Emergency Location Transmitter, ELT, is a type of emergency transmitter used in aircraft. ELT is required to be present in every aircraft according to regulations. ELT transmits the aircraft's current position information to Search and Rescue (SAR) teams in the event of an accident or serious incident. The pilot can manually operate the ELT using the remote control switch and control panel indicator in the cockpit, or the ELT can automatically engage itself by detecting environmental factors such as excessive pressure (detected by the gravity switch) in the event of a crash. In such an emergency, ELTs begin broadcasting their location to satellites via signals at 121.5 or 406 MHz every 50 seconds. However, the International COSPAS-SARSAT Program discontinued 121.5 MHz satellite surveillance on February 1, 2009. Currently, only the 406 MHz frequency is being monitored. ELTs must be able to transmit their signals for at least 24 to 48 hours.
ELTs must be re-inspected within 12 months after the last inspection for correct installation, battery corrosion, control and crash sensor functionality, and whether there is adequate signal at the antenna. Due to built-in test equipment, testing can be performed without triggering an emergency signal. The remainder of the inspection is performed visually. Technicians are not advised to use the ELT to send an emergency distress signal. The inspection and new battery expiration date must be recorded in maintenance records. This should also be written on the outside of the ELT.
How Does an ELT Work?
ELT transmits its signal at 406 MHz to satellites in an emergency or crash situation. Low-altitude Earth orbit (LEO) satellites or Geostationary Earth orbit (GEO) satellites detect the incoming distress signal. When a Local User Terminal (LUT) is within range, the satellite system sends the signal containing position 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 determine and display the aircraft's location within a radius of approximately 1.8 km. The processed data is sent to the Mission Control Center (MCC). Search and Rescue activities begin as soon as an appropriate Rescue Coordination Center (RCC) receives the data from the MCC.
It is important to know that each activation of the device is considered an emergency. Therefore, if the device is accidentally activated, this causes a false alert. Each false alert has a harmful effect on other search and rescue activities. Approximately 90% of false alarms are caused by misuse of the device during system testing and maintenance. However, a hard landing can also cause activation of the ELT. In the case of a false alert, having a registered ELT can help SAR personnel save time and resources. Calling the person to whom the ELT is registered is the simplest way for SAR personnel to verify a false alert. A signal emitted from a registered ELT contains a digital code that can be used to identify the owner. Operators should also ensure that ELT tests are conducted in accordance with manufacturer's instructions and FAA regulations.
Author: Can Önal ([email protected])
