Use of Rad Alt on approach as decision altitude

P

pstan

Pre-takeoff checklist
Joined
May 17, 2009
Messages
168
Display Name
Display name:
Stan
I'm trying to understand how one flies the final part of this approach. ILS 24R SA cat 1 at KCLE Cleavland Hopkins Ohio. Sorry, don't know how to post it, cannot someone upload? SA means special authority I presume.

"Requires specific.....approval and use of HUD to RA"

The minimums box for the S ILS says "RA 150/14 150 DA930"

So here's my question. The mins box shown above shows "RA 150/14" in bigger font than "150 DA 930". Do the pilots just watch the rad alt digits, and use RA of 150 feet agl as a decision height? And if so, do they use the altimeter to determine the DH as well? Or is the altimeter reading not to be one of their decision cues?

Or do they look to the smaller font "150 DA930" and use 930 feet on the altimeter as the decision altitude?
 
pstan said:
I'm trying to understand how one flies the final part of this approach. ILS 24R SA cat 1 at KCLE Cleavland Hopkins Ohio. Sorry, don't know how to post it, cannot someone upload? SA means special authority I presume.

"Requires specific.....approval and use of HUD to RA"

The minimums box for the S ILS says "RA 150/14 150 DA930"

So here's my question. The mins box shown above shows "RA 150/14" in bigger font than "150 DA 930". Do the pilots just watch the rad alt digits, and use RA of 150 feet agl as a decision height? And if so, do they use the altimeter to determine the DH as well? Or is the altimeter reading not to be one of their decision cues?

Or do they look to the smaller font "150 DA930" and use 930 feet on the altimeter as the decision altitude?
Click to expand...

You can't use that approach. "SA" means special authorization. This is one of the new Super Category I IAPs.


When RA is charted, the DA is determined by the radar altimeter unless a particular operator has an exception in its ops specs. Charted RA sites are surveyed and flight inspected.


I haven't looked at the FAA charts, but Jeppesen charts this procedure on a separate chart.
 
Thanks aTerpster.

So...the pilots do not concentrate on the tape type or circular type altimeter display, but instead focus mainly on a digital readout in the flight display of the radio altimeter, and watch these digits count down to the DA. Is this correct?

Does uneven terrain on short final make the countdown of the radar altimeter a bit uneven, or a bit irregular? If so, does this have any human factors issues over a nicely trending altimeter that one uses with a normal cat 1 approach?
 
To expand on Wally's comment, if you are certified to use that RA instead if decision altitude, you know how to do it. If you don't know, you must not be certified and you aren't authorized to use it, so just stick with decision altitude measured on your regular barometric altimeter.

Note that decision height is measured above the runway threshold (THRE in the new nomenclature replacing TDZE), while RA is measured above the terrain below the point where you will be on the approach when you reach the desired missed approach point, which is typically lower than the THRE. So, if the decision height is 100 feet, and the ground slopes off from the runway so it's five feet lower than the runway when you reach the intended MAP, the RA would be 105 feet even though the DH is 100 and the DA is 100 above the THRE.
 
pstan said:
So...the pilots do not concentrate on the tape type or circular type altimeter display, but instead focus mainly on a digital readout in the flight display of the radio altimeter, and watch these digits count down to the DA. Is this correct?
Click to expand...
Not sure if "concentrate" is the right word, as you do want to keep your scan moving, but the radar altimeter and published RA is what you'll use to determine arrival at the MAP instead of the usual reliance on the barometric altimeter and published DA.

Does uneven terrain on short final make the countdown of the radar altimeter a bit uneven, or a bit irregular?
Click to expand...
It certainly can, depending on the nature of the terrain.

If so, does this have any human factors issues over a nicely trending altimeter that one uses with a normal cat 1 approach?
Click to expand...
It's certainly something one must learn in training to consider operationally.
 
thanks Ron and Aterpster, pretty well answers my queries.

Stan
 
pstan said:
Thanks aTerpster.

So...the pilots do not concentrate on the tape type or circular type altimeter display, but instead focus mainly on a digital readout in the flight display of the radio altimeter, and watch these digits count down to the DA. Is this correct?

Does uneven terrain on short final make the countdown of the radar altimeter a bit uneven, or a bit irregular? If so, does this have any human factors issues over a nicely trending altimeter that one uses with a normal cat 1 approach?
Click to expand...

You set the radar altimeter with a bug, so a light goes on at the height above terrain shown on the chart. If your scan is correct, you continue to make the baro altimeter primary except when nearing DA.

As you know, the decision whether to land or go around is supposed to be completed by DA, but with this Super CAT I and CAT II with visibility at minimum RVR, it all can become a blur of queues, especially at 140 knots or so.
 
Typically for this type of approach the airplane is equipped with dual or triple radio altimeters in a voting configuration through the FMS. Below 500 feet the pilot hear RA altitude call outs that alert him of the incoming DH. This ILS approach also has a 75 Mhz Inner Marker (IM) at this point to alert the pilot of his position. Unlike the traditional GA radio altimeter the ones used for this approach have 1 foot resolution, like the Honeywell ALA-52.

José
 
Usually on a Cat II or Cat III approach it will depend on how the ops specs are written but when I was doing it yes we used RAD ALT to Mins. The Pilot Flying is inside and the PNF is outside the window looking for the runway. If the PF does not hear runway in sight he/she goes around. If they here the runway/lights in sight it looks like we will be landing.

So just trying to tie that to your question, yes they can use RAD ALT toward the end of the approach to make the final decision. Hope that little tangent about CAT II helps answer your question.

The notes section says that you need specific OPSECS etc... to do this approach and the bottom near the RA DA says special aircrews, so they are approved to do this approach.
 
I'd be willing to wager that those operators who are approved are also two pilot crews. Generally, the PM (pilot monitoring) is making call outs and will call minimums based on RA, instead of a barometric DH.

Trivia time: most CAT II approaches are based on RA while CAT III approaches generally don't have minimums. You plan to autoland and use the RA to determine an alert height. This the the decision point as to wether you continue or go around. As always, there are exceptions.
 
jonnyjetprop said:
...CAT III approaches generally don't have minimums. You plan to autoland and use the RA to determine an alert height. This the the decision point as to wether you continue or go around.
Click to expand...
Yeah, and when you choose to land Cat IIIc and your autobrakes bring you to a stop and you can't see the runway from the cockpit, what do you do now? Answer: You do like United and don't land Cat IIIc without 300 RVR even if the FAA says you can land 0 RVR.:wink2:

BTW, Cat IIIa and IIIb approaches do have mins -- 700 and 600 RVR respectively. Only Cat IIIc has no mins other than those the operator wishes to self-impose. And I think only United and Continental among the major US carriers do Cat IIIc -- the rest do Cat IIIa/b.
 
Ron Levy said:
Yeah, and when you choose to land Cat IIIc and your autobrakes bring you to a stop and you can't see the runway from the cockpit, what do you do now? Answer: You do like United and don't land Cat IIIc without 300 RVR even if the FAA says you can land 0 RVR.:wink2:

BTW, Cat IIIa and IIIb approaches do have mins -- 700 and 600 RVR respectively. Only Cat IIIc has no mins other than those the operator wishes to self-impose. And I think only United and Continental among the major US carriers do Cat IIIc -- the rest do Cat IIIa/b.
Click to expand...

You can use the airport diagram on your NAV display combined with EVS on your HUD to find your way around the airport.

José
 
I recall only one time we had to stop and call a tug because we couldn't see the runway right below the windows. But we rolled into the fog that covered only one end of the runway and the ramp. We didn't land in it.
 
Ron Levy said:
Yeah, and when you choose to land Cat IIIc and your autobrakes bring you to a stop and you can't see the runway from the cockpit, what do you do now? Answer: You do like United and don't land Cat IIIc without 300 RVR even if the FAA says you can land 0 RVR.:wink2:

BTW, Cat IIIa and IIIb approaches do have mins -- 700 and 600 RVR respectively. Only Cat IIIc has no mins other than those the operator wishes to self-impose. And I think only United and Continental among the major US carriers do Cat IIIc -- the rest do Cat IIIa/b.
Click to expand...


Fire up the FLIR on your HUD and taxi to the gate. That's what I would do...assuming I had Cat IIIc capabilities, a FLIR and a HUD.
 
All true. I was referring to a DH minimum. We are limited to 600 RVR for the very reason you stated.


Ron Levy said:
Yeah, and when you choose to land Cat IIIc and your autobrakes bring you to a stop and you can't see the runway from the cockpit, what do you do now? Answer: You do like United and don't land Cat IIIc without 300 RVR even if the FAA says you can land 0 RVR.:wink2:

BTW, Cat IIIa and IIIb approaches do have mins -- 700 and 600 RVR respectively. Only Cat IIIc has no mins other than those the operator wishes to self-impose. And I think only United and Continental among the major US carriers do Cat IIIc -- the rest do Cat IIIa/b.
Click to expand...
 
Ron Levy said:
Yeah, and when you choose to land Cat IIIc and your autobrakes bring you to a stop and you can't see the runway from the cockpit, what do you do now? Answer: You do like United and don't land Cat IIIc without 300 RVR even if the FAA says you can land 0 RVR.:wink2:

BTW, Cat IIIa and IIIb approaches do have mins -- 700 and 600 RVR respectively. Only Cat IIIc has no mins other than those the operator wishes to self-impose. And I think only United and Continental among the major US carriers do Cat IIIc -- the rest do Cat IIIa/b.
Click to expand...

The answer is FLIR.
 
Ron Levy said:
...which are equally useless in fog so thick that RVR is zero.
Click to expand...

On some FLIR/EVS equipped aircraft they have infrared taxi lights that get through fog. Others use the infrared spectra emitted by regular taxi lights. With FLIR systems you do not need to illuminate the objects to see them through fog. FLIR offers a tactical advantage in detecting the enemy hiding in the fog or at night. This is why the CUAV has been so effective.

José
 
Ron Levy said:
No doubt there's a doctor in a Cirrus somewhere using the SVT that way.
Click to expand...

It amazes me the number of pilots that believe SVT has the same integrity and accuracy as the real dirt.
 
aterpster said:
It amazes me the number of pilots that believe SVT has the same integrity and accuracy as the real dirt.
Click to expand...

SVT may not have the same accuracy or dynamics as looking out the window but it conveys the approach data in a more natural form to the pilot than a plain HSI. On the other hand CAT-IIIc approaches can only be performed by the autopilot being controlled by the ILS/FMS/IRS/ADC down to the touchdown. Where the pilot crosscheck the approach on a HUD similar to an SVT. Keep in mind that there are several flavors of SVT that are not driven by an IRS thus attitude perception is not as accurate.

José
 
Piloto said:
SVT may not have the same accuracy or dynamics as looking out the window but it conveys the approach data in a more natural form to the pilot than a plain HSI. On the other hand CAT-IIIc approaches can only be performed by the autopilot being controlled by the ILS/FMS/IRS/ADC down to the touchdown. Where the pilot crosscheck the approach on a HUD similar to an SVT. Keep in mind that there are several flavors of SVT that are not driven by an IRS thus attitude perception is not as accurate.

José
Click to expand...

SVT, used with an understanding of its limitations, is a valuable addition to instrument flying technology. But, those who are tempted to bust minimums using it are on a fool's errand.

I am not sure where you are going with CAT III. I flew my share of those with neither HUD nor SVT. Never saw anything until the nose wheel touched down more than once. That's all about the quality of the ILS and the redundancy of the auto-land system. I flew two types that did CAT III, one of them did not have IRUs. (L1011)
 
aterpster said:
It amazes me the number of pilots that believe SVT has the same integrity and accuracy as the real dirt.
Click to expand...

Pretty damned close, and we paid dearly for it. It was all generated on Space Shuttle flights and is some high accuracy stuff for dirt. Regardless I apply limitations to accuracy as I would with any system. However, to imply that there is no credible difference in the ability to detect and avoid impinging terrain with the use of SVT would be seriously misstating the case.
 
Henning said:
Pretty damned close, and we paid dearly for it. It was all generated on Space Shuttle flights and is some high accuracy stuff for dirt. Regardless I apply limitations to accuracy as I would with any system. However, to imply that there is no credible difference in the ability to detect and avoid impinging terrain with the use of SVT would be seriously misstating the case.
Click to expand...

The data are 1:250,000. IAPs, at least in this country, use 1:24,000 topographical data for critical parts of the procedure.

The Shuttle data accuracy also falls off significantly at higher latitudes. It is a good system (generally) for a macro view of the terrain. And, except for the U.S. and some of Europe, there are no man-made structures in SVT databases.
 
aterpster said:
SVT, used with an understanding of its limitations, is a valuable addition to instrument flying technology. But, those who are tempted to bust minimums using it are on a fool's errand.

I am not sure where you are going with CAT III. I flew my share of those with neither HUD nor SVT. Never saw anything until the nose wheel touched down more than once. That's all about the quality of the ILS and the redundancy of the auto-land system. I flew two types that did CAT III, one of them did not have IRUs. (L1011)
Click to expand...

Since the L1011s were used for Pacific and Atlantic crossings the early ones were equipped with the Delco Carousel INS/IRU. The attitude data used by the autoland system came from these units. I saw many of these at the United MRO in SFO. I do not know of an autoland system approved without some form of IRS. You can see more on autoland at http://en.wikipedia.org/wiki/Autoland

José
 
Piloto said:
Since the L1011s were used for Pacific and Atlantic crossings the early ones were equipped with the Delco Carousel INS/IRU. The attitude data used by the autoland system came from these units. I saw many of these at the United MRO in SFO. I do not know of an autoland system approved without some form of IRS. You can see more on autoland at http://en.wikipedia.org/wiki/Autoland

José
Click to expand...

I flew for TWA. We had some 40, or so, L1011s, some of which were equipped for international with three INSes, and some of which were used on domestic only. The domestic-only models had no INS, but they had the exact same autoland system and CAT III alert height authorization as the international version. In other words I was there.:)
 
You must log in or register to reply here.
Back
Top