Recently we've had the 737-MAX debacle, where it increasingly appears that the MAX on-board MCAS system repeatedly would issue nose-down events, leading to the Lion Air crash, and possibly another
On the Lion Air flight, when the MCAS pushed the jet’s nose down, the captain pulled it back up, using thumb switches on the control column. Still operating under the false angle-of-attack reading, MCAS kicked in each time to swivel the horizontal tail and push the nose down again.
Apparently there is a notification light for MCAS that was an optional package but will now be required.
It reminds me of two other incidents that lead to crashes
- Air France 447 A330 - A frozen pitot tube caused the computer to switch to Alternate Law 2, which meant that the computer would no longer prevent dangerous flight inputs. While not the same as the MCAS issue, it lead to confusion of the cockpit crew (who had been making maximum nose-up inputs while at TOGA power), and thus the plane crashed due to stall. It was noted that there was nothing direct to alert the pilots that the switch had occurred.
- Scandanavian Air 751 MD81 - Ice accumulated on the wings. When the plane took off, the ice fell off, striking the engines. The pilots noted the engines were surging and reduced the throttle, but an auto-throttle system not disclosed to the pilots kept increasing power back to full, thus causing engine failure and a crash landing.
Has anyone ever stated why aircraft systems are allowed to make changes without notifying the pilots? Is it something that just hasn't been a large enough problem to address until now?