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Radio / radar altimeter applications on turbo props

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Bernoulli

Well-known member
Joined
Jan 4, 2003
Posts
227
I know the main reason for a radio altimeter is for doing Cat II and Cat III aproaches. My question is: why do most twin turbo props that are unable to do a Cat II or Cat III aproach have a radio / radar altimeter? Is it just for a back up for putting in the wrong altimeter setting into the kollsman window... or maybe it's a required instrument for GPWS??? If it is not what I listed above how would you use the radio altimeter on a light twin turbo prop? thanks in advance.
 
I don't know that they can't do Cat II and III, but many aren't equipped or trained. EGPWS still uses RADALT, so it's gotta be on the plane, anyway.

I think many planes display it, but don't really use it.
 
After being furloughed from an airline that does CAT III C's, and now flying a Cessna 421 with a RA, I like having one more backup to telling me where the ground is. It is incorporated into my scan. Gives you a good idea if the ground is a little too close.
 
Some planes use it as a safety device to arm systems like reversers, anti-skid, etc...

-Also, a lot of aural warnings are delayed or inhibited below a certain altitude, to prevent distractions.
 
So if you were flying a non cat II / III airplane that had a radio altimiter, and you were flying an approach, would you dial in an altitude like MDA or just keep it on zero and keep it in your scan?
 
So if you were flying a non cat II / III airplane that had a radio altimiter, and you were flying an approach, would you dial in an altitude like MDA or just keep it on zero and keep it in your scan?

PDTs Dash's have radio altimiters, and all the required equipment for CAT II approaches - but the pilots are not trained to do CAT II. We leave the DH/MDA set to zero and the RA is really just additional information.
 

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