Help, I've crashed and I have no TV reception!


January 2009


If you are worried about 121.5 MHz no longer being monitored by satellite and are considering purchase of a 406 MHz ELT, this month’s ShopTalk will try to dispel the confusion about the 406 MHz ELT situation; and will fail.


A 406 MHz ELT is part of a world-wide established system using satellites monitoring 406 MHz distress signals. This system, COSPAS-SARSAT, has been available since 1985 (actually, the first rescue was in 1982), primarily used by mariners. The specifications for the new ELT signal include a digital pulse encoded with a unique registration number. This number is entered into a database for correlation with information about the vessel, the owner/operator and emergency contacts. In the U.S., NOAA is responsible for administering that database. At 5 watts of power, a 406 MHz ELT signal is almost instantly received by a geosynchronous satellite and the registration number is relayed to a ground station. Non-geosynchronous satellites will also receive the signal when overhead. Because the ELT signal has a unique registration, it will be used to access the database information which is then used to contact the owner and others. This virtually eliminates false alerts and facilitates earlier launch of SAR (search and rescue) assets than with older ELT signals. The digital pulse specification allows the optional inclusion of vessel registration (N number) and GPS data.


Most of us know that in February, 2009 the satellites that monitor 121.50 MHz ELT signals will no longer be listening (also, analog TV signals will cease). Realize that it is only the monitoring of 121.5 by satellite that is being suspended. Other search and rescue functions in the U.S. are remaining the same (for now). The FAA would want all aircraft owners to install a new 406 MHz ELT in their aircraft (as per the Airman's Information Manual) but there are a few problems with this idea.


Are you as the airplane owner mandated to install a 406 MHz ELT? No, currently there is no requirement for a GA plane to have a 406 MHz ELT (in the U.S.). The applicable FAR is 91.207. Nowhere does this regulation mention the frequency of the ELT. So, for now, ELTs that are approved under TSO-C91a (the 121.5/243 MHz ELT specifications) are still allowed, even in new installations. The 406 MHz specifications are in TSO-C126 (which also allows 121.5/243 MHz).


There are currently three approved 406 MHz ELTs that could be considered in the price range of most GA aircraft owners: Emergency Beacon Corp. EBC406AP & AF for about $1300, Airtech ME406 at under $1000 and Ameri-King AK-451 at about $850. All integrate 121.5 MHz and the AK-451 includes 243 MHz (Air Force SAR). Units with a panel-mounted remote switch will also require a sound annunciator to be installed. The EBC406AP mounts in the cabin and needs no remote switch, lowering installation cost. It does still require running a coax to an external antenna.


If 406 MHz is so advanced, why do these units still include 121.5 MHz? Because having only 406 MHz radiating from your ELT presents some practical problems during this transition phase. SAR aircraft (such as Civil Air Patrol) may not yet have 406 MHz Doppler equipment available. Having a 121.5 MHz homing signal facilitates location by radio direction finder, which many SAR units have.


Adding GPS capability to an ELT raises the cost by at least $1100. A GPS capable ELT must be purchased outright. As of this date, no manufacturer has an upgrade path to add GPS capability to a non-GPS ELT. The ELT must interface with a TSO approved built-in aircraft GPS, through RS-232 or ARINC 429 protocol. Having a GPS equipped beacon improves target location accuracy (using just the 406 MHz signal) from 1-3 nm to about 100 yards. This is why, without GPS enhancement, the 121.5 MHz homing signal is important. With GPS, location is known with the first alert.


OK, that's the overview of the system. What about installation? The 406 MHz ELTs have the same installation requirements as their predecessors. In some cases, some of the components may be reused (such as the mounting tray). One manufacturer includes all components needed in the purchase price. One option worth consideration is to install dual antennas. In a crash, a single antenna may become inoperable; two antennas increase the probability that the ELT beacon will be transmitted.


Physical installation will, at least require replacement of the antenna and its coaxial cable assuming reusing existing equipment. If replacement of the mounting tray, activation switch and wiring is required, costs, of course, will increase. All 406 MHz ELT installations are currently done with a Form 337 field approval. Plan for the physical installation (for a non-GPS ELT) to run from $400 to $1000 (or more).


One aspect of the installation (and yearly maintenance required by FAR 91.207) that will increase costs is the requirement that the ELT is functioning, i.e. transmitting a signal. Anyone testing any ELT should follow the manufacturer’s recommended procedures. If those procedures are not specified, NOAA has approved this procedure: The old system's signal radiation (121.5 MHz) could be checked by placing an AM radio near the antenna and hearing the distinctive ELT homing signal. Test only during the first five minutes of each hour and coordinate with any nearby ATC facilities. Tests should be no longer than three audible “weeps”. That still works for the 121.5 MHz signal on a new ELT, but turning the system on to do this also readies the 406 MHz system for a beacon burst. Limiting the test to no more than 30 seconds prevents crossing the 50-second threshold for transmission of the 406 MHz beacon. Do not confuse this procedure with the self-test function which does not send out a 406 MHz alert beacon. The FCC aggressively prosecutes false 406 MHz ELT alerts. Last year, they fined one of the manufacturers for improperly testing their ELT.


OK, aircraft owners; I am asking you to do your mechanic a big favor. When you bring her/him your aircraft for an annual (probably to include the FAR 91.207(d) yearly ELT maintenance) remind her/him that there is a 406 MHz ELT installed. The test procedures are different, complex and if improperly done, can trigger a false alert! Also, there is a good chance that your mechanic can no longer do the FAR 91.207(d)(4) maintenance and you will have to go to a shop that can. The FAA has not yet addressed this maintenance issue.

Actual testing of the 406 MHz signal operational function is a bit more complex and this is where the increased costs are. All the new units have a self test function, but that does not test the signal radiated from the antenna, as per 91.207(d)(4). In fact, it is not allowed to operate the ELT unit installed on the aircraft by transmitting as that signal would probably trigger an alert. An approved test unit must be used in which the ELT unit is placed in a container designed to block the signal (a Faraday shield) or, if the antenna is removable, a dummy load may be installed. At this time, the FAA is requiring full testing of the 406 MHz radiated signal. Self-test functions do not meet their requirements. Since current test units cost over $2500, few maintenance shops are going to have one. Obviously, this creates some serious (expensive) logistics problems for the aircraft owner.


Other maintenance issues with the new ELTs can also be a bit more complex than the old systems. Some ELTs have Lithium batteries which may, as per manufacturer's requirements, only be replaced by authorized maintenance facilities. Other ELTs utilize field replaceable batteries, both Lithium and NiCad. Typical battery life is five years.


All 406 MHz ELTs must be registered before becoming operational. This can be done by mail or most easily on NOAA's web site: ELTs must be registered every two years or when installed. If units are swapped from inventory or another aircraft, a new registration must be completed. A registration label will be sent to the owner to be affixed to the ELT. These requirements are FCC regulations.

International Travel: Canada and Mexico


Air Transport of Canada is ready to mandate that all GA aircraft traveling through their airspace north of 55°N, west of 80°W or north of 50°N, east of 80°W must have an approved 406 MHz ELT installed. Without a 406 MHz ELT, travel to Alaska along the west coast (over Ketchikan) is allowed as one crosses into Alaskan airspace just south of 55°N. After February 1, 2011, all Canadian airspace will require a 406 MHz ELT installed.

Information for Mexico has been difficult to obtain. The following comes from a posting on the Baja Bush Pilots website:


406 MHz ELTs are required for all aircraft in Mexican airspace after July 1, 2008. There is an allowance, however, for aircraft that do not have a 406 MHz ELT. An existing 121.5 ELT may be used until July 1, 2009 or when the battery of that ELT is due for replacement, which ever is soonest. Then a 406 MHz ELT must be hardwired into the aircraft with its activation switch, except that a personal EPIRB may be used if the flight is only over land.

My take on all of this is to remember past history and, if possible, never purchase the first generation of any complex device, especially if it is under regulation. It is possible the FAA will implement some requirement that is not in the original 406 MHz ELT TSO and the early adopters will have to upgrade then. Over the years, ELTs have been the subjects of many airworthiness directives and the 406 MHz ELTs, being new to GA, might be next.


For the above reasons, I have been recommending my customers purchase an 406 MHz EPIRB (emergency position-indicating radio beacon) and hang it nearby (or around your neck) for easy access. This is a affordable method of transmitting GPS location data with the beacon alert. These do not have automatic activation, so must be activated manually. Once more manufacturers produce 406 MHz ELTs and they have been in use for a while, then consider upgrading your aircraft.


As always, if you have a question about this article, you may contact me at my aircraft repair shop, 307-789-6866 or via e-mail. Until the next ShopTalk, enjoy flying your Mooney.