Top

Emergency Locator Transmitter

Introduction:

Radar Service for VFR Aircraft in Difficulty:

  • Radar equipped ATC facilities can provide radar assistance and navigation service (vectors) to VFR aircraft in difficulty when the pilot can talk with the controller, and the aircraft is within radar coverage. Pilots should clearly understand that authorization to proceed in accordance with such radar navigational assistance does not constitute authorization for the pilot to violate CFRs. In effect, assistance is provided on the basis that navigational guidance information is advisory in nature, and the responsibility for flying the aircraft safely remains with the pilot
  • Experience has shown that many pilots who are not qualified for instrument flight cannot maintain control of their aircraft when they encounter clouds or other reduced visibility conditions. In many cases, the controller will not know whether flight into instrument conditions will result from ATC instructions. To avoid possible hazards resulting from being vectored into IFR conditions, a pilot in difficulty should keep the controller advised of the current weather conditions being encountered and the weather along the course ahead and observe the following:
    • If a course of action is available which will permit flight and a safe landing in VFR weather conditions, non-instrument rated pilots should choose the VFR condition rather than requesting a vector or approach that will take them into IFR weather conditions; or
    • If continued flight in VFR conditions is not possible, the non-instrument rated pilot should so advise the controller and indicating the lack of an instrument rating, declare a distress condition; or
    • If the pilot is instrument rated and current, and the aircraft is instrument equipped, the pilot should so indicate by requesting an IFR flight clearance. Assistance will then be provided on the basis that the aircraft can operate safely in IFR weather conditions

Transponder Emergency Operation:

  • When a distress or urgency condition is encountered, the pilot of an aircraft with a coded radar beacon transponder, who desires to alert a ground radar facility, should squawk Mode 3/A, Code 7700/Emergency and Mode C altitude reporting and then immediately establish communications with the ATC facility
  • Radar facilities are equipped so that Code 7700 normally triggers an alarm or special indicator at all control positions. Pilots should understand that they might not be within a radar coverage area. Therefore, they should continue squawking Code 7700 and establish radio communications as soon as possible

Emergency Locator Transmitter:

  • ELTs of various types were developed as a means of locating downed aircraft. These electronic, battery operated transmitters operate on one of three frequencies. These operating frequencies are 121.5 MHz, 243.0 MHz, and the newer 406 MHz. ELTs operating on 121.5 MHz and 243.0 MHz are analog devices. The newer 406 MHz ELT is a digital transmitter that can be encoded with the owner’s contact information or aircraft data. The latest 406 MHz ELT models can also be encoded with the aircraft’s position data which can help SAR forces locate the aircraft much more quickly after a crash. The 406 MHz ELTs also transmits a stronger signal when activated than the older 121.5 MHz ELTs
    • The Federal Communications Commission (FCC) requires 406 MHz ELTs be registered with the National Oceanic and Atmospheric Administration (NOAA) as outlined in the ELTs documentation. The FAA’s 406 MHz ELT Technical Standard Order (TSO) TSO−C126 also requires that each 406 MHz ELT be registered with NOAA. The reason is NOAA maintains the owner registration database for U.S. registered 406 MHz alerting devices, which includes ELTs. NOAA also operates the United States’ portion of the Cospas−Sarsat satellite distress alerting system designed to detect activated ELTs and other distress alerting devices
    • In the event that a properly registered 406 MHz ELT activates, the Cospas−Sarsat satellite system can decode the owner’s information and provide that data to the appropriate search and rescue (SAR) center. In the United States, NOAA provides the alert data to the appropriate U.S. Air Force Rescue Coordination Center (RCC) or U.S. Coast Guard Rescue Coordination Center. That RCC can then telephone or contact the owner to verify the status of the aircraft. If the aircraft is safely secured in a hangar, a costly ground or airborne search is avoided. In the case of an inadvertent 406 MHz ELT activation, the owner can deactivate the 406 MHz ELT. If the 406 MHz ELT equipped aircraft is being flown, the RCC can quickly activate a search. 406 MHz ELTs permit the Cospas−Sarsat satellite system to narrow the search area to a more confined area compared to that of a 121.5 MHz or 243.0 MHz ELT. 406 MHz ELTs also include a low-power 121.5 MHz homing transmitter to aid searchers in finding the aircraft in the terminal search phase
    • Each analog ELT emits a distinctive downward swept audio tone on 121.5 MHz and 243.0 MHz
    • If “armed” and when subject to crash− generated forces, ELTs are designed to automatically activate and continuously emit their respective signals, analog or digital. The transmitters will operate continuously for at least 48 hours over a wide temperature range. A properly installed, maintained, and functioning ELT can expedite search and rescue operations and save lives if it survives the crash and is activated
    • Pilots and their passengers should know how to activate the aircraft’s ELT if manual activation is required. They should also be able to verify the aircraft’s ELT is functioning and transmitting an alert after a crash or manual activation
    • Because of the large number of 121.5 MHz ELT false alerts and the lack of a quick means of verifying the actual status of an activated 121.5 MHz or 243.0 MHz analog ELT through an owner registration database, U.S. SAR forces do not respond as quickly to initial 121.5/243.0 MHz ELT alerts as the SAR forces do to 406 MHz ELT alerts. Compared to the almost instantaneous detection of a 406 MHz ELT, SAR forces’ normal practice is to wait for either a confirmation of a 121.5/243.0 MHz alert by additional satellite passes or through confirmation of an overdue aircraft or similar notification. In some cases, this confirmation process can take hours. SAR forces can initiate a response to 406 MHz alerts in minutes compared to the potential delay of hours for a 121.5/243.0 MHz ELT
  • The Cospas−Sarsat system has announced the termination of satellite monitoring and reception of the 121.5 MHz and 243.0 MHz frequencies in 2009. The Cospas−Sarsat system will continue to monitor the 406 MHz frequency. What this means for pilots is that after the termination date, those aircraft with only 121.5 MHz or 243.0 MHz ELT’s onboard will have to depend upon either a nearby Air Traffic Control facility receiving the alert signal or an overflying aircraft monitoring 121.5 MHz or 243.0 MHz detecting the alert. To ensure adequate monitoring of these frequencies and timely alerts after 2009, all airborne pilots should periodically monitor these frequencies to try and detect an activated 121.5/243.0 MHz ELT
  • Battery operated transponders react to forces (detecting a crash) and should operate for 48 hours continuously
  • Transmit on 121.5 and 243 MHz (guard) and the newer 406 MHz
    • 121.5/243 MHz are analog devices while 406 MHz is a digital transmitter encoded with owners contact and aircraft data; can transmit aircraft position and transmits a much stronger signal
    • 406 transmitters must be registered with NOAA
  • Pilots should be able to activate and deactivate the ELT manually for testing or in the event of an emergency when they have failed to activate autonomously

Testing:

  • ELTs should be tested in accordance with the manufacturer’s instructions, preferably in a shielded or screened room or specially designed test container to prevent the broadcast of signals which could trigger a false alert
  • When this cannot be done, aircraft operational testing is authorized as follows:
    • Analog 121.5/243 MHz ELTs should only be tested during the first 5 minutes after any hour. If operational tests must be made outside of this period, they should be coordinated with the nearest FAA Control Tower or FSS. Tests should be no longer than three audible sweeps. If the antenna is removable, a dummy load should be substituted during test procedures
    • Digital 406 MHz ELTs should only be tested in accordance with the unit’s manufacturer’s instructions
    • Airborne tests are not authorized
Emergency Locator Transmitter Testing Instructions Example
Figure 1: Emergency Locator Transmitter Testing Instructions Example

False Signals:

  • Caution should be exercised to prevent the inadvertent activation of ELTs in the air or while they are being handled on the ground. Accidental or unauthorized activation will generate an emergency signal that cannot be distinguished from the real thing, leading to expensive and frustrating searches. A false ELT signal could also interfere with genuine emergency transmissions and hinder or prevent the timely location of crash sites. Frequent false alarms could also result in complacency and decrease the vigorous reaction that must be attached to all ELT signals
  • Numerous cases of inadvertent activation have occurred as a result of aerobatics, hard landings, movement by ground crews and aircraft maintenance
  • These false alarms can be minimized by monitoring 121.5 MHz and/or 243.0 MHz as follows:
    • In flight when a receiver is available
    • Before engine shut down at the end of each flight
    • When the ELT is handled during installation or maintenance
    • When maintenance is being performed near the ELT
    • When a ground crew moves the aircraft
    • If an ELT signal is heard, turn off the aircraft’s ELT to determine if it is transmitting. If it has been activated, maintenance might be required before the unit is returned to the “ARMED” position. You should contact the nearest Air Traffic facility and notify it of the inadvertent activation

Inflight Monitoring and Reporting

  • Pilots are encouraged to monitor 121.5 MHz and/or 243.0 MHz while inflight to assist in identifying possible emergency ELT transmissions. On receiving a signal, report the following information to the nearest air traffic facility:
    • Your position at the time the signal was first heard
    • Your position at the time the signal was last heard
    • Your position at maximum signal strength
    • Your flight altitudes and frequency on which the emergency signal was heard: 121.5 MHz or 243.0 MHz. If possible, positions should be given relative to a navigation aid. If the aircraft has homing equipment, provide the bearing to the emergency signal with each reported position

No person may operate a U.S. Registered civil airplane unless:

  • There is attached to the airplane, an approved automatic type ELT in operable condition
  • Except after June 21, 1995, an ELT that meets the requirements of TSO-C91 may not be used for new installations (see FAR 91.207 for more)
  • Must be attached in such a way that the transmitter is not likely to be damaged in a crash, as far aft as possible
  • Batteries must be replaced if the ELT has run more than an hour (cumulative) or 50% of its useful life
  • The ELT itself must be inspected within 12 calendar months after the last inspection (see FAR for inspection items)

Exceptions:

  • Ferry a newly acquired airplane from the place where possession of it was taken to a place where the ELT transmitter is to be installed
  • Ferry an airplane with an inoperative ELT from a place where repairs cannot be made to a place where they can
  • No other people than the required crew may be carrier aboard a ferried airplane
  • Does not apply to turbo-jets before January 1, 2004
  • Aircraft engaged in schedule flights by scheduled air carriers
  • Aircraft while engaged in training operations conducted within 50 NM radius of the airport
  • Aircraft engaged in flight operations incident to design and testing
  • Aircraft certified by the Administrator for research and development purposes
  • Aircraft while used for showing compliance with regulations, crew training, exhibition, air racing, or market surveys
  • Aircraft equipped to carry not more than 1 person
  • Any aircraft with the ELT removed must be placarded with the date of removal, make, model, serial number, and reason for removal
  • No person may operate more than 90 days after the ELT is initially removed
  • On and after January 1, 2004, aircraft with a maximum payload capacity of more than 18,000lbs when not used for air transportation

Conclusion:

  • ELTs are required for most General Aviation airplanes
  • Manufacturers of ELTs are required to mark the expiration date of the battery, based on 50 percent of the useful life (or for rechargeable batteries at 50 percent of their useful life of charge) on the outside of the transmitter
    • Batteries are required to be changed on that date or when the transmitter has been in use for more than 1 cumulative hour

References: