Radio / radar altimeter applications on turbo props

[TheInsider]

So my understanding is, if you are not applying the instrument for a cat II or III you should simply leave it at zero and keep it in the scan for situational awareness. Anyone else have any other cool applications they use it for?

When I flew props with RADAR altimeters (no CAT II), for sit. awareness, I would set it to 2000' in mountainous terrain and 1000' in non-mountainous. On approach I would always set it to 50' above DH and 100' above MDA.

 

[yournextFO]

Also, some aircraft use the RA to adjust the autopilot gain when on approach (to prevent excessive A/P corrections as you get closer to the runway.)

The RA can also be used to inhibit the stick shaker and/or pusher near the ground. In fact, there are a surprising number of systems that tie into the RA, though probably more so on a jet than a TP.

 

[Bernoulli]

When I flew props with RADAR altimeters (no CAT II), for sit. awareness, I would set it to 2000' in mountainous terrain and 1000' in non-mountainous. On approach I would always set it to 50' above DH and 100' above MDA.

Good applications of the RA. I like it. Does anyone see any problems with the above applications of the RA if appropriate situational awareness is applied?

 

[Morettis]

Good applications of the RA. I like it. Does anyone see any problems with the above applications of the RA if appropriate situational awareness is applied?

I don't see a lot of point to setting it to 1000/2000 enroute because if you're IFR, as long as you fly the MEAs they guaranty terrain separation, and if you're VFR you should be looking outside and know exactly where the ground is.

Nothing wrong with setting it a little high for the approach to give yourself a warning that you're approaching your minimums and to start leveling off / looking outside.



The bottom line is that the Radar Altimeter isn't a primary instrument, its a supporting instrument. Just like the moving map on the GPS or an RMI, you don't get to do anything special because you have it, but if you use it correctly its one more tool to improve your situational awareness.

 

[trainer8]

So my understanding is, if you are not applying the instrument for a cat II or III you should simply leave it at zero and keep it in the scan for situational awareness. Anyone else have any other cool applications they use it for?

TCAS II uses the RA for operations below 1000' AGL while on approach. TCAS logic roles to TA mode only. Typically, if you MEL the RA, you also inop and MEL the TCAS by default.

And, as previously stated, EGPWS logic.

Many GPS's have their own terrain data base info, not requiring RA data.

T8

 

[PeanuckleCRJ]

The RA bug should always be off unless used for a cat ii/iii approach. Otherwise it is wonderful SA.

The only bug on a barometic only approach should be the MDA bug. The RA should never ever be used on a barometric approach.

 

[Tristar]

Not all RA bugs can be parked out of range, and it's a technique whether you use it or not in the ways previously suggested. There is nothing wrong with setting the bug as an additional alert (unless your companies procedures prohibit doing so).

However you are correct, you absolutely cannot use the RA on a baro approach to establish DH or MDA. I may not have made that adequately clear.

 

[av8tor19]

To answer your question, Cat I operations, the DH is a barometric reading and the RA is a backup. CAT II/III, the approach area around the runway (I don't know how far out) is surveyed and leveled. That is why you can use the RA for decision alt. The runway has to be certified as well as the plane. Cat II airplanes also have to have 2 separate autopilots I think.

 

[Sig]

To answer your question, Cat I operations, the DH is a barometric reading and the RA is a backup. CAT II/III, the approach area around the runway (I don't know how far out) is surveyed and leveled. That is why you can use the RA for decision alt. The runway has to be certified as well as the plane. Cat II airplanes also have to have 2 separate autopilots I think.

DING DING!

I (thought) I posted this earlier, alas- I'm an ass.


Try using the RA on a CAT I ILS into BGM, AVP, CRW... it is cute to watch, but absolutely irrelevant.

It helps our NDs who have lost their depth perception to know when to flare the Dash. The ones who don't use RA use the old "saw" technique: Pulling back and forth on the yoke until the plane finally contacts the runway.

Good times.

 

[Mickey]

The Mooney Ovation I used to fly had one.

 

[PeanuckleCRJ]

Note the CAT II into MSP on 30L.. that is a barometric only CAT II due to the terrain off the approach end.

Av8tor19, that is a good point about non-parkable (is that a word?) RAs... the previously described techniques would be appropriate- probably the 1000 foot being the most appropriate in most situations. However, even in the ratty King Airs I used to fly, the RA min bugs were able to be parked. So... this is just my logic when it can't be parked. Doesn't mean it's right (mainly becuase there really is no right answer as long as you aren't using it to base your approach off of it).

 

[Tristar]

Cat II airplanes also have to have 2 separate autopilots I think.

Actually, they don't (at least some don't). There are a lot of ways to get to Cat II - IIRC at ATA the 737 guys could hand fly a Cat II using the HUD. I know of several other aircraft which though they had two (or more) autopilots, could still operate Cat II with one deferred. Also, there was an article some years back in AOPA pilot on how you could qualify an average, well equipped single for Cat II. I don't recall the details, but it was possible (I belive it was related to an exemption for aircraft with a low approch speed - maybe Catagory A or something like that).

 

[trainer8]

DING DING!

I (thought) I posted this earlier, alas- I'm an ass.


Try using the RA on a CAT I ILS into BGM, AVP, CRW... it is cute to watch, but absolutely irrelevant.

It helps our NDs who have lost their depth perception to know when to flare the Dash. The ones who don't use RA use the old "saw" technique: Pulling back and forth on the yoke until the plane finally contacts the runway.

Good times.

Indeed. We could start a whole new thread on landing techniques of the Dash-8. I used to get so agitated at the "saw" landers. You'd thing they put different length main gear struts on various S/N numbered Dash-8s 'cause these guys would feel their way down.

T8

 

[Donsa320]

To answer your question, Cat I operations, the DH is a barometric reading and the RA is a backup. CAT II/III, the approach area around the runway (I don't know how far out) is surveyed and leveled. That is why you can use the RA for decision alt. The runway has to be certified as well as the plane. Cat II airplanes also have to have 2 separate autopilots I think.

All of our DC-9's and 15 of our 18 B-727's at the old Republic Airlines were CAT II with only one auto-pilot. I think you are confusing that with auto-land which is not required for CAT II.

Three of the 727's were leased and had flight directors which always went to GA when the auto-pilot was disconnected in approach mode. The Feds did not like that so ...no CAT II.

DC

 

[WMUSIGPI]

All of our DC-9's and 15 of our 18 B-727's at the old Republic Airlines were CAT II with only one auto-pilot. I think you are confusing that with auto-land which is not required for CAT II.

Three of the 727's were leased and had flight directors which always went to GA when the auto-pilot was disconnected in approach mode. The Feds did not like that so ...no CAT II.

DC

I wouldn't like that either......

 

[belchfire]

I don't know that they can't do Cat II and III, but many aren't equipped or trained. EGPWS still uses RADALT, so it's gotta be on the plane, anyway.

I think many planes display it, but don't really use it.

GPWS and EGPWS use radar altimeters to generate various terrain and configuration alerts required on multi engine turbine equipment.