ELT operation

Can someone explain the accuracy limitation of an ELT
? While the signal on 121.5 can only be automatically
detected and located to within 12 miles or so, if an
airborne search is started would a homing receiver
not guide the aircraft right over the spot ? Or are
ADFs not carried anymore in searching aircraft ?

Ian

On 6/22/04 10:40 AM, in article , "Ian Cant"
wrote:

Can someone explain the accuracy limitation of an ELT
? While the signal on 121.5 can only be automatically
detected and located to within 12 miles or so, if an
airborne search is started would a homing receiver
not guide the aircraft right over the spot ? Or are
ADFs not carried anymore in searching aircraft ?

Ian





Yes, the search aircraft will be guided right over the spot. They carry
special very directional antennas. The same antennas that can be carried by
hand by the search crews. The 12 mile or so is simply a place to start the
search. If the ELT signal is good, an airborne search can very quickly
narrow it down much further.

--
Bob
bobgreenblattATmsnDOTcom --fix this before responding

Brian Milner found this article that explains a lot of what happened
to us in Mifflin recently.

http://www.ltronics.com/lhtm-1.htm

Dale Kramer
K1

Locating an ELT is partly science and partly art. ALthough gliders crash in
clear weather, many of the airplanes lost are during bad weather and the
search aircraft cannot get close because of the weather.

I am a ground searcher. In the last crash, we beat the Air National Guard
to the scene - the next day. Weather hampered the air search. Although
aircraft can be swift, I have been called out a number of times where we are
the only ones searching. This is especially true because the information
often gets to the Sheriff after dark. Although the Air National Guard
searches at night using thermal imaging, they often cannot search because of
other reasons. Because of those delays, we are often called out long after
dark and we search in cars. The hills in our county cause diminished
signals and also reflections.

One hint is that crashing is better in the morning than late in the
afternoon.

Without an ELT, we would be cruising around hopelessly. We recently had a
massive search for a homebuilt aircraft that crashed. The ELT was destroyed
so we just guessed where it might be and drove around in our cars. Found it
about 4 hours later because it was in the clearing. Had it been in the
trees, it could still be lost.

You mentioned adf. This is a low frequency that works near the broadcast
band. It is nearly obsolete and would not work on the aviation frequency.
Airplanes searching will either home in by monitoring the signal strength or
some CAP aircraft are equipped with true vhf direction seeking equipment.

The first general location of the 121.5 MHz ELT is by satellite. However,
at 121.5 it takes a numbe rof passes of the satellites and it is only the
general area and is sometimes ambiguous. Another problem is that it takes
hours for the information to filter down to the searchers. The 406 MHz
beacons are much more precise in regard to the initial location, although
the ground searches still rely on the secondary signal broadcast on 121.5
MHz.

For optimum chances of being recovered, it is best to crash in the clear in
an area that is frequented often and during the early morning hours.

Colin



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On 6/22/04 8:03 PM, in article
, "Dale Kramer"
wrote:

Brian Milner found this article that explains a lot of what happened
to us in Mifflin recently.

http://www.ltronics.com/lhtm-1.htm

Dale Kramer
K1
Thanks. Good article. Explains a lot.

--
Bob
bobgreenblattATmsnDOTcom --fix this before responding