A Rundown On Aircraft ELTs

An Emergency Locator Transmitter (ELT) is a battery-operated transmitter developed to locate a downed aircraft and is a component of the many emergency services available to pilots.

ELTs transmit a signal that allows the location of a downed aircraft on three distinct frequencies. These three frequencies are the 121.5 MHz, 243.0 MHz, and 406 MHz.

The 121.5 MHz and 406 MHz frequencies are used for civilians, while the 243.0 MHz frequency is used for military purposes.
ELTs that transmit on the 121.5 Mhz and 243.0 MHz frequencies are analog, while ELTs that transmit on the 406 MHz frequency are digital.

All ELTs transmit a distinctive downward swept audio tone and can be activated when subject to crash-generated forces when armed. The locating signal transmitted by an ELT is designed to automatically activate and emit their signal continuously for at least 48 hours over a wide temperature range.
Pilots and passengers alike should be aware of how to activate the aircraft's ELT manually if needed and verify if the ELT is transmitting after a crash or manual activation.

Originally, ELTs only transmitted on the 121.5 and 243.0 MHz frequencies.

ELTs that were activated were capable of being detected by both ground and satellite monitoring stations. However, a large number of ELT activations ended being activated inadvertently or by accident. This resulted in many false positives and ultimately led to the discontinuance of satellite-based monitoring in 2009 for 121.5 MHz and 243.0 MHz ELTs.

Therefore, pilots that continued to fly aircraft with 121.5 MHz ELTs required nearby air traffic control or overflying aircraft to notify search and rescue teams in the event of a crash—posing a significant risk to aircraft operations in remote locations.

In 2019, the FCC prohibited the manufacture, importation, or sale of 121.5 MHz. Aircraft owners that previously had 121.5 MHz ELTs are still allowed to operate those ELTs in their aircraft.

The purpose of prohibiting the manufacture, importation, or sale of 121.5 MHz ELTs is to accelerate the transition to 406 MHz ELTs.

406 MHz ELTs are the newest advancement in ELT technology. Since 406 MHz ELTs are digital instead of analog, their capabilities are much greater than traditional analog ELTs.

406 ELTs transmit on the 406 MHz frequency. Their digital signal is much stronger than the 121.5 MHz ELT and can be encoded with the owner's contact information or aircraft data. Additionally, 406 ELTs can be encoded with the aircraft position from a GPS onboard the aircraft, allowing search and rescue teams to find downed aircraft much more rapidly than before.

The 406 MHz frequency is monitored by the Cospas-Sarset satellite distress alerting system and is operated by the National Oceanic Atmospheric Administration (NOAA). All 406 ELTs are required to be registered with NOAA by the owner before they may be used.

If a properly registered 406 ELT is activated, the Cospas-Sarset satellite distress alerting system can decode the signal and provide the owner's contact information and location to the appropriate search and rescue centers.

This ability provides two key benefits:

The first is the ability for search and rescue centers to contact the owner of the ELT and determine if it is an accidental activation and potentially avoid a costly search and rescue mission.

The second is that if an aircraft is involved in an accident, search and rescue teams can narrow an area of search and find the accident site much more quickly than if a 121.5 MHz ELT was used.

ELT regulations are located under 14 CFR Part 91.207.

This regulation encompasses when and how ELTs need to be installed, inspection requirements and intervals, battery requirements, and operations that do not require an ELT to be installed. 

All U.S. registered civil airplanes must have an operational approved automatic type emergency locator transmitter attached to the aircraft for the following operations:

1. Operations governed by the supplemental air carrier and commercial operators rules of part 121 and 125.
2. Charter flights governed by the domestic and flag air carrier rules of part 121.
3. Operations governed by part 135.

Any operation other than the 3 specified above must have an approved automatic or personal type emergency locator transmitter attached to the aircraft and in operable condition. 

ELTs must be attached to the airplane in a way that the probability of damage to the transmitter in the event of a crash is minimized. Fixed and deployable automatic type emergency locator transmitters must be attached to the airplane as far aft as possible. 

ELTs are required to be inspected every 12 calendar months and must be inspected for the following 4 items:

1. Proper installation
2. Battery corrosion
3. Operations of the controls and crash sensor
4. The presence of a sufficient signal radiated from the antenna

Batteries used in an emergency locator transmitter must either be replaced or recharged:

1. When the ELT has been in use for more than 1 cumulative hour; or
2. When 50% of their useful life, or useful life of charge for rechargeable batteries, has expired as determined by the ELT manufacturer. 

The new expiration date for replacing or recharging the batteries must be legibly marked on the outside of the transmitter and entered in the aircraft maintenance record. 

These requirements do not apply to batteries that are essentially unaffected during probably storage intervals, such as the case with water-activated batteries. 

ELTs are not required when a person:

1. Ferries a newly acquired airplane from the place where possession was taken to a place where the emergency locater transmitter is to be installed. 
2. Ferries an airplane with an inoperative emergency locater transmitter from a place where repairs or replacements cannot be made to a place where they can be made. 

When a person is ferrying an airplane, only the required crewmember may be carried aboard. 

Additionally, ELTs are not required for the following operations:

1. Before January 1, 2004, turbojet-powered aircraft;
2. Aircraft engaged in scheduled flight by scheduled air carriers;
3. Aircraft engaged in training operations conducted entirely within a 50-nautical mile radius of the airport from which such local flight operations began;
4. Aircraft engaged in flight operations incident to design and testing;
5. New aircraft engaged in flight operations incident to their manufacture, preparation, and delivery;
6. Aircraft engaged in flight operations incident to the aerial application of chemicals and other substances for agricultural purposes;
7. Aircraft certificated by the Administrator for research and development purposes;
8. Aircraft used for showing compliance with regulations, crew training, exhibition, air racing, or market surveys;
9. Aircraft equipped to carry not more than one person;
10. An aircraft during any period for which the transmitter has been temporarily removed for inspection, repair, modification, or replacement. 
    1. Requires the aircraft records to contain an entry which includes the date of initial removal, the make, model, serial number, and reason for removing the transmitter, and a place card located in view of the pilot stating "ELT not installed."
    2. The aircraft may not be operated more than 90 days after the ELT is initially removed from the aircraft.
11. On and after January 1, 2004, aircraft with a maximum payload capacity of more than 18,000 pounds when used in air transportation.