As commercial GA flyers with Cat I approval we are not allowed to use our RA for anything else but a GPWS sensor.
Presumably, that’s because one can use a RADALT for altitude only at airports where the “quality” of the approach path terrain is documented for that purpose, and that’s only for CAT3 (or Cat 2?), and one doesn’t ever need a RADALT for Cat 1.
What would be nice is to have the landing gear warning interlocked into it, but none of the installations I have seen (which are all KRA10As) have that.
What would be nice is to have the landing gear warning interlocked into it, but none of the installations I have seen (which are all KRA10As) have that.
Enhanced ground proximity warning systems (EGPWS) have that. Everything is connected. But it can be quite a nuisance. Approaching my homebase from the west (runway 07) there is a hill to overfly which regularly generates “too low flaps” or even “too low gear” warnings even if we fly according to our SOPs (configured and stable at latest 500ft above minimum).
Presumably, that’s because one can use a RADALT for altitude only at airports where the “quality” of the approach path terrain is documented for that purpose, and that’s only for CAT3 (or Cat 2?), and one doesn’t ever need a RADALT for Cat 1.
Exactly. Cat I and NPA minima (all other minima as well of course) are defined as heigts measured directly above the runway threshold. In order to get that from a radio altimeter, the terrain in front of the runway has to be level, even and flat for at least half a nautical mile. Otherwise flying by radio altimeter readings can be incorrect, misleading and possibly even dangerous (in case of terrain sloping upwards towards the runway).
But doing the NPA into Narsarsuaq I can tell you a RADALT is very comforting…..
But doing the NPA into Narsarsuaq I can tell you a RADALT is very comforting…..
GPS altitude even more, because it’s accurate everywhere. Radalt is a thing from the past, just like the ADF. As already said, it is still required for Cat II, III and autoland and as part of GPWS but apart from that there is no real benefit.
I remember some years ago, I flew as safety pilot with a former student on a piston twin. During an ILS approach, the “DH” light driven by the radio altimeter illuminated. So as 1000 times before, I looked outside and said “no contact – go around!”. Then the guy wanted to start a discussion “Oh, I think I forgot to reset the minimum from the previous flight, we must be much higher than that”. Had we really been at two hundred feet at that point, we might have hit something… So when such a device is installed and intended to be used, there must be clear procedures to follow (like going around when it says “minimum” and no lights are in sight, regardless of wether it might have been set wrongly), otherwise it is just another distraction in the cockpit.
So when such a device is installed and intended to be used, there must be clear procedures to follow (like going around when it says “minimum” and no lights are in sight, regardless of wether it might have been set wrongly), otherwise it is just another distraction in the cockpit.
Well yes. I think you either use baro alt or rad alt for your minima. Not both.
GPS altitude even more, because it’s accurate everywhere
Agreed and that is how my TAWS-B and synvis work. But I still like to know my actual alt over the ground. I don’t think it is like ADF. ADF is a completely deprecated technology that is inaccurate. radalt is very accurate.
In most modern glass panels you choose either rad alt or baro for the minimums. It has never been suggested to me that I should use anything except the baro mode, nobody teaches the use of rad alt
Radalt isn’t a thing from the past. An aural Radalt callout is a fairly firm and reliable warning that you’re getting close to terrain, and is a vital thing to add to your situational awareness.
Can you elaborate on how exactly one would determine the appropriate callout height in a light GA scenario, Josh?
An aural Radalt callout is a fairly firm and reliable warning that you’re getting close to terrain, and is a vital thing to add to your situational awareness.
Agreed, when it is part of a GPWS system.
I think you either use baro alt or rad alt for your minima.
For Cat I ILS and non precision approaches you use baro alt and nothing else. If you try using rad alt at places like ELLX you have a good chance of ending between the approach lights. On our yearly SIM refresher courses in the UK, the instructors and examiners, who work as by-the-book as possible, always insist on us turning the RA minimum off.
I’m not sure how much latitude you have in programming voice callouts through say a G500 or G1000 setup with an RA input, but from EGPWS we get a callout at 2500, then 1000 RA. You also get a 500RA call if you don’t have a valid glideslope signal If 2500RA isn’t at an altitude roughly around field elevation +2500’ it should start you thinking.
