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

Originally Posted by Musician

You may be surprised to learn that aircraft sometimes need full thrust on the ground.
TCMA requires that the pilot pulls the thrust levers back to idle, and that the engine fails to spool down to idle as commanded. Only then will it shut off the engine (on the ground).
Pilots try to avoid pulling the thrust levers back to idle when they're taking off.
For that reason, TCMA has never triggered during take-off before.

Originally Posted by rigoschris

With such high redundancies and a large degree of isolation between the engines, if it was indeed a simultaneous dual-engine shutdown, we don\x92t know of a single hardware component that could have worn out and caused it (as far as I know)

Originally Posted by rigoschris

In terms of power, each FADEC has its own alternator driven by the engine. But there\x92s a failover connection to the AC bus of the plane. Not sure if there\x92s a physical relay keeping it disconnected in normal operations.

Originally Posted by AirScotia

Thanks, makes sense.

Technically, then, if TCMA deployed erroneously during takeoff, there would be no way for the pilots to restart the engines?

Originally Posted by EXDAC

tdracer posted - " Commanded engine cutoff - the aisle stand fuel switch sends electrical signals to the spar valve and the "High Pressure Shutoff Valve" (HPSOV) in the Fuel Metering Unit, commanding them to open/close using aircraft power. The HPSOV is solenoid controlled, and near instantaneous. The solenoid is of a 'locking' type that needs to be powered both ways (for obvious reasons, you wouldn't want a loss of electrical power to shut down the engine). The fire handle does the same thing, via different electrical paths (i.e. separate wiring)."

Search this thread for "HPSOV" if you need confirmation of the quote.

Note there are two shut off fuel valves per engine - the HPSOV and the Spar valve. Both stay where they are if power is lost.

Originally Posted by Crossky

Hello, this is my first post on pprune; as a 787 pilot I\x92m also puzzled by this accident. All seem to agree that for some reason there was a complete electrical failure and RAT deployment. With a complete electrical failure all six main fuel pumps fail. Each engine also has two mechanically driven fuel pumps. On takeoff, if there is fuel in the center tank, it will be used first, pumped by the two center tank pumps.
My airline\x92s manuals don\x92t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren\x92t able to suction feed well enough from the center tanks to sustain engine operation. If there was fuel in the center tanks, a complete electrical failure would soon lead to center tank fuel pumps failure (all fuel pumps failure as stated previously) and fuel starvation of both engines. A rescue from this situation would be an immediate selection of both center tank fuel pumps OFF (not if my airline\x92s non-normal checklists) and waiting for successful suction feed from the L and R main tanks to occur, this would take a number of seconds.

Originally Posted by Seamless

Just for me to understand: How would you shut off the engine driven pumps if there is no electrical connection whatsoever? If there is a "powered" valve, wouldn't this (also) cut fuel suppy in case of a complete electrical failure?

Originally Posted by ignorantAndroid

It is a battery, not a supercapacitor. Most commonly nickel-cadmium, because that chemistry has been used in aircraft for decades. They're safe and readily accepted by regulators. Li-ion can be used, but a "special condition" from the regulators is needed, plus the weight savings would be negligible.

The 10-minute limit has nothing to do with the battery capacity. It's to prevent the recorder from continuing to operate after an accident and thus overwriting the audio of interest. There's a timer in the RIPS module. It will stop providing power after exactly 10 minutes, regardless of state of charge.

Originally Posted by Aerospace101

Without going round the hamsterwheel again does anyone have an actual reference for this? Because I've gone back through each of tdracer's very informative posts about this see here and there is a discrepancy in the two points he makes below in adjacent posts. Is tdracer talking about the same HPSOV valves? Can anyone confirm that with both AC power loss and and a temporary DC power loss there are no critical engine related shutoff valves that will fail safe (unpowered) in a closed position?

Originally Posted by CloudChasing

according to multiple Indian media sources, refuelling at AMD took longer than usual as the plane was fully refuelled, despite only needing 53% for the journey

Originally Posted by Capn Bloggs

And it should be on the loadsheet.

Originally Posted by Seamless

In which way would TCMA act, in the case of an electrical failure just before TO? Would TCMA - if not affected - read a difference in thrust setting (no signal e.g.) to the read engine thrust, which would then lead to an engines shut down?

Originally Posted by Mechta

The Centre Wing Tank is as it says the centre of the wing. The top and bottom skins continue the aerofoil section through the fuselage, with the front and rear spars' webs forming the fore and aft ends. The inner surfaces of the top and bottom skins have spanwise 'stringers' (well that's what we called them at Airbus), which are 'I' sections attached to the inside to provide stiffness to the skins. The inner faces of the centre wing tank are the tank. There is no separate fuel bag.
The tank is unpressurised. It is vents to atmosphere throughout the flight. There is a fuel tank inerting system which feeds nitrogen-enriched air into the ullage (air space above the fuel). On the 787 it does this on all tanks. Other airliners only do it on the centre wing tank (and any other fuselage tanks if fitted).
Entry to the tanks once they have had fuel in, generally needs breathing apparatus once it has been in service.

Pictures of the inside of a completed 787 Centre Wing Tank aren't easy to find. This shows either the upper or lower skin with its stringers.

Originally Posted by DIBO

With 'intact' being the crucial part of these recent posts. It is my understanding that a suitably equipped LAME can simply download the FDR data from an installed EAFR (CVR requires dismounting). So downloading as such, isn't the issue.

However more importantly, as implied by another poster 'patience' is of the essence in this thread ...

Originally Posted by Tailspin Turtle

This is my latest attempt to square the circle using all the data points and minimal assumptions. The main shortcoming of the analysis is not knowing the maximum L/D and the speed for maximum LD with the gear down, flaps 5, and the RAT extended. However, if I use a reasonable number in my opinion for the L/D in that configuration and assume that the airplane is being flown at the speed for it, it will not get to the crash site. The distance from the runway of the crash site is from a previous graphic (1.55 km); the rotation point from fdr, permalink 314; 200 feet max height above the runway being generally accepted; crash site 50 feet below the runway elevation cited previously. An average speed of 180 knots is consistent with the dimensions given and 30 seconds flight time. A flare at 50 feet will briefly increase the L/D to 20, maybe even 30 (500 feet more than shown) but still not enough to make up the shortfall, In fact, with a head wind the L/D will be lower than assumed as well as if the speed being flown is higher or lower than required for maximum L/D in that configuration. In other words, there must have been some thrust available.