Originally Posted by
BuzzBox
I'm not sure - Honeywell says that envelope modulation is used at certain locations to either expand the Mode 4 envelope for improved alerting, or to desensitise it to prevent nuisance alerts. However, the only Boeing reference I can find says that envelope modulation lowers the radio altitude limits to prevent nuisance alerts.
Classic Boeing, dumbing down the manual to what we ‘need to know’
