आपातकालीन लोकेटर ट्रांसमीटर (ELT)

अवलोकन

The Emergency Locator Transmitter (ELT) is a self-contained radio beacon designed to activate automatically upon a crash and transmit distress signals that enable search-and-rescue (SAR) services to locate the aircraft wreckage and survivors. Modern aviation ELTs operate on 406 MHz and transmit digitally encoded messages that include the aircraft's unique 24-bit ICAO address (allowing database lookup of registration, operator, and emergency contacts), the beacon's serial number, and — critically — GPS-derived position data with accuracy typically better than 100 metres. These transmissions are received and processed by the international COSPAS-SARSAT satellite constellation, which relays alerts to national Mission Control Centres within minutes of activation.

यह ��ैसे काम करता है

The ELT unit is mounted in the aircraft's tail section, chosen because this structure often survives impact with less deformation than the forward fuselage. An inertial crash sensor — a G-switch or multi-axis accelerometer — detects the deceleration signature of a crash and triggers transmission automatically. The unit can also be activated manually via a cockpit switch or directly on the unit itself. Upon activation, the ELT transmits a 406 MHz digital burst every 50 seconds containing the encoded identification and position data, while simultaneously transmitting a 121.5 MHz homing signal that SAR aircraft and rescue personnel can home in on at close range using directional antennas.

Satellite detection is near-instantaneous for aircraft equipped with GPS-integrated ELTs because the satellites do not need to calculate a Doppler position — they simply relay the GPS coordinates included in the transmission. Without GPS integration, older 406 MHz ELTs rely on Doppler processing across multiple satellite passes, which can take up to 90 minutes for a first position fix and introduces position error of several kilometres. The transition to GPS-integrated ELTs, now mandated for new aircraft in most jurisdictions, has dramatically improved SAR response times.

प्���मुख घटक

406 MHz Transmitter: Solid-state transmitter meeting COSPAS-SARSAT specification C/S T.001, capable of operating across a wide temperature range and powered by a dedicated lithium battery with a minimum 24-hour life at -20 °C.

GPS Receiver: Integrated GPS module providing position fix encoded into each 406 MHz burst. Some designs use a separate antenna or share the aircraft's GPS antenna via an antenna splitter.

121.5 MHz Homing Transmitter: Analog carrier wave providing a continuous tone for close-range direction-finding by SAR aircraft equipped with automatic direction-finding (ADF) receivers.

Crash Sensor: Multi-axis accelerometer or G-switch calibrated to activate on impact loads characteristic of a crash (typically 3–5 g sustained) without false activation during turbulence or hard landings.

Remote Cockpit Switch: Allows crew to manually arm or activate the ELT, and to cancel an inadvertent ground activation before it generates an unnecessary SAR response.

विमान में अनुप्रय���ग

All commercial transport aircraft certificated under FAR Part 25 or CS-25 are required to carry at least one ELT. The Boeing 737-800 and Airbus A320 typically carry a single automatic fixed ELT in the tail. Wide-body aircraft such as the Boeing 777-300ER and Boeing 787-9 may carry additional deployable ELTs or Underwater Locator Beacons (ULBs) on the flight recorders — the latter transmitting 37.5 kHz acoustic signals to assist in deep-sea wreckage location. Following the disappearance of MH370 in 2014, ICAO strengthened requirements for flight tracking and ELT performance, accelerating the transition to GPS-integrated 406 MHz units across global fleets.

लाभ और सीमाएँ

GPS-integrated 406 MHz ELTs represent a transformative improvement in SAR capability: position accuracy has improved from kilometres to metres, and alert delivery time has compressed from hours to minutes. The COSPAS-SARSAT system has been credited with saving over 50,000 lives globally since 1982. Limitations include the possibility of crash-induced antenna damage preventing transmission, deep-water immersion beyond ELT depth rating, and the requirement for the unit to survive the impact loads of a catastrophic crash. False activations — triggered by hard landings, maintenance, or improper handling — remain a burden on SAR resources, although improved crash sensors and mandatory registration of beacon IDs have reduced nuisance alerts significantly.