Posts about: "ADSB" [Posts: 141 Pages: 8]

FR24 coverage (and any other ADS-B system) is poor at VAAH. Attached a 24h coverage plot. You'll note that the backtrack section of the runway has practically nil coverage, so they may well have backtracked but it didn't show up on ADS-B.

QNH, 1001, right?

12hPa = 324 feet overstated altitude.
Airport 189 feet.
Sum = Should show 513feet on ground so 500 or 525 from the ADS-B.

Max altitude shown = 650 feet.

FR24 Shows zero on ground but adopts to ADS-B atitude after takeoff.

Possible timeline (all timing after brake-release)

Rotation +33s
Mayday call +44s, circa 300 ft altitude (ADS-B)
Peak altitude +49s, 625 ft (Flightradar24)
Impact +58s, crash site 1.6 km from runway

The crew did not take an intersection departure (despite people jumping to that conclusion off of clearly spotty ADS-B data).

In my opinion we should all find such things hard to believe, and it is very strange that people are so easily believing the incredible about this crew off of practically nothing.

It was confirmed about 60 posts prior to yours that it wasn't an intersection departure (that was jumping to conclusions based on a 4\xbd minute hole in the ADS-B data).

Still, it's a useful indication as to who does or doesn't bother to read previous posts before posting ...

That's interesting.

The single (so far) airborne ADS-B plot, with that widely-quoted pressure altitude of 625', is at a point more or less overhead the piano keys at the 05 end.

Adjusting for a QNH of 1001 hPa gives approx 285' AMSL or 95' AAL.

The video from the NE end of the runway, beside the RVR sensor shows a liftoff occurs abeam the closed high speed taxiway between C and D. Thats at 1250m to run to the DER. The first 10 seconds of flight is steady, and then the aircraft stops climbing and starts a gentle descent, and 5 seconds later the pitch starts to increase in 2 stages with impact around 20 seconds after liftoff. This is not the ADSB data, it is the video at the boundary on F/B.

The video take from the south end of the airport appears to show the RAT deployed.

The flight VAAH-EGLL is not a particularly heavy departure, the takeoff distance is not unreasonable for a twin jet, at under 7,000' from brakes release. I have limited developmental time only on the 787 before EIS, and I cannot recall any surprising latent threat in the performance of the aircraft for a premature flap retraction, and that certainly would not result in a RAT deployment. An accidental ATR low level off capture might get exciting for a few seconds, but it would not result in a RAT either.

The seat 11A pax survivor is remarkable.

No, the FR24 ADS-B data is accurate.

It's the conclusions that people have jumped to while ignoring the fact that there's a 4\xbd minute gap in the data that have turned out to be incorrect.

Would not be the first time that an accident has uncovered unintended consequences of a particular fallback configuration that was never able to be checked by either/any of Airbus, McDD or Boeing developmental test-pilots. Thinking of the automatic thrust augment/restoration on the MD81 (regn OY-KHO) that crashed 27Dec91 near Gottrora in Sweden (double engine failure). Design Boffins failed to realize that ice-sheet ingestion (sliding off the wings to be ingested by both rear-mount engines) would not benefit at all from each engine hiccup causing a continual uprating of the other (and vice-versa). To be found/uncovered in a simulator you would have to be testing various pilot inadvertencies (rather than rote expected actions). Then again, don't always believe the outcomes to be seen in a simulator. They don't necessarily faithfully emulate what would happen systems-wise in an aircraft... particularly when it comes to complex materiel failure modes or illogical sequiturs (e.g. MCAS)

So, if such an untestable circumstance were to happen to a competent crew and they were to inadvertently shut-down the wrong engine (and then/were in "clean-up mode":

a. The residual hyds would break the downlocks - but not retract the gear (and it would appear to be still selected down)
b. The alternate flaps might start to retract (gear downlocks not being now "made") once selected, but the slats remain out.
c. the RAT would deploy

The point at which all thrust ceases (and the climb vector flattens/reverses) is easily seen
in the video shot from the 6:30 clock position from about a km away. It's readily apparent.

An engine failure just off the runway after V1 in a fully loaded 787-8 in high ambient temperatures would assuredly have a crew thinking about a "toute suite" shutdown of a misbehaving donk. That's human nature. When the PERF is quite sluggish you will be thinking that a quick clean-up of the situation is certainly called for. That's just human nature unfortunately, particularly when you are under the time compression of dire circumstance (and the airframe is performing like a lame dog, just due to the environmentals and the early failure). I think that what the pilot reportedly said to ATC in his Mayday bears that out as being his instant mindset (quite clearly). Been in that "fools rush in" circ myself. You just have to "sit on your hands" and fly the beast.
But then again, if the RAT was NOT found deployed, then it's a case of the right seat mistakenly sucking in the flaps and slats... and that will do it... whatever the power/TOGA might be.
https://tinyurl.com/4zzkeeud
Rotation +33s
Mayday call +44s, circa 300 ft altitude (ADS-B)
Peak altitude +49s, 625 ft (Flightradar24)
Impact +58s, crash site 1.6 km from runway

If those numbers are correct about 120kts then. Interesting

I'm pretty convinced that everyone is watching different videos, which wouldn't surprise me in the least given how much images and footage can get mangled from being downloaded/re-uploaded to different services. Personally I've seen at least two different videos (and slightly different variants of each): one that's a direct recording of the aircraft and one that's a recording of a phone playing a recording of the aircraft. The buzz of a propeller was quite audible in the former but not in the latter, and the engines are notably quiet compared to any 787 takeoff I've ever been close to.

I do think that at this point people are working backwards from the cause being retracting the flaps, rather than working forwards from the evidence towards an explanation. If everything else was as it should be apart from flaps being retracted instead of gear, you'd at the very least expect the aircraft to reach a higher speed than is suggested by how little distance there is between the end of the runway and the crash site. Coupled with the apparently parabolic trajectory seen in the airport CCTV video, the crew (allegedly) reporting engine problems on the radio, the surviving passenger testifying about flickering cabin lights, the plausible deployment of the RAT, the fact that the ADS-B data cuts out well before impact...surely at some point one must consider a lack of thrust, no matter how improbable. Recognising the what doesn't need a full thesis on the how .

I wonder if (given all the facts and rumours about the situation so far) the flaps would be so high on everyone's minds if they weren't already a hot topic from the initial, largely baseless speculation that they somehow took off with flaps retracted.

SLF here, retired physicist, but with much engineering (esp. systems engineering) background and considerable interest/experience in fault-finding in complex (not aircraft) systems.

I think it is helpful here to work through some possible failure scenarios in some detail. You could usefully partition these into two separate groups: “RAT was deployed” and “RAT was not deployed.” I’ll mostly follow the former here.

\xb7 By following this path, I think we can exclude incorrect flaps setting or premature flap retraction as the primary cause of the crash. It’s difficult to see how improper use of the flaps would be correlated with RAT deployment. Everything in this case points to a loss of engine thrust.

\xb7 The first question is, why did the RAT deploy? As I understand it, manual deployment by a pilot is possible, or automatic deployment caused by detection of major electrical or engine failures. I haven’t found an authoritative, detailed discussion of this, or about the time to deployment, which is relevant here as there is so little time involved.

\xb7 According to tdracer , if the primary issue was a major electrical failure, that should not have caused any engine rollback. Thus, absent pull back of the throttles (which surely would have been corrected by the pilots), there should not have been a loss of thrust.

\xb7 Thus we are left with engine rollback as the likely underlying problem. Absent other issues, a single engine rollback should not have been a major problem, so dual rollback, unlikely as it might be, seems a reasonable conclusion.

\xb7 This is consistent with the reported mayday call, although that report needs confirmation.

\xb7 It is difficult to understand a dual engine rollback. Various causes have been suggested but ruled “unlikely” here. However, it is not possible to rule out a unicorn event, like the dual engine rollback experienced by BA 38. Leaving aside the cause, it is useful to look at the consequences.

\xb7 There would have been a major loss of electrical power (apart from battery backup), assuming the APU was not running. I don’t know if is possible the APU might be used at takeoff (e,g., to unload the main engines), or if any evidence from the tail photo at the crash site provides a meaningful indication (e.g., intake door status).

\xb7 Are there other indications of loss of electrical power? The reported statements of the surviving passenger may have some relevance, but I would want to see the results of an interview by crash investigators.

\xb7 What about the loss of Flight Aware ADS-B data shortly after takeoff? There have been a few mentions of this, but not much discussion. Could this indicate loss of electrical power?



I hope this is of some use. I’m happy to defer to professionals or others here for better information/analysis.

The Daily Telegraph has apparently put out a photo that is of the rear view of the aircraft, showing the TE flaps have a visible gap between the flap element and the wing, that is, the flaps are extended. If they were not, you get to see nothing. Int he gap, you can clearly see the fan exit of both engines.... ergo, the TE flaps are deployed. This same article then highlights this and exclaims that the flaps were retracted.

Is it safe to assume that the education standard of writers and editors of UK papers has been depleted somewhat?

Such comments are inflammatory to those that have lost family in this tragedy, and directly impugn the flight crew, and are factually, grossly wrong. This isn't just sloppy journalism, it is defamatory to those that cannot speak in their own defence. Sorry Mods, but someone needs to stand up for those that cannot against offensive drivel that passes for informed media commentary.

Here is a photo of the aircraft at the point that some numpties have stated the flaps are not employed. Apparently the authors should visit spec savers, or get a guide dog at least. At least, they get great blue coloured parking. In the same image, the RAT is observable.

The comments that are floated that some experts suggest that the crew may have not been able to get the gear up and may have retracted the flaps shows an utter lack of understanding of the certification basis of our aircraft. The flaps are out at a relevant TO flap extension setting for the conditions.

The same bastion of British broadsheets shows an image that is already on this thread, of a takeoff from mid field, while at the same time showing a still of the NE corner video near the RVR gauge east of the PAPI at the N end of the runway. One can only conclude that there is a dearth of good loo paper in the UK, and this standard of rigorous investigative reporting can be best applied to ones soft spots for personal hygiene. take 5 minutes out and do an triangulation from the point of observation, and surprise, the aircraft lifts off abeam the closed high speed taxiway. Not at the end of the runway, 1250 meters north of the DER. Taking ADSB data and not running a validation of it is mentally lazy and leads to hurtful assumptions that taking a slight amount of reasonable due care would have avoided.

rude letter follows...







https://www.telegraph.co.uk/news/202...a-plane-crash/


This is interesting enough without dealing with the media who show once again the mental acuity and sharp insight of a bowling ball.

Combining all the bits and pieces of info from this thread so far, IMO we can theoretically sequence it thus using the video from the left:

00:18 Rotation. Normal takeoff config.
00:24 Gear up starts. per Raffael with FF.
......... FR24 ADSB last transmission (71ft, 172kt) just before runway threshold. Matches with video aircraft altitude at 1/2 wingspan.
......... ? Full power flameout leaves N2 ~ 60%; Airspeed < 200k so N2 will decay to 15% in 8-10s?
......... ? Takeoff EGT of 900C needs 25-35s to fall below 250C ?
00:27 Gear up stops. per Raffael with FF. Bogies tilted.
......... ? APU starts. 20-55s to 95%N?
......... Per 787 dual-engine fail/stall memory items, PM initiates Fuel Cutoff and Run.
00:28 Visible loss of thrust. Alt ~ 200ft using aircraft wingspan as measure.
......... Matches with eyewitness "within 5-10s ... it was stuck in the air".
......... Per 787 dual-engine fail/stall memory items, PM initiates RAT Switch for 1s. Whether auto or manual, the RAT initiates.
......... RAT "bang" heard by survivor
......... RAT coming online accounts for eyewitness "lights started flickering green and white".
......... Per 787 QRH below 1000ft, PF makes no change to Main Landing Gear and flaps, aircraft pointed straight for best glide.
00:31 Descending visibly, somewhere beyond the runway threshold. Alt ~ 200ft using aircraft wingspan as measure.
......... ? Because EGT > 250C FADEC blocks fuel (T-HOT hot restart inhibit?) so no relight though N2 > 15% ?
......... 787 glide ratio between 16:1 to 25:1 with MLG down, Flaps 5. About 15-20s and 3-5000ft of glide from 200ft?
......... Some flap accounts for the ground pictures.
00:34 ? N2 has presumably decayed to 15%, FADEC flips to X-START: airspeed outside envelope? No hope of relight now.
......... PM/PF transmits Mayday?
......... Video showing RAT deployed.
00:46 APU reaches some fraction of 95%N (APU sound accounting for survivor's perception of thrust?).
00:48 Impact. 4200ft from descent start, 3990ft from airport boundary road. 17s from visible descent start.

if this is a valid sequence, the only remaining question is why the dual-engine failure at ~200ft agl?

with condolences to the families and people affected.

1. The video from the NE of the airport shows that the TO run was not excessive, the ADSB data is erroneous. That would suggest that the thrust set was reasonable
2. An altitude capture at the engagement of VNAV will result in the thrust coming back very rapidly. It has happened and will happen again. It doesn't need crew error in all cases, a failure of the MCP digitiser used to cause the same problem, despite the desired target being shown above the alt strip. It was one of the oddball cases where what is displayed is not necessarily what is being targeted. In such a case however, the ATR unless it has been turned off will still wake up again if it has been disconnected by the throttle instinctive disconnects, when a low airspeed has been detected.

The WDMs will be getting scrutinised up in Seattle at the very least.

Perhaps worth noting that the end of the runway is not the only possible source of dust in the aircraft's vicinity - from maps and videos of the airport, the sides would also have plenty. Couldn't the dust cloud also be indicative of a yaw? The paved surface is fairly narrow (45m/148ft), so I imagine given a 787's wingspan that it doesn't have to get particularly far off the centerline for it to start kicking up debris while rotating.

Available ADS-B data while limited does have the aircraft crossing the piano keys at a height of a good hundred or so feet, for what it's worth. (625ft reported altitude, QNH 1001, 37\xb0C, field elevation 189ft)

The ADS-B data is incomplete and subject to interpretation. The media, for example, doesn't have a clue about the difference between pressure altitude and height AAL, and sadly some PPRuNers have also failed to make that distinction.

But "erroneous" ? In what respect ?

I'm reading a lot of the comments, speculation is something we all like, but some things just do not add up, even with a RAT deployed

if they had dual engine failure around 50 feet where you raise the gear, how can they still find the energy to climb, since they would be at VR/V2 speed (not V2+20 at that altitude, what VNAV would command after take off, especially with a take off weight of around 205/210 tons, the 787 wings are amazing but not miracles

if they had a normal departure, why did they not raise the gear, they had a positive rate since they were climbing and the speed according to ADS-B was a constant. if they were single engine ! this would have saved them with this weight and weather, one of the first things you learn when EFATO with a 787, raise the gear, your climb performance increases dramatically

if they did an intersection departure with they're genex 64-70K engines, they would have had a take off limited weight of around 172 tons, I estimate that they were close to 205/210 tons, (max zfw of around 161 tons and around 45/50 tons of fuel) even full length would have been a stress for the engines, with the prevailing weather conditions, intersection take off can be ruled out, they would have never made it, full length is already difficult.

When we see the video, the airplane is still climbing / flying straight and level (not losing altitude), yet we hear what we think might be the RAT, I can't imagine that they had the kinetic energy to do this with no engines. if they had dual engine failure, they would have been a brick, Hot and High, no thrust, flaps 5, zero chance.

flickering of lights etc. seen by the survivor and the loud bang heard, I would not trust pax observations, because of the things they had to go through, also and I've said this before, if it was a loud bang, where is the smoke and fire in the engines, or in the video, its not audible

lets see what the report will say, but it it could be a lot to swallow for some

There should not be a max pre-start EGT limit in-flight - that should only occur on the ground for a pilot-initiated Autostart where the starting EGT redlines are lower than for in-flight.

In-flight, the Autorelight function should attempt to restart the engine as soon as a flameout is detected, and for an engine flaming out at high power it might catch it before it even goes sub-idle. Generally, Autorelight will continue attempting until some cutoff N2 at which time it will stop attempting, or if the pilot move the fuel switch to Cutoff. And while the EEC is still powered (via its own PMA) down to roughly 10% N2, the ignition exciters required for Autorelight do get their power from the airplane.

If you read the MMEL for the 787, like most passenger jets there's a LOT of stuff that can be inop and you can still dispatch. APU, one of two center hydraulic pumps, etc. Not suprising to those if you in the industry but perhaps mildly disturbing to the rest of us. I'm wondering how much other stuff could be not working without being noticed. Specifically I'm wondering about the suction pumping of fuel on the engines. Since the normal mode is to run all of the fuel pumps, the suction pump mode is always overridden by boost pressure from the electrics. Might it be possible for wear, improper maintenence or some other issue to cause this standby suction feature to not actually work? Is it routinely tested and if so, how often? The idea here is that if the engines were not capable of sucking up fuel on their own, the airplane would be operated indefinitely without anyone knowing until one day there is a catastrophic electrical malfunction at an inopportune time. In this case, that might correspond with the cessation of the ADS-B data.

I'm asking this as a question, not claming to have "cracked the case". I'm not an aviation fuel system expert. Can anyone who is or has direct knowledge comment? The reason I thought of it is that I've seen very similar issues with diesel engine systems where the mechanical injection pump can typically suck fuel but is normally fed with pressure. An internal (or external) leak can cause it to not be able to suction fuel properly but as long as the other pumps keep it pressurized it can work forever.