What is Emergency Location Transmitter (ELT)?

Emergency Location Transmitter, ELT, is a type of distress beacon which is used in aircraft. ELT must be present in an aircraft per regulations. ELT provides the current location information of the aircraft to Search and Rescue (SAR) services in case of an accident or serious incident. The pilot can activate the ELT manually using the remote switch and control panel indicator in the cockpit or it can automatically activate itself by detecting environmental factors such as immense pressure (detected by the gravity switch) in the event of an accident. During such an emergency, ELTs start broadcasting the location via their signals every 50 seconds on 121.5 or 406 MHz to satellites. Nevertheless, the International COSPAS-SARSAT Program stopped satellite surveillance of 121.5 MHz on February 1st, 2009. Currently, only the 406MHz frequency is being monitored. ELTs must be able to transmit their signals for at least 24 hours up to 48 hours.

ELTs must be examined within 12 months after the last inspection for proper installation, battery corrosion, control and crash sensor functionality, and the availability of a sufficient signal at the antenna. Because of the built-in test equipment, testing may be done without triggering an emergency signal. The remainder of the inspection is performed visually. It is not recommended that technicians use the ELT to send an emergency distress signal. The examination, as well as the battery’s new expiration date, must be noted in maintenance records. This must also be written on the exterior of the ELT.

How does ELT work?

ELT transmits its signal on 406 MHz to satellites in case of an emergency or accident. Low-altitude Earth orbit (LEO) satellites or Geostationary Earth orbit (GEO) satellites detect the incoming distress signal. When a Local User Terminal (LUT) is in range, the satellite system sends the signal that contains the location information. The range of a LUT can be approximately 2500 km. However, when the LUT is out of range, the satellite system caches the distress signal until it can be transmitted. After receiving the signal, the LUT automatically interprets the distress signal to identify and show the aircraft’s position within a radius of roughly 1.8 km. The processed data is sent to the Mission Control Center (MCC). Search and Rescue activities begin as soon as an available Rescue Coordination Center (RCC) receives the data from the MCC.

It is important to know each activation of the device is considered an emergency. Thus, if the device is activated mistakenly this will cause a false alert. Each false alert is a diversion and has a detrimental impact on other search and rescue activities. Approximately 90% of erroneous alarms are caused by beacon misuse during system testing and maintenance. However, also a hard landing may cause the activation of the ELT. In case of a false alert, having a registered ELT can assist SAR personnel save time and resources. A phone call to the person to whom the ELT is registered is the simplest way for SAR personnel to validate a false alert. The emitted signal from a fully registered ELT includes a digital code that may be used to identify the owner. Operators should also make certain that ELT self-tests and yearly testing are carried out in accordance with the manufacturer’s instructions and FAA regulations.