Radar Altimeter: no where to go

Guest Discussion
1

Radar Altimeters measure the plane’s altitude above ground level (AGL) directly by bouncing a radio wave off of the ground and measuring the time it takes and turning this time into a distance. They are normal on transports and unusual in small GA A/C. I feel they are underrated. Both King/Bendix and Collins make units for the GA market and both cost about $3k before installation.

Question: what are people’s experience with Radar Altimeters? Perhaps there’s some limitation I’m not familiar with that makes them so rare.

Question: where would one put the indicator on the SR22 panel? (it fits in a standard instrument hole) It seems like Cirrus thought they had given us everything they could ever want … but certainly they haven’t. It would be ideal to put the information from the RA on the big Arnav display, but that would require cooperation from Arnav.

I’ve thought about taking the analog signal from the RA unit and turning that into a synthesized voice which calls out altitude like a GPWS (Ground Proximity Warning System) in a transport A/C. But I’d prefer a canned solution. Also, is there some provision in the Garmin audio panel for audio annunciators? One could always use another speaker and just blast it out into the cabin loudly enough to get through the headsets. It would have a “quiet” button.

I know about EGPWS and the GA versions which use GPS, altitude, and a terrain database to give something which theoretically is even better than a radar altimeter. I’m all for this kind of thing. However, as far as I know, this is not available yet on the Arnav, the 430’s, or the Sandel EHSI. Also, I believe that the RA will be more accurate and is much simpler. And unless you’re flying in fast planes in steep terrain, EGPWS gives no more warning than good old RA/GPWS.

Thanks for any corrections, insights, suggestions, etc. you folks have.

For a little background on my personal interest in RA’s: my brother botched an instrument approach 20 years ago and got himself killed. Right solution: better training, but a RA would have saved his bacon. My approach: good training and avionics to back me up in case brain fade hits at the wrong time. Good training does not mean one never makes mistakes, etc.

2

From the limited amount I’ve seen in high-end GA (bizjets), RAs take up panel space but don’t seem to get looked at (or turned on much). I believe they are required for Cat II and III approaches, and if you’re landing a 747 they’re handy for helping with the sight picture. They will also light up the “DH” light on a flight director if you have one. I suppose that having one could add a level of situational awareness in an approach but it’s something else thrown into your scan at a critical time.

Regular ground prox is pretty limited, as it just looks down. I know pilots that pull the breaker because it starts shouting at you in the middle of a stabilized approach. “500!” “Minimums!”

Enhanced ground prox is something way beyond RA/ground prox, and it does help even with fast planes and steep terrain, as it paints a picture of the terrain in front of you. I’ve seen it a couple of times and it looks like the right gizmo for the job. It shouldn’t be long before we see this in a GA-priced box, since it can be done with nothing more than GPS, an altitude encoder, and a terrain database. For that matter, the ARNAV has a very crude version of this already included.

This seems like a much more useful thing than a radar altimeter.

3

Radar Altimeters measure the plane’s altitude above ground level (AGL) directly by bouncing a radio wave off of the ground and measuring the time it takes and turning this time into a distance. They are normal on transports and unusual in small GA A/C. I feel they are underrated. Both King/Bendix and Collins make units for the GA market and both cost about $3k before installation.

Question: what are people’s experience with Radar Altimeters? Perhaps there’s some limitation I’m not familiar with that makes them so rare.

Question: where would one put the indicator on the SR22 panel? (it fits in a standard instrument hole) It seems like Cirrus thought they had given us everything they could ever want … but certainly they haven’t. It would be ideal to put the information from the RA on the big Arnav display, but that would require cooperation from Arnav.

I’ve thought about taking the analog signal from the RA unit and turning that into a synthesized voice which calls out altitude like a GPWS (Ground Proximity Warning System) in a transport A/C. But I’d prefer a canned solution. Also, is there some provision in the Garmin audio panel for audio annunciators? One could always use another speaker and just blast it out into the cabin loudly enough to get through the headsets. It would have a “quiet” button.

I know about EGPWS and the GA versions which use GPS, altitude, and a terrain database to give something which theoretically is even better than a radar altimeter. I’m all for this kind of thing. However, as far as I know, this is not available yet on the Arnav, the 430’s, or the Sandel EHSI. Also, I believe that the RA will be more accurate and is much simpler. And unless you’re flying in fast planes in steep terrain, EGPWS gives no more warning than good old RA/GPWS.

Thanks for any corrections, insights, suggestions, etc. you folks have.

For a little background on my personal interest in RA’s: my brother botched an instrument approach 20 years ago and got himself killed. Right solution: better training, but a RA would have saved his bacon. My approach: good training and avionics to back me up in case brain fade hits at the wrong time. Good training does not mean one never makes mistakes, etc.

I have looked at the possibility of putting a Radar Altimeter in the SR22. My prior inquiries

to Cirrus indicated they had no information on any Radar Altimeter installation.

There are a series of Radar Altimeters made by Trimble that use the small rectangular format display which is the same size as the altitude preselect for the STec autopilot. I don’t know enough about the panel space available to know if that could be fitted in on the left side of the SR22 panel.

The Trimble unit is about $3500 or so. It has a digital display and will display AGL altitudes beginning at 2500’. You can set DH and the DH display consists of a light on the display unit when the set DH is arrived at. As far as I know, it will not support any audio announcements. I sort of doubt that Cirrus would handle the installation. I think it would be a great asset. I would like to have all of the information available, and information on the actual AGL altitude would certainly be helpful.

While on the subject of additional instruments, another good possibility would be a backup attitude indicator. BFGoodrich Avionics makes a 2 1/4" backup attitude indicator, which would fit in place of the OAT/Clock/Voltmeter Davtron unit which Cirrus puts in the top left of the left side of the panel. The backup AI can be installed with a separate battery source charged by the avionics bus, if desired. There would have to be a new place for the OAT/Clock/Voltmeter found on the right side of the panel. I don’t know if this is possible.

Anybody have any specific information on the panel space available for either of these possibilities?