# Alex - 80' mentioned in the AMM b777. For ARINC installations, standard AIDs are 20, 40, 57 and 80 ft depending on the size of the aircraft. The B-737, for example, uses a 57 foot AID. Thanx for your reply. With regards to your answer 3 whether in a calm lake/surface water will the radio altimeter give correct height over water, may I ask any reference to that for b777?
# pattern - appreciate your input. I am pretty sure both a/c altimeters read exactly 29000/31000 it was a company b777 and there was no TURB. I have never seen a continuous cruise flight on a 777 with primary altimeters reading even 10 feet different than what's set on MCP. My assumption has no technical backing but AID is always subtracted from the measured reading. So 1920 was too much of a co- incidence hence the doubt
I wouldn't rule out any other possibility as you mentioned but intention is to dig deeper until proven wrong if possible.