AAIB initial report out on BA B777 crash at LHR
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Here's a couple of rumours to mull over:
- The Times newspaper states that investigators focusing on avionics systems that control the engines. http://www.timesonline.co.uk/tol/new...cle3216042.ece
- Overheard very vague conversation that perhaps this a/c had a previous tech log write up for similar loss of power on both engines.
OK - go ahead shoot me down! This is after all a rumour network.
Bgrd's
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- The Times newspaper states that investigators focusing on avionics systems that control the engines. http://www.timesonline.co.uk/tol/new...cle3216042.ece
- Overheard very vague conversation that perhaps this a/c had a previous tech log write up for similar loss of power on both engines.
OK - go ahead shoot me down! This is after all a rumour network.
Bgrd's
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How would you know?
Questions for the pros:
I fly props only and I know that if I have an engine failure it's impossible to miss, but in a 777 how do you know if your engines have stopped working after a long descent at flight idle? Is it possible that the engines were completely dead but the pilots didn't notice? Would turbine temperature dropping cause an alarm? There's got to be something telling the pilots that the engines are no longer developing thrust...
If the reports that the RAT had deployed are true then it's most likely that both engines were no longer developing power, but could the RAT deployment instead be triggered by a software glitch if the computers thought the engines were out? This doesn't seem very likely to me: why would you design an emergency electricity generator to be triggered by software that needs electricity. I imagine that it's an independent system.
If the engines were dead the descent was likely keeping them spooling until the 3 degree glideslope was attained and when the descent was arrested and airspeed lowered the generated power from the engine spooling dropped below minimums which triggered the automatic RAT and APU deployment. Am I right about this or am I speculating?
I fly props only and I know that if I have an engine failure it's impossible to miss, but in a 777 how do you know if your engines have stopped working after a long descent at flight idle? Is it possible that the engines were completely dead but the pilots didn't notice? Would turbine temperature dropping cause an alarm? There's got to be something telling the pilots that the engines are no longer developing thrust...
If the reports that the RAT had deployed are true then it's most likely that both engines were no longer developing power, but could the RAT deployment instead be triggered by a software glitch if the computers thought the engines were out? This doesn't seem very likely to me: why would you design an emergency electricity generator to be triggered by software that needs electricity. I imagine that it's an independent system.
If the engines were dead the descent was likely keeping them spooling until the 3 degree glideslope was attained and when the descent was arrested and airspeed lowered the generated power from the engine spooling dropped below minimums which triggered the automatic RAT and APU deployment. Am I right about this or am I speculating?
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Fuel Management: copy of post put on Stupid Questions forum
I am labouring under perhaps the misguided notion that the B777 was at 600ft in the normal landing configuration, gear down, flaps in the normal landing position, autopilot out with John Coward having his right hand on the control column and his left hand over the two thrust levers. (thrust levers...its a Boeing thing!).
If they were being good boys as I am sure they were, they should have been on a stabilised approach by then which means the engines should have been spooled up to a decent thrust level and very little adjustment would have been needed in the last 600 ft of the approach.
John would have sub-consciously seen a slight drop in airspeed or perhaps a slight dip below the glideslope or PAPI indicators at the threshold (two independent forms of glideslope angle).
As the thrust levers were squeezed forward John would have expected the thrust to increase slightly and the slight speed decay to stop and be back on the glide slope at the target speed.
When the slight squeeze forward did not rectify the problem the obvious action is push the thrust levers forward a little further until it dawned that the engines were not developing that little bit of extra thrust.
It is safe to assume that if the aircraft was stabilised down to 600ft with a normal approach power set then that power would take you to the runway albeit landing a little before the aiming point. I think I am with the team that suggests that the engines gently ran down, I know nothing about the B777 but the first real warning would probably be the generator dropping off line but it would have been supplying a common bus bar so probably no services would have been lost. There would have been a slight de-stabilisation of the approach due to the assymetric thrust and eye witnesses seem to suggest some bank greater than normal corrections being observed.
The second engine running down at some point later would similarly not manifest itself until its generator dropped off line but that would cause the bus bar to go dead and that would get your attention as you would now be supplied by the battery bus that powers essential instruments and services. I don't know the standard procedure for the APU, is it started in flight as a backup air and electrical supply or has fuel conservation knocked that one on the head? With no APU the windmilling engines and their respective hydraulic pumps would have been the sole source of hydraulic power for the control surfaces until the Ram Air Turbine had lowered and got up to speed.
My first thought is that the engines have been starved of fuel for whatever reason. Plenty of fuel on board apparently and the crew would have seen a gross figure that they were happy with or they would have declared an emergency or landed en route in Stansted/Amsterdam. I am absolutely convinced the crew believed that they had sufficient fuel plus an adequate margin.
So for all the people who know the B777 systems, How many fuel tanks does the aircraft have? What is the normal fuel config for landing? Is there any scope for a slip up when balancing the fuel? Are all fuel panel selections monitored?
I think there are many crew who must remember being in the hold waiting for an approach at LHR and after the third hold and getting a bit bored, a suggestion being made to tidy up the fuel ie balance it up across the four tanks. When you have 10,000kgs/20,000kgs or more in each tank a couple of hundred kilos difference is not significant, when you are down to a 2000kgs in each tank, 200kgs is now 10%.
So a decision is taken to balance the fuel, the crossfeed cock is opened and the respective pumps switched off but the fuel tank page is left displayed. As we all know we are human and only need something to distract us to wind up draining two tanks at an inappropriate time. You don't get a fuel assymetry warning as they drain down at approx the same rate.
As this is a forum for stupid questions and answers, a forum for off the wall ideas, I am curious that I have not seen any reference to fuel management. I can see how it could happen and I know for sure engines have been run down on multijets in the past due to finger trouble on the fuel panel.
If they were being good boys as I am sure they were, they should have been on a stabilised approach by then which means the engines should have been spooled up to a decent thrust level and very little adjustment would have been needed in the last 600 ft of the approach.
John would have sub-consciously seen a slight drop in airspeed or perhaps a slight dip below the glideslope or PAPI indicators at the threshold (two independent forms of glideslope angle).
As the thrust levers were squeezed forward John would have expected the thrust to increase slightly and the slight speed decay to stop and be back on the glide slope at the target speed.
When the slight squeeze forward did not rectify the problem the obvious action is push the thrust levers forward a little further until it dawned that the engines were not developing that little bit of extra thrust.
It is safe to assume that if the aircraft was stabilised down to 600ft with a normal approach power set then that power would take you to the runway albeit landing a little before the aiming point. I think I am with the team that suggests that the engines gently ran down, I know nothing about the B777 but the first real warning would probably be the generator dropping off line but it would have been supplying a common bus bar so probably no services would have been lost. There would have been a slight de-stabilisation of the approach due to the assymetric thrust and eye witnesses seem to suggest some bank greater than normal corrections being observed.
The second engine running down at some point later would similarly not manifest itself until its generator dropped off line but that would cause the bus bar to go dead and that would get your attention as you would now be supplied by the battery bus that powers essential instruments and services. I don't know the standard procedure for the APU, is it started in flight as a backup air and electrical supply or has fuel conservation knocked that one on the head? With no APU the windmilling engines and their respective hydraulic pumps would have been the sole source of hydraulic power for the control surfaces until the Ram Air Turbine had lowered and got up to speed.
My first thought is that the engines have been starved of fuel for whatever reason. Plenty of fuel on board apparently and the crew would have seen a gross figure that they were happy with or they would have declared an emergency or landed en route in Stansted/Amsterdam. I am absolutely convinced the crew believed that they had sufficient fuel plus an adequate margin.
So for all the people who know the B777 systems, How many fuel tanks does the aircraft have? What is the normal fuel config for landing? Is there any scope for a slip up when balancing the fuel? Are all fuel panel selections monitored?
I think there are many crew who must remember being in the hold waiting for an approach at LHR and after the third hold and getting a bit bored, a suggestion being made to tidy up the fuel ie balance it up across the four tanks. When you have 10,000kgs/20,000kgs or more in each tank a couple of hundred kilos difference is not significant, when you are down to a 2000kgs in each tank, 200kgs is now 10%.
So a decision is taken to balance the fuel, the crossfeed cock is opened and the respective pumps switched off but the fuel tank page is left displayed. As we all know we are human and only need something to distract us to wind up draining two tanks at an inappropriate time. You don't get a fuel assymetry warning as they drain down at approx the same rate.
As this is a forum for stupid questions and answers, a forum for off the wall ideas, I am curious that I have not seen any reference to fuel management. I can see how it could happen and I know for sure engines have been run down on multijets in the past due to finger trouble on the fuel panel.
Last edited by Rover90; 21st Jan 2008 at 13:33.
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So a decision is taken to balance the fuel, the crossfeed cock is opened and the respective pumps switched off but the fuel tank page is left displayed. As we all know we are human and only need something to distract us to wind up draining two tanks at an inappropriate time. You don't get a fuel assymetry warning as they drain down at approx the same rate.
If the engines were dead the descent was likely keeping them spooling until the 3 degree glideslope was attained and when the descent was arrested and airspeed lowered the generated power from the engine spooling dropped below minimums which triggered ... blah... blah!
Maybe the other thread called 'The thread for silly questions..' might have been the better place for gregpend to air this and all his other fanciful ideas.
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Normal config for that stage of flight would be tank to engine, i.e, left tank to left engine, right tank to right engine and in all likelyhood the center tank would be empty. As soon as the 2nd engine failed, the APU would start up and the RAT would deploy for both hydraulics and electrical, with hyraulics having priority.
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Rover90
What is the normal fuel config for landing?
At this stage of the flight (as the centre tank is emptied first) the feed would have been tank to engine (L tank to L engine, R tank to R engine).
Is there any scope for a slip up when balancing the fuel? Are all fuel panel selections monitored?
First of all in in the six years that I flew the aircraft I never had to balance the fuel due to imbalance. However, should the need arise, the fuel panel (tanks, flow lines, valves, crossfeeds etc) display is selected on the lower EICAS, and pump/crossfeed selections made on the overhead panel, confirmed from switch lights and the display.
If the 11000 kgs which has been quoted as being in the tanks is correct I would be surprised if there was more than a 100kg difference between the two wing tanks.
Without suggesting what might have happened, if one engine had run down first then the associated warnings/cautions from elecs, fuel and hyd systems would have appeared on the upper EICAS (including "L/R Eng Fail") for the associated engine. However if the two engines (and hence their alternators) failed at the same time then the EICAS displays would have lost their power supply.
The Fly-by-wire "backup batteries" would have powered the relevant computers all be it is a very basic control mode. The APU automatically started to restore AC power to the aircraft (APU door can be seen open from photo's) Alas in the remaining time that the aircraft was airborne the APU would not have reached its governed speed and not be providing AC power.
The "gliding" exercises with two engines failed from height in the simulator were always conducted with the APU started prior to the failure. In the four attempts (approaches) we made (from between 10,000 and 20,000 feet) we were successful every time. The option if I remember was using the FMC to either arrive at the outer marker with an extra 60kts at the "normal" height or the "normal" speed at twice the height. Thereafter "suitable" gear and flap selections were made
gregpend
The fact that, with AC power still available, the command sector on the EPR gauge (difference between commanded and achieved) would be in view, and at some time the "L/R eng fail" message. However, as mentioned above, if both gens dropped off line at the same time there may well have been no messages/no EICAS, just the standby instruments powered.
So for all the people who know the B777 systems,
At this stage of the flight (as the centre tank is emptied first) the feed would have been tank to engine (L tank to L engine, R tank to R engine).
Is there any scope for a slip up when balancing the fuel? Are all fuel panel selections monitored?
First of all in in the six years that I flew the aircraft I never had to balance the fuel due to imbalance. However, should the need arise, the fuel panel (tanks, flow lines, valves, crossfeeds etc) display is selected on the lower EICAS, and pump/crossfeed selections made on the overhead panel, confirmed from switch lights and the display.
If the 11000 kgs which has been quoted as being in the tanks is correct I would be surprised if there was more than a 100kg difference between the two wing tanks.
Without suggesting what might have happened, if one engine had run down first then the associated warnings/cautions from elecs, fuel and hyd systems would have appeared on the upper EICAS (including "L/R Eng Fail") for the associated engine. However if the two engines (and hence their alternators) failed at the same time then the EICAS displays would have lost their power supply.
The Fly-by-wire "backup batteries" would have powered the relevant computers all be it is a very basic control mode. The APU automatically started to restore AC power to the aircraft (APU door can be seen open from photo's) Alas in the remaining time that the aircraft was airborne the APU would not have reached its governed speed and not be providing AC power.
The "gliding" exercises with two engines failed from height in the simulator were always conducted with the APU started prior to the failure. In the four attempts (approaches) we made (from between 10,000 and 20,000 feet) we were successful every time. The option if I remember was using the FMC to either arrive at the outer marker with an extra 60kts at the "normal" height or the "normal" speed at twice the height. Thereafter "suitable" gear and flap selections were made
gregpend
The fact that, with AC power still available, the command sector on the EPR gauge (difference between commanded and achieved) would be in view, and at some time the "L/R eng fail" message. However, as mentioned above, if both gens dropped off line at the same time there may well have been no messages/no EICAS, just the standby instruments powered.
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Radio interference may have been part of the problem (laptops or cell phones turned on) - but it would be notoriously difficult to prove. Much lab time and effort is currently being spent in trying to correlate cell phones and lap top WiFi technology with brain cancers - but with no measurable success to date. The BioElectroMagnetics Society in the USA have yet to report any reproducable positive effects - though there have been a number of “one off” reports that defy duplication.
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A fine theory if aircraft descended onto the glide slope, but as it happens, they don't. They tend to fly level, BELOW glide, WITH POWER, until intercepting it.
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couple of points:
The flash point of JetA1 is above 30 degrees C, therefore unlikely an issue given ambient temp on the day that fire was a risk. Freeze point of JetA1 around -60C. unlikey an issue at low level flight. My guess is electronic failure, fuel contamination or fuel mismanagement. For what it's wortrh, my money is on options 1,3 and 2 in that order. The pictures give new meaning to the trrm 'engine braking'!
cheers
Octane
The flash point of JetA1 is above 30 degrees C, therefore unlikely an issue given ambient temp on the day that fire was a risk. Freeze point of JetA1 around -60C. unlikey an issue at low level flight. My guess is electronic failure, fuel contamination or fuel mismanagement. For what it's wortrh, my money is on options 1,3 and 2 in that order. The pictures give new meaning to the trrm 'engine braking'!
cheers
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It is great that nobody was seriously hurt. The B744 has a great record, perhaps statistically better than the 777, since there was only one accident causing fatalities (Taipei) and one hull loss (Hong Kong) and that one could have been saved until they blew the tail off with explosives.
So Boeing knows how to build great airplanes.
You guys have eliminated all causes, leaving only one: the engines were turned off manually. (this did happen on the 757).
I hope you are happy now.
So Boeing knows how to build great airplanes.
You guys have eliminated all causes, leaving only one: the engines were turned off manually. (this did happen on the 757).
I hope you are happy now.
Boofhead
The 744 hull loss at Kai Tak was inevitable after the 2 days it spent in the water of Victoria Harbour before they blew the tail off!!:
and one hull loss (Hong Kong) and that one could have been saved until they blew the tail off with explosives.
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Haven't seen it mentioned but a vote of thanks must go to the Boeing designers responsible for crashworthiness and to the authorities who have been working over the years to establish standards that ensure that passengers actually do survive in survivable accidents.
For this accident, in spite of the impact forces, the door frames did not distort so allowing the doors to be opened, the slides deployed succesfully, the cabin overhead luggage compartments did not break free and collapse onto the pax, seats remained attached to the floor, and there was no fire when one might have been expected.
Well done!
For this accident, in spite of the impact forces, the door frames did not distort so allowing the doors to be opened, the slides deployed succesfully, the cabin overhead luggage compartments did not break free and collapse onto the pax, seats remained attached to the floor, and there was no fire when one might have been expected.
Well done!
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The bleeding obvious ?
Pardon me if this has already been stated, but it hasn't been in all the posts I've read;
Not even old hands or current 777 experts can say what happened; so why aren't Trent 777's grounded for now ?
Is the answer to the crash actually known already - a distinct possibility, but if not it must be down to £/$...
Not even old hands or current 777 experts can say what happened; so why aren't Trent 777's grounded for now ?
Is the answer to the crash actually known already - a distinct possibility, but if not it must be down to £/$...
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Ladies, Gentlemen & Officers!
The first thing we learn at IFALPA about Accident Investigation is to abstain from speculation. The investigators in this case have all the evidence and the recorders in good shape at their disposal. We will get a preliminary report quite soon. As profesionals we should keep our twitchy fingers off the keyboards.
Let us respect our colleagues who did a wonderful job. The MOST IMPORTANT fact is there was NO LOSS OF LIFE.
MORE THE MERRIER!
The first thing we learn at IFALPA about Accident Investigation is to abstain from speculation. The investigators in this case have all the evidence and the recorders in good shape at their disposal. We will get a preliminary report quite soon. As profesionals we should keep our twitchy fingers off the keyboards.
Let us respect our colleagues who did a wonderful job. The MOST IMPORTANT fact is there was NO LOSS OF LIFE.
MORE THE MERRIER!
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IvanBogus,
you are missing the point ( or a wind -up merchant ); plane fell out of sky, engines may well be spiffing, but this would seem to indicate there's a dodgy bit - or several - between them & cockpit.
As no answer publicly known - why allow similar a/c to fly ?
you are missing the point ( or a wind -up merchant ); plane fell out of sky, engines may well be spiffing, but this would seem to indicate there's a dodgy bit - or several - between them & cockpit.
As no answer publicly known - why allow similar a/c to fly ?