New emergency locator technologies

New Emergency Locator Technologies They're here! By Bob Chambers and Bryan Chambers March 1998 Congress mandated emergency locator technology (ELT) carriage as an aid to search and rescue operations in an amendment to the 1970...

The 406 Mhz system can also be coupled with a NAV interface which puts GPS coordinates in the data stream for the search and rescue operations. This brings the accuracy of the 406/Nav system down to 100 meters worldwide, which can be picked up by the geostationary satellite within one minute for positive identification and position on the earth.

The same system is used worldwide by the marine industry on the 406 Mhz frequency which works with the same satellites and search and rescue teams as the aircraft industry.

FAA Requirements
There are three different classifications of ELTs that are present today. The first, and the oldest, is the FAA, TSO C91 beacons. These beacons represent the oldest technology in ELTs and are being replaced by the new TSO C91a beacons. All general aviation aircraft that are operating within the United States are required to carry a TSO C91 ELT.

The difference between the two TSOs is that the latter can withstand much more severe abuse in a crash. Also, it utilizes a remote switch in the cockpit that enables the pilot to activate or reset the ELT. Any aircraft that currently has a TSO C91 ELT installed, must replace it with a TSO C91a beacon if it is unrepairable.

The last type of ELT available today is the TSO C126 beacons. Again, these units must withstand even more stringent abuse than the latter beacon. The main difference between this technology is the fact that these units operate on three frequencies rather than two. The third frequency (406.025 MHz) has a much higher accuracy from space than the other two, and the 406 transmitter is much more stable and transmits a digital signal at 5 watts up to the satellites. Currently no aircraft operating within the United States is required to carry a TSO C126 ELT, but many countries are mandating the use of this product worldwide.

ELT Installation
Many original ELT installations are inadequate as far as unit location and surface rigidity are concerned. Just because the old ELT was located in a particular position does not mean the new ELT should be located there.

Statistics show that the tail section of an airplane is least likely to be damaged during a crash and, therefore, provides a good mounting environment for the ELT unit.

Accessibility of the unit is an important factor in the location of the ELT. Mount the unit as far aft as practical but where it can be easily retrieved for maintenance.

The mounting surface must be extremely rigid; therefore, mounting the ELT directly to the aircraft skin is unacceptable.

The mount location must be able to support 100 "G"s of force in any direction with no appreciable distortion. It must also be able to withstand a 350-pound force in any direction without tearing or breaking the aircraft structure. This is derived at by 100 "G" force multiplied by the weight of the ELT. In this case, the ELT weighs 3.5 pounds and a 350-pound force must be used.

The FAA guidelines for mounting an ELT are in RTCA DO-183 Section 3.1.8.

United States To insure continued reliability of the ELT, it must be inspected for damage and wear which could be caused by age, exposed elements, vibrations, etc. Even the best designed equipment, if not properly maintained and cared for, will eventually fail.

The units must be inspected at least once a year unless required more frequently by FARs (e.g. 100-hour inspections). FAR Parts 91.207, 91.409, and 43 Appendix D make detailed ELT inspections mandatory.

How detailed should your inspection be? FAR 43, Appendix D(I) states, in part, that each person performing an annual or 100-hour inspection shall inspect the following components of the ELT.
1. ELT unit and mount — for improper installation and insecure mounting.
2. Wiring and conduits — for improper routing, insecure mounting, and obvious defects.
3. Bonding and shielding — for improper installation and poor condition.
4. Antenna, including trailing antenna — for poor condition, insecure mounting, and improper operation.

To ensure continued reliability, the ELT must be performance tested within the 12-month period preceding installation in an aircraft and within 12-month intervals thereafter.

For Canadian installations, all maintenance shall be performed in accordance with DOT Engineering and Inspection Manual, Part II, Chapter III, Section 3.12.7.

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