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Procedure turn distance determination by FAA

Asked by: 588 views Instrument Rating

For procedure turns on VOR approaches, it is usually 10nm from IAF, but I am having trouble understanding why it is 10nm and how they derived the value of 10NM.

I guess the distance should be enough for the higher Categories to go outbound and turn FAC within specified distance, still is the question even after looking up TERPS.

Also in G1000 MFD, it shows overlays, along with 10nm magenta dotted line, does anyone know on what basis the overlays are drawn ?



2 Answers

  1. fugae fuit malleator on Mar 31, 2017

    Great technical question. Here is a selection from FAA-H-8083-16A pg 4-49:

    –If Category E airplanes are using the PT or there is a descent gradient problem, the PT distance available can be as much as 15 NM. During a procedure turn, a maximum speed of 200 knots indicated airspeed (KIAS) should be observed from first crossing the course reversal IAF through the procedure turn maneuver to ensure containment within the obstruction clearance area. Unless a holding pattern or teardrop procedure is published, the point where pilots begin the turn and the type and rate of turn are optional. If above the procedure turn minimum altitude, pilots may begin descent as soon as they cross the IAF outbound.–

    So the answer to your question, it is meant to accommodate the category of aircraft flying the approach. Higher category = larger remain within distance. It is also based on the obstruction clearance actions taken by the team that designs and certifies the approach. It costs many less clams to study and clear an area closer to the airfield.

    However, without digging through every approach out there I suspect VORs with course reversals are becoming less popular to the extent that TERPS actions have started using a standard fixed remain within distance. Sadly, GPS approaches with terminal area arrivals to both ends of the same runway render the VOR procedure turn much less useful.

    Not sure about the programming on the G1000.

    Hope that helps….


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  2. Best Answer

    Russ Roslewski on Mar 31, 2017

    If you are asking “why is it almost always 10 nm”, then the answer is simple – because that’s what the book says to do.

    8260.3C, para 2-4-5b:

    “The minimum PT distance is 10 NM when CAT B, C, or D minimums are authorized. Decrease this distance to 5 NM where only CAT A aircraft or helicopters are to be operating, and increase to 15 NM to accommodate operational requirements, or as specified in paragraph 2-4-5.d. …………. When a PT is authorized for use by approach CAT E aircraft, use a 15-NM PT distance.”

    So, 10 nm unless it’s only Cat A, then down to 5 nm is okay. If the chart has Cat E, then it’s 15 nm. “Operational necessity” (like having to lose a lot of altitude) can result in distances that are greater than the minimums in each of these cases, but in any event, no more than 15 nm.

    You won’t see a whole lot of these non-standard distances, because if the obstacle environment is tight, there are usually other ways to accomplish the same thing (such as a Hold-In-Lieu-Of-Procedure-Turn).

    If you’re asking “why is it 10 nm and not 9, or 11, or something else”, pretty much the reason is that 10 nm was determined decades ago to be a good standard for most purposes. It accommodates most aircraft that are going to be performing the PT, and is a nice round number too. I imagine there was some kind of study and thought put into it at the time, but that has likely been lost to history.

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