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model 10 · 14-11-2014, 17:45

CAP = Civil Air Patrol, DF= direction finder, ELT= emergency location transmitter. All planes that fly more than 25 miles from home base have one, or use too. I sail now so I don't know much any more.

MBWhite · 14-11-2014, 17:51

Civil Air Patrol, the auxiliary arm of the USAF responsible for most SAR missions over the continental US in regards to lost aircraft. There are exceptions, for example if an aircraft is suspected of being lost in Lake Michigan it is a USCG search mission and not CAP. DF is the acronym for Direction Finding.

Anyway, the procedure is called an "Aural Null Pattern" . Google brings up a bunch of links, but essentially you map when/where you start to hear a signal and map where you lose it. Then you can fly a reciprocal course and turn 90 degrees when you have flown half the distance back. If the signal fades quickly you have turned away, so do a 180. Now you can do another leg on that heading and when the signal nulls again, you can chart out the center of both legs (perpendicular to each other) you have flown which is hopefully around where the ELT is located.

ShaktisBoy · 14-11-2014, 18:47

I was a SAR pilot in the cap for 5 years in the 90s. If you knew where your com antennas were on the aircraft you were flying you could perform a steep turn and when the signal nulled you could determine direction to the transmitter pretty accurately, I.E if you were in a high wing 182 with on top antennas when the signal faded the transmitter was on the high wing side at approximately 90 degrees. I heard some of the ground team members talking about using a strip of aluminum to block one side of their handheld receivers antenna and basically get the same results. Never tried it though.