A320 ALERT HEIGHT : from theory to practice
After having read all the definitions and explanations on Alert height as given in the relavent Airbus Manuals ( not really pilot friendly ) I am trying to decide whether or not I fully understand the precise concept .
As far as I understand, Alert height is nothing more than a Airbus defined cut-off value . The is nothing system related , when we talk of AH. The value chosen by Airbus ( in the case of A320F being 100ft RA) it is just a value that Airbus accessed as being safe to ignore any single failure (relating to systems that affect the auto land capability) and continue for a CAT 3B auto-land. The 100ft RA being a value that from a probability point of view it’s almost impossible to have another failure till touchdown affecting the auto land system .
Assuming I gave the explanation of the concept of AH correctly , then why is it that from the moment the AH is set at 100 ft , Airbus system logic freezes the landing capability at 200ft? ( that is to say if you had a single failure below 200ft RA , CAT 3B would still be indicated . )
Shouldn’t that be occurring at or below 100ft RA?