near-total loss of thrust.

The alternate theories seem to be a) flaps (basically discounted), b) suction feed failed after total electrical failure, or c):

• A/T rolled engines back
• Crew interpreted this as dual engine failure
• Crew didn't push throttles forward
• Crew did switch each engine off & on again and maybe deployed RAT manually as well.

I think it has been suggested that the upload only happens every 30 minutes or so.

Loss of electrical power will not affect fuel supply to the engines, if the fuel boost pumps in each tank are inop, suction will open their respective bypass valves. It would take two completely separate electrical commands, to two completely separate LPSOV\x94s to drive them to the closed position and cut fuel to the engines.

FIFY But your original text is likely to be correct in the specific circumstances of this tragedy.

This is a very plausible scenario. Above 400 ‘ AGL, memory items.

Most large aircraft including the 787 have overriding fuel pumps. The centre tank pump on each side delivers the highest pressure so they supply the fuel under normal conditions.

If/when the centre tank is fully used or the pump fails, the two wing tank pumps supply the on-side engine. This happens on every flight that takes off with more than ~34t of fuel (two wing tanks) and lands with less.

If neither on-side pump is operating, the pressure in the supply line drops below that of the tank and pulls open the suction check valve.

The only 'reconfiguration' the pilots can do is open the crossfeed valve, or turn off pumps.

(Sorry, Airbus here and not familiar with Boeing) Flap 5 to 1 reduction on the Boeing triggers autothrust reduction, is that correct? If so, are there any other conditions that need to be met for this to happen like being in some kind of takeoff mode? Just thinking whether this would have potential otherwise in other regimes to cause issues, discontinued approach perhaps.

Am slightly puzzled as to why if flap reduction triggering climb thrust is part of the standard logic (and presumably clean-up technique) then partial dual thrust loss wouldn\x92t be immediately recognised as the classic symptom of gear / flap retraction handling error? I presume Boeing pilots / air India are just as aware of this it as everyone else, strikes me as odd that one would immediately go into full dual EF mode. My instinctive reaction without knowing the Boeing would be to firewall both TLs, would this have worked in the early flap retraction logic scenario? Many thanks all

It could do it, assuming fuses/contactors didn't vapourise first.

I expect the VFSG shafts would be designed to fuse/slip long before the main radial shaft feeding the gearbox, as noted.

But if it occurred, it would knock out not just your FADEC alternator but also the high pressure fuel pumps. Engine would stop dead near instantly.

It would partly be a question of how much interlocking is present. I guess bypassing/mis-adjusting mechanical interlocks is something poor maintenance could & would do.

What you suggest might be plausible. I had a tower shaft snap on a 767. The engine quits immediately. You lose fuel flow, oil pressure, generator and hydraulic pressure instantly. That could account for the gear not coming up. In a normal shutdown or flameout hydraulic pressure is maintained for a considerable period of time and windmilling will provide some pressure. I would have expected the gear to move further up in the retraction cycle. Tie this in with claimed electrical issues and the concept is at least interesting.

Retired engineer here. Following my post a while ago on the avionics electrical system I have read all the posts and also noticed mention of the hydraulics system.
Returning to my original source, which is Book 1 Introduction to B787 Avionic/Electrical, I read on p. 96 that the RAT will deploy if any of three conditions are met.

https://fliphtml5.com/quwam/qhdw/Boo...ics_Electrical

These conditions for deployment of the RAT specifically are:
Loss of both engines
Loss of power to the instrument buses
Loss of all three hydraulic systems

The latter one may be worth a close look because it would appear that problems took place when the wheels left the runway and I assume there was a change of states in various sensors. I surmise these sensors are different from the engine systems where both commands and power are needed to force a change of state in, say, fuel pumps. Is it the same for thrust control?
It says there are three hydraulic systems but is there a common reservoir? I'm not an expert in that field but google tells me that B787 has a bootstrap reservoir system which I understand to mean that a pressure of 5000 psi is maintained using a piston arrangement.

At this point think timeline, and changes of states.
There is an operational change when the wheels leave the ground. The associated sensors would send that data to the CCS. What was sent? Maybe the CCS read Hydraulic L + Hydraulic R + Hydraulic C = incorrect or fail, which would trigger deployment of the RAT. What would the electrical and control system do then? More importantly what exactly did all the systems do on this aircraft following such an event.
Was there a problem with the fluid in the hydraulics? Does hydraulic fluid ever 'go off' in very hot conditions. Or maybe there wasn't as much fluid in there than there should have been? How would hydraulics systems be compromised if indeed that was the case.
All speculation - but forensic system analysis is a bit like that.
Finally - what was the noise the survivor heard? Was it before or after the lights flickered? It may have been a bit of the airframe hitting something and snapping.
The survivors in the doctor's hostel heard a noise too which may be jet engines running. They would know the difference between that and other noises being close to an airport. Need a timeline for everything here.
Apologies for the long post. Just my thoughts.
RIP to all who didn't survive.

Three hydraulic systems, each with their own reservoir, pumps, and accumulators. Engine bleed air (I think; some newer aircraft have a semi-permanent nitrogen charge) keeps a few tens of PSI of positive pressure in the reservoir to prevent pump cavitation; loss of this is not an emergency.

Left and right hydraulics have an engine driven pump that will keep turning as long as the engine is turning unless explicitly disabled.

Low reservoir levels are both a maintenance check and something that will raise an EICAS warning.

If TCMA cut fuel flow while still on the runway the aircraft would have been decelerating from the moment it lifted off, which is not what the ADS-B data indicates. The kinetic energy in the rotating parts of the engine wouldn't add much speed to the aircraft as the engines run down with no more energy being added via fuel.

I have been really wondering what single point of failure could take out both engines simultaneously as seems to be the case here. One single main bus contactor closing in error seems to possibly be such a single point fault.
Online/running generators connected together by accident/fault will cause a HUGE load on everything, electric connections, generator itself and the shafts and gears driving the generators. Heck, I wouldnt be surprised if the generator could disintegrate due to such an electromagnetic shock load.
So, the question is if there is something between the generators that could limit the electric current. A VFD possibly would as the VFD maybe would not be able to pass the current required for shearing the drive shaft for example. But then again, electronic switches like IGBT/MOSFET and such are able to pass an incredibly large over current for some milliseconds before exploding. Possibly 50 to 100 times the nominal current. So I am not sure if a VFD really would save the rest of the system in a situation with two generators connected together in error.
So, where is the VFD part installed, directly on each generator or somewhere else in the system? Are there physical interlocks on the contactors or only electric interlocks?

Correct. That was the original purpose of the calculation. In addition to the sound itself having the measurable harmonic signature from other rat videos.
What this plot also does however is tell you the speed if you know the height or height if you know the speed.

The iphone used to film this were pictured somewhere, knowing the iphone model, and thus the characteristics of the camera, and the dimensions of the airplane it wouldn't be impossible to calculate height from the video imo.

Just throwing it out there if anyone sees the use and feels the call.

My personal amateur speculation still centers around the cut off switches.
I have spilled coffee and sweet tea over complex electro/mechanical switches/panels before(large format audio consoles with 8000 buttons) and seen unexpected things happen.

I am sure the switches are spectacularly well built, but they are in close proximity and thus prone to the same external factors.
Does anyone know if these two cut-off switches in such close proximity has the exact same installation, or they differentiated in some way that makes a freak failure mode in one not neccesarily affect the other the same way?

There's some possible fuel contamination mechanisms which would only affect one aircraft

- The fuel truck’s water-absorbing “monitor” element breaks up, the first aircraft after the break gets the bead slug; later uplifts may be clear once the hose is flushed. The beads jam metering valves almost immediately.
- After pipe maintenance, the first few hundred litres can carry residual cleaning surfactant that strips protective films and causes filter-monitor “soap lock”.
- Biofilm growth happens inside one aircraft’s wing tanks when it sits in humid conditions or does short hops with warm fuel. On the next flight the biofilm shears off, blocks strainers,

This is a regular test during maintenance at my airline (British operator of 787s)
Carried out as part of a 12k check.

Fuel level in the wing tanks made to be between 3100 kg & 3400kg. Engines are started, APU shut down and boost pumps are selected off.
As long as the engines keep running, it\x92s test passed. (Just have to remember to fire the APU back up before shutting the engines down!)

Seems to be funny that no-one has mentioned the Battery, which because of its age could have failed either Short-circuit or Open-circuit.
Maybe some Boeing Electro Techs, could explain what role the battery has in this circumstance.
The simultaneous failure of both engines points towards an electrical problem, unless the high temperature had adversely affected the fuel flow.

This discussion happened after Jeju. I note that one of the video sources here is actually leaked (camera-pointed-at-screen) airport CCTV. Do not mistake airport CCTV not being publicly available for it not existing.

We'd need to know the impedance/available fault current of the generators. 50x would be unusually high in an industrial setting.

VFDs are for frequency conversion to drive the motors (CAC/pumps/engine start). They won't be carrying the full generator load for galleys and anti-ice; that will be handled by cross-ties, which is a big black box on the 787.

Fast fuses can be faster acting than circuit breakers, but are one-shot. I'm not sure how fast-acting and effective the generator contactors/controllers are; conventional ACBs/MCCBs will blow open magnetically under sufficient fault current regardless of what the trip unit or close coil commands.

I wouldn't really expect electrical reconfiguration to happen on climbout, and I wouldn't expect it to be the first time this contactor gets used since maintenance - everything should get a good workout during sequential APU/engine starts.

Not designed to parallel, but you still need to switch each generator on/off buses and tie or separate buses.

In a very simple main-tie-main arrangement you can close any two of three breakers and still keep the sources separate. It gets much more complicated when you have ten different sources.

I suspect the 'large motor power centre' might parallel the rectified output of some generators.

The 787 flight controls remain almost entirely hydraulic except for stab trim and two spoiler pairs. The centre system is now electric- or RAT-only with no ADP backup. Left and Right systems are still driven by EDPs and will remain pressurised as long as there's fluid and the engines turn.

1.5MW is the figure for all six generators; only four can be used at once.

There's no indication they had any flight control issues.

Battery is essentially unused in normal operations other than to start the APU and keep the clocks running. It's there for emergencies (like after the engines fail). And yes, been discussed.

However\x85Cathay Pacific flight 780 from Surabaya to Hong Kong (2010) suffered just such a fuel contamination incident. This did not lead to immediate total engine shutdown. The function of the engines seriously degraded as the problems compounded during the flight, which reached the ground safely in Hong Kong both by dint of good fortune and serious skills of both Captain and Copilot. The aircraft did not drop out of the sky 20 seconds after leaving the ground.