osiris30 wrote:flybucky wrote:I wasn't satisfied with the FR24 charts I had seen because:
1. the x-axis was by data point and not true time interval
2. most of them put several data series that had vastly different number ranges on the same chart, which reduced the "resolution" of the y-axis.
So I made a chart that used true time intervals on the x-axis (seconds elapsed since airborne). This makes it easier to look for time interval patterns. Also, I plotted the Pressure Altitude relative to 7200 ft (which is the first Pressure Altitude reported after airborne). That fits it on the chart better and also gives a good approximation for altitude gained since takeoff. Finally, I used a secondary y-axis for ground speed so you can see the resolution better.
Some observations I had:
- Vertical speed already dropped between 7-10 seconds after airborne, and did not recover until the 20-25 second mark.
- Ground speed increased very steadily, which seems to indicate no engine problems? (Ground Speed should be accurate even if the airspeed sensors on the plane were unreliable, since the Ground Speed is based on GPS).
- I looked for 10 second Vertical Speed decrease intervals. It does look like there could be some at 51-61s, 72-82s, 91-101s. But the Vertical Speed decreases started before 51s. And there were also additional decrease intervals afterwards that were not 10 seconds.
Something was VERY wrong on this flight. IF the FR data is right they rotated at 89kts... Based on what I see in the data they basically took off stalling.
At 89 kts the airplane would probably not be capable of producing the lift to takeoff. They would have kept rolling nose up (trying to rotate) until the airplane gained enough speed to lift off. Then they would have been on the edge of a stall in a very unstable flight regime at low altitude.
If this was the case, it is possible that MCAS had nothing to do with the accident, and it was simply unreliable airspeed/pilot error. An airspeed discrepancy during the takeoff roll would in my opinion justify an aborted takeoff. That is why there are “cross check” calls at either 80 or 100 kts between CA and FO airspeed indications.
The FR24 data may very well be inaccurate and they rotated at the correct speed. Still, how would MCAS operate with flaps down? Perhaps a faulty airspeed indicator triggered the MCAS somehow. Is it only the AOA sensor or does MCAS monitor airspeed as well?