VDP for a Glide slope greater than 3 degrees

[Krapflier]

How do you calculate a VDP for a Glide slope greater than 3 degrees? Asked on an interview to calculate a VDP for Aspen Colorado LOC approach, which is 6.59-degree slope.

The only thing I could think of was to use 650 feet per nautical mile for a DME calculation instead of 300 feet per nautical mile. That is dividing the HAA by 650 instead of HAA by 300 and then add that DME distance to the MAP DME. Anyone know? I don’t…


Problem:
FAF = 7 DME
MAP = 3.9 DME
HAA (circling only approach) = 2320’ (Cat C aircraft)

 

[glasspilot]

Why would you want a VDP greater than 3 deg?

If you have to do a space shuttle approach to get down when you go visual why not go missed? A VDP is for planning purposes anyway, so why plan a shuttle approach? Plan a normal 3 deg descent to the runway. That's my answer.

 

[cush]

Why would you want a VDP greater than 3 deg?

If you have to do a space shuttle approach to get down when you go visual why not go missed? A VDP is for planning purposes anyway, so why plan a shuttle approach? Plan a normal 3 deg descent to the runway. That's my answer.

Have you flown in ASE? Good luck with that.

 

[cush]

How do you calculate a VDP for a Glide slope greater than 3 degrees? Asked on an interview to calculate a VDP for Aspen Colorado LOC approach, which is 6.59-degree slope.

The only thing I could think of was to use 650 feet per nautical mile for a DME calculation instead of 300 feet per nautical mile. That is dividing the HAA by 650 instead of HAA by 300 and then add that DME distance to the MAP DME. Anyone know? I don’t…


Problem:
FAF = 7 DME
MAP = 3.9 DME
HAA (circling only approach) = 2320’ (Cat C aircraft)

In ASE your TOD is DBL, no computations required. From there, you better be fully configured or you have little chance of making a stabilized approach...period end of story. You answer that way in a interview, they'll know you've been there.

 

[glasspilot]

Have you flown in ASE? Good luck with that.

Yup. And from DBL it's a near 3 deg glide slope. Like I said, a VDP is for planing a decent from the MDA. Why would you plan a non-standard decent from the MDA?

 

[DO-82 driver]

Speaking of ASE.....how is that new LOC approach to 15 working out?


I flew it VMC a few months back. Not having the plate infront of me I cannot recall if it is straight in or not...I believe it is.

 

[captain dad]

Yup. And from DBL it's a near 3 deg glide slope. Like I said, a VDP is for planing a decent from the MDA. Why would you plan a non-standard decent from the MDA?

That is exactly right. The VDP is a figure that will give you about a 3 degree from where you break out until touchdown. The final stage in landing should always be standard and stablized in normal configuration at about 3 degrees. (1,000' / 3miles DME or 10% of the MDA in AGL subtracted from your time)

There are some acceptions to that but not many. Take ASE. Yes if you go straight in on either the LOC or the VOR/GPS you will go beyond 3 degrees. That is why the minimums are so high and they are all circling not straight in mins. It's not so you can circle to land on 15. It is so you can break out (hopefully by ALLIX or DOYPE) and then descend in the valley to the southeast and set up a nice 3 degree visual.

If you are too fast or try to force a true straight in you will go beyond 3 degrees, cause the GPWS to go off, and scare yourself.

Personally, if I don't break out by ALLIX I am already planning to go to Rifle and set up a Limo for two reasons. 1.Yea I might make it in but I won't get out. (probably due to snow hello it's ASPEN) 2. Rifle is the quickest drive back to ASE

Just something to think about.

May all your beer flow like Wine.

 

[cush]

Yup. And from DBL it's a near 3 deg glide slope. Like I said, a VDP is for planing a decent from the MDA. Why would you plan a non-standard decent from the MDA?

Most swept wing jets that I know of, can't fly this Cat. C due to the steep angle. Cat. D is not authorized therefore it's illegal for them to fly past DBL, unless it's visual all the way down. Therefore my VDP is DBL... in a DA2000.

 

[learflyer]

When are these bull #$#$ questions going to go by the wayside in interviews?

 

[rice]

How do you calculate a VDP for a Glide slope greater than 3 degrees? Asked on an interview to calculate a VDP for Aspen Colorado LOC approach, which is 6.59-degree slope.

The only thing I could think of was to use 650 feet per nautical mile for a DME calculation instead of 300 feet per nautical mile. That is dividing the HAA by 650 instead of HAA by 300 and then add that DME distance to the MAP DME. Anyone know? I don’t…


Problem:
FAF = 7 DME
MAP = 3.9 DME

HAA (circling only approach) = 2320’ (Cat C aircraft)

Well to begin with; The FAF (DOYPE) is not 7 DME from the threshold of RW15. Note that the IASE physical location is at south end of 15.
That leaves you with only 5.7 DME to lose 3970' (11700'/DOYPE minus RW15 elev 7680 + 50 =7730) , which according to my calculator is approx. 697'/nm and would require a descent rate over 1620 ft/min at 140kts GS.
Whats the point of even thinking about a VDP in this situation?????

 

[CL604DRVR]

When are these bull #$#$ questions going to go by the wayside in interviews?

And what kind of questions would you suggest?

 

[AC560]

And what kind of questions would you suggest?

Ok there is a plane and it is on a treadmill....

 

[gunfyter]

Well to begin with; The FAF (DOYPE) is not 7 DME from the threshold of RW15. Note that the IASE physical location is at south end of 15.
That leaves you with only 5.7 DME to lose 3970' (11700'/DOYPE minus RW15 elev 7680 + 50 =7730) , which according to my calculator is approx. 697'/nm and would require a descent rate over 1620 ft/min at 140kts GS.
Whats the point of even thinking about a VDP in this situation?????

The point is to recognize you will NOT have a normal descent rate if you plan on landing straight in to 15.

Go to RIL.

 

[rice]

The point is to recognize you will NOT have a normal descent rate if you plan on landing straight in to 15.

Go to RIL.

Jeez GF,
Never thought of that????? Guess you missed the sarcasm in my post.
Never the less, my point was that there is much much more to consider when operating into KASE (or any mountain airport) and the fact that the originator of this thread started out with a flawed premise (7.0 DME FAF to RW15) is proof of that.
BTW, you will not have a normal descent rate on ANY of the approaches into Aspen, not even a visual. Does that mean no one should go there??????
With the proper aircraft, training, planning, and execution of procedures, KASE operations can be conducted safely in day/night and IMC conditions. Assuming one spends the time and effort to get trained on one of the two SAAAR approaches available.
Not saying its fun or my first choice for an adrenalyn rush but it can and has been done for years.
I agree RIL is a good Alt.

 

[learflyer]

And what kind of questions would you suggest?

NONE! You ought to be looking out the window once past dbl going into aspen, not heads down on a calculator figuring out a BS VDP.:beer:

 

[gutshotdraw]

Speaking of ASE.....how is that new LOC approach to 15 working out?


I flew it VMC a few months back. Not having the plate infront of me I cannot recall if it is straight in or not...I believe it is.

Shot the new one for real and for the first time in IMC last tour. Visibility reported of about 5 miles. Allix is my miss point on the VOR but I wasn't sure where the go around spot was for the LOC (homie don't circle at ASE). Saw the runway at about 11000 with enough room to get down. It is straight in with a slight offset. It's better than the VOR but not by much.

 

[DO-82 driver]

What's the chances of the Company of giving us guidance on the approx missed approach for that one should be?...slim to none.

I wonder if it could be done in the sims in CMH?

Might be nice to know some of these things....but they are quick to tell us that we are no longer carrying Caf Free Diet Cokes!!!!!!!!!

 

[gutshotdraw]

We're still waiting for the high holy blessing for our RNP 0.3 baro-VNAV approach into ASE. Mins for the G-IV are about 600 feet and 2 miles and even lower for the G-V. We've been training it for two years but still waiting for Fed approval.

As for company guidance....some don't think there's any problem with circling.