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I just saw a YouTube video with an A340 landing. There were the regular altitude callouts (1000, 500, etc.) until the callout "110". I was quite puzzled by this.

What are the conditions that the automatic callout would call "one hundred and ten" instead of one hundred?

Parenthetically, I'm almost certain - though I can't recall the details right now - that I've also heard a callout "seventy" in some other video, possibly with another plane type.

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From the same channel and also an A340 at 4:26 in this video the standard '100' can be heard.

The reason is a built-in timeout, if a certain time elapses between callouts—say due to non-standard [shallower] descent rate, perhaps due to high headwind for example—the current height is called out. In other words, you get to hear a callout at regular intervals.

From an A340 manual, here is the bit about the intermediate callouts:

enter image description here

Just a bit of history: one of the early TAWS systems (Mk II I believe) had a rising tone instead of the 100, 50, etc., you can watch it here.

Note on terminology: those callouts are heights (radio), not altitudes (barometric).

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    $\begingroup$ What a great answer, cheers! $\endgroup$
    – user12873
    Jan 1, 2018 at 5:02

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