NigelOnDraft

Airbus effectively does this, since the PFD "characteristic speeds" are Alpha derived, and hence if weights are wrong, the PFD and FMGC speeds disagree I would imagine B777 type technology has something similar...

NoD

GearDown&Locked

I think the cavitation found in the pumps is probably misleading the line of thought of everyone in this forum. IMHO cavitation could have happened prior to the event in question, like a couple of days (or the sector) before. So leaving the cavitation signs aside:

If the fuel metering device was giving a “false” reading, somewhat bellow true fuel flow, when the A/T commanded an increase of thrust it would have increased initially to the requested value but then the excess of fuel in the burners would made it drop dramatically but not entirely. Thrust decays, FADEC opens fuel valves even further to compensate, but instead of correcting it worsens the problem.

Too far off the mark?

GD&L

Green-dot

Or was the excess of fuel in the burners in this scenario a mix of fuel, ice and water?

Thawing Ice, perhaps shedding from the compressor stages as the engines revved up from approach idle to a new target thrust setting, quenching or partially blocking the annular combustion chambers on both engines? In this case the anticipated EGT increase with reduced gas flow may have been negligible due to the cooling effect of water, hence no RPM increase but instead (partial) rollback to somewhere above idle?


Green-dot

snowfalcon2

I'm fairly convinced the subject of a possible "stretching the glide" will be included in the accident report. As I see it, the report may suggest one of three things:
a) do nothing;
b) recommend additional flight crew training for handling low-level double engine failure;
c) recommend improved autopilot designs that automatically trim the plane for optimum glide range when sensing a power loss situation.

Each of the alternatives need to be judged on basis of the resulting increase in safety compared to the probability of this type of engine failure, as well as the implementation costs. Also we have to await the outcome of the search for the primary engine failure reason. In case that is not found, the case for doing something (b or c) becomes stronger.

ChristiaanJ

Unless autopilot design has fundamentally changed since my days, the (pitch) autopilot would have no way to 'sense' an uncommanded power loss.
It did its job, i.e., keeping the aircraft on the 3 degree glideslope by increasing pitch (and thus AoA) until things got too hairy and it disconnected.
It 'expected' the autothrotlle to keep the speed up.

CJ

snowfalcon2

that's exactly my point, with today's computer technology it would be no big deal to design a capable integrated autopilot/autothrottle. It's about time, too, considering the technology advances in most airplane systems.

Joetom

Talking about inputs that an A/P system may get in the future, I can think of two off the top of my head.

1. Fuel Temp.

2. Amout of Water in the Fuel.

Smilin_Ed

Reheat, thanks for a very good article. The most important part is: "AOA information is most important when approaching stall." The U.S. Navy has used it to very good advantage for about 50 years now in making carrier approaches.

ChristiaanJ

Joetom,
Again confusing A/P and A/T.

Phil1980's

Have a read of this...noone seems to be thinking of googling past events
200204444

Golden Rivit

Dont know if this has been seen before, http://www.iasa.com.au/folders/Safet...eculative.html

PAXboy

snowfalcon2Non pilot speaking
My guess as to why these things might take longer to get more closely integrated - is the certification process. How long would it take to get approval of a new set of controls, software, interlocks and all the rest? The manufacturers will work on the basis that it ain't broke and if the customer ain't demanding it ...?

NotPilotAtALL

Hi,

http://www.iasa.com.au/folders/Safet...eculative.html

Thank you.
This was published on the IASA site the 01 Feb 08 and rely to a official report.
Wonder if no more official news was released from this date.

Cheers.

misd-agin

You shouldn't need an AOA gauge to understand that at a slow speed reducing speed increases your AOA, which will decrease your gliding distance.

Decreasing speed from 1.3 Vso to close to stick shaker speed will not stretch the glide at altitude. It does in the end game, and allows some airspeed to 'flare' as opposed to hitting the ground at whatever sink rate you have at, or close to, stickshaker.

Reducing flaps from 25/30(Landing slat configuration - full) to 20 (Takeoff slat configuration - mid) might be critical to improving your gliding distance.

Obviously the lowest drag configuration is best, but sometimes the gain achieved via decreased drag doesn't make up for the increased sink rate generated by the need to increase flying speed to your new, and faster, approach speed. Early? Yes. Late? No. Beats me what the actual difference between 'early' vs. 'late' is. That's the gut check time.

thinkingpilot

may i ask anyone who knows how long its going to be before the aaib comes out with a FINAL report . they have had 6 months, all the facts , the airplane itself ,and the crew at their disposal. speaking as a 777 driver myself we fly everyday wondering what happened . delay in releasing reports in my experience, i am sorry to say,. sometimes indicates cover up. excuse my poor typin skills

atakacs

@thinkingpilot

Our best guess is "as soon as they have something"... As far as one can tell they are at loss for an explanation.

And I'm pretty sure "we don't know" won't be good enough for you, especially if you really are a 777 driver

snowfalcon2

Yes, basically the requirement has to be included in the aircraft certification standards in order to get things to happen. And for that to happen there usually needs to be evidence of a number of accidents that could have been avoided.

Now in this case I don't immediately remember any other case of a low-level double engine power loss of this "sneaky" type, on approach with autopilot engaged. Those that come to my mind have happened on take-off (SAS 751, MD-82 ice ingestion, and the recent Citation at Farnborough, Kent) which is an altogether different situation. However, the proposed integrated autopilot/autothrottle might also have helped in the "Gimli Glider" case (which occurred at cruise altitude), had the captain not happened to be an experienced sailplane pilot.

Anyway the key issue, as I see it, is whether this type of fault has a high enough probability to justify new safety measures and their associated costs. The investigation will hopefully shed more light on this.

arcniz

Fundamental changes of method also go through a cost-benefit filter and a "testability" filter.

Given at least a few incidents of unpowered flight, approaches, and landing sequences in heavy jets, it would seem the cost-benefit (with reference to passenger safety, in particular) argument could be made.

As regards testability, however, the questions are harder to answer. The low, slow, zero-power flight envelope is about as dangerous as it gets for flying a large, heavy aircraft. One can do testing at higher altitudes, of course, but realistic "ground effect" and flare phenomena combined might either require some live tests of each type or a major research effort to create a data-set that could be used for simulation of all reasonable types. The potential variables are so many (for a 'general-case' solution) and the cost of error so high, it would take some considerable courage for an airframe manufacturer to add this function set and pronounce it usable. Would be pretty much a lifetime career for some bunch of lawyers to litigate about that forever after.

Even with all the computers, maybe seasoned pilots and 'seat-of pants' flying still are occasionally the best choice, after all?


.

Milt

Thinkingpilot

We all share your thoughts on the unseemly delay in the determination of the cause/s of the problem. It's looking as though we will never know and the natives are getting restless!

Then we are intrigued that you as a 777 pilot with less than average keyboard skills can manage to accurately input all of the necessary data using the push buttons, knobs and switches by which you now fly.

Is it a problem or have you had a heavy week?

Mismatch

There is a subsystem installed on each and every aircraft, with the purpose to evaluate the trajectory of the aircraft under those conditions. They call it the pilot.