This lowly Archer has a RADALT am wondering if the crew is hoping to work their way to CAT II :)
Why would light GA bother with RADALT although you see a few vintage Bonanzas having them, am guessing as a nostalgia novelty item for ex airline pilots.
It’s cool. Does it yell “retard, retard”?
RobertL18C wrote:
This lowly Archer has a RADALT am wondering if the crew is hoping to work their way to CAT II :)Why would light GA bother with RADALT although you see a few vintage Bonanzas having them, am guessing as a nostalgia novelty item for ex airline pilots.
@RobertL18C, now you make me thinking…
I know that going CAT II is not the smartest move in a SEP, but legally, is there anything stopping it?
A_and_C wrote:
I am told that Air Alaska did CAT 3 on the B727 using just the HUD bit I cant find the reference for this.
So did (does?) Southwest.
arj1 wrote:
I know that going CAT II is not the smartest move in a SEP, but legally, is there anything stopping it?
Dual AP, dual crew, special air crew and operator authorisation?
In FAA land Cat2 seems possible for GA but probably makes little sense:
https://www.ifr-magazine.com/avionics/you-could-fly-a-cat-ii-ils/
I have flown with radar altimeters for nearly 10 years and it is of little use. I assume this was different in the old days before there was GPS with terrain, synthetic vision etc.
The FAA does allow Cat2 ILS operation for Part91 without Radar Altimeter as long as one apply “PEC error” to altimeter…they also allow zero/zero takeoff for Part91 !
I doubt there are any takers for 50ft DH though but zero/zero takeoff would be nice 
CAT2 does not use RADALT. That is a special aircraft+crew authorisation, possible in Europe (I knew someone who got it in a twin turboprop Commander). It just lets you fly an ILS down to about 150ft.
RADALT is used for CAT3 autoland, where the V guidance switches from baro to RADALT at around 150ft. H guidance remains on the LOC signal.
I have heard experienced heli pilots speak very well of a RADALT, but it doesn’t seem useful in a GA fixed wing. Only a few airports have adequately prepared ground ahead of the runway for a sensible reading. It is also a sizeable piece of kit, and costs about 10k plus installation. A useful feature would be to connect up a gear-up interlock. As a funny aside, I knew of a TB20 with one (KRA10A) which suffered a truly fantastic rate of KFC225 servo burnouts; he had a permanent HBK extended warranty and his avionics shop (who reads EuroGA) loved him
The FAA does allow Cat2 ILS operation for Part91 without Radar Altimeter as long as one apply “PEC error” to altimeter
Really?
See Part91.205 and Appendix, you can do without RADAR ALT as long as your BARO ALT is “corrected” and you have an IM marker
https://www.law.cornell.edu/cfr/text/14/91.205#d
https://www.law.cornell.edu/cfr/text/14/appendix-A_to_part_91
Radar alt becomes mostly interesting while already over the runway, particularly in CAT III ops but also CAT II to an extent. CAT II has minima of 100 ft AGL and therefore you reach the minimum within the protected area. In those cases where a CAT II approach is defined, RA DA will be present on the approach chart.
That technologically speaking even autoland works fine for GA, Garmin have proven. To implement that, and with it CAT III, would be technically possible but I would estimate that regulators will not have it. It may also become a capacity problem: Airports tend to have massive capacity reductions while under LVP and the last thing they would need in such a case is a 70 kts approach speed airplane between the 150 kts airliners in a CAT II/III setting.
While it may well be a bit of a “toy” for most GA applications, if there was a proper present day technology radar alt device at a reasonable price (which is an illusion for avionics, but there used to be the Terra ones which were not that expensive) I’d think it would be cool to get the voice announcements like on the airliners with their 50,40,20,10 retard calls…
