Use of Radio Altimeters

[Wizofoz]

DH = Decision HEIGHT --> OK to use RADALT as a backup (DA minus/plus RWY elevation) but your BARALT remains primary with your DA.

Sorry Copter, but Decision Heights are SPECIFICALLY associated with Cat II and III approaches and are SOLEY based on RADALT.

[pakeha-boy]

connection fee....as with the previous threads....Rad Alt on Cat2/3 a/bc apps for sure unless app plate stipulates RA not to be used....many apps(mostly Cat2) where terrain features make it impossible to use the RA ...eg SEA ILS 16R.....Iflew The D0-328 for many years and we had the HUD (Heads Up Display) on the capts side....Remarkable piece of euipment,but to do the app to CAT111 MINS IE 0/0...it is all based on the RA readout....hence 3RA,S on the A/C for redundancy......kia kaha

[Pierre Argh]

Wizofoz...

Decision Heights are SPECIFICALLY associated with Cat II and III approaches and are SOLEY based on RADALT

... whilst I believe this forum is intended for Aus/NZ flying, and therefore may have some local basis in fact, you are not totally correct... UK Military for one, uses QFE as their landing datum, hence procedures have a DH or MDH measured on a Pressure Altimeter (Bloody stupid POMs you might scream, but it's a fact?)

I'm not Aus/NZ based and found this thread when searching for a similar subject... I've said many times on PPRuNe threads, we must be careful about posting "facts" on a global site, where your information can be taken from any corner of the globe?

How does a radalt work when you're flying upside-down anyway?

[Wizofoz]

Hi Pierre,

I'm actually now based and flying in the UK and , in fact, my only experience of Cat II and III is here as neither exist in Aus.

I stand corrected from both your and pakeha-boys posts. Altimeter based DHs are not used in JAR-OPS, but military and other places, I bow to superior knowledge.

I'm actually rather amased to read paheha-boy talk about CatII approaches using the altimeter for minima. Do they really descend to 100'/200m using an barometric altimeter??

[pakeha-boy]

wizofoz.....in reply to your question....sorry for the confusion.....the example I give(and there are others) there is an ILS RWY 16R CAT 11/111 into KSEA....normally you would require the use of the RA to do this app,but because of terrain features peculiar to this airport app, the app plate stipulates the the:

CAT 11 ILS,RA NOT AUTH....they then give you a DA (H) of 530(100)....rvr 1200(BARO)......Airport Elevation is 433.....ie you shoot the app to 100 agl.....please note ,that these are few but there are several.......yet because the DO-328 had 3 RA,s....and because we were approved we could actually do the Cat 111 using the HUD(heads up display)on the same app......most airlines do not have the HUD,Ibelieve we were one of only three...expensive stuff but truly great euipment.....under normal conditions we never an app....kia kaha