Originally Posted by
Denti
The fail operational 737 can continue the autoland with a complete groundstation failure (loss of ILS/GLS signal) below 200ft (alert height). However, it might not be able to completely cover sudden changes in wind direction and therefore a go around is advised. We tried it in the simulator though and even a windshift of 25kts crosswind from one direction to the opposite, basically a 50kts wind shift in less than 50ft, did not lead to a displacement of more than 8m from the centreline.
Haven't tried it in the airbus yet, but a loss of G/S signal above 100ft or a loss of LOC signal above 15ft lead to a red autoland light which requires a go around.
Any chance that you could let me know where I can find a written reference for that
Denti as I can't find it in the 737 FCOM? As you say the Airbus is quite specific in detailing its triggers for an autoland warning below alert height whereas Boeing seem to be a bit more vague. I'm an SME in the world of ATPL training and EASA have an exam question which asks what you'd do if the glideslope signal was lost at 80ft on a fail operational autoland approach. Clearly the A320 would have no problem as it wouldn't trigger an autoland warning but allegedly ( according to EASA) the correct answer is 'a warning will be triggered and a go around must be initiated'. I suspect tthat this is because the EASA learning objective states:
'Describe typical failures that, if occurring below the alert height, will trigger a warning: all autopilots disengage; loss of ILS signal or components thereof; excessive ILS deviations; radio-altimeter failure. Having already dismissed this as bo**ocks from an Airbus persepective I'd like to do the same for fail operational equipped 737's.