Posts by user "jdaley" [Posts: 7 Total up-votes: 6 Pages: 1]

slf/ppl here - with a respectable amount of experience in software delivery for real-time/embedded/safety critical systems. Software development in this area really is an engineering discipline and bears no resemblance to common practice in other areas. Couple that with the requirements for function duplication/triplication, harness separation et al then IMHO the chances of FADEC etc software errors are effectively zero.


I'm commenting to make that point but also to link the videos and the FR-24 dataset - (below with my deltas for height/time added)



Extract from FR24 csv dataset


As noted in both threads to date everything was normal until it wasn't - the two values for fpm above are subject to FR24 variance of +/- 25' so even these suggest a normal climb at this stage of flight ca 2,000fpm. FR24 Lat/Longs all follow the centre line.


On this data the climb stops at around 70' AGL and electrical failure around 2s later. Again, as noted in the threads, this aligns with when gear up might have been expected. If the climb stopped because of fuel shutoff then 2s for spool down to electrical failure isn't out of the question.


Looking at the two videos.

The CCTV video indicates a total flight time, from rotation, of about 32s, subjectively levelling off ~14s after rotation.

The rooftop video has a flight time ~14s suggesting the video starts ~18s after rotation.


The rooftop video evidences the RAT as deployed from the beginning - meaning it must have been deployed by at least 16s after rotation - which aligns with the ADS-B indicated electrical failure.


If the forward flight recorder really is being sent to the US for recovery then it's reasonable to assume that the rear recorder contains nothing after the electrical failure and they are hoping the forward recorder captured something from the cockpit in the final 16s.


I don't have any experience of flight deck CRM but I don't see how those timings allow problem identification/misidentification and subsequent action - ie it wasn't down to the crew.


However:

The maximum aircraft height in the CCTV video, as judged by wingspan, appears higher than 71' - though it is certainly less than a wingspan height at the beginning of the rooftop video.


I haven't seen, in the threads, any statement of what happens on the flight deck with a total electrical failure - is it a 4s blackout whilst the RAT deploys and systems restart? - or are there batteries that keep something alive?

FR24 has the GPS lat long position at each time - ground speed is then simply distance travelled over the time interval. The METAR quoted 25007KT and that should increase with height hence the nominal decrease in ground speed over the later ADS-B values - and probably the slight drift off the centre line once airborne.

An earlier poster defined the 787 ADS-B transmits with a height granularity of 25' - which explains the FR24 figures and I might posit that it was just about to transmit a 25' height increase when the electrical failure occurred.

The rooftop video records a nominal 14s flight time with RAT out throughout.
The CCTV video records a nominal 32s (from rotation) and subjectively the aircraft stops climbing 14s after rotation - meaning 18s of descent of which 14s are captured in the rooftop video.

If we accept the RAT is out then it must have been deployed about 12-16s after rotation, presumably immediately after the 4s of ADS-B data.

Another post referenced the RAT only supplying electrical power after 10s - I find that hard to believe, not instant obviously because there has to be some stabilisation time and startup/boot time but it would imply the LH flight instruments would only be active very late. Hopefully the RAT hydraulics would be effective quicker than that.

That doesn't seem to be contradicted by the only data we have - computed bearings, allowing for GPS error margins don't show any lateral course change after rotation.

computed bearings from ADS-B positions

Given the ADS-B height figures are reported to have a granularity of 25' it's compatible with the video to assume a height around 90' at the last ADS-B data point. A simple ballistic calculation - speed 88m/s (171kt), 11degrees, 30m height, results in a maximum height of 145' - given the impact of aerodynamics the observed height in the video isn't in dramatic disagreement - ie it's possible nothing interrupted the flight path after rotation.

Given the clearer land 100' to the left of the flight line the "in out of controlled flight" is sadly very feasible.

ADS-B stops 330' from the end of the runway, well before top of climb. A previous poster stated that ADS-B granularity on the 787 was 25'. As the aircraft obviously climbed higher than 71', it's reasonable to assume that ADS-B was about to transmit 96' when the electrics failed. Looking at the CCTV, subjectively, the aircraft reaches the height of a wing about 7s after rotate and top of climb about 7s later.

understood - I quoted one wing as an approximation to 96' ie the height at which electrics had disappeared. Top of climb was ~7s later when it appeared to be at least a wingspan high.

hear, hear.

Subjectively the aircraft continued climbing for ~7s after the last ADS-B value, achieving around 200'. 7s at say 160Kt is 574m.
The last ADS-B point was 1.6km from the hostel so the descent was around ~1km from ~200' an 18:1 ratio.

L/D of 12 would have needed the aircraft to be at 270' 1km out, 13 needs 250'.

The cctv neither confirms nor denies that top of climb could be as high as 270'. My 1km/200' estimate was conservative. I guessed 160kt average over the 7s to allow for the 25007 wind
and some deceleration.

Basically you cannot rule out loss of thrust around the time of loss of electrics.