Thursday, March 08, 2007

The 4 NM Hold

Holding patterns based on distance rather than timed legs are becoming increasingly common, particularly for GPS approaches. Whether it is a turn around holding in lieu of a procedure turn or holding at the missed approach waypoint, 4 nm legs are becoming quite common.

The traditional method for making a teardrop entry into a hold is to turn approximately 30° away from the outbound heading, making the turn so as to stay inside the protected area of the hold, and fly for approximately one minute before turning back to intercept the inbound course. (See "A Eureka Moment".) This time honored technique works quite well for holds based on one-minute inbound legs, but it doesn’t work so well for the 4 nm holds. If you make the conventional turn for a teardrop entry and fly until you are 4 nm away from the holding waypoint, you might be far enough away from the inbound course to make intercepting it problematic.

So consider a variation on the teardrop entry. In this method, after crossing the holding waypoint, turn to the heading for the teardrop entry and fly for one minute. At the end of one minute, turn to the outbound heading and parallel the inbound course until 4 nm from the holding fix. Then turn to intercept the inbound course.

Below is shown the track of a turn around holding for a procedure turn at NOVSY, from the GPS-12/OWA. The turn around holding was flown by one of the instructors at Sim Flite Minnesota, who wanted to do some sim work to keep her instrument skills sharp.

I would say from the track, that her skills are quite good. Try this technique for a hold with 4 nm legs. It works quite well.

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