How would you get an altimeter settings in IFR lost COMM?

z987k said:
For no VHF coms in IMC, approach to mins? I'd certainly set DH.
Click to expand...

Unless the approach specifically calls for use of radar altimeter, it's not the best way to determine minimums. I don't trust mine too much...

My airplane can't set DH... It can set DA or MDA, which gives me a minimums call out predicated on altimeter reading.
 
cencal83406 said:
Unless the approach specifically calls for use of radar altimeter, it's not the best way to determine minimums. I don't trust mine too much...

My airplane can't set DH... It can set DA or MDA, which gives me a minimums call out predicated on altimeter reading.
Click to expand...
The radar altimeter works pretty well right at DA. Anything else and it's not trustworthy because the terrain can be going all over the place.
You have a radar altimeter and can't set DH? That doesn't make a ton of sense unless I'm not understanding something.
On mine I can set it to call out DA/MDA off of the barro altimeter and I can set DH off the radar altimeter and it will give me a light.
 
Option 1 - Use my battery-powered handheld radio
Option 2 - See if my tablet's data plan will connect to grab the latest METAR
Option 3 - Use last available, and consider reports I got during preflight and the location of any pressure systems to consider a need for extra padding on DH/MDA if a low was moving in that might put me in the dirt.
 
If I was going someplace remote - a la Adak, and didn't have ADS-B or couldn't use TWEB, I'd use GPS altitude until the radar altimeter came alive.
 
Use an ILS ground based with vertical guidance, if the middle marker and outer marker are working, those are known alts on the glide slope and you can get a rough number at those points... and radar altimeter...
 
z987k said:
The radar altimeter works pretty well right at DA. Anything else and it's not trustworthy because the terrain can be going all over the place.
You have a radar altimeter and can't set DH? That doesn't make a ton of sense unless I'm not understanding something.
On mine I can set it to call out DA/MDA off of the barro altimeter and I can set DH off the radar altimeter and it will give me a light.
Click to expand...

We have a RA. All we have ours for is for call outs 1000, 500, 100, 50-10, as well as for EGPWS. There is no way to set "DH" on the RA in my aircraft. We use MDA for precision/non-precision and DA for CAT-II.
 
I feel like this was an instrument written question? Answer found in the Instrument Flying Handbook?
 
If I was truly NORDO (including ForeFlight and cellphone), I'd head to the best-weather, in-range airport that I had in my briefing. The circumstances would be rare that EVERYTHING in range was at mins, and therefore critical for you to have an accurate altimeter setting.
 
For the radar altimeter technique- fly over a known point (a navaid) and add the radar altimeter reading to the known elevation. Should be close. Military teaches this technique (called "combat" altimeter setting).

I would still recommend using the preflight altimeter, unless you know a front has blown through. Preflight is likely to be right <100'....the "combat" altimeter setting is more likely to have >100' error, depending on how reliable your radar altimeter is and the variation in the terrain.
 
Last edited:
You must log in or register to reply here.
Back
Top