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AAIB initial report out on BA B777 crash at LHR

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AAIB initial report out on BA B777 crash at LHR

Old 20th Jan 2008, 11:37
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whats the certified environmental envelope for a 777?

Some one questioned CDA earlier in the thead.

Long descent at idle may have masked a fuel problem until thrust demand at 600'

New air traffic systems may well have introduced new failure modes previously unknown.
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Old 20th Jan 2008, 11:38
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The fuel freezing point is the temperature at which wax crystals, which form in the fuel as it cools, completely disappear when the fuel is rewarmed. (This should not be confused with the fuel becoming cloudy upon cooling, which results when water dissolved in the fuel freezes, forming a suspension of very fine ice crystals. Airplane fuel and engine systems are designed to handle water ice crystals safely.)

The Jet A fuel specification limits the freezing point to a maximum of 40C; the Jet A-1 limit is 47C maximum.

The 777 has a fuel temperature probe located between ribs 9 and 10 of the left main tank. The probe is approximately 12.6 in from the lower wing skin and is located one rib over, approximately 40 in outboard, from the aft boost pump inlet. Because the left wing tank contains a single heat exchanger, its fuel can be slightly colder than that in the right wing tank, which contains two hydraulic heat exchangers.

Fuel temperature on the 777 is displayed in white on the primary EICAS in the lower right corner. If the fuel temperature reaches the established minimum, the indication turns amber in color and the FUEL TEMP LOW advisory message is displayed.

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Old 20th Jan 2008, 11:49
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Dayavaan

Until the AAIB determine the cause of the accident it would be prudent for all operators to advise pilots to disconnect/reconnect the auto pilot & auto-throttles before commencing the approach. Also in view of limited landings (due long sectors) performed pilots must carry out manual approaches in VFR conditions. This is from an old timer who commanded DC-3, F-27, B-737 & A-300 types.
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Old 20th Jan 2008, 11:50
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In the old days

In the days of the Comet 1 fuel waxing was a problem!
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Old 20th Jan 2008, 11:54
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With regard to fuel temperatures, Flight Planning on the B767 on long sectors (Heathrow-Vancouver/Seattle) often required the cruising height in the latter part of the sector to be reduced to maintain he fuel temperature above the minimum.

The B777 however, on simular sector lengths and OAT's didn't seem to have the same problem. The fuel never seemed to get as cold as it did on the B767.

At least the data will be available on the fuel temperature and one would assume some fuel remained (on board) on which tests can be carried out.
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Old 20th Jan 2008, 11:56
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Fuel Balancing

Fuel waxing I believe is rare indeed.

Also the chances of simultaneous engine failures or engines failing to respond simultaneously due to waxing must be very small.

One interesting point that may be worth mentioning is fuel crossfeeding.

The Boeing 777 FCOM states that "Fuel balancing may be done in any phase of flight".

I am not implying in any shape or form that the 777 was balancing fuel at the time of the incident, but would it be more prudent NOT to balance fuel close to the ground, when you would be feeding both engines from one tank, and raising your chances of power losses due to contaminated fuel etc. in that specific tank?

I do not know whether fuel balancing on the approach, landing or go around is permitted on other Boeing or Airbus types. Perhaps someone can comment.

What is the fuel balancing/crossfeeding policy of Airlines in the UK?
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Old 20th Jan 2008, 11:56
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2 quick points

two quick points:

1. At 600 feet (if they were @ the usual 750 ft p. min on the glide), they only had less than 48 seconds to recognize and react.

Probably much less, since at the very last bit, they were just falling (stalling), so the rate of descent increased.

2. If the pilots had extended the gear only a very few seconds earlier, the demand for the thrust would have been earlier, and the crash would have occurred abit furthur back from the runway!!!!! So everyone involved was really really really lucky!
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Old 20th Jan 2008, 11:57
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Dayavaan

Until the AAIB determine the cause of the accident it would be prudent for all operators to advise pilots to disconnect/reconnect the auto pilot & auto-throttles before commencing the approach. Also in view of limited landings (due long sectors) performed pilots must carry out manual approaches in VFR conditions. This is from an old timer who commanded DC-3, F-27, B-737 & A-300 types.
Why? It appears the auto throttle didn't have any problem at all...
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Old 20th Jan 2008, 11:58
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Passengers Evacuating.

This has been a bug-bear of mine for many years in my piloting life.

A few posts mention the fact that there was apparently no command from the flight deck to initiate an evacuation. While this may or may not be the case, it might be worth considering another aspect of the incident while we wait for the AAIB report.

It may not be appropriate, as has been queried earlier, for passengers to initiate an evacuation but they will, whatever the Cabin Crew try to tell them to the contrary.
If you are sitting over the the trailing edge of the port wing and see large chunks of raggedy metal sticking through the once smooth wing, mud and debris flying past your window along with the fact that it is grass underneath you and not the usual tarmac/concrete, then you might be forgiven for thinking that something is very wrong. Any spilled liquid will only add to your sense of unease and you will try to get away from the surrounding situation just as soon as you can. Hence, if nothing is heard or even 'Stay in your seats', you will ignore them, self preservation will be paramount. Indeed, passengers have a much better view from their nice big windows and so have a better understanding of what is going on outside than the cabin Crew with their needlessly tiny door windows. Cabin Crew need to be aware that the passenger panicking near the over-wing might well be doing so for a very valid reason!

Evacuation studies carried out since the very survivable Manchester BA B737-200 fire in 1985 have some interesting results. Cranfield University, using a Trident fuselage and more recently a B737 Cabin Simulator along with a two deck wide-body simulator have shown that passengers, me amongst them on the Trident, behave in many and varied ways to such a situation. At one extreme, a number will be moving towards the exits even before the aircraft has come to rest, others will sit and do nothing no matter how hard you shout at them.

Incidentally, the command from the cockpit found to be the most use in our multi-lingual era is 'Open your seat belts and get out.' Any other form of words, particularly the use of, 'unfasten', 'evacuate', 'exits,' were all found to be confusing and less well understood. If your company uses anything other than this form of words,get them to change them, now!

I suspect that perhaps half of the passengers on BA038 have English as a second language or perhaps speak little or even none at all. In this instance, everyone survived. I shudder to think how long the other thread would have been if even a few unlucky passengers had perished in any fire there might well have been.

Philosophy 101

In this instance, the aircraft touched the ground 'relatively' gently and the fuselage stayed intact, the grass was wet and soggy, so slowing the aircraft rapidly and causing no sparks, the fuel spilt was very cold, so less inclined to vapourise, there was no smoke in the cabin, all exits were usable, there were many empty seats and the Cabin crew were very well trained.

You can rewrite the previous paragraph with all the positives as negatives and see for yourselves how the outcome could well have been different.

My point is that no matter how hard we all train to be as professional in our aviating lives as we possible can be, no matter how skilled we are and how hard we try to influence the outcome of an event, fate/schiksal/karma/God, in all his forms, is the final arbiter of the outcome of so much that occurs in our lives. The slimmest margins make the difference between good and bad outcomes to so many things in our lives that we will never know just how lucky we are to be alive!

Happy Landings!
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Old 20th Jan 2008, 12:14
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To reinforce Borderlines comments could I suggest that anyone commenting on the auto throttle performance refer firstly to NSEU's excellent factual post (No.38).

The response of the electronic control of the engines is (amongst other things) from data obtained regarding TLA (thrust lever angle). Whether the movement of the TLA forwards was from the autothrottle system or a manual input/override the resulting demands for more power was exactly the same.

Perhaps all posts should be made, as with other forums, through moderators who could remove these red herrings before they are posted and (by some) taken up as fact! Just a thought.
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Old 20th Jan 2008, 12:22
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Borderline wrote:

The 777 has a fuel temperature probe located between ribs 9 and 10 of the left main tank. The probe is approximately 12.6 in from the lower wing skin and is located one rib over, approximately 40 in outboard, from the aft boost pump inlet. Because the left wing tank contains a single heat exchanger, its fuel can be slightly colder than that in the right wing tank, which contains two hydraulic heat exchangers.
It's interesting the ground evidence (photos of fan blades) suggests the left engine was still making some power when it hit the dirt, while the right engine was not, the opposite of what you might expect from a fuel freezing incident with this heat exchanger arrangment. Sounds like the temp probe is in the colder tank, which was a good design choice. Is the fuel temp recorded on the FDR?
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Old 20th Jan 2008, 12:27
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Rubik101.....thats got to be the best post here since this all "kicked off"!

We, all of us, are human (I hope!) and naturally will speculate and draw conclusions based on our knowledge and the evidence we are presented with, be it a 777 pilot, engineer, controller, eye witness or a drunken Aussie!

However, to post your personal speculation and cause the old wildfire to spread throughout the aviation fraternity and other "members of the public" who read this is plain irresponsible.

I appreciate this is a RUMOUR network but that doesn't mean we should all try and out do each other with our theories and level of knowledge....leave it to the experts to come up with the facts and present them in a timely and accurate manner.

Despite my suspicions of BA, AAIB, Boeing, I am sure that if they had ANY indication so far that the problem was fleet wide, they would have been grounded or at the least, SBs issued.

In the meantime lets have an informed discussion about the a/c systems and intelligent questions regarding evacuation procedures etc but from those discussions let pleassssssssseeeeeeeeee stop speculating in public
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Old 20th Jan 2008, 12:51
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Where have you got the info that the CSD decided to evacuate I have seen no concrete info that this occurred, rather, than say the evacuation was initiated from the Flt Deck
The pax testimony I heard was that after they came to a halt some pax jumped up and were told to sit down - 'then a red light came on over the doorway' and the crew evacuated the pax. I don't know whether that refers to the red Exit sign or one of the crew signals.

Whatever else happened the co-pilot remembered rule #1 - 'fly the plane' - had he attended to other things some seem concerned about (mayday calls, brace instructions) then this might be a very different thread indeed.
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Old 20th Jan 2008, 12:53
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Could we have an idea of the 777's environmental envelope temperature limits please?
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Old 20th Jan 2008, 12:56
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Stranex
To have a informed discussion about aircraft systems includes inherently some speculation. If everything would be crystal clear, why discuss it??

Therefore and nevertheless now another hypothesis concerning systems: If i go about the RR Trents on the T7, there is a possibility of no malfunction but still having the effect described. The engine anti-ice is mostly switched to "AUTO". I have witnessed its reluctance to go to "ON" more than once. Lets assume the inlet PT probe was iced up, apparently a ice warning was out that day and prolonged holding in the FL80 to 120 is a ice prone region. As the EEC uses EPR as parameter for thrust setting, in conjunction with the thrust lever angle, a demand either by the auto throttle or the pilots might have been ignored by the EEC, simply because with a PT inlet iced up and PT outlet not, the difference would fake "differential pressure", thus thrust, to the EEC. It would say "I am already giving you what you're asking for", not increasing FF and the result would be the low thrust setting persisting with a functioning and happy EEC.
Far fetched?
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Old 20th Jan 2008, 12:59
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Woodpecker,

The reason why 767s get colder fuel temperatures than 777s in the same enviroment, is that fuel temperatures are closely (but not exactly) related to the TAT and not the OAT. The higher speeds on the 777 keep the fuel warmer.
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Old 20th Jan 2008, 13:06
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Pitch control

As an A330 pilot I am most interested in the aspect of 'pitch control' during the seconds after the double flame out.

I do not want to start another A vs B discussion but want ask a question about the 777 flybywire.

1. I do not think that pulling your aircraft (any aircraft) into a stall will postpone your impact. The impact will be earlier instead.

2. Loss of all engines during approach is not trained in the simulator, because it is regarded as negative training; there is no way you can prevent a crash landing.

3. The confrontation with loss of all engines in real life will make your brains and thus body go into survival mode; only the very most essential tasks will be executed. (Making a PA call is certainly not one of them)

4. While in survival mode, I can imagine the brain has difficulties with smooth control inputs. (Just like too much brake application during an emergency stop in your car.) I think on the Airbus the FlybyWire system would give you a "superhuman" postponement of the impact in this situation, just by pulling the stick fully backwards all the time. (This is why you have to do exactly this after a terrain warning)

While waiting patiently on the investigation what caused the engine problems, my question is: Is it possible to stall a B777 with manual inputs?

Last edited by astonmartin; 20th Jan 2008 at 13:08. Reason: typo
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Old 20th Jan 2008, 13:11
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Fuel freezing/waxing

Straight from Boeing Web

Operations and procedures with low fuel temperatures.

During long-range operations at high altitudes, fuel tank temperatures can approach the freezing point of fuel. On long flights, the fuel temperature tends to adjust to the temperature of the aerodynamic boundary layer over the wing skin. This boundary layer temperature is slightly lower than the TAT because theoretical TAT is not achieved. Initially, TAT is much lower than the fuel probe temperature because of the thermal lag of the fuel. Thermal analysis of the 747-400, 777, and MD-11 airplanes shows that the fuel tank temperature is driven more by TAT than airplane configuration.

In flight, a temperature differential must be maintained between the observed temperature indication and the freezing point of the fuel. For the 747-400, 777, and MD 11, the observed fuel temperature must remain at least 3C above the specified freezing point. (The actual fuel freezing point may be used if known.)
When fuel temperature decreases to 3C above the freezing point, a message of FUEL TEMP LOW displays in the 747-400 and 777 flight decks; the message FUEL TEMP LO is displayed in the MD-11 flight deck. If this condition is reached, the flight crew must take action, as described below, to increase the TAT to avoid further fuel cooling.

In consultation with airline dispatch and air traffic control, the flight crew decides on a plan of action. If possible, the action should include changing the flight plan to where warmer air can be expected. Another action is to descend to a lower altitude. The required descent would be within 3,000 to 5,000 ft of optimum altitude. In more severe cases, a descent to 25,000 ft might be required. Recent experience on polar routes has shown that the temperature may be higher at higher altitudes, in which case a climb may be warranted. The flight crew also may increase airplane speed; an increase of 0.01 Mach results in a TAT increase of 0.5 to 0.7C. (It should be noted that any of these techniques increases fuel consumption, possibly to the point at which refueling becomes necessary.)
It takes approximately 15 min to 1 hr for a change in TAT to affect the fuel temperature. The rate of cooling of the fuel is approximately 3C/h. A maximum of 12C/h is possible under the most extreme cold conditions.
A minimum in-flight fuel temperature advisory message provides a margin of safety under all atmospheric and operational conditions to ensure that the fuel will continue to flow to the boost pump inlets. Besides the 3C margin between the advisory message temperature and fuel freezing point, there typically is a 6C difference between the freezing point and pour point of fuels, which provides an additional margin. A review of the service history of transport airplane operations worldwide for the past 40 years does not show a single reported incident of restricted fuel flow because of low fuel tank temperatures. This service history affirms that the criteria used to establish the advisory message are adequate and conservative.
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Old 20th Jan 2008, 13:11
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It is not normal that the a modern 200T twin jet as the 777 simply "shut off" at the last 10s of a 11hrs flight. Here are the facts. This event is fascinating us but we must not speculate until AAIB report is issued. AAIB staff has everything to do its job: plane, crew, witnesses. But it does not mean it will be easy unless basic cause explains the failure.

In the other case, the more complex the systems, the more complex may be the causes. Event if a 1.50$ piece of copper might crash a system, the job is to find the evidence.

While waiting the report, may I suggest to remember the following events:
- Dual engine failure of an Austrian Fokker 70 on approach in Munich in january 2004 - landing on a field - mechanical failure of ice impact panels.
- Nearly stall of a B777 at FL390 in 2005 - ADIRU failure - see AD 2005-18-51
- Byzantine faults of complex systems - google 'Flight Control System Software Anomalies'

I mean, we all try to do our job to our best of knowledge, but we will always learn about flying from experience.
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Old 20th Jan 2008, 13:12
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Giant Bird,

Really your questions indicate a position that bears distant relation to the real world of commercial aviation.

Its not a perfect world and these guys did a fantastic job. The result is more important than the method in cases like this.

So it's provocative and inappropriate of you to start your introspective judgemental thing at this time so please don't.

V
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