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I ask as a dilettante, so please feel free to correct or emend this.

I transcribe the radio altimeter enunciations for https://www.youtube.com/watch?v=Vr-0LiQA6wo:

0m 21s: 400

0m 23s: 400

0m 36s: 100 above

0m 41s: 200

0m 49s: 100

  1. Are the radio altimeter verbalisations part of the Ground Proximity Warning System?

  2. Why was 400 uttered twice? Isn't the A380 descending?

  3. Same question for 100 at 49 s, compared with 36 s?

  4. What does the above imply?

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up vote 12 down vote accepted

"Four hundred" was likely annunciated twice due to a bit of a dip in the terrain that would cause it to pass the 400ft level twice. The "hundred above" call-out is for 100 feet above decision height to let the crew know they will need to make their decision soon to either continue or go around. After that, you hear the "two hundred" and "minimum" call-outs right after one another. The "one hundred" call-out afterwards signifies 100 feet above ground level.

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The radio altimeter callouts are indeed based on the actual terrain before the runway threshold, so if there was a little delve before the threshold, the 400 would be called twice. You can edit your answer to reflect this. – SentryRaven Aug 4 '14 at 10:07

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