Classic British Flight Sim

Garry Russell wrote:I think there is a confusion here with aerial deployment and unintentional/uncommanded aerial deployment

Gary, you are quite correct. I was speaking of unintentional deployment. The 777 has a "squat switch" on it that will not allow the reversers to be deployed until the aircraft is on the ground and the wheels have spun up above a certain RPM to prevent air deployment.

Interesting discussion.

As someone who is totally ignorant, I've a couple of questions that have got me a little baffled.

Obviously (and this is of course not to say we know the cause....) - in the absence of proof that some system failure was to blame, I'm interested in the fuel 'problem' theory so here are the questions...

1: Is it possible to under-fill a 777 in a manner similar to the 'Gimli' 767? (Note that this does not imply I am aiming any thought that the 777 was)
2: On larger aircraft, does the 'percentage' of fuel make any difference to available pressure feed to the engines?
3a: On fuel contamination, what is the primary worry? Water in the fuel or some other contaminant?
b: Is there any form of fuel filtration in-line from the tanks to the engines? Assuming filthy fuel could these clog up?
c: Assuming the other fuel theory - lack of - is there any thought as to how a leak could occur?
d: Is the reserve on large AC so low that contamination bad enough to ruin fuel left?****
***I ask as a meaningful diversion fuel qty for a 777 should be 'large' thus any contamination must be *very* significant

I suspect that like most incidents, this will prove to be a combination of factors - not simply one thing (as usual).

Of course all the above is pure interest on my part, not any attempt to theorise the cause!!

Now the reporters have commandeered a simulator to re-enact this accident.
Click on BA Pilot relied on training.

http://video.news.sky.com/skynews/video/

Nigel.

As far as I know ......that's quite normal.

Garry

forthbridge wrote:1: Is it possible to under-fill a 777 in a manner similar to the 'Gimli' 767? (Note that this does not imply I am aiming any thought that the 777 was)

Possible, yes. Likely? Not in this case. The aircraft was being fueled in a country using metric unit on an aircraft using metric gauges. Gimli happened because of a failure to convert properly between metric and imperial units due to a failed gauge. In addition, the inoperable gauge refueling procedure was not properly followed, resulting in unnecessary calculations being performed leading to the failed conversion. In this case, no such conversion would have been required, although I suspect we would have heard if there was an INOP fuel gauge on the airplane already. The 777's fuel gauges are very reliable and I only had 1 occasions of an INOP gauge during my time at Denver on a 777 and it was due to the fact the valve lights on that tank were INOP so I had to manually fuel the airplane and not rely on the auto system to shutoff properly.

2: On larger aircraft, does the 'percentage' of fuel make any difference to available pressure feed to the engines?

Not usually. All pressure is created by the fuel pumps. They should be able to create a constant pressure until such time as the pump pickup becomes uncovered.

3a: On fuel contamination, what is the primary worry? Water in the fuel or some other contaminant?

Water is the primary, but there could also be things like dirt, rust, and other particulates that can get into the fuel from pipelines and truck fuel tanks.

b: Is there any form of fuel filtration in-line from the tanks to the engines? Assuming filthy fuel could these clog up?

Yes there are screens, but depending on the amount of contamination, it is certainly possible to clog the filter which could then result in a filter bypass and the contamination reaching the engine potentially causing a shutdown. If it's a large "slug" of contamination that enters the system at the same time (as does happen) it's possible to overwhelm the filter screen and then shutdown the engines within a matter of moments.

c: Assuming the other fuel theory - lack of - is there any thought as to how a leak could occur?

Every single joint, connection, and inspection panel could potentially spring a leak due to flexing during flight over repeated flights. Also, any removable fitting can come loose. Everything is safety wired to hopefully prevent anything coming loose, but safety wire can break, so it's possible. However, with the systems on the 777, any time the projected fuel on arrival drops below the required reserves on landing, it will scream at you that you're not going to have enough fuel. Had that happened, the crew would have reported that situation and diverted to a suitable airfield short of Heathrow.

d: Is the reserve on large AC so low that contamination bad enough to ruin fuel left?

Depends on how much contamination there is and where it's at (i.e. floating or settled). Think of this - in a 777, a mere inch of fuel in one of the main tanks represents almost 200 gallons of fuel. So it's not hard to have plenty of fuel left in the tanks but still get contamination into the fuel pickups.

-

Chris

You forgot to point out that 200 galls of JetA on any flat surface looks like a "substantial" fuel spill which is what
the Monty Orangeball crowd keep saying :roll:

Leif

Thanks to both Chris and Leif for those clear explanations!

Thought I'd add a bit to Chris's reply re fuel sytems and this is 'generic' info not type specific;

1) Most of the time fuel for an individual engine will be drawn only from its' respective tank ie
left tank feeds left engine, right tank feeds right engine (in the case of the 'gimli glider' the source of the problem, a broken fuel pipe at the engine,was exacerbated by crew using 'cross-feed' to feed fuel from opposite tank to affected side)

2) Big aeroplanes usually have more than one pump in each tank, colloquially known as 'booster pumps' each one is capable of supplying all the necessary fuel to the engine driven high pressure pump, and below @ 10,000 ft, the 'suction' pressure alone from the engine pumps will keep engines running

ttfn

Pete

Nigel H-J wrote:Now the reporters have commandeered a simulator to re-enact this accident.

Nigel.

Thanks for the clip, Nigel. It was interesting to see how the press jump to conclusions.

A couple of points on the report.

1. The reporters have commandeered a 737 simulator. As no expert, I have no idea of the relevance of 737 glide characteristics to that of a 777-200.

2. From the clip, it appears that the simulator is flown at flight idle from 600 ft. The incident report (as I have read it), only states that no increase in thrust was available. There is no mention as to whether the engines were at flight idle or not.

Just shows, how well the press look into the facts.

Regards

Kevin