June 20, 2025, 01:02:00 GMT
permalink Post: 11906517
It is very, very, very close:
Both engines failed: yup, both engines have failed.
Triple hydraulic pressure low: either you've been hit by a SAM/uncontained engine failure causing massive fluid leaks, or both engine driven pumps have failed (likely because the engines have failed) and all four electric pumps have failed (because the engines have failed).
Loss of all electric power to flight instruments both sides: total AC electric loss, and I think battery/static inverter too? Given four generators and four buses, either massive electrical failure (swimming pool in E&E bay) or engines have failed. Note failure of an individual contactor that can tie two buses together should not cause a quad-bus outage.
Loss of all four electric motor pumps: total AC failure, see above.
Both engines failed: yup, both engines have failed.
Triple hydraulic pressure low: either you've been hit by a SAM/uncontained engine failure causing massive fluid leaks, or both engine driven pumps have failed (likely because the engines have failed) and all four electric pumps have failed (because the engines have failed).
Loss of all electric power to flight instruments both sides: total AC electric loss, and I think battery/static inverter too? Given four generators and four buses, either massive electrical failure (swimming pool in E&E bay) or engines have failed. Note failure of an individual contactor that can tie two buses together should not cause a quad-bus outage.
Loss of all four electric motor pumps: total AC failure, see above.
June 20, 2025, 01:11:00 GMT
permalink Post: 11906519
This incident is very perplexing to me. This is my first post on here and I am not a pilot. I have over a decade of experience in the RAAF as an engine fitter on Mirage and Hornet aircraft. Albeit a bit of time ago.
I have watched the video's and looked at the FR-24 data a hundred times. To me it looks like a normal rotation and at WoW everything starts to go wrong.
Airspeed starts dropping off immediately going by the FR-24 data. If reports are correct the pilot makes his Mayday call. FR-24 data stops.
In the video from the balcony I agree the RAT is out and operating but I can also hear the engines at idle or just above (maybe flight idle).
If the captain manually deployed the RAT this makes sense to me. In both video's I don't see any aircraft behavior that would suggest they are not flying the aircraft.
Is there an electrical fault at WoW that renders the cockpit dark and therefore manually deploying the RAT (possibly initiating APU start, inlet door is open at crash site) would make sense to restore cockpit power.
I can't understand any pilot shutting down both engines at 200ft AGL. He would surely know that his fight is over at that point.
I am not ruling out pilot error (configuration or otherwise) but my hat goes off to two pilots that I believe were trying to fly this aircraft until it hit the ground.
Sorry if my wording is a bit off but mine is military background not commercial.
I have watched the video's and looked at the FR-24 data a hundred times. To me it looks like a normal rotation and at WoW everything starts to go wrong.
Airspeed starts dropping off immediately going by the FR-24 data. If reports are correct the pilot makes his Mayday call. FR-24 data stops.
In the video from the balcony I agree the RAT is out and operating but I can also hear the engines at idle or just above (maybe flight idle).
If the captain manually deployed the RAT this makes sense to me. In both video's I don't see any aircraft behavior that would suggest they are not flying the aircraft.
Is there an electrical fault at WoW that renders the cockpit dark and therefore manually deploying the RAT (possibly initiating APU start, inlet door is open at crash site) would make sense to restore cockpit power.
I can't understand any pilot shutting down both engines at 200ft AGL. He would surely know that his fight is over at that point.
I am not ruling out pilot error (configuration or otherwise) but my hat goes off to two pilots that I believe were trying to fly this aircraft until it hit the ground.
Sorry if my wording is a bit off but mine is military background not commercial.
June 20, 2025, 01:13:00 GMT
permalink Post: 11906520
It is very, very, very close:
Both engines failed: yup, both engines have failed.
Triple hydraulic pressure low: either you've been hit by a SAM/uncontained engine failure causing massive fluid leaks, or both engine driven pumps have failed (likely because the engines have failed) and all four electric pumps have failed (because the engines have failed).
Loss of all electric power to flight instruments both sides: total AC electric loss, and I think battery/static inverter too? Given four generators and four buses, either massive electrical failure (swimming pool in E&E bay) or engines have failed. Note failure of an individual contactor that can tie two buses together should not cause a quad-bus outage.
Loss of all four electric motor pumps: total AC failure, see above.
Both engines failed: yup, both engines have failed.
Triple hydraulic pressure low: either you've been hit by a SAM/uncontained engine failure causing massive fluid leaks, or both engine driven pumps have failed (likely because the engines have failed) and all four electric pumps have failed (because the engines have failed).
Loss of all electric power to flight instruments both sides: total AC electric loss, and I think battery/static inverter too? Given four generators and four buses, either massive electrical failure (swimming pool in E&E bay) or engines have failed. Note failure of an individual contactor that can tie two buses together should not cause a quad-bus outage.
Loss of all four electric motor pumps: total AC failure, see above.
June 20, 2025, 18:10:00 GMT
permalink Post: 11907171
Retired engineer here.
I remain convinced that the mentioned non-functioning air conditioning system is significant to the subsequent loss of electrical power. A passenger on the incoming leg complained about the air conditioning.
https://www.cnbctv18.com/india/air-i...l-19620259.htm
To explore the electrical system further see p. 86 of this document. I decided to trace out some electrical paths to equipment and do a few simple calculations.
https://fliphtml5.com/quwam/qhdw/Boo...cs_Electrical/
The electrical path to a CAC (cabin air conditioner) starts from the engine driven 235V ac bus which could be L1 or R1.
From there 235V ac is the input to a ATRU (auto transformer rectification unit) which converts to +/- 270V DC and that is the input to a CMSU (common motor starter controller) and the output of one of those feed a CAC on the L or R side. This gear is in the aft electrical bay in the P700 and P800 racks.
These get hot and need to have the heat dissipated by the PECC cooling system.
If one CAC or several doesn't work it is either the CAC unit(s) or some part(s) upstream back to the starting point of the 235V ac bus.
Surely the fault would have been noted upon landing at Ahmedabad and items fixed or switched out of circuit. If not, something is pulling down current in a fault condition and may modify how much power is available for other things.
Moving to take off at Ahmedabad the ADS-B fails shortly after rotate.
This is powered by 115V ac which is derived from the 235V ac bus via an ATU (auto transformer unit) and then via a RPDU (remote power distribution unit). The elapsed time from take off commencement to loss of the ADS-B device is probably the point when the RAT is automatically deployed.
The RAT is rated at 235V ac/10 kVA which calculates as 42A of available ac current. There will be conversion losses in the derivation of 115V ac and 28V DC, so not a lot of current and limits on how it can be used.
The RAT needs 130 knots for full power and if that wind speed drops so will the power. As far as I can see the RAT keeps certain gear working that was working in the first place. Could be wrong there and feel free to put me straight.
None of the above accounts for simultaneous engines flameout but it does contribute to the timeline.
A big question is whether the RAT deployed due to electrical failure which subsequently stopped the engines, or did the RAT deploy due to the engines stopping alone which took out the primary electrical 235V ac buses.
Just a few thoughts, after reading all the posts.
I remain convinced that the mentioned non-functioning air conditioning system is significant to the subsequent loss of electrical power. A passenger on the incoming leg complained about the air conditioning.
https://www.cnbctv18.com/india/air-i...l-19620259.htm
To explore the electrical system further see p. 86 of this document. I decided to trace out some electrical paths to equipment and do a few simple calculations.
https://fliphtml5.com/quwam/qhdw/Boo...cs_Electrical/
The electrical path to a CAC (cabin air conditioner) starts from the engine driven 235V ac bus which could be L1 or R1.
From there 235V ac is the input to a ATRU (auto transformer rectification unit) which converts to +/- 270V DC and that is the input to a CMSU (common motor starter controller) and the output of one of those feed a CAC on the L or R side. This gear is in the aft electrical bay in the P700 and P800 racks.
These get hot and need to have the heat dissipated by the PECC cooling system.
If one CAC or several doesn't work it is either the CAC unit(s) or some part(s) upstream back to the starting point of the 235V ac bus.
Surely the fault would have been noted upon landing at Ahmedabad and items fixed or switched out of circuit. If not, something is pulling down current in a fault condition and may modify how much power is available for other things.
Moving to take off at Ahmedabad the ADS-B fails shortly after rotate.
This is powered by 115V ac which is derived from the 235V ac bus via an ATU (auto transformer unit) and then via a RPDU (remote power distribution unit). The elapsed time from take off commencement to loss of the ADS-B device is probably the point when the RAT is automatically deployed.
The RAT is rated at 235V ac/10 kVA which calculates as 42A of available ac current. There will be conversion losses in the derivation of 115V ac and 28V DC, so not a lot of current and limits on how it can be used.
The RAT needs 130 knots for full power and if that wind speed drops so will the power. As far as I can see the RAT keeps certain gear working that was working in the first place. Could be wrong there and feel free to put me straight.
None of the above accounts for simultaneous engines flameout but it does contribute to the timeline.
A big question is whether the RAT deployed due to electrical failure which subsequently stopped the engines, or did the RAT deploy due to the engines stopping alone which took out the primary electrical 235V ac buses.
Just a few thoughts, after reading all the posts.
Last edited by T28B; 20th June 2025 at 18:33 . Reason: white space is reader-friendly for step by step posts
June 20, 2025, 21:16:00 GMT
permalink Post: 11907327
Hello, this is my first post on pprune; as a 787 pilot I’m 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’s manuals don’t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren’t 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’s 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.
My airline’s manuals don’t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren’t 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’s 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.
June 20, 2025, 22:57:00 GMT
permalink Post: 11907382
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.
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.
FWIW, according to earlier posts, the fuel load was about 50T, leaving about 18T in the centre tank, so (I think) about 25-30% full. A full centre tank might allow engine pump suction to work fine, but this might not? (Contrary to what some have said.)
Anyway, FWIW, not everyone agrees with RAT Deployment - see recent post by shep69. Would love to know why he doesn't go with RAT deployment...
June 20, 2025, 23:08:00 GMT
permalink Post: 11907388
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.
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.
Furthermore the preference of the center tank while it's filled is just by the higher fuel pressure those center pumps deliver. There is no valve that controls that, which might be triggered by switching off pumps.
June 20, 2025, 23:18:00 GMT
permalink Post: 11907389
Sorry but that doesn't really make sense. Once the power failed and all pumps are off where is the point of switching of the center fuel pumps off? Without power they aren't running anyways.
Furthermore the preference of the center tank while it's filled is just by the higher fuel pressure those center pumps deliver. There is no valve that controls that, which might be triggered by switching off pumps.
Furthermore the preference of the center tank while it's filled is just by the higher fuel pressure those center pumps deliver. There is no valve that controls that, which might be triggered by switching off pumps.
June 20, 2025, 23:34:00 GMT
permalink Post: 11907392
This has been mentioned several times.
June 21, 2025, 00:24:00 GMT
permalink Post: 11907404
It's not possible to shut them down without power - they are already shut down by the power loss. That was exactly my point.
June 21, 2025, 00:26:00 GMT
permalink Post: 11907405
Hello, this is my first post on pprune; as a 787 pilot I’m 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’s manuals don’t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren’t 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’s 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.
My airline’s manuals don’t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren’t 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’s 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.
On the 320 (equipped with the old system (fuel pumps), not the newer system (transfer valves)) the center tank pumps are inhibited when the airplane is airborne with the slats extended.
Check these certification rules:
https://www.ecfr.gov/current/title-14/section-25.953
and
https://www.ecfr.gov/current/title-1...-25#p-25.903(b )
June 21, 2025, 00:59:00 GMT
permalink Post: 11907419
It's starting to look more like a massive electrical or computer issue which resulted in both engines failing, the landing gear may have been left down longer than normal due to startle effect.
It could be maintenance related or a latent condition in the B787 which only occurred due to the required factors all being present on this occasion i.e. the holes in the Swiss cheese all lined up.
Boeing and Air India will be wanting to blame each other, hopefully having the UK AAIB involved will provide a balance as they don't have a dog in the fight.
If this turns out to be another MCAS, it will be difficult for Boeing to continue in it's present form. The B787 has been beset with problems since its introduction, the B777X has had numerous issues during development and the B737 is overdue for replacement. Airlines are starting to drop Boeing due to quality, safety and delivery issues. China is on the rise and if the C919 proves itself, it might be the main alternative to the A320.
It could be maintenance related or a latent condition in the B787 which only occurred due to the required factors all being present on this occasion i.e. the holes in the Swiss cheese all lined up.
Boeing and Air India will be wanting to blame each other, hopefully having the UK AAIB involved will provide a balance as they don't have a dog in the fight.
If this turns out to be another MCAS, it will be difficult for Boeing to continue in it's present form. The B787 has been beset with problems since its introduction, the B777X has had numerous issues during development and the B737 is overdue for replacement. Airlines are starting to drop Boeing due to quality, safety and delivery issues. China is on the rise and if the C919 proves itself, it might be the main alternative to the A320.
Last edited by krismiler; 21st June 2025 at 01:19 .
June 21, 2025, 01:04:00 GMT
permalink Post: 11907425
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.
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.
If you go and chat to the engineers, have a look in the IPC or MM I Ch 28, you should find a good description of the fuel boost pumps. It's been a while but I recall they are Eaton designs, the general arrangement is similar to the B777. They both have a suction feed that permits fuel feed in the event of a loss of all boost pumps. The only impact of that arises at high altitude and high thrust levels, where the engine driven fuel boost pumps may capitate and reduce the available fuel feed resulting in a lower thrust level.
Refer page 12.20.02 in the TBC's B787 FCTM, or search for "SUCTION FEED".
At sea level, full thrust will be achieved without any boost pump on the aircraft. Recall that the CWT boost pumps are known as Override boost pumps, they are feeding from the CWT when there is fuel and they are running, as the output pressure is higher from these pumps than the 2 wing boost pumps. Whether there is fuel in the CWT or not, or the CWT pumps are energised, is immaterial to whether fuel will be supplied to the engine driven fuel pumps.
Note that with BA038, the fundamental problem was blockage of wax/ice formed in the piping that blocked the FOHE, and that will cause a problem with those engines that have such architecture, but is not associated with the availability of the boost pumps themselves. Even then, the engines did not technically fail, as they have both done simultaneously with the B788 of AI 171, BA's engines were running but not able to provide significant thrust due to the FOHE blockages.
June 21, 2025, 02:51:00 GMT
permalink Post: 11907453
Under a complete electrical failure all electrically powered fuel pumps will fail, but the engine driven mechanical pumps will not fail, but according to information in my manual and what I\x92ve seen online, the engine driven pumps can only suction feed the engines from the main tanks. The 787 will burn fuel from the center tanks first, because they provide a greater pressure than the main fuel tank pumps.
June 21, 2025, 06:13:00 GMT
permalink Post: 11907514
Hoover from the generally respected Pilot Debrief channel put up his analysis.
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place. That being the case what is the "cloud of particles" that appear to the left of the aircraft ?
He discounts electrical failure affecting both engines due 787 design, and fuel contamination due both engines fed from separate tanks unlikely to affect both engines at the same time.
The possibility that one engine failure occurred at a critical point in the take off and that possibly the wrong engine fuel cutoff switch was pulled.
camera angle with shack and suggested point of rotation
whats this..
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place. That being the case what is the "cloud of particles" that appear to the left of the aircraft ?
He discounts electrical failure affecting both engines due 787 design, and fuel contamination due both engines fed from separate tanks unlikely to affect both engines at the same time.
The possibility that one engine failure occurred at a critical point in the take off and that possibly the wrong engine fuel cutoff switch was pulled.
camera angle with shack and suggested point of rotation
whats this..
June 21, 2025, 06:36:00 GMT
permalink Post: 11907525
Hoover from the generally respected Pilot Debrief channel put up his analysis.
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place. That being the case what is the "cloud of particles" that appear to the left of the aircraft ?
He discounts electrical failure affecting both engines due 787 design, and fuel contamination due both engines fed from separate tanks unlikely to affect both engines at the same time.
The possibility that one engine failure occurred at a critical point in the take off and that possibly the wrong engine fuel cutoff switch was pulled.
camera angle with shack and suggested point of rotation
whats this..
He analyses the point of rotation looking at the airport layout and using the video with the shack showing the aircraft rotate behind it, in that case the aircraft rotates at a reasonably normal place. That being the case what is the "cloud of particles" that appear to the left of the aircraft ?
He discounts electrical failure affecting both engines due 787 design, and fuel contamination due both engines fed from separate tanks unlikely to affect both engines at the same time.
The possibility that one engine failure occurred at a critical point in the take off and that possibly the wrong engine fuel cutoff switch was pulled.
camera angle with shack and suggested point of rotation
whats this..
I repeat, do NOT post repeats of discussions already had unless there is something of value which may change or enhance previous posts. This is a prime example of a post which should be vetted and dismissed before pressing Submit Reply 🙈
June 21, 2025, 10:53:00 GMT
permalink Post: 11907657
FR24 has the GPS lat long position at each time - ground speed is then simply distance travelled over the time interval. The METAR quoted 25007KT and that should increase with height hence the nominal decrease in ground speed over the later ADS-B values - and probably the slight drift off the centre line once airborne.
An earlier poster defined the 787 ADS-B transmits with a height granularity of 25' - which explains the FR24 figures and I might posit that it was just about to transmit a 25' height increase when the electrical failure occurred.
The rooftop video records a nominal 14s flight time with RAT out throughout.
The CCTV video records a nominal 32s (from rotation) and subjectively the aircraft stops climbing 14s after rotation - meaning 18s of descent of which 14s are captured in the rooftop video.
If we accept the RAT is out then it must have been deployed about 12-16s after rotation, presumably immediately after the 4s of ADS-B data.
Another post referenced the RAT only supplying electrical power after 10s - I find that hard to believe, not instant obviously because there has to be some stabilisation time and startup/boot time but it would imply the LH flight instruments would only be active very late. Hopefully the RAT hydraulics would be effective quicker than that.
An earlier poster defined the 787 ADS-B transmits with a height granularity of 25' - which explains the FR24 figures and I might posit that it was just about to transmit a 25' height increase when the electrical failure occurred.
The rooftop video records a nominal 14s flight time with RAT out throughout.
The CCTV video records a nominal 32s (from rotation) and subjectively the aircraft stops climbing 14s after rotation - meaning 18s of descent of which 14s are captured in the rooftop video.
If we accept the RAT is out then it must have been deployed about 12-16s after rotation, presumably immediately after the 4s of ADS-B data.
Another post referenced the RAT only supplying electrical power after 10s - I find that hard to believe, not instant obviously because there has to be some stabilisation time and startup/boot time but it would imply the LH flight instruments would only be active very late. Hopefully the RAT hydraulics would be effective quicker than that.
June 21, 2025, 13:50:00 GMT
permalink Post: 11907772
Hello, this is my first post on pprune; as a 787 pilot I’m 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’s manuals don’t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren’t 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’s 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.
My airline’s manuals don’t go into much detail, but I read on another site that if both the center tank pumps fail, the engine driven pumps aren’t 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’s 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.
Further up the thread one of the posters mentions that it is very unlikely that any crew action (checklist, QRH) would have got anywhere near to changing a fuel pump switch position.
June 21, 2025, 15:24:00 GMT
permalink Post: 11907841
Resubmitting following some Mod Feedback and a significant re-write. Yes, it is speculative
I have a theory that I'd like to share. It brings together various pieces of known information, along with 30+ years of my experience as an aircraft engineer that forms a plausible (IMO) explanation of what may have happened.
We Know - From the Video's and the ADSB Data:
That up to and for the first few seconds after take-off appears relatively normal.
The AC appears to lose thrust without e.g. birdstrike or other spectacular smoke /fire producing event.
That the RAT deployed.
That the pilot reported 'Thrust not achieved' [Edit - We dont 'know' this - it is heavily reported]
We can see that the AC had a relatively busy schedule in the few days prior to the accident flight, so there was no significant downtime for maintenance activities that could have caused incident.
The AC flew DEL-CDG on 11 Jun with quite a racy turnaround in CDG of 1h12m. The centre tank would have been empty at CDG on arrival, and would have been partially filled for the return CDG-DEL.
CDG-DEL Arrived 01:47 am IST. Again the Centre Tank would have been empty. But quite a bit of fuel in the wings.
8 Hrs later, at 09:48 am IST the AC departed DEL-AMD. For such a short-hop, Fuel upload would have been minimal, merely a 'topping up' if at all. Certainly nothing into the Centre Tank.
DEL That night was fairly hot and humid - 57% at 02:30, 54% at 05:30, 44% at 08:30. That wing tank fuel could have picked up a fair amount of water.
The flight DEL-AMD would have only used the wing pumps. Thus any water in that 'overnight' fuel would have been vigorously stirred and evenly suspended. At concentrations that would cause no ill-effect at all.
The AC was on the ground at AMD for 2 Hrs, from 11:17am to 1:17 pm IST. The AC would have re-fuelled, first filling up the wing tanks to the top, then filling the centre-tank to whatever quantity necessary. There was enough time for water in the wing tanks to settle out.
The B787 Fuel system has pumps in the wing tanks, and pumps in the centre tanks. The Centre Tank pumps are also known as 'override' pumps because they output a higher pressure than the wing tank pumps, thus ensuring that with all pumps running, the centre tank fuel is used first.
Should the centre tank pumps stop, due to either filure or running out of fuel to pump, the wing tank pumps then produce the pressure.
In the event that all pumps stop running (e.g. an electrical failure), the engines will suck the fuel from the wing tanks. The 'sucked' fuel comes from a dedicated pipe in each tank through the 'Suction Feed Check Valve' (so that pumped fuel doesn't just exit through the suction tube). The suction tube pickup is in a slightly different position to the wing pump pickups.
It is conceivable to me that the suction tube pickup could have been immersed in water, settled out from the fuel in the wing tanks.
Then - at start-up of the aircraft in AMD, The engines would have been supplied with fuel from the centre tank. Fresh Fuel. All OK. Wing pumps running and doing not much. But, I speculate, the suction pick-ups immersed in water. Waiting.
Start up and taxi out was all normal. Runway acceleration up to v1 appears normal. V1 - Rotate - (positive rate - Gear up? - Not my debate).
But somewhere around that time, I speculate that a significant electrical failure occurred. Enough for the RAT to deploy. Enough for the fuel pumps to stop. I'll not speculate on the cause. We know that it can occur, that's why the RAT was designed to operate.
The engines at that point were at TOGA thrust. In a significant electrical failure, the engines will keep on doing what they were last told. Keep that thrust stable. So the AC climbed for a few seconds more. The pilots did what they were trained to do for a power failure, manage that, thankfully the engines were still going well...
But there was only so much 'good' fuel in the lines. The engines sucking fuel themselves, the fuel would now be coming from the suction pickups, a different supply. A supply likely heavily water contaminated. It would take a few seconds for that contaminated fuel to actually reach the engines, but when that contaminated fuel hit, Thrust would have been significantly reduced. The EEC's would have been doing their best to maintain the thrust, firewalling the throttles would probably have little effect at that exact moment. The engines would have likely worked through that bad fuel in a shortish period of time, but a period of time that our crew did not have. A fully loaded aircraft producing less than take-off thrust, is not sustaining enough thrust for continued flight. The rest - is down to the skill of the crew in deciding exactly where to hit the ground within the very narrow range of choice they had.
I have a theory that I'd like to share. It brings together various pieces of known information, along with 30+ years of my experience as an aircraft engineer that forms a plausible (IMO) explanation of what may have happened.
We Know - From the Video's and the ADSB Data:
That up to and for the first few seconds after take-off appears relatively normal.
The AC appears to lose thrust without e.g. birdstrike or other spectacular smoke /fire producing event.
That the RAT deployed.
That the pilot reported 'Thrust not achieved' [Edit - We dont 'know' this - it is heavily reported]
We can see that the AC had a relatively busy schedule in the few days prior to the accident flight, so there was no significant downtime for maintenance activities that could have caused incident.
The AC flew DEL-CDG on 11 Jun with quite a racy turnaround in CDG of 1h12m. The centre tank would have been empty at CDG on arrival, and would have been partially filled for the return CDG-DEL.
CDG-DEL Arrived 01:47 am IST. Again the Centre Tank would have been empty. But quite a bit of fuel in the wings.
8 Hrs later, at 09:48 am IST the AC departed DEL-AMD. For such a short-hop, Fuel upload would have been minimal, merely a 'topping up' if at all. Certainly nothing into the Centre Tank.
DEL That night was fairly hot and humid - 57% at 02:30, 54% at 05:30, 44% at 08:30. That wing tank fuel could have picked up a fair amount of water.
The flight DEL-AMD would have only used the wing pumps. Thus any water in that 'overnight' fuel would have been vigorously stirred and evenly suspended. At concentrations that would cause no ill-effect at all.
The AC was on the ground at AMD for 2 Hrs, from 11:17am to 1:17 pm IST. The AC would have re-fuelled, first filling up the wing tanks to the top, then filling the centre-tank to whatever quantity necessary. There was enough time for water in the wing tanks to settle out.
The B787 Fuel system has pumps in the wing tanks, and pumps in the centre tanks. The Centre Tank pumps are also known as 'override' pumps because they output a higher pressure than the wing tank pumps, thus ensuring that with all pumps running, the centre tank fuel is used first.
Should the centre tank pumps stop, due to either filure or running out of fuel to pump, the wing tank pumps then produce the pressure.
In the event that all pumps stop running (e.g. an electrical failure), the engines will suck the fuel from the wing tanks. The 'sucked' fuel comes from a dedicated pipe in each tank through the 'Suction Feed Check Valve' (so that pumped fuel doesn't just exit through the suction tube). The suction tube pickup is in a slightly different position to the wing pump pickups.
It is conceivable to me that the suction tube pickup could have been immersed in water, settled out from the fuel in the wing tanks.
Then - at start-up of the aircraft in AMD, The engines would have been supplied with fuel from the centre tank. Fresh Fuel. All OK. Wing pumps running and doing not much. But, I speculate, the suction pick-ups immersed in water. Waiting.
Start up and taxi out was all normal. Runway acceleration up to v1 appears normal. V1 - Rotate - (positive rate - Gear up? - Not my debate).
But somewhere around that time, I speculate that a significant electrical failure occurred. Enough for the RAT to deploy. Enough for the fuel pumps to stop. I'll not speculate on the cause. We know that it can occur, that's why the RAT was designed to operate.
The engines at that point were at TOGA thrust. In a significant electrical failure, the engines will keep on doing what they were last told. Keep that thrust stable. So the AC climbed for a few seconds more. The pilots did what they were trained to do for a power failure, manage that, thankfully the engines were still going well...
But there was only so much 'good' fuel in the lines. The engines sucking fuel themselves, the fuel would now be coming from the suction pickups, a different supply. A supply likely heavily water contaminated. It would take a few seconds for that contaminated fuel to actually reach the engines, but when that contaminated fuel hit, Thrust would have been significantly reduced. The EEC's would have been doing their best to maintain the thrust, firewalling the throttles would probably have little effect at that exact moment. The engines would have likely worked through that bad fuel in a shortish period of time, but a period of time that our crew did not have. A fully loaded aircraft producing less than take-off thrust, is not sustaining enough thrust for continued flight. The rest - is down to the skill of the crew in deciding exactly where to hit the ground within the very narrow range of choice they had.
Last edited by GroundedSpanner; 21st June 2025 at 17:52 . Reason: Thrust not achieved comment is not proven.
June 21, 2025, 15:42:00 GMT
permalink Post: 11907854
Resubmitting following some Mod Feedback and a significant re-write. Yes, it is speculative
I have a theory that I'd like to share. It brings together various pieces of known information, along with 30+ years of my experience as an aircraft engineer that forms a plausible (IMO) explanation of what may have happened.
We Know - From the Video's and the ADSB Data:
That up to and for the first few seconds after take-off appears relatively normal.
The AC appears to lose thrust without e.g. birdstrike or other spectacular smoke /fire producing event.
That the RAT deployed.
That the pilot reported 'Thrust not achieved'
We can see that the AC had a relatively busy schedule in the few days prior to the accident flight, so there was no significant downtime for maintenance activities that could have caused incident.
The AC flew DEL-CDG on 11 Jun with quite a racy turnaround in CDG of 1h12m. The centre tank would have been empty at CDG on arrival, and would have been partially filled for the return CDG-DEL.
CDG-DEL Arrived 01:47 am IST. Again the Centre Tank would have been empty. But quite a bit of fuel in the wings.
8 Hrs later, at 09:48 am IST the AC departed DEL-AMD. For such a short-hop, Fuel upload would have been minimal, merely a 'topping up' if at all. Certainly nothing into the Centre Tank.
DEL That night was fairly hot and humid - 57% at 02:30, 54% at 05:30, 44% at 08:30. That wing tank fuel could have picked up a fair amount of water.
The flight DEL-AMD would have only used the wing pumps. Thus any water in that 'overnight' fuel would have been vigorously stirred and evenly suspended. At concentrations that would cause no ill-effect at all.
The AC was on the ground at AMD for 2 Hrs, from 11:17am to 1:17 pm IST. The AC would have re-fuelled, first filling up the wing tanks to the top, then filling the centre-tank to whatever quantity necessary. There was enough time for water in the wing tanks to settle out.
The B787 Fuel system has pumps in the wing tanks, and pumps in the centre tanks. The Centre Tank pumps are also known as 'override' pumps because they output a higher pressure than the wing tank pumps, thus ensuring that with all pumps running, the centre tank fuel is used first.
Should the centre tank pumps stop, due to either filure or running out of fuel to pump, the wing tank pumps then produce the pressure.
In the event that all pumps stop running (e.g. an electrical failure), the engines will suck the fuel from the wing tanks. The 'sucked' fuel comes from a dedicated pipe in each tank through the 'Suction Feed Check Valve' (so that pumped fuel doesn't just exit through the suction tube). The suction tube pickup is in a slightly different position to the wing pump pickups.
It is conceivable to me that the suction tube pickup could have been immersed in water, settled out from the fuel in the wing tanks.
Then - at start-up of the aircraft in AMD, The engines would have been supplied with fuel from the centre tank. Fresh Fuel. All OK. Wing pumps running and doing not much. But, I speculate, the suction pick-ups immersed in water. Waiting.
Start up and taxi out was all normal. Runway acceleration up to v1 appears normal. V1 - Rotate - (positive rate - Gear up? - Not my debate).
But somewhere around that time, I speculate that a significant electrical failure occurred. Enough for the RAT to deploy. Enough for the fuel pumps to stop. I'll not speculate on the cause. We know that it can occur, that's why the RAT was designed to operate.
The engines at that point were at TOGA thrust. In a significant electrical failure, the engines will keep on doing what they were last told. Keep that thrust stable. So the AC climbed for a few seconds more. The pilots did what they were trained to do for a power failure, manage that, thankfully the engines were still going well...
But there was only so much 'good' fuel in the lines. The engines sucking fuel themselves, the fuel would now be coming from the suction pickups, a different supply. A supply likely heavily water contaminated. It would take a few seconds for that contaminated fuel to actually reach the engines, but when that contaminated fuel hit, Thrust would have been significantly reduced. The EEC's would have been doing their best to maintain the thrust, firewalling the throttles would probably have little effect at that exact moment. The engines would have likely worked through that bad fuel in a shortish period of time, but a period of time that our crew did not have. A fully loaded aircraft producing less than take-off thrust, is not sustaining enough thrust for continued flight. The rest - is down to the skill of the crew in deciding exactly where to hit the ground within the very narrow range of choice they had.
I have a theory that I'd like to share. It brings together various pieces of known information, along with 30+ years of my experience as an aircraft engineer that forms a plausible (IMO) explanation of what may have happened.
We Know - From the Video's and the ADSB Data:
That up to and for the first few seconds after take-off appears relatively normal.
The AC appears to lose thrust without e.g. birdstrike or other spectacular smoke /fire producing event.
That the RAT deployed.
That the pilot reported 'Thrust not achieved'
We can see that the AC had a relatively busy schedule in the few days prior to the accident flight, so there was no significant downtime for maintenance activities that could have caused incident.
The AC flew DEL-CDG on 11 Jun with quite a racy turnaround in CDG of 1h12m. The centre tank would have been empty at CDG on arrival, and would have been partially filled for the return CDG-DEL.
CDG-DEL Arrived 01:47 am IST. Again the Centre Tank would have been empty. But quite a bit of fuel in the wings.
8 Hrs later, at 09:48 am IST the AC departed DEL-AMD. For such a short-hop, Fuel upload would have been minimal, merely a 'topping up' if at all. Certainly nothing into the Centre Tank.
DEL That night was fairly hot and humid - 57% at 02:30, 54% at 05:30, 44% at 08:30. That wing tank fuel could have picked up a fair amount of water.
The flight DEL-AMD would have only used the wing pumps. Thus any water in that 'overnight' fuel would have been vigorously stirred and evenly suspended. At concentrations that would cause no ill-effect at all.
The AC was on the ground at AMD for 2 Hrs, from 11:17am to 1:17 pm IST. The AC would have re-fuelled, first filling up the wing tanks to the top, then filling the centre-tank to whatever quantity necessary. There was enough time for water in the wing tanks to settle out.
The B787 Fuel system has pumps in the wing tanks, and pumps in the centre tanks. The Centre Tank pumps are also known as 'override' pumps because they output a higher pressure than the wing tank pumps, thus ensuring that with all pumps running, the centre tank fuel is used first.
Should the centre tank pumps stop, due to either filure or running out of fuel to pump, the wing tank pumps then produce the pressure.
In the event that all pumps stop running (e.g. an electrical failure), the engines will suck the fuel from the wing tanks. The 'sucked' fuel comes from a dedicated pipe in each tank through the 'Suction Feed Check Valve' (so that pumped fuel doesn't just exit through the suction tube). The suction tube pickup is in a slightly different position to the wing pump pickups.
It is conceivable to me that the suction tube pickup could have been immersed in water, settled out from the fuel in the wing tanks.
Then - at start-up of the aircraft in AMD, The engines would have been supplied with fuel from the centre tank. Fresh Fuel. All OK. Wing pumps running and doing not much. But, I speculate, the suction pick-ups immersed in water. Waiting.
Start up and taxi out was all normal. Runway acceleration up to v1 appears normal. V1 - Rotate - (positive rate - Gear up? - Not my debate).
But somewhere around that time, I speculate that a significant electrical failure occurred. Enough for the RAT to deploy. Enough for the fuel pumps to stop. I'll not speculate on the cause. We know that it can occur, that's why the RAT was designed to operate.
The engines at that point were at TOGA thrust. In a significant electrical failure, the engines will keep on doing what they were last told. Keep that thrust stable. So the AC climbed for a few seconds more. The pilots did what they were trained to do for a power failure, manage that, thankfully the engines were still going well...
But there was only so much 'good' fuel in the lines. The engines sucking fuel themselves, the fuel would now be coming from the suction pickups, a different supply. A supply likely heavily water contaminated. It would take a few seconds for that contaminated fuel to actually reach the engines, but when that contaminated fuel hit, Thrust would have been significantly reduced. The EEC's would have been doing their best to maintain the thrust, firewalling the throttles would probably have little effect at that exact moment. The engines would have likely worked through that bad fuel in a shortish period of time, but a period of time that our crew did not have. A fully loaded aircraft producing less than take-off thrust, is not sustaining enough thrust for continued flight. The rest - is down to the skill of the crew in deciding exactly where to hit the ground within the very narrow range of choice they had.