nuts & bolts

technical counselor Emergency Locator Transmitters Requirements and maintenance D I C K KOEHL E R , E A A 1 6 1 4 2 7

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viation emergency locator transmitters (ELTs) were the first emergency beacons developed. Most civil airplanes in the United States are required to carry them. ELTs were intended for use on frequency 121.5 MHz, to alert aircraft of a signal from below. A major limitation is that another aircraft must be within range and listening to 121.5 MHz to receive the signal. Different types of ELTs are currently in use, with approximately 170,000 of the older generation (121.5 MHz) ELTs in service. Unfortunately, these have proven to be highly ineffective. Some studies indicate a 97 percent false alarm rate, and that they activate properly in only 12 percent of crashes. Another drawback is that they provide no identification data. To address these problems, 406 MHz ELTs were developed to work specifically with the CospasSarsat system. These ELTs dramatically reduce the false alarm impact on search and rescue (SAR) resources, have a higher accident survivability rate, and decrease the time required to reach accident victims by an average of six hours. The Cospas-Sarsat satellite-based rescue system was developed to provide a better receiving source for these signals and to provide location data for each activation (something that over-flying aircraft were unable to do). Cospas-Sarsat is an international SAR program that uses satellite-aided tracking. It’s the group pushing the transition to 406 MHz ELTs because its signals provide more information—with greater accuracy—than the current ELTs. The 406 MHz ELT is the same personal locator bea104

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con (PLB) that can be found in department and sporting goods stores. Most airplane operators are required by FAR 91.207 to carry an ELT and have the option to choose between either a 121.5 MHz ELT or a 406 MHz ELT. In August 2005, the FAA issued a notice to airmen (NOTAM) announcing

In August 2005, the FAA issued a notice to airmen (NOTAM) announcing plans to end satellite processing of ELT distress signals broadcast over 121.5 MHz and 243 MHz on February 1, 2009. plans to end satellite processing of ELT distress signals broadcast over 121.5 MHz and 243 MHz on February 1, 2009. This came at the request of the Cospas-Sarsat program. Reasons to discontinue use of 121.5 are driven by guidance from the International Maritime Organization (IMO) and the International Civil Aviation Organization (ICAO). These two agencies are responsible for regulating the safety of ships and aircraft on international transits and handle international standards for maritime and aeronautical search and rescue missions. As a result, it may be mandatory to have a 406 MHz ELT to fly in some foreign countries. There is currently no plan to change FAR 91.207 to require either an upgrade to the 406 system or a ban on installing the 121.5 units. Therefore, after 2009, ELTs transmitting over 121.5 MHz will continue to satisfy FAA requirements and be legal, but the rescue folks can provide only limited assistance in the event of an accident,

FAR 91.207 (b) says the ELT must be attached to the plane as far aft as possible and in such a manner that the probability of damage to it in the event of a crash is minimized. For this reason it is usually bolted in aft of the baggage compartment or in the tail cone as seen in this Piper Cherokee installation.

because the satellites will no longer receive the 121.5 signals. However, the FAA and Department of Defense will monitor 121.5 ELTs from the ground. The new 406 MHz ELTs use digital technology to transmit information specific to you and your aircraft, including your GPS coordinates and personal contact information. For this reason, it is mandatory to register a 406 ELT with Cospas-Sarsat.

ELT Requirements for Homebuilders When in doubt, always reference the FARs, and FAR 91.207 covers ELT requirements. It starts out, “(a) Except as provided for in paragraphs (e) and (f)…no person may operate a U.S. registered civil airplane unless—(1) There is attached to the airplane an approved automatic type emergency locator transmitter that is in operable condition for the following operations, except that after June 21, 1995, an emergency locator transmitter that meets the requirements of TSO-C91 may not be used for new installations.” The listed subparagraphs that this paragraph refers to include 121, 125, and 135 operations (airlines and charters). The next paragraph, (2), is the section of the regulation that applies to homebuilt airplanes. It reads, “For operations other than those specified in paragraph (a)(1) of this section, there must be attached to the airplane an approved personal type or an approved automatic type emergency locator transmitter that is in operable condition, except that after June 21, 1995, an emergency locator transmitter that meets the requirements of TSO-C91 may not be used for new installations.” Paragraph (a)(2) allows use of either an approved personal type (406 MHz) or the standard approved ELT in 121.5 and 243 MHz. Note

that an ELT must meet TSO-C91a for new installations. Be careful if buying a used ELT. It may have been made in accordance with the old TSO-C91. A C91 unit is not acceptable for a new installation in your homebuilt. The next FAR 91.207 paragraph, (b), states the ELT must be attached to the plane in such a manner that the probability of damage to it in the event of a crash is minimized. It goes on to state that the ELT should be attached to the plane as far aft as practicable. It must be bolted in—usually aft of the baggage compartment or in the tail cone. You can’t get by with a panel mount or a portable unit in your nav bag. All ELTs that I have installed came with detailed installation instructions. Paragraph 91.207 (c) covers ELT batteries, and (d) requires an inspection every 12 calendar months. But let’s skip these for the moment and instead look at the exception paragraphs (e) and (f), which were called out at the start of paragraph (a). Paragraph (e) allows a new airplane without an ELT to be ferried to a place to have the ELT installed, and an airplane with an installed but inoperative ELT to be ferried to a place to have it fixed. However, in either case, only minimum crew (pilot for a homebuilt) is allowed in the plane for the flight. Paragraph (f) has a whole bunch of exceptions to the need for an ELT. For instance, if you built a turbojet-powered homebuilt before January 2004, you are not required to have an ELT! There’s also an exclusion for airplanes during flight testing. This would seem to indicate that your homebuilt would not need an ELT during its initial phase 1 flight-test period. While this is technically correct, many FAA inspectors and designated airworthiness representatives want to see an ELT installed when they perform the airworthiness inspection. Undoubtedly it will make your life easier durEAA Sport Aviation

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Courtesy of NASA

The 406 Mhz Cospas-Sarsat system uses digital technology to transmit information specific to you and your aircraft, including your GPS coordinates and personal contact information.

ing the inspection if you have an ELT installed rather than having a discussion with the inspector regarding the flight-testing exclusion.

ELT Maintenance All ELTs must be inspected and tested annually in accordance with FAR 91.207(d), on homebuilt or certificated aircraft, whether 121.5 or 406. FAR 91.207(d) says that “Each ELT (if required to be installed)… Must be inspected within 12 calendar months of the last inspection for (1) Proper installation; (2) Battery corrosion; (3) Operation of the controls and crash sensor; and (4) The presence of a sufficient signal radiated from its antenna.” Let’s look at each of these separately: • Proper installation. You can do this by looking at the mount structure and the antenna connections. Look for corrosion, proper attachment, and anything loose. I have found antennas disconnected, corrosion from leaking alkaline batteries, and missing parts. I have also found them turned off. • Battery corrosion. Look for cracks in the case and leaks. The liquid from 106

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leaking batteries is clear, but it leaves a black smudge on most metals and is sticky to the touch. On some ELTs, leaking batteries will directly get into the transmitter unit, since the circuit card is not in any way protected from the top of the battery case. You will have to disassemble the unit by removing four screws as if you were changing the battery pack. If you detect any leakage, the battery pack must be replaced, and the transmitter cleaned and inspected for corrosion damage. After cleaning, everything should be washed down with a good water-displacing aircraft preservative. • Operation of the controls and crash sensor. A label on the ELT indicates the direction for force activation. An early TSO-C91 ELT should be able to be activated by a quick rap with the palm of the hand. A later TSO-C91a ELT can be activated by using a rapid forward (throwing) motion coupled by a rapid reversing action. (Don’t let it slip out of your hands.) Follow the manufacturer’s instruction for this check, and verify that turning on the “On” switch can activate the ELT by listening with a handheld aircraft radio or a wattme-

ter. Be sure to do this test only within the first five minutes of the hour, and only allow three sweeps of the transmitter audio modulation or the Civil Air Patrol may be paying you a visit. • The presence of a sufficient signal radiated from its antenna. Reinstall the ELT in its mount. Using a low quality AM broadcast radio receiver or a handheld radio without the antenna installed, activate the ELT using the “On” or “Test” switch. Hold the radio about 6 inches from the ELT antenna and you should hear the ELT aural “woop-woop” tone. Because a handheld is more sensitive, you should hold it at least a wingspan away, and it may still give a false positive of signal strength. Again, remember to perform this test only within the first five minutes of the hour. Per 91.207(c) the ELT battery must be replaced (1) when the transmitter has been on for more than one cumulative hour; or (2) when 50 percent of the batteries’ useful life has expired, as established by the ELT manufacturer. Usually you will be replacing the batteries because they have exceeded This Personal Locator Beacon (PLB) from ACR Electronics, Inc. is a one-button activated emergency signaling device that operates on the 406 MHz frequency used by the CospasSarsat satellite system.

their calendar life limit, as noted on the ELT. The pilot, per the Preventative Maintenance Limitations of 43.3(h), can replace batteries on certificated aircraft, but since Part 43 doesn’t apply to experimental aircraft, anyone can replace the batteries on your homebuilt. The new battery expiration date is required to be legibly marked on the outside of the transmitter and entered in the aircraft maintenance record. One last note: The 12-calendar month inspection requirement is the same as the annual inspection requirement, meaning it is good through the last day of the month, 12 months after the last inspection. This is why we usually do it as part of the aircraft’s annual condition inspection, and it should be logged as “ELT inspected in accordance with 14 CFR 91.207(d) and found to function correctly. Battery due ____,” or words to that effect.

Unfortunately, all ELTs (including the $800 units) suffer from the propagation problems of 121.5 MHz. In a couple of years, the satellites will stop looking for you, and your chances of being found are pretty poor unless the search team comes within a few miles of you, assuming there is a search team sent out at all. In addition, some countries may require a PLB to fly in

their airspace, but all official positions (FAA) say that an ELT is all you are going to need to fly legally in the United States for many years. On the other hand, you could get a 406 MHz ELT/PLB. Artex makes a bare-bones unit that does not have a GPS interface for about $900. Artex also makes a couple of other models that have a GPS interface and meet all

My Views Now that we have reviewed the legal requirements for installing and maintaining the ELT, let me offer my personal opinion on the 121.5 versus 406 MHz systems. This could be a list of potential birthday gifts, so feel free to tear this out and leave it for your spouse to find. First off, be sure to carefully read FAR 91.207 to understand if you need an ELT at all. Remember that the regulation specifically says “airplane.” If your homebuilt is a gyroplane, helicopter, powered parachute, or trike, you are not required to have an ELT installed. And if your airplane is a single-seat, you don’t have to have one. Homebuilt airplanes with more than one seat are required to have an ELT. You can buy a new, TSO-C91a compliant ELT for less than $200. Additionally, there are models in this price range that can be legally powered by Duracell D batteries, avoiding the every two-year battery replacement costs of $25 to $60. EAA Sport Aviation

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technical counselor the international requirements, but they run from $1,300 to more than $3,000, depending on antennas, interfaces, etc. Of course, you will also need a GPS unit onboard that sends the correct format latitude and longitude information to the ELT/PLB. This will probably require some sort of newer panel-mounted GPS unit, since most of the handheld GPS units

have limited or no data output capability. If you do not have the GPS interface, the 406 MHz unit will allow the satellite to get a fix of about 3 nautical mile accuracy within about 90 minutes. However, if you do have the GPS interface, your position will be known to about 100 foot accuracy within about 3 minutes! Therefore, if you want the best chance of being

located after an aircraft accident, you really want a PLB with GPS, but be prepared to shell out at least $1,300, plus the cost of the GPS input. If you want the advantages of quick response offered by a PLB, but can’t stand the cost for a unit with a technical standard order (TSO) in your plane, another option is to install the inexpensive ELT to meet the FAA requirement, and then carry a portable PLB. You can buy these units for about $500 without GPS, and about $600 with GPS. The bad news is that these units do not automatically activate in the event of a crash. You will have to flip the switch. I suspect that with a little bit of thinking, the average homebuilder could design an automatic switch flipper in the event of a high-g crash. The mechanical inertia switch on Emergency Beacon Corporation’s series of ELTs comes to mind as a possible design to activate your low-cost PLB. I have an old ELT, but plan to buy a portable PLB. Of course, I am not planning on an around-the-world flight any time soon, so I don’t need the TSO’d PLB. Now, if I can just get my wife to read this, I may get the perfect gift on my birthday. Richard Koehler is associate professor of aerospace sciences at the University of the District of Columbia and has been an EAA member since 1980. He is an active airframe and powerplant mechanic with inspection authorization, a commercial pilot with instrument and multi-engine ratings, and a technical counselor and flight advisor.

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Civil Air Patrol www.CAP.gov Federal Aviation Administration www.FAA.gov International Civil Aviation Organization www.ICAO.int

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