Author Topic: Approach Question  (Read 1341 times)

Scott Newpower

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Approach Question
« on: April 22, 2012, 10:53:40 PM »
Last week I was flying with my new panel trying to get used to it, practicing some approaches by myself. One of the approaches I did was the GPS Rwy25 into KBIL. I let the computer and autopilot fly the whole thing until it was time to descend on the electronic glideslope and then clicked off altitude hold. I let the A/P fly the nav part all the way to the missed. When I got to the tower for work the day the girl that was working me on approach asked why I went out more than the 4 miles called for on the plate. This one:

http://155.178.201.160/d-tpp/1204/00048R25.PDF

I said I didn't notice but next time I go I'll check it out. I took a friend from work up today and we did that approach again. This time I watched and sure enough the Garmin 530 took us to a max 6.6 miles from MUMEE as it commanded the autopilot. It flew a 6 mile holding pattern. I had the approach plate up on the 796 and since it shows your aircraft on the plate you could clearly see we were outside the charted holding pattern. The chart is up to date as well as the 530 so what's the deal? If you notice this while flying how would you get the 530 to keep you in the charted airspace?

Richard Druschel

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Re: Approach Question
« Reply #1 on: April 23, 2012, 12:54:59 PM »
Hi Scott, I am not familiar with your instruments and can only ask a question for you to think about. What speed were you flying during the holding pattern procedure turn? I would suggest 100 to 120 kts for that maneuver. If you were excessively fast I could see the equipment needing extra space to do the procedure. Of course, there could be a number of other parameters that need to be checked by an avionics shop. If your speed was reasonable then I would talk with the shop that did the installation.
Dick

Scott Newpower

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Re: Approach Question
« Reply #2 on: April 23, 2012, 01:45:32 PM »
I was indicating about 130 MPH so right in your ballpark. The way I look at it is the autopilot should roll the plane into the turn at 4 miles from the fix.  In this case the Garmin doesn't call for the turn until 6 miles ultimately reaching a max of 6.6 miles from the fix. I still think the approach is wrong in the data base.  And I think people could end up with a pilot deviation if they let the 530 fly the approach for real.

Steve Zeller

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Re: Approach Question
« Reply #3 on: May 06, 2012, 07:45:32 PM »
This from a CFII buddy of mine who flies a lot of Garmin equipped aircraft:

I have not had a 430/530 or G1000 do this on the missed in a hold where the legs were designated in nm. I would check with the chart supplier (Garmin or Jeppesen). My original thought was the 530 software was set to use MILES rather than NM; but, that would not be the case with a +2 mile difference. There could be an issue with the GPSS roll steering to the Autopilot. If he can find another hold with legs in NM, I would fly that (in VMC) and see if the problem repeats itself. That would determine if the data base is wrong or there is an issue in the 530, GPSS steering, or the Autopilot.



Scott Newpower

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Re: Approach Question
« Reply #4 on: May 06, 2012, 10:30:44 PM »
We figured it out.  The government approach plate is wrong with a 4 mile holding pattern. The Jepp plate is correct at 6 miles. Naturally at the next update the FAA will change the holding pattern to 5 miles.

Charles Waldrop

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Re: Approach Question
« Reply #5 on: May 07, 2012, 08:08:08 AM »
As I recall, the hold altitude which is 6ooo provides safety for a 10 radius from the final approach fix which is FASOK and that is 6 miles from the hold point of MUMEE which could account for the 4 mile hold.

Scott Newpower

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Re: Approach Question
« Reply #6 on: May 08, 2012, 11:17:21 AM »
As I recall, the hold altitude which is 6ooo provides safety for a 10 radius from the final approach fix which is FASOK and that is 6 miles from the hold point of MUMEE which could account for the 4 mile hold.

6000 would be good all the way to the Appalachians from here, no idea why they limit the holding pattern size.