Question to engineers/system designers/knowledgeable 73NG pilots:
- Is there no redundancy for the radar altimeter? If yes, why does the FMGC not use it?
- Why is rad alt the only source of truth? What about 'classical' alt (and it's five redundancies), GPS alt, DME distance (should be on any ILS no?), IRS alt etc. etc.??
Shouldn't the A/P and A/T disconnect if any of these sources do not reconcile??
If the autopilot only relies on rad alt without considering any other parameters, this accident shows quite a shocking design weakness, no? I would understand it on the 737 prototype, but the NG?
Please enlighten the rest of us...
B737/200/300/400 were part of my school, specially the /200. As I remember it, they had FCC's, which is problably what you were referring too, but I may be mistaken.
The LRRA antennas, mainly due to the position they must be installed, have a way shorter reliability than the computers. One can install that kind of redundacy, but than you would have to make it compatible "inter-systems", meaning AP1 would have to be able to use either RA signal. Given the usual complexity of an LRRA functional test (usually requires ramp testers), that would very much enlarge the amount of time needed to troubleshooot any AP failure (because you would have to check that), Airlines and their associations (e.g. AEA) tend to see that as not necessary and lobbie as such. (meanwhile, lifes are lost)
And no, the LRRA signal is not the only one, and any of the others would kill the AP also.
I guess we will have to wait for more conclusions, for example, was the GPWS working? The Bar ALT ALERT should also give some sort of warning...
These things usually happen when a series of factors are saidly combined.
Mercy on their souls