Originally Posted by
Water pilot
I have a very strong feeling that the designers of the MCAS programming had no idea of the effect of speed upon the forces required to move the stabilizer trim, indicated by the fact that they slightly changed the algorithm to account for speed sometime during the certification process.
Not sure on that, might not even have been the same people. If what we have heard on this site is true, MCAS was originally designed and implemented only for high mach numbers (and possibly documented - some sites show Boeing documentation stating: "
The MCAS only operates at extreme high speed pitch up conditions that are outside the normal operating envelope.").
The original designers may have done calculations for high speed and less trim authority and found it was ok.
The "extreme high speed" regime is probably also the reason why MCAS apparently has no altitude dependency, since as-designed it would only engage at high altitude. Erroneous activation at low alt is clearly more hazardous, but possibility of AOA
and IAS failing high, to give erroneous activation at low alt, might be suitably remote (despite the slight dependency in the ADIRU).
Later on in flight testing, a problem was found at low mach as well, so someone decided it should activate there (and therefore possibly at low alt), and with much more authority.
That change quite possibly didn't require code changes, just configuration data. The sort of change you
can get an "intern" to do... in fact the more junior the team member you can find the better - junior staff tend to bend awfully (and understandably) easily when leaned on from on high.
Did they redo the entire safety case for the new activation regime and authority levels and then just "forget" to update the certification documents, or did they "forget" to update a lot more than the cert docs? Did they just decide that the late discovery that the dynamite packing cases had a few screws missing wasn't a problem because they had a fully certified hammer, they'd just have to hit them a bit harder?