3.1 Accuracy
To locate a specific beacon the satellites, upon sensing 406 ELT activation, determines position
by calculating differential Doppler shift. LEO (Low Earth Orbiting) satellites pass overhead and
chart the position as it passes over the beacon.
The time required to listen to the short message format and make this calculation using the initial
detection of the orbiting satellites is about 45 minutes, maximum 90 minutes. Subsequent
satellite passes every 60 minutes will refine the position, with a maximum time of 90 minutes for
each pass.
Cospas/Sarsat reports that 1-3 nm (2-5 km) accuracy on average is determined this way. This
makes the search area approximately 25 sq. nm (65 sq. km) or about 3700 square acres. The
accuracy is increased by multiple passes over your position by the satellite.
406 ELTs equipped with GPS send a long message format that includes the latitude and
longitude within 4 seconds (as in degrees>minute>seconds) of the location. This gives you an
accurate position of better than 300 feet.
GPS position that is sent on the first burst or initial alert provides a near-instantaneous accurate
fix using the SARSAT geostationary satellites.
Proprietary software allows the GPS to be updated every second and that information is cached
for analysis and “trend monitoring”. This allow for any “nominal” signal information that is out
of norm to be discounted and thereby insuring a high degree of reliability. Every15 seconds the
ELT buffer is updated with the latest combined data. After the first burst the data is only updated
each 5 minutes per Cospas/Sarsat requirements.
Each 406 beacon sends a specific ID combined with registration data that provides for point of
contact information. This allows for a potential near real-time immediate launch of SAR assets to
your exact location. There is no need to wait for LEO satellites to come around and check your
position over and over to provide a manageable search area for SAR.
Emerging Lifesaving Technologies 406 ELT with GPS can be activated while still in the air.
After the first burst the data is only updated each 5 minutes per Cospas/Sarsat requirements.
This can provide SAR the ability to calculate the course and speed. If for some reason the aircraft
is too damaged to send information to SAR after the incident, this could mean the difference
between rescue and recovery.
3.2 Remote Switch Operation
If required, the pilot can activate the system by using the remote switch in flight. The unit can be
reset from the cockpit should the crew determine an emergency no longer exists.
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