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Old 23rd Jun 2005, 08:20
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OzExpat


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Using expedients like triple drift in a 1-minute holding pattern is rather different to applying it to a 2 or even 3 minute outbound leg of a base turn procedure. For a start, there is a whole lot more protection area around the holding procedure and, as I've already indicated, the timing is vastly different as well.

The splay angle is a function of the outbound time and the TAS. In a nil-wind situation, you would arrive at the FAT very neatly. There is quite a bit of protection for the reversal. Pans Ops allows the designer to use a 2h+47 wind or a "statistical wind" in developing the protection area. If the Pans Ops standard 2h+47 is used then, for example at 5,000 feet, the accounted wind strength would be 2 x5 +47, or 57 knots. I would think that if a statistical wind value was used at a place that experiences a lot of 50+ knot winds, that would be taken into account. And the wind is applied omni-directionally so that we account for it from every direction.

So, putting all of that together, no its not a good idea to modify the outbound track of the initial approach procedure. You would have no idea whether you'd be within the protection area or not, by the time you reached the end of the outbound timing. There is every chance that the strong wind has been taken into account in the protection of the turn. So, while you are certain to fly through the FAT, you simply keep the turn coming around.

Then, as has already been said, once within your regulated tracking tolerance (5 degrees in most places), commence descent while still intercepting the FAT. Then just hope there's enough time to reach the MDA, at or before the MAPt. Slowing the speed a bit in such a situation might help to improve your chances of using the remaining time on final approach.

There is a fair bit more to the design of a non-precision procedure, like ensuring that the rate of descent on final approach does not exceed Pans Ops limits for the nominal timing, but I hope this has helped.
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