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| Sailvi767
July 18, 2025, 01:32:00 GMT permalink Post: 11924794 |
Apologies for the delay in responding to your posts. I see that you and others have stepped in, thanks.
I think for various reasons the ADSB data's absolute values are offset by some amount, for possibly all of the parameters. But there should be consistency in the deltas for the timestamp (by receiving station), the raw baro altitude, the Flightradar24 AGL values, and the airspeed. Flightradar24 themselves note that for altitude " ... the data is not above ground level, but it is consistent to itself." 08:08:46.55 ... 575ft ... 21ft ... 184kt 08:08:48.14 ... 600ft ... 46ft ... 179kt 08:08:48.61 ... 600ft ... 46ft ... 177kt 08:08:49.01 ... 600ft ... 46ft ... 177kt 08:08:49.46 ... 625ft ... 71ft ... 177kt 08:08:49.92 ... 625ft ... 71ft ... 174kt 08:08:50.39 ... 625ft ... 71ft ... 174kt 08:08:50.87 ... 625ft ... 71ft ... 172kt From the Preliminary Report's airport cctv picture, the RAT was seen deployed at, by my estimate here , 150ft baro altitude, between 4-7 seconds after rotation. So the ADSB readings have to be prior to that. What's interesting is that the ADSB data covers: - 4-5 seconds of time (let's approximate 4 seconds from 46.55 to 50.55, ignoring the 0.32s for the moment) - 50ft of altitude gain - Declining airspeed from the 1st reading to the last in this final segment from the runway. Big questions in my mind: 1. If the loss of ADSB corresponds to the E1/E2Fuel Cutoff switches being moved from RUN -> CUTOFF, why is the airspeed declining for the prior 4 seconds? 2. In 4 seconds, why is there only 50ft of altitude gain? that seems odd. 3. To account for only 50ft of alt gain, if we assume the 1st reading is on the runway just before rotation, the intermediate +25ft alt gain is at rotation (Nose up but MLG still on the runway), and the last 4 readings are in the air (nose up an additional 25ft), that means that 1 second or less after lift-off, ADSB was lost - this is before E1/E2 FCO RUN-> CUTOFF. It's just weird . The widely watched video shows a very normal initial rotation and climb. |
| appruser
July 18, 2025, 03:43:00 GMT permalink Post: 11924815 |
I am not sure why 50 feet in 4 seconds seems odd right after liftoff in a heavy aircraft. That corresponds to 750 FPM. Seems entirely normal to me. The rate would have been increasing as the timeline advanced. I would also point out that RAT deployment verses the rat coming online fully are two different times. When that RAT is singled to deploy it bangs out nearly instantly. It begins producing its rated electrical and hydraulic power sometime after deployment.
The widely watched video shows a very normal initial rotation and climb. Since the preliminary report states E2 cutoff after 3-4 seconds after lift-off, if that cutoff corresponds to ADSB interruption and which itself was only transmitting for 4 seconds, then 50ft after liftoff is a bit anemic? But if we include the first 25ft after rotation but before lift-off, then, because the ADSB duration is only 4 seconds, it means that ADSB was interrupted before the E2 FCO operation. I don't know if there is a sliding window - part after rotation, part after lift-off that might meet all of these constraints. That still leaves unexplained the declining airspeed seen in the ADSB data... did prior discussions on the ADSB data cover this? is there a good explanation? Last edited by appruser; 18th July 2025 at 04:03 . Reason: fixed heights |
| Mrshed
July 18, 2025, 05:07:00 GMT permalink Post: 11924844 |
Apologies for the delay in responding to your posts. I see that you and others have stepped in, thanks.
I think for various reasons the ADSB data's absolute values are offset by some amount, for possibly all of the parameters. But there should be consistency in the deltas for the timestamp (by receiving station), the raw baro altitude, the Flightradar24 AGL values, and the airspeed. Flightradar24 themselves note that for altitude " ... the data is not above ground level, but it is consistent to itself." 08:08:46.55 ... 575ft ... 21ft ... 184kt 08:08:48.14 ... 600ft ... 46ft ... 179kt 08:08:48.61 ... 600ft ... 46ft ... 177kt 08:08:49.01 ... 600ft ... 46ft ... 177kt 08:08:49.46 ... 625ft ... 71ft ... 177kt 08:08:49.92 ... 625ft ... 71ft ... 174kt 08:08:50.39 ... 625ft ... 71ft ... 174kt 08:08:50.87 ... 625ft ... 71ft ... 172kt From the Preliminary Report's airport cctv picture, the RAT was seen deployed at, by my estimate here , 150ft baro altitude, between 4-7 seconds after rotation. So the ADSB readings have to be prior to that. What's interesting is that the ADSB data covers: - 4-5 seconds of time (let's approximate 4 seconds from 46.55 to 50.55, ignoring the 0.32s for the moment) - 50ft of altitude gain - Declining airspeed from the 1st reading to the last in this final segment from the runway. Big questions in my mind: 1. If the loss of ADSB corresponds to the E1/E2Fuel Cutoff switches being moved from RUN -> CUTOFF, why is the airspeed declining for the prior 4 seconds? 2. In 4 seconds, why is there only 50ft of altitude gain? that seems odd. 3. To account for only 50ft of alt gain, if we assume the 1st reading is on the runway just before rotation, the intermediate +25ft alt gain is at rotation (Nose up but MLG still on the runway), and the last 4 readings are in the air (nose up an additional 25ft), that means that 1 second or less after lift-off, ADSB was lost - this is before E1/E2 FCO RUN-> CUTOFF. It's just weird . |
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