I’ve agonised for a couple of days whether to post this question because having read all the posts on both this and the Lion Air thread, I’m very aware of the understandable annoyance the professional pilots and qualified aircraft industry types on this forum feel when posters are too lazy to read or even search for answers to a question which has been asked perhaps several times before, or ask dumb questions. But, as explained below, I’m very puzzled, I don’t think my question has been asked so I’ll risk being flamed.
It seems to be accepted that there are such similarities between the Indonesian and the Ethiopian crashes that – I suspect – a lot of people are assuming the cause of the accidents will also be similar. However, one difference between the two crashes which doesn’t appear to have aroused all that much speculation, at least as far as I can determine, is the fact that the Ethiopian 737 only managed to get to perhaps 1000 feet (according to Flightradar24), whereas the Indonesian 737 appeared to achieve 5000 feet and the pilots consciously settled for that altitude.
This is where my non- aircraft background becomes apparent and the reason for my question; which is basically what caused ET 302 to be unable to get above 1000 feet? My simplistic flying control knowledge can think of only two things which might be possible causes. (Ignoring engine problems as the Flightradar 24 data indicated airspeed was increasing throughout the flight). One problem could be with the flaps which are extended to give extra lift on take-off, so presumably not having them extended fully, or to the extent required – particularly at an airport with the elevation of Addis – would make the aircraft really struggle. But this is really very basic and surely would have been recognised very quickly and remedied. The only reason I suggest it is that flaps not extended is supposedly a parameter for MCAS to function.
The other reason for inability to gain altitude would be for the stabiliser to be trimmed in a way for it to be forcing the nose down – supposedly the faulty AoA/MCAS scenario which is suggested caused the Indonesian 737 crash. An argument against this being the cause is that it has been said in posts on this forum, but without actual proof as far as I have seen, that there is a low altitude limit below which MCAS does not operate. If 1000 feet is classed as low altitude, I don’t know what is.
This brings me to a point which was raised on this thread a long while back as to whether a coding error could have been made when the altitude limit (if it existswas coded into MCAS, and which would only be manifest at a high altitude airport like Addis (eg ASL used instead of AGL). Pretty basic error IF it was I know, but I’m reminded of the Mars Climate Orbiter fiasco in 1999
“A NASA review board found that the problem was in the software controlling the orbiter's thrusters. The software calculated the force the thrusters needed to exert in pounds of force. A separate piece of software took in the data assuming it was in the metric unit: newtons."
Again, apologies for probably dumb questions and a lack of knowledge which probably has eyebrows raised and heads shaken in disbelief, but I would appreciate it if anyone could be bothered to answer, or preferably offer more soundly based reasons.
Regards