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Newsgroups: comp.lang.ada
Date: Thu, 18 Apr 2019 08:07:00 -0700 (PDT)
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Subject: Re: Boeing 737 and 737 MAX software
From: tranngocduong@gmail.com
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Xref: reader01.eternal-september.org comp.lang.ada:56156
Date: 2019-04-18T08:07:00-07:00
List-Id: <comp.lang.ada>

On Thursday, April 18, 2019 at 8:50:27 PM UTC+7, Simon Wright wrote:
>=20
> > In the crashed Ethiopian 302 aircraft, ~30 seconds before impact, the
> > nose points 40 deg. toward ground, and the AoA indicates 75 deg. As 40
> > + 75 =3D 115 > 90 deg., this would imply negative airspeed.
>=20
> I think that if it implied anything it would be that the speed over the
> ground was negative and the aircraft was descending extremely
> rapidly. Neither of which is impossible.

The 115 deg. is the [elevation angle of] airspeed (i.e. speed of the aircra=
ft relative to the air), not groundspeed (ie. relative to the ground). That=
's because the AoA is the angle between the aircraft and the airspeed.=20

It is true that even airspeed can be negative. Negative airspeed is not exc=
eptional for acrobatic and fighter aircraft. For the 737 however, that woul=
d be an exceptionally unusual situation.=20

Unusual enough to believe that a sensor, most likely the AoA sensor, failed=
. Enough to disable all AoA sensor-based flight control algorithms, such as=
 the MCAS. Enough to trigger an alternative algorithm, raise an alert, or c=
ompletely disengage the flight control computer.

>=20
> But, as Maciej hs been saying, what makes you think that this
> caluclation was ever performed?

I don't think so. I think that the software must perform many redundant cal=
culations similar to this one. Sensors and flight computers are redundant, =
just like hydraulic systems and control surfaces. This calculation demonstr=
ates that redundant calculation can help detect possible sensor failure eve=
n without a second AoA sensor.