Modern ELTs primarily transmit a digital signal on the 406 MHz frequency, which can include GPS position information for improved accuracy.2 This 406 MHz frequency is monitored by the COSPAS-SARSAT satellite system.2 There are several types of ELTs, including Automatic Fixed (ELT(AF)), Automatic Portable (ELT(AP)), Automatic Deployable (ELT(AD)), and Survival (ELT(S)), each with distinct activation methods and uses.1 An ELT(AF) is permanently attached to an aircraft and activates automatically upon impact, while an ELT(S) is removable and manually activated by survivors.1

ICAO Annex 10, Volume V, mandates that ELTs operate on both 406 MHz and 121.5 MHz.1 Satellite monitoring of the 121.5 MHz frequency was discontinued in 2009.1

In an emergency, the squawk 7700 and the MAYDAY call initiate a response.3 Emergency procedures are part of the ATPL theory Communications exam.4 The role of 121.5 MHz also comes up in the ATPL theory Communications exam.4 All 406 MHz ELTs must be coded and registered with the national agency responsible for initiating Search and Rescue.1 The 121.5 MHz frequency is still used for homing by search and rescue teams.1 ELT batteries must be replaced or recharged when the transmitter has been in use for more than one cumulative hour or when 50% of the battery's useful life has expired.5 A legislative proposal in Russia aims to mandate satellite beacons on all aircraft, following a Mi-8 crash where the missing helicopter lacked such a beacon.3 Poor visibility flights over mountains in remote regions, such as the Labrador Airways Twin Otter air ambulance crash near Goose Bay, show the risks of visual flight rules in bad weather.3

Pilots cannot use the radio without a current English Language Proficiency (ELP) certificate, which restricts flights to aerodromes where radio communication is optional.3