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Tailspin Turtle
June 12, 2025, 15:20:00 GMT permalink Post: 11899329 |
My impression was very similar: they never had enough thrust for level flight with the gear down, used up the whole runway accelerating to something close to Vr, rotated and started to climb but very soon started slowing and had to reduce the angle of attack, starting the descent.
Subjects: None |
Tailspin Turtle
June 14, 2025, 21:22:00 GMT permalink Post: 11901853 |
You might want to rethink that.
It's approximately 1km glide from where the aircraft was at roughly 200ft, not 2 km. 1km equals about 3000ft, so that is a glide ratio of 15. Taking into account a bit of excess speed to bleed off before reaching alpha max, this sounds very feasible to me. Aeronautical engineer, CFI, unused ATP rating, 3,000 hours in airplanes, rotorcraft, and gliders Subjects: None |
Tailspin Turtle
June 15, 2025, 03:47:00 GMT permalink Post: 11902079 |
IMO
In the CCTV video, the aircraft stops climbing at 00:28. 3 seconds after, it starts visibly descending. At peak altitude, using the 197ft wingspan as a measure, the altitude is around 200ft or below. The fireball is at 00:48, 17s after descent starts visibly. Per google maps and the impact location mapped at avherald, the impact point is ~3990ft from the airport boundary road and about 4200ft from the midpoint of the runway threshold and the airport boundary road. 16:1 to 25:1 is what I could find for the 787 glide ratio range (unpowered) with main landing gear down and flaps 5. So the aircraft could cover 16 to 25 ft horizontally for every 1 ft of descent. With a starting altitude of 200ft, that would imply it could have covered 3200ft.to 5000ft during unpowered descent. The actual distance covered, around 4000ft, certainly seems to suggest that the descent was unpowered. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): AvHerald CCTV |
Tailspin Turtle
June 17, 2025, 12:46:00 GMT permalink Post: 11904272 |
Based on approximate distances and heights, the time line, the aircraft configuration, surface wind, the published L/D (gear up reduced to a guess for gear down and RAT out), and probable off-optimum speed for maximum L/D in that configuration, it's my opinion (aeronautical engineer, unused ATP rating, and glider pilot, national contests) that we can't rule out both engines being at idle or very low thrust at or shortly after rotation,
rather than shut down.
Last edited by Tailspin Turtle; 17th June 2025 at 16:28 . Reason: Added final phrase for clarification Subjects (links are to this post in the relevant subject page so that this post can be seen in context): RAT (All) |
Tailspin Turtle
June 19, 2025, 23:38:00 GMT permalink Post: 11906487 |
Can someone help me with the calculations on how far from the point of our last ADS-B readout we can expect the stricken jet to fly/glide?
I am assuming the take off mass around 190-200 tons with 50 tons of fuel. For the glide phase this is of no importance, however. Data on the Internet puts the glide ratio of a 789 around 18-21:1. Gear and flaps/slats out should have a significant negative effect. Does anyone have a good take how much? Minus 40%? From the available data we can infer the plane never was higher than 200\x92 AAL, maybe even 100\x92. If I understood the online sources correctly, the point of impact was only about 20\x92 lower than the average runway level. If I am not mistaken the distance from the last ADS-B point to the impact site is about 2 km as per Reuters and the Guardian. That would put it at 6,500\x92. I just can\x92t get these numbers over each other without the aircraft producing thrust. Please help me correcting the numbers. Subjects (links are to this post in the relevant subject page so that this post can be seen in context): ADSB RAT (All) |
Tailspin Turtle
June 20, 2025, 00:28:00 GMT permalink Post: 11906506 |
Therefore the crew could have manually deployed it... (there's a button for that). If I saw the engines winding down and couldn't be sure that they would stop at idle, I'd be inclined to deploy the RAT instead of waiting for airplane to do it.
Last edited by Tailspin Turtle; 20th June 2025 at 00:53 . Reason: Add a reason for manual deployment of the RAT Subjects (links are to this post in the relevant subject page so that this post can be seen in context): RAT (All) RAT (Deployment) |
Tailspin Turtle
June 29, 2025, 19:09:00 GMT permalink Post: 11913181 |
Do we think the engines are fully 'off', shutdown - Or are they struggling to provide thrust?
Listen to the rooftop video in Capn Bloggs excellent Side-By-Side video . Ignore the RAT. Try and focus on all the sound that is not RAT. I think I can hear a pulsing, a chunk-chunk-chunk' sound. Do we think that is the engines struggling to work? Subjects (links are to this post in the relevant subject page so that this post can be seen in context): RAT (All) |
Tailspin Turtle
June 29, 2025, 22:41:00 GMT permalink Post: 11913278 |
Thanks but I want to separate the RAT issue from the engines/thrust issue.
Its possible that the RAT was deployed for other reasons, prior to the engines losing thrust. So, leaving the RAT out of the equation for a bit, do we think there is a sound of engines TRYING to run? Subjects (links are to this post in the relevant subject page so that this post can be seen in context): RAT (All) RAT (Deployment) |
Tailspin Turtle
July 01, 2025, 02:09:00 GMT permalink Post: 11913983 |
This is my latest attempt to square the circle using all the data points and minimal assumptions. The main shortcoming of the analysis is not knowing the maximum L/D and the speed for maximum LD with the gear down, flaps 5, and the RAT extended. However, if I use a reasonable number in my opinion for the L/D in that configuration and assume that the airplane is being flown at the speed for it, it will not get to the crash site. The distance from the runway of the crash site is from a previous graphic (1.55 km); the rotation point from fdr, permalink 314; 200 feet max height above the runway being generally accepted; crash site 50 feet below the runway elevation cited previously. An average speed of 180 knots is consistent with the dimensions given and 30 seconds flight time. A flare at 50 feet will briefly increase the L/D to 20, maybe even 30 (500 feet more than shown) but still not enough to make up the shortfall, In fact, with a head wind the L/D will be lower than assumed as well as if the speed being flown is higher or lower than required for maximum L/D in that configuration. In other words, there must have been some thrust available.
![]() Subjects (links are to this post in the relevant subject page so that this post can be seen in context): RAT (All) RAT (Deployment) |
Tailspin Turtle
July 01, 2025, 03:33:00 GMT permalink Post: 11914003 |
Yes - Higher numbers are better. The 787 has one of the best for an airliner, almost 21 power off.
Subjects: None |
Tailspin Turtle
July 01, 2025, 13:05:00 GMT permalink Post: 11914261 |
There is easily-correctable available data with the aircraft's altitude at pretty much the end of the runway and it is not at 200 feet (it's around 100\xb112.5 feet).
As the aircraft visibly continues to climb past that height (and for a longer period than ADS-B data covers, if the camera's perspective casts doubt on that), it seems rather clear to me that it reached its peak height past the end of the runway. In light of this I find the fact that people keep calculating a glide from the runway to the crash site to be a bit strange. Wouldn't the first step of any math be to try to determine where it started descending? Subjects (links are to this post in the relevant subject page so that this post can be seen in context): ADSB RAT (All) |
Tailspin Turtle
July 13, 2025, 23:43:00 GMT permalink Post: 11921782 |
Thank you for your reply! I'm aware you know more about ADS-B than I do, and I'm happy to learn.
As you know, I'm referring to the map view and data on https://www.flightradar24.com/blog/f...rom-ahmedabad/ . That's what I thought at first, based on the time stamps. 08:08:50.87 last full ADS-B message (172 kts) 08:08:54 APU inlet door starts to open, per the report. My problem here is that the report also says that the maximum speed was 180 knots IAS at about 08:08:42. And we have 2025-06-12T08:08:46.550875Z,8005ec,23.069138,72.625871,575 associated with 184 kts as the first ADS-B message in the sequence. Given that the clocks of ADS-B receivers are sometimes off, I think this might actually represent the moment of maximum speed; but then the AFS-B clock would be 4 seconds fast. And that's why I adjusted my times. A way to cross-check would be to track the aircraft position over time from the point of rotation, or to use the new photo in the report that shows the RAT over the runway to triangulate where that was. Yes. Would low pressure and high temperature make IAS lower than ground speed, even with the 7 knot headwind? Either way, if they were decelerating at approximately 3 knots per second, then they would've ended up at about 150 knots IAS, which is less than Vr. When I look at the CCTV video, 13 seconds into the flight, the aircraft is just "over the hump" and starts descending, so that tracks. At this point, I don't know what having the engines spool up instead of being dead weight would've done to that flight path; and how successfully the aircraft could've been recovered from that. Maybe they had only 4 seconds to flip those switches, instead of 5 seconds? Still, the best bet is to not ask questions, but flip these switches back ASAP, no? Subjects (links are to this post in the relevant subject page so that this post can be seen in context): ADSB APU CCTV Engine Failure (All) Engine Shutdown Preliminary Report RAT (All) Timeline (Preliminary Report) |
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