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el_kab0ng

Impossible descent altitudes in '30 miles or less'?

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This happens to me on rare occasion, but when it does it creates a pretty annoying condition. RC4 has a tendency to give an extreme (on the order of 13,000 feet or more between altitude points) descent in '30 miles or less' while I'm flying a prop. This usually means a 2000ft or higher descent profile which is almost like a high speed dive when you don't have air brakes. Is there some configuration setting somewhere which starts the descent further out so the reduction of altitude isn't so extreme?

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More information is required please. A flight-plan, cruise altitude/level and what descent instructions you were given.

Although I don't fly prop aircraft I've not experienced the situation you describe with jets.

 

Are you sure you selected the correct aircraft type in Options? It will make a big difference in how you are instructed.

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I was doing a regional hop from KTKI to KAUS at FL200. I confirmed RC4 was configured for prop (that was the first thing I did when it happened last time). I was originally given a descent to 11,000 'at pilot's discretion' and then within 45 seconds was given another descent to 6000 'in 30 miles or less'. Again, this doesn't happen all the time, but when it does, it's almost impossible to achieve the altitude request by ATC without going into a steep profile. When that happens, I usually just miss the descent point and let ATC bark at me until I reach the correct altitude.

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Hmm. Something doesn't sound quite right. You would normally be ordered down early enough for you to reach 11,000ft 40 miles from KAUS. That's hard-coded into RC4. I wouldn't expect you to be given a lower clearance until you had reached 11000ft and were handed over to Approach. That's how it works for jets so I would expect much the same for props.

 

I don't understand why it only goes wrong sometimes. What's different? Does it work okay when you're cleared to 12000ft? And does it only happen with KAUS?

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KAUS was the latest flight where the anomaly occurred, but it's not the only time it's happened. I'll track these moments closer and try to provide as much detail as I can when it happens and report back. 

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Read the manual on how to create a log. If the problem persists and we can't help on the forum send the log to John Dekker along with a description of the problem.

 

Be aware logs can get very large but zipping them up will help.

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Ray, I've had this when flying jets on several occasions. In fact there have been many times when I've been turned on to final approach at ludicrously high altitudes. Very annoying.

 

It may be I'm doing something wrong but I can't think what it is.

 

Iain Smith

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Iain,

 

Flight plan would be a good start plus cruise level and did you start down when instructed or request a PD?

 

Speed is another factor. For near-side approaches it's essential to get speed back to 210kts pretty quickly after passing through 10,000ft.

 

If you're descent rate is around 2,000fpm there really shouldn't be a problem.

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Ray,

 

I can't remember which flights it happened on but I always start down when instructed and at a descent rate of at least 1800 to 2000 fpm. I may have stayed at 240 kts for too long so maybe that's the problem. But having to circle while reducing altitude is a bit unrealistic and might worry some passengers! :lol:

 

Next time it happens I'll note everything I did and attach the flight plan.

 

Iain

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Iain,

 

I see you fly a range of aircraft but when using the PMDGs use the FIX option on the CDU to create a waypoint 41 miles out from arrival. Then insert a speed and altitude constraint such as 245/120. When in VNAV mode the aircraft should be able to make it. If it's descending at too high a speed engage spoilers to keep the speed to 260kts or below.

 

If you're descending at 2000fpm it can only be excessive speed that causes you to miss the restriction.

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I use the range rings around the destination airport. On the Smiths Boeing CDU on the fix page I enter the ICAO of the destination for the fix and /40 for the place-bearing which on the nav display will give you a range ring. I then use speed and V/S on the MCU and watch the descent arcs to insure I am down before 40 nm out to the crossing restriction. I prefer this method since I do not know which runway will finally be designed so I do not use a hard waypoint.

 

The range ring may help you however in picking an existing waypoint if convenient to choose to place a hard altitude at.

 

I also see in cockpit videos pilots entering a 30 nm range ring to denote the airport traffic area proximity.

 

I'm using the classic PMDG 737NG series.

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