Originally Posted by
TacomaSailor
Non-pilot but expert number cruncher with a basic questions about the DATA shown in post 69 and several prior to that.
Looking at the ADS-B numbers, in ascending time sequence from the start of the takeoff roll at 05:38:01Z, I see:
18 seconds with 0 elevation gain (to 7,200') and acceleration from 0 to 93 knots (ETH-302 still on the runway?)
5 seconds with 25' elevation gain (to 7,225') and acceleration from 93 to 105 knots (ETH-302 still on the runway?)
11 seconds with 00' elevation gain (to 7,225') and acceleration from 105 to 154 knots
11 seconds with 25' elevation LOSS (to 7,200') and acceleration from 154 to 183 knots (did ETH-402 try to lift off runway and then settle back on to it?)
14 seconds with 25' elevation gain (to 7,225') and acceleration from 183 to 200 knots
59-seconds after beginning the takeoff roll - the plane was at 200-knots and had gained NO altitude above the runway (based on elevation at 105-knots). Is that possible?
At 59-seconds there could not be much of the ~12,465' runway left ahead of the plane since it had been doing an average of 150-knots (250 fps) for 33-seconds (8,250') and had travelled about 3,000' accelerating in the first 26-seconds.. At what point would the takeoff be rejected? Or is this just a normal takeoff at a hot and high airport?
I assume MCAS could not have been active during the first 60-seconds of the takeoff event.
Originally Posted by
DaveReidUK
The aircraft was approximately 125' AAL (7750' AMSL) at the 59 second point (05:38:59Z). See the profile I posted a couple of days ago, where the altitudes are drawn to scale.
Yes, Dave, that was
an interesting graphic you posted but did not your plots only commence at the end of the runway? Indeed, the 7750' AMSL plot is some 1600 feet beyond the 25L landing threshold if the position reports are to be believed, and due to a fairly marked dip in terrain beyond that per Google Earth, a true AGL may have been nearer 175'. But have you tried plotting the take-off roll? Clearly the simple ADS-B "on_ground" algorithm used on ET302 to determine ground/airborne status was auto-switched to "airborne" earlier in the take off roll when ET302 had not yet actually become airborne as it was only registering 93kts in a possible 10kt headwind. Nothing unusual about the early ADSB switching, but given the confirmatory and accurate ADSB pressure altitudes transmitted thereafter, which seemingly correctly did detect the slight 20 foot rise in the first half of the runway, I found myself asking the same question as Tacoma Sailor about whether a rotation may have been attempted which resulted in that 7250' pressure altitude transmission at 05:38:45Z.798, and the strange 7075' just 1½ seconds later.
Tacoma Sailor also seems to be right with his suggestion that at 59 seconds into the roll, ET302 must surely have been near the end of the runway - indeed (again if the ADS-B position reports can be believed) it seems it was 1600 feet beyond 25L landing threshold and with no paved area remaining beneath it.
There will be eventual explanations for all the numbers, but like Tacoma Sailor, I'm intrigued by those transmitted from the runway.
One question about how the transmitted pressure altitude is auto-calibrated prior to flight. Clearly a complex aircraft like this on the ground at a well charted licensed airfield knows exactly where it is and at what altitude, so does it continuously calibrate itself whilst it is on the runway up to the point WOW and groundspeed, and GPS data tell it it may be airborne?