Starting on February 1st, 2009 all satellites will seize to respond on any alarm signal transmitted on the 121,5 MHz and 243 MHz frequencies. Those who are wanting to be rescued, before being reported missing, will need an ELT transmitting on the 406 MHz frequency.

It has been 38 years since two US congress men and their plane have disappeared. They never came back. In response to this event the Emergency Locator Transmitter (ELT) has been introduced. This device is able to transmit automatic bearing signals in case of a crash of while floating on the water. These signals are being transmitted on the international 121.50 Mhz aviation emergency frequency. As a kind of military opponent for this civil emergency frequency the 243 MHZ frequency has been chosen. All with the goal that planes passing by chance would receive emergency signals and pass the emergency call on towards a ground station. And in order to give help on the ground the ability to search for the crashed plane without loosing much time.

In the mean time sveral shortcomings of the system have become clear. On the one hand there are no regulations for passenger planes that require listening to the emergency frequency all the time. On the other hand you cannot expect personnel of any plane to do so because of the many false emergency alarm calls. Unwelcome experiences have shown that eletronic devices of all kinds, used in daily life out of the aviation world, can cause an alarm on the aviational emergency frequency. False alarms are estimated at almost 100% of all emergency calls!

Until some years ago, those who really needed help, could only hope that a plane passing by coincidence would pick up the emergency call by chance because having tuned in to the emergency frequency. But: a decent analysis of the signal, telling where its origins could be located, cannot be provided by even the best pilot. The best he can do is warning the ground station he picked up an emergency call from a certain region.

Satellite technology has proven its value
Because of the weak components of this emergency system, specialists in the early eighties started developing the Cospas/Sarsat Satelliten-System (http://www.cospas-sarsat.org). The system is homed in om receiving emergency signals transmitted on the new international 406 MHZ emergency frequency. Next to geostationary satellites the system is also based on satellites flying in changing orbits. This set of orbits can guarantee that an emergency signal is being picked up by one of the satellites within 4 hours. Modern technology can locate an ELT within 3 nautical miles even if the ELT doesn't transmit its location to the satellite directly. Data are being recorded and saved by satellites and as soon as possible forwarded to the next ground station. When a 406 MHZ ELT is being sold, several data on its new owner are being collected. This way, in case of an emergency signal, the ground station can match the signal with the owner so the identity of the transmitter is known right away. By analysing known data and emergency signal in some cases even false alarms can be detected efficently.

The 406 MHZ emergency system has been tested for the last 8 years.
Final conclusion: almost no false alarms and many succesful rescue operations.
As a result of this, Switzerland has obligated commercial planes to carry 406MHZ ELTs from early 2005.
Side effect: conventional emergency frequencies like the 121.5 and 243 MHz are covered by satellites since testing began, however with major technical limitations: the origin of signals can only be determined with a precision of a 10 NM radius (almost 20 kilometers). Because satellites cannot save data colected at conventional frequencies they must be in contact with one of almost 50 ground stations in order to be able to respond to of forward the emergency call. Because of numerous false alarms ground stions will wait for a second confirmation of the emergency signal befor setting out any rescue operations. All this makes the sytem a weak emergency service that will be abolished in September 2009.

Ultimately it's all a matter of price
To the owner of a non commercial plane this means that if you want to be rescued within 4 hours you should have a 406 MHZ ELT built in as soon as possible, preferably by a specialized company. Those who file in their flightplan in advance and stick to it will be served as well as before satellite emergency services had been abolished. As soon as a plane is overdue it will be searched for by choppers and planes. And these choppers and planes will -also in future times- still be able to receive 121.5 MHZ emergency calls enabling them to determine the location transmitting the signal. If you're very lucky, the 121,5 MHz emergency call might even be detected sooner than the 406 MHz call being transmitted into a satelliteless sky.

ELT - Artex ME406 (Price about €700,-)

ELT- ACK E-01 (Price about €348,-)

* Niklaus Wächter is a photographer and aviation journalist and also writes articles for the Schweizer Tagespresse (a swiss newspaper agency). Furthermore he is a satisfied Taifun 17 E II owner.