Rad alt missed call

[applecrumble]

Does anyone know why the radio altimeter sometimes misses a call? For instance it won't say "50" or it won't say "two thousand five hundred".

[Dougie_diesel]

Is there perhaps a higher priority call-out at the same time?

A/P disconnect for example?

[Skyjob]

Depends on make/model.
B737 omits certain calls when there's a such closure rate which would prohibit it making its next call...
This could be due rising terrain under the approach path or the obvious high descent rate...

[CCA]

Rolling from a reasonable bank turn to wings level also can cause the Rad alt to omit the call, noticed several for the 2500' call while descending in a turn.

[applecrumble]

Originally Posted by Skyjob

Depends on make/model.
B737 omits certain calls when there's a such closure rate which would prohibit it making its next call...
This could be due rising terrain under the approach path or the obvious high descent rate...

So this is to prioritise the next call in a way?
The 320 does the same

[underfire]

I seem to remember there is an option, depending on the system and airline, as to the frequency of callouts below certain altitudes.

2500, 500, 40, 20, 10...
reference altitude for the +100 and Minimum call outs for precision approaches (DH) and baro altitude (MDA/MDH) for non precision approaches.

There are Smart 500 and Hard 500 options as well, depending

[Piltdown Man]

Ours misses calls very regularly. The most common one missed us 2,500. The next is the 500' call. To date, I do not recall the 50, 40, 30 etc. calls ever being missed.

[applecrumble]

Originally Posted by underfire

I seem to remember there is an option, depending on the system and airline, as to the frequency of callouts below certain altitudes.

2500, 500, 40, 20, 10...
reference altitude for the +100 and Minimum call outs for precision approaches (DH) and baro altitude (MDA/MDH) for non precision approaches.

There are Smart 500 and Hard 500 options as well, depending

What is the difference between smart and hard 500?

When I noticed it I was in a turn, rolled out of the turn and the 2500 call was missed.
In our airlines pin programme the next call is 1000. I presume rolling out of the turn and then having the rad Alt pointing directly down instead of at an angle showed a sudden rate of descent and so the system doesn't call 2500 so it can call 1000. Presumably at that rate of descent it decided by the time it has said "two thousand five hundred" you would already by at 1000.

[Jwscud]

The "smart 500" call is only given under certain conditions - at my previous airline it only came if you were not receiving ILS signals, i.e. Only on non-precision approaches. In my current airline we get a "hard 500" on every approach.

[Skyjob]

500' calls can be programmed to be used only when flying non-ILS approaches.
The 2500' can be suppressed but should sound when rad alt becomes first active, this sometimes can be prior to the 2500' on approach. In turns, if 2500' is reached/lost, this can confuse the logic, as the duration may not be long enough to trigger the aural, similar how it is inhibited when an aircraft passes exactly below for a short duration of time.

[underfire]

There can be 3 options for you to select in the box, depending on the make/options. Some of these are on different menus in the box, and not necessarily active globally.

'Hard 500' call option selection is for all approaches, with 'five hundred' announced once.
'Smart 500' call option selection is for non-precision approaches. 'five hundred' announced with other altitudes.
'500 above field' option selection. This call is based on GPS altitude, not rad alt.

[Jwscud]

My favourite radalt call though is the "1000" you sometimes get on airways passing directly overhead opposite traffic

[Kerosine]

No-one likes hearing "50, 20" on the flare. It very very occasionally misses the "30" if closure rate is high.

[applecrumble]

I think I can guess which carrier you fly for based on which numbers you have written there. Does your airline not have a 40 call?

So to summarise, it happens due to a high closure rate which would make it unable to make the next call; so the logic omits the current call.

[Escape Path]

Funny enough, I've never heard it miss the retard call...

I've noticed the A320 can call 2500 once, but if terrain is irregular and radio altitude goes above 2500 after initially triggering the radio alt, it won't call 2500 again