Originally Posted by
Uplinker
Not automatically descending just because you have reached the computer predicted descent point, is a good thing. ATC might have denied descent clearance - there might be something below you, which the aircraft would hit if it descended without a pilot's say so. The decelerate message is to try not to get too far above the profile.
The approach mode engages automatically when you are in managed nav and you fly over the decelerate icon, the "strawberry", some call it. If you are flying vectors using heading, approach mode will not automatically engage - again, another safety feature, requiring the pilots say so before starting an approach.
Both these functions make perfect sense to me because the aircraft does not know everything and cannot make such decisions on its own. And I think one has to rely on at least one pilot being professional, engaged and awake in commercial operations, otherwise we might as well all give up and let Mr Musk or someone build us pilotless passenger aircraft.
Proper training. Proper testing of pilots. Following proper SOPs and proper CRM does work. We know how to do this now. It is very sad that in 2020, aircraft are still continuing unstable approaches and crashing.
Of course proper training and testing is relevant.
That said, it is interesting that a 737, even a classic, can automatically switch into the approach phase even on vectors, and does of course descend automatically if a "descend when ready" clearance has been given and the lower altitude has been selected on the MCP (or FCU in airbus speak). It simply makes life easier for the pilot. Of course it does not follow the managed descend profile blindly without a clearance entered into the aircraft system.
Probably quite irrelevant in this instance, but i have been caught out by it, so have many pilots that have switched from boeing to airbus. The airbus requires extra help to do simple stuff, it is in many ways quite old fashioned. Does it explain this case? Obviously not, but it could be a tiny part of the chain.