U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Installation and Inspection Procedures for Emergency Locator Transmitters and Receivers Date: 2/1/18 AC No: 91-44A Initiated by: AFS-300 Change: 1
1. PURPOSE OF THIS ADVISORY CIRCULAR (AC). This AC describes installation and inspection procedures for emergency locator transmitter (ELT) systems. This AC is intended to be used in conjunction with or as a supplement to the installation, maintenance, and inspection requirements found in the documentation that came with and was used to install the ELT device being maintained or inspected. Title 14 of the Code of Federal Regulations (14 CFR) part 91, § 91.207 is the regulatory basis for this AC. This AC is not mandatory and does not constitute a regulation. This AC describes an acceptable means, but not the only means, to install, maintain, and inspect ELT systems. However, if you use the means described in the AC, you must follow it in all important respects.
2. PRINCIPAL CHANGES. This change updates and reorganizes the information in the AC to provide procedures for the installation, maintenance, and inspection of ELT systems. It also changes the title (formerly Operational and Maintenance Practices for Emergency Locator Transmitters and Receivers).
PAGE CONTROL CHART Remove Pages Dated Insert Pages Dated Pages 1 thru 15 12/12/80 Pages 1 thru 12 2/1/18
John S . Duncan Executive Director, Flight Standards Service
U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Operational and Maintenance Practices for Emergency Locator Transmitters and Receivers Date: 12/12/80 AC No: 91-44A Initiated by: AFS-300 Change:
1 PURPOSE OF THIS ADVISORY CIRCULAR (AC). This AC describes installation and inspection procedures for emergency locator transmitter (ELT) systems. This AC is intended to be used in conjunction with or as a supplement to the installation, maintenance, and inspection requirements found in the documentation that came with and was used to install the ELT device being maintained or inspected. Title 14 of the Code of Federal Regulations (14 CFR) part 91, § 91.207 is the regulatory basis for this AC. This AC is not mandatory and does not constitute a regulation. This AC describes an acceptable means, but not the only means, to install, maintain, and inspect ELT systems.
However, if you use the means described in the AC, you must follow it in all important respects.
2 AUDIENCE. This AC applies to aircraft owners, operators, and aviation maintenance technicians who install, maintain, and inspect ELT systems.
3 WHERE YOU CAN FIND THIS AC. You can find this AC on the Federal Aviation Administration’s (FAA) website at http://www.faa.gov/regulations_policies/advisory_circulars.
4 WHAT THIS AC CANCELS.
AC 20-81, Accidental or Unauthorized Activation of Emergency Locator Transmitters (ELT), dated October 10, 1972.
AC 20-85, Emergency Locator Transmitters and Receivers, dated March 16, 1973.
AC 20-87, Airborne Homing and Alerting Equipment for Use With Emergency Locator Transmitters, dated May 7, 1973.
AC 20-91, Lithium Batteries Used in Emergency Locator, Transmitters, dated April 11, 1975.
AC 91-44, Emergency Locator Transmitters Operational and Maintenance Practices, dated February 20, 1976.
5 B ACKGROUND. On December 29, 1970, Congress amended the Federal Aviation Act of 1958 to require the installation of an ELT on most civil airplanes of U.S. registry. The FAA implemented this statute in § 91.207. With certain exceptions, U.S.-registered civil airplanes must be equipped with an ELT meeting the performance standards specified in
2 Technical Standard Order (TSO)-C126( ), 406 MHz Emergency Locator Transmitter (ELT), and Cospas-Sarsat Specification C/S T.001, Specification for Cospas-Sarsat 406 MHz Distress Beacons. RTCA DO-204A, Minimum Operational Performance Standards (MOPS) for 406 MHz Emergency Locator Transmitters (ELT), dated December 6, 2007, provides the basis for TSO-C126( ). While aircraft may continue to operate that have been equipped with ELT devices meeting the requirements in TSO-C91a, Emergency Locator Transmitter (ELT) Equipment, new installations of ELT equipment must meet the requirements in TSO-C126( ). This AC provides installation, maintenance, and inspection information that should be followed to ensure ELT systems and devices perform their intended function. Persons performing maintenance, alteration, or preventive maintenance on an ELT system should use the methods, techniques, and practices prescribed in the current manufacturer’s maintenance manual or instructions for continued airworthiness (ICA) prepared by its manufacturer, or other methods, techniques, and practices acceptable to the FAA, such as those in 14 CFR part 43, § 43.16.
6 TYPES OF ELTs. There are five basic types of ELTs: automatic fixed (ELT-AF), automatic portable (ELT-AP), survival (ELT-S), automatic deployable (ELT-AD), and distress triggered (ELT-DT). Federal Communications Commission (FCC) regulations specify authorized ELT operations. ELTs approved for aircraft service are not to be used when “backpacking,” (i.e., recreational or wilderness exploration on foot).
6.1 Automatic Fixed (ELT-AF). ELT-AF devices are permanently attached to the aircraft and designed to stay attached even after a crash to aid Search and Rescue (SAR) teams in locating a crash site.
6.2 Automatic Portable (ELT-AP). While attached to an aircraft, ELT-AP devices can be removed from the aircraft and continue to function. These devices act as an ELT-AF and can be activated by a crash, but can also be removed and tethered to a liferaft or person, or carried to a safe location away from the crash site. This type of device is designed to bring SAR teams to the survivors (e.g., on a liferaft in the ocean), rather than the wreckage.
6.3 Survival (ELT-S). ELT-S type devices are portable in nature, are manually activated, and are the type typically carried by backpackers.
6.4 Automatic Deployable (ELT-AD). ELT-AD devices are designed to be attached to an aircraft, but deploy (detach) automatically after a crash event has been detected. ELT-AD devices must be capable of floating on water and are designed to help crash investigators locate the crash site.
6.5 Distress Triggered (ELT-DT). ELT-DT devices are designed to be activated by the aircrew, or automatically by an internal or external trigger. In-flight events and detection criteria are defined in European Organization for Civil Aviation Equipment (EUROCAE) Specification ED-237, MASPS for Criteria to Detect In-Flight Aircraft Distress Events to Trigger Transmission of Flight Information, dated February, 2016.
3 7 INSTALLATION CONSIDERATIONS.
7.1 Location for Inertial Activation. To meet the g force requirements of TSO-C126( ), ELT-AF devices are inertially activated ELTs. These devices should be placed to facilitate activation by an inertial force, parallel to the longitudinal axis of the aircraft, when installed in accordance with the manufacturer’s instructions.
7.2 Location of ELT.
7.2.1 ELT-AF devices should be attached in a location free of moving parts, such as cables or other objects that may strike and inadvertently trip the g sensor.
7.2.2 Devices should not be mounted to thin walls that may vibrate and, as a result of vibration, trip the inertial sensor.
7.2.3 Devices should not be mounted in luggage compartments or areas used for stowage, as they will be susceptible to being bumped and inadvertently activated.
7.2.4 Aircraft-mounted devices should be mounted as far aft as practicable.
7.2.5 ELT-AF and ELF-AP devices meeting TSO-C126( ) are not to be mounted using hook-and-loop fastener systems such as Velcro®. Furthermore, attachment of ELT-AF devices solely by means of hook-and-loop fastener systems is strongly discouraged, since this type of fastener may act as a shock absorber and fail to trip the inertial g sensor within the ELT. Devices installed with hook-and-loop fastener mounting systems may fail to hold the device securely, leading to damage of the unit, antenna, or antenna cabling in a crash.
7.2.6 Manufacturers’ instructions should be consulted when installing portable ELT devices.
7.2.7 The ELT system should be installed such that inadvertent activation in flight will not adversely affect any aircraft systems that perform a function whose failure would prevent the continued safe flight and landing, or significantly reduce the capability of the airplane, or the ability of the flightcrew to respond to an adverse operating condition.
7.3 Location and Access of Controls. If used, remote controls are required to be within reach of seated crewmembers if the ELT device is not readily accessible in flight.
Aircrews must be able to control the ELT system directly or through the use of remote controls to allow them to deactivate the system if it is inadvertently set to “on” in flight by severe turbulence or other events.
7.4 Location of Antenna. Care should be given to antenna placement since this can have a significant impact on signal detection if the ELT is activated.
7.4.1 Exterior Antenna Placement.
If practical, ELT antennas should be placed on the exterior of the fuselage.
Typically, ELT antennas should be placed at least 30 inches (76.2 cm) away from other very high frequency (VHF) antennas. Testing should be performed to ensure ELT transmissions will not disrupt VHF systems if an ELT antenna is placed within 30 inches of a VHF antenna.
The antenna should be fully extended and in a vertical position when the airplane is in the normal flight attitude.
7.4.2 Interior Antenna Placement.
ELT antennas should only be installed inside an aircraft fuselage whenever an external mount is not practical.
Consideration should be given to placing the antenna so that it is in a vertical position when the airplane is in the normal flight attitude.
If an ELT antenna is mounted on a radio transparent aircraft, the antenna should be mounted to a ground plane.
In metal-framed aircraft, if the antenna cannot be mounted on the outside of the fuselage, the antenna should be as close to a window or similar radio frequency (RF)-transparent opening as possible since metal frames can block or diminish a radiated ELT signal.
If the antenna is placed in a window, the antenna should be located in the approximate center of the window so that at least 12 inches of the antenna length is exposed. The window should be at least 12 inches high and 12 inches wide to accommodate the antenna.
7.5 Location of Antenna Cable.
7.5.1 Care should be given to antenna cable placement. Installers should be familiar with AC 43.13-1( ), Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair, and in particular, Chapter 11, Section 8, Wiring Installation Inspection Requirements.
7.5.2 Cabling should be mounted in a manner to preclude inadvertent damage from moving aircraft components, such as flight control cabling, or damage caused by items being frequently stowed on or near them.
7.5.3 In areas where the cable or antenna may come in contact with metal, such as a window frame, a fire sleeve meeting the requirements of SAE Aerospace Standard (AS) 1072, Sleeve, Hose Assembly, Fire Protection, should be installed to better prevent post-accident grounding of the antenna.
7.6 Use of Hook-and-Loop Fasteners. Hook-and-loop fastener systems, such as Velcro®, should not be used to mount ELT devices to aircraft.
7.6.1 ELTs mounted to aircraft using hook-and-loop fastener systems have been found to dampen g forces, which directly impact the ability of the ELT to trigger.
7.6.2 Hook-and-loop fastener systems can allow an ELT device to vibrate free of its mount and change its orientation, which affects its ability to correctly detect a g shock.
7.6.3 Crash investigators have also noted hook-and-loop fastener systems have allowed ELT devices to be thrown from a crashed aircraft, breaking the antenna connection in the process, and rendering the device useless.
7.6.4 Special Airworthiness Information Bulletin (SAIB) HQ-12-32, Hook and Loop Style Fasteners as a Mounting Mechanism for Emergency Locator Transmitters (ELTs), dated May 23, 2012, provides more information on the recommended use of hook-and-loop fasteners. Hook-and-loop fastener systems are not allowed to be used to mount ELTs that meet the requirements of TSO-C126b or later revision.
7.6.5 For the reasons stated above, hook-and-loop fasteners are strongly discouraged on ELTs certified prior to the issuance of TSO-C126b.
7.7 Post-Installation Test. Installers should carefully follow manufacturer’s instructions and perform any post-installation tests to verify that the ELT will function as intended.
7.8 ELT Registration. Owners of ELT equipment should carefully follow manufacturers’ and Cospas-Sarsat’s instructions and register the ELT system. Proper registration of a 406 MHz ELT device will aid SAR teams, should the need arise. Registering the beacon will provide SAR authorities crucial information about the ELT owner and the aircraft it is installed on, and provide emergency contact information of people that can provide additional valuable information that may save a life in an emergency. If a beacon transmission is detected, the information on file will be forwarded to the Government Search and Rescue Point of Contact (SPOC) who will respond to the alert. Also, by contacting the person or persons on file, rescue authorities will be better able to determine if the alert is real or inadvertent. If the alert is real, this information will improve the chances of finding the people in distress and saving their lives. If the alert is inadvertent, limited SAR resources will not be expended or possibly diverted from someone else experiencing a real emergency. An ELT can be registered at www.406registration.com.
8 ACCIDENTAL ACTIVATIONS.
8.1 General.
8.1.1 Inadvertent activation of ELT systems is a serious problem that expends resources and can divert equipment and manpower away from real emergencies. Furthermore, high false alarm rates can desensitize response teams that may think the event is not real.
While all ELT activations trigger a response from emergency response teams, only a
6 small fraction are real emergencies. For this reason, it is important that all personnel that work around and with ELT equipment understand how the units are activated and deactivated, and what should be accomplished if one is inadvertently turned on.
8.1.2 Besides triggering an emergency response, ELT activation near an airport may render some radio communications channels useless. FCC regulations specify what constitutes authorized ELT operations.
8.1.3 It is important that all aircraft operators, maintenance personnel, and pilots understand the seriousness of inadvertent activations. The pilot in command (PIC) of an aircraft equipped with an ELT is responsible for its operation. Such activations have been known to occur after hard landings and sometimes as a result of aerial acrobatics.
8.1.4 If an ELT is inadvertently activated, it should be shut off immediately and the nearest FAA tower or flight service facility should be notified of the event. Maintenance may be required before the ELT is returned to the “armed” condition.
8.1.5 ELTs approved for aircraft service are not to be used by persons traveling on foot for recreational purposes, such as backpacking or wilderness exploration.
8.2 Over-Air Testing Considerations.
8.2.1 Care should be taken to prevent accidentally triggering a SAR response. Accidental activation of an ELT will generate an emergency signal that cannot be distinguished from that of an actual emergency and could lead to expensive and frustrating searches.
Moreover, the unwarranted ELT signal could tie up the emergency frequencies such that a genuine emergency signal would not be picked up. In addition, if an ELT signal is transmitted on or near an airport, it may render some radio communications channels unusable.
8.2.2 Regardless of where the ELT is, or the duration of activation, a 406 MHz beacon broadcast will be detected by at least one Geostationary Local User Terminal (GEOLUT) and possibly every Low Earth Orbit Local User Terminal (LEOLUT) in the Cospas-Sarsat System. Alert messages will be routed to every Mission Control Centers (MCC) in the Cospas-Sarsat System for coordination around the world and a response will be made (unless prior coordination is made with Cospas-Sarsat and local authorities).
8.2.3 Direct connect testing is preferred to prevent inadvertent activation of the SAR response system. Over-air testing should always be avoided if possible. Use of an antenna boot or a direct connection from test equipment to the antenna port is preferred.
8.2.4 Testing an ELT system in a metal hangar will not guarantee the radiated signal will not be detected by the Cospas-Sarsat System. Technicians testing ELT devices in a hangar should treat the test as if they were testing outside.
8.2.5 When testing an ELT, a 50-ohm dummy load or antenna boot should be used to prevent the signal from being radiated into space. The signal must be attenuated to less
7 than -51 dBW (a power flux density of -37.4 dB (W/m2) or a field intensity of -11.6 dB (V/m).1
8.2.6 Owners of ELTs should carefully follow owner manual instructions and when possible limit testing to the “Self-Test” function.
8.2.7 If over-air testing must be accomplished, technicians should carefully follow Cospas-Sarsat instructions and use the built-in test message on the ELT device. The ELT test message is different from messages transmitted during an emergency, but is still detectable by the Cospas-Sarsat System. Cospas-Sarsat should be contacted prior to performing over-air testing. Cospas-Sarsat can be contacted at https://www.cospas-sarsat.int/en/.
8.2.8 If over-air testing must be accomplished, the local air traffic control (ATC) facility should be contacted in advance.
8.2.9 Follow test set instructions or place the test set a minimum of 12 meters, (39.4 feet) from the ELT antenna. Test in each mode and frequency the ELT unit transmits.
9 INSPECTION INFORMATION. Each ELT required by § 91.207(a) must be inspected within 12 calendar-months after the last inspection for proper installation, battery corrosion, operation of controls and sensors, and radiated signal strength. Due to the variety of ELTs and the different ways they can be installed, the ELT owner’s manual should be followed when performing a system inspection. With this in mind, inspections of an ELT system should consider the following:
9.1 Proper Installation.
Verify the ELT is not installed in an area prone to being bumped or damaged, such as a luggage compartment.
Verify the ELT is installed on a rigid airframe component not subject to vibrations that may trip the ELT system.
Verify the ELT or associated antenna cables are not installed near moving parts, such as flight control rods or cables, that may come in contact with the ELT system.
For fixed-wing aircraft, verify the ELT device is mounted as parallel to the longitudinal axis of the aircraft, as practical. For rotorcraft, ensure antenna is mounted per manufacturer’s instructions.
Note: On some helicopters this may mean the ELT device is forward facing and may be pointing downward at a 45 degree angle, ± 15 degrees.
1 Reference: Section 2.2 of C/S T.007, Cospas-Sarsat 406 MHz Distress Beacon Type Approval Standard, Issue 5, Dated May 2017.
8 Verify the ELT device is installed using the correct hardware per the manufacturer’s instructions.
Verify the controls for the ELT are within reach of the pilot. If the unit has a remote control, verify the controller is within reach of the pilot.
For externally mounted antennas, inspect for security, damage, and that the antenna is pointed up.
For internally mounted antennas, inspect for security and damage. Verify location is near a window or RF-transparent area and pointing up as much as possible.
Inspect antenna cabling for chafing and proper connection.
For TSO-C126b or later revision devices, verify hook-and-loop fastener systems are not used to mount the unit to the aircraft.
9.2 Battery Corrosion.
Inspect the ELT’s battery. Replace if signs of internal damage and/or corrosion are noted.
Visually inspect the ELT (other than the battery) for damage caused by battery corrosion. Correct discrepancies if noted.
Inspect the ELT battery compartment for damage or corrosion. Clean, repair, or replace as needed.
9.3 Operation of Controls and Sensors.
Review paragraph 8.2 of this AC before testing ELT controls and sensors.
Verify operation of ELT controls in each mode.
If installed, operate the ELT remote control in each mode to determine that the equipment is operating according to the manufacturer’s instructions.
For devices that can be remotely operated, verify the remote control works correctly in each position. Ensure the unit is returned to the “off” or “armed” position if equipped.
Using manufacturer recommendations, apply g-load to verify the crash sensor will activate the ELT. Reset the system if necessary.
If installed, inspect the water-activated switch. Repair or replace if damage is noted.
If equipped with a water-activated circuit, activate the ELT by shorting the water-sensing leads and determine if the system is radiating a 406 MHz signal. Ensure the system is reset if necessary.
9.4 Radiated Signal Strength. Signal strength of an ELT must be checked periodically to ensure the radiated signal is sufficiently strong to be received by a satellite in an emergency.
9.4.1 406 MHz Testing Considerations. Review paragraph 8.2 of this AC before testing radiated signals.
9.4.2 406 MHz Testing.
Verify the device is outputting a signal of not less than 17dBm (50mW) and not greater than 26dBm (400mW).
Verify the device is transmitting on the correct frequency. This can be done by running the ELT self-test and detecting the signal with an ELT test set.
Receiving and decoding a test message is an indication the unit is transmitting on a correct frequency.
Using appropriate test equipment and shielding, note the ELT code transmitted and verify that the ELT code is registered with Cospas-Sarsat. The testing technician or aircraft owner should verify the information on file with Cospas-Sarsat is accurate and up to date.
Determine that the ELT aural indicator can be heard in the cockpit with the aircraft engine(s) off, and that the visual indicator can be seen from the crew’s normal sitting position. If possible, this should be performed in a way that will prevent a SAR response (e.g., with a dummy load installed).
Perform an operational check of the g switch. This should be performed in a way that will prevent a SAR response (e.g., with a dummy load installed).
Replace if the g switch fails to activate.
Ensure all cables except the 406 MHz transmitter output are reconnected.
Ensure the 406 MHz transmitter is connected to a test set if possible. Activate the ELT (use the remote switch if installed), and determine if the system is radiating a strong 406 MHz signal. Ensure the system is reset if necessary.
If equipped with a water-activated circuit, connect the ELT to a test set if possible. Activate the ELT by shorting the water-sensing leads and determine if the system is radiating a strong 406 MHz signal. Ensure the system is reset if necessary.
9.4.3 121.5 MHz Testing Considerations. If the ELT includes a 121.5/243.0 MHz homing source, it is advisable to also check the integrity of these systems.
Note 1: Cospas-Sarsat no longer monitors 121.5 MHz; however, some SAR teams may use this signal as an additional means for additional homing in on a crashed aircraft.
Note 2: Review paragraph 8.2 of this AC before testing radiated signals.
9.4.4 121.5 MHz Testing. Testing the functionality of a 121.5 MHz transmitter should be accomplished per manufacturer’s instructions.
9.5 Battery Replacement.
9.5.1 Determine if the battery is serviceable. Serviceable batteries have less than 1 cumulative hour of use, and more than 50 percent of its useful life left (for rechargeable batteries, this is 50 percent of the useful charge), as established by the transmitter manufacturer.
Unserviceable batteries must be removed and replaced.
9.5.2 If updated, the new expiration date for replacing (or recharging) the battery must be legibly marked on the outside of the transmitter and entered in the aircraft maintenance record.
Note: This does not apply to “dry” batteries that are stored without an electrolyte, such as those that are water-activated, since they are essentially unaffected during prolonged storage.
9.6 Ground Inspections Outside of the United States. The focus of this AC is ELT systems used in the United States. Aircraft owners and operators should note inspection requirements may be different in other countries.
10 ACRONYMS.
14 CFR Title 14 of the Code of Federal Regulations AC Advisory Circular AS Aerospace Standard ATC Air Traffic Control cm Centimeter dB Decibel dBm Decibel-Milliwatts dBW Decibel-Watts ELT Emergency Locator Transmitter ELT-AD ELT Automatic Deployable ELT-AF ELT Automatic Fixed ELT-AP ELT Automatic Portable ELT-DT ELT Distress Triggered ELT-S ELT Survival EUROCAE European Organization for Civil Aviation Equipment FAA Federal Aviation Administration
11 FCC Federal Communications Commission GEOLUT Geostationary Local User Terminal ICA Instructions for Continued Airworthiness LEOLUT Low Earth Orbit Local User Terminal MCC Mission Control Centers MHz Megahertz mW Milliwatt PIC Pilot in Command RF Radio Frequency
RTCA RTCA SAIB Special Airworthiness Information Bulletin SAR Search and Rescue SPOC Search and Rescue Point of Contact VHF Very High Frequency V/m Volt per Meter W/m2 Watt per Square Meter 11 RELATED DOCUMENTS (current editions).
11.1 Applicable CFR Parts. Available at http://www.ecfr.gov/.
11.1.1 Title 14 CFR:
• Part 25, § 25.1415.
• Part 29, § 29.1415.
• Part 43, § 43.16.
• Part 91, §§ 91.205, 91.207, and 91.509.
• Part 121, §§ 121.339 and 121.353.
• Part 125, § 125.209.
• Part 135, §§ 135.167 and 135.168.
11.1.2 Title 47 CFR. Part 87, §§ 87.193 through 87.199.
11.2 ACs. AC 43.13-2, Acceptable Methods, Techniques, and Practices — Aircraft Inspection and Repair. Available at www.faa.gov/regulations_policies/advisory_circulars/.