Upgrading from the 121.5 Mhz Emergency Locator Transmitter (Elt) to the 406 Mhz Elt free essay sample

| Upgrading Your ELT | Upgrading from the 121. 5 MHz Emergency Locator Transmitter (ELT) to the 406 MHz ELT| | | Alford Duncan| Embry Riddle Aeronautical University| The purpose of this document it to provide a brief history of ELTs, the satellite system that monitors ELT deployment, a summary of how the ELT works, and how it’s installed. I will also attempt to show the benefits of upgrading your existing 121. 5 MHz Emergency Locator Transmitter to the newer and more efficient 406 MHz ELT. I also outline in general terms how to register a new 406 MHz ELT, and give a comparison of the two types of ELT systems (121. MHz and the 406 MHz). Finally I give you a brief summary of the regulations pertaining to the use of ELTs. | A brief history Emergency Locator Transmitters (ELTs) aren’t new; they’ve been around since the 1960s. The technology however wasn’t sufficient for the requirements. It wasn’t until 1971 that the FAA issued its first TSO or Technica l Standard Order (TSO-C91) pertaining to ELTs. A Technical Standard Order is a minimum performance standard for a specific item. In other words the FAA said; if you install an ELT in your aircraft it must meet a set criterion for operation. An example of the criteria would be G-loading, placement in the aircraft, and battery life. All of these had meet or exceed the TSO stated minimums. It was this TSO that set into motion a determined push to make ELTs mandatory and uniform in performance for all civil aircraft. Two high profile crashes also played a major role in making ELTs a required fixture in civil aircraft. The first incident was a single engine Cessna 195, owned and operated by Alvin Oien, his wife Phyllis Corbus-Oien, and their daughter, 15-year old Carla Corbus. Their aircraft impacted terrain 4,500 feet up in California’s Trinity Mountains. What separates this accident from the many other accidents occurring during that time was no one died as a result of the March 11th crash. Carla and her mother starved to death while Corbus Oien went missing while trying to hike out after 30 days. Carla and her mother survived for nearly 6 weeks. Carla, who kept a diary, wrote that she heard aircraft overhead daily but they weren’t spotted because of cloud cover and the almost daily snowfall. The following spring the scattered bones of Carla and her mother were discovered by a hunter amid the wreckage of their aircraft. As it turns out they were only nine miles from US Route 299. Mandating the use of ELT’s in General Aviation aircraft got another big push after the October 16, 1972 crash of a Cessna 310 carrying then House Majority Leader Hale Boggs and Representative Nick Berish of Alaska. The Coast Guard, Navy, and Air Force searched for 39 days but they were never found. From the mid 1970s to the early 1980s the number of ELTs in service totaled more than a quarter million. The United States and Canada began investigating the use of low earth orbit satellites programmed to detect the 121. MHz (analog) distress frequency. Prior to this all ELT’s transmissions were terrestrial, line of sight transmitters. During this time rescue authorities were becoming plagued with almost constant false alerts. Of these alerts only about 2 in 1000 proved to be from an actual crash. It was exploiting a lot of resources to track these false alarms and it greatly reduced the response time. Instead of l aunching a search immediately rescue authorities were waiting for more confirmation (i. e. an overdue aircraft report) before committing resources to a search. The ELT’s themselves were not very robust. Prior to 1995 there wasn’t even a requirement to test ELTs. To verify their suspicions the FAA performed a maintenance survey of six Fixed Base Operators (FBOs) that encompassed 107 ELT inspections. Of the 107 ELTs inspected, 64% were discrepancy free but 36% (39 ELTs) had a total of 52 discrepancies. Some of these discrepancies were serious enough to cause the ELT to not function at all. A number of the ELTs would start transmitting without being activated by the pilot, or activate with G-force below the 5G minimum limit. Some of the most common problems with nonemergency ELT activation are hard landings which could set off the ELT and the pilot not know it. A lot of early ELT’s didn’t have an audible tone, meaning that a person could walk past an aircraft and not know that the ELT was transmitting. Walking past an aircraft on the flight line and bumping the aircraft near where the ELT was mounted would set it off (example of a low â€Å"G† threshold). Rough ground handling will also set off an ELT as well as some restaurant equipment being known to produce a signal on 121. 5 MHz. As the number of aircraft owners who purchased ELT’s increased, more and more false alarms resulted. In a 1990 report to NASA by Bernard J Trudell and Ryland R Dreilbis, of the Atlantic Research Corporation, titled â€Å"Current Emergency Locator Transmitter Deficiencies and Potential Improvements Utilizing TSO-C91a ELTs†, Mr. Trudell and Dreilbis reported that from 1984 through 1987 the Rescue Coordination Center at Scott AFB opened 6,626 rescue missions to locate transmitting ELTs. Of the 6,626 missions 6,421 (97%) were false alarms. NASA and the FAA realized that something must be done, so in June of 1995 the FAA wrote FAR 91. 207. Part 91. 207 outlines for mechanics the steps necessary to test ELTs We’ll go into that a little more deeply later on in the paper. The Satellites In 1979 an understanding was reached between the United States, Canada, France, and Russia which became known as the COSPAS SARSAT agreement. COSPAS is a Russian acronym for Cosmicheskaya Systyema Poiska Avariynich Sudov or Space System for the Detection of Vessels in Distress. SARSAT is an acronym meaning â€Å"Search and Rescue Satellite Aided Tracking† The first COSPAS-SARSAT satellite launch was in 1982 by the Soviet Union. Within a few days of the satellite stabilizing in orbit a 121. MHz signal was detected in Canada. The Canadian government launched a search and found a downed small aircraft in British Columbia, Canada with three survivors. The United States Launched its first satellite the following year. The COSPAS-SARSAT system consists of two types of satellites Low altitude earth orbit (LEOSAR) and geostationary e arth orbit (GEOSAR) satellites. These satellites are the key to the modern SAR system. They detect and locate 406 MHz signals worldwide and until February 2008, detected 121. 5 MHz alerts for more than 60% of the worlds surface (to include oceans). These satellites orbit the earth between 500 and 700 miles and complete an orbit about every 100 minutes. If a distress beacon is picked up by a SARSAT it stores the data and continually downloads it for up to 48 hours. Another important link in the SARSAT chain is the use of Local User Terminals or LUTs. LUTs can be stationed on a building or as a mobile unit on a trailer. The LUT consists of a dish antenna, a downlink converter and processer, a GPS antenna and an optional display system (PC with monitor). The LUTs receive data from the SARSAT where it then processes the data and transmits it to a Mission Control Center or MCC. There are approximately 37 MCCs spread out across the globe. The MCC analyzes the data and contacts the nearest Rescue Control Center or RCC. The RCC notifies the Search and Rescue Point of Contact (SRPOC) who in turn launch aircraft and/or ground assets to search for the source of the alert. There are 294 national and international SRPOCs listed by the COSPAS SARSAT organization. Currently there are 6 fully functional LEOSAR satellites in Low Earth Orbit (Sarsat-7 thru 12) and 4 GEOSAR satellites in geostationary earth orbit. After February 2008 none of these satellites monitor 121. 5 MHz. The ELT The primary purpose of the modern 406MHz ELT and encompassing hardware is to alert search and rescue in the event of an accident, to have the signal recognized as your aircraft, and to help the SAR teams locate you in the event of an accident. ELTs are designed to activate automatically when a specific amount of gravity (2. 5Gs) closes a switch after a hard impact. Older ELT’s transmit an anonymous warble tone on 121. 5 MHz and or 243 MHz UHF (243 MHz being for the military). They produced only about 0. 1 watt of power. New 406 MHz ELTs transmit a digital signal and produce 5 watts of power and can sustain it for up to 24 hours. The 406 MHz signal is picked up and tracked by the COSPAS SARSAT network. New 406 MHz ELT’s are Lithium battery powered and self contained. The batteries have a shelf life of 5 years. However, per FAR 91. 207, batteries installed in ELTs, on aircraft, will be changed every 2 years. 406 MHz ELTs transmit a digital signal to the LEOSAR and GEOSAR satellites. They also transmit on the 121. 5 MHz frequency. The satellites process the 406 MHz signal and retransmit the data to Local User Terminals or LUTs. The LUT is an earth based receiving station (or downlink) that receives the retransmitted beacon signals sent by the COSPAS-SARSAT. The LUT then processes this signal and identifies and alerts the closest Mission Control Center or MCC. The MCC notifies the closest SAR asset to prosecute the mission. The ELTs themselves are typically 4†x4† and differ in length from 10† to 14†. ELTs typically weight from 4 to 7 lbs and are usually bright yellow or orange in color. All new 406 MHz ELTs come equipped with an external antenna and remote switch. The ELT must be mounted in such a way and location to minimize damage in the event of a crash. In most aircraft this will be as far aft in the fuselage as possible or in the trail area of smaller aircraft. The antenna should be mounted as high as possible on the fuselage. The ELT must be installed so that its longitudinal access is aligned to within 10 degrees of the aircrafts longitudinal axis. The ELT must also be mounted to the aircrafts primary load carrying structures (not the skin). The same care must be taken when mounting the antenna. Mounting anything to the aircraft skin without reinforcement will produce stress points, fatigue cracking, and lead to potentially fatal results. Before the antenna is mounted, measure the length of the coax to make sure it will reach. For any distance apart greater than the length of the coax provided, the shop doing the install should contact the ELT manufacture to see if a longer length coax can be used. The instrument panel mounted remote switch can be activated by the pilot if there is enough time prior to making the emergency landing. This small amount of time can make the difference between life and death, or in the event of a post crash fire the difference between the ELT surviving the fire to transmit or not. The remote switch must be mounted in the instrument panel in such a way that the pilot can easily see it and operate it from a normal setting position. The remote switch also has its own internal battery and must be checked when doing the ELT inspection. Another important piece of the 406 MHz ELT system is the ELT to NAV interface. This interface is connected between the ELT and the aircraft Flight Management Computer (FMC) or GPS. The interface unit continually updates itself and stores the aircrafts Latitude and Longitude. About 60 seconds after activation the ELT transmits the stored data to COSPAS-SARSAT. After February 2008 detection of the 121. 5 MHz signal is primarily achieved by overflying aircraft (if they are in range) and triangulation with ground stations or other aircraft. The effective range of an ELT operating at 121. 5 MHz is about 15 nm and upwards to 50 nm (best possible case). The idea is that pilots will monitor 121. 5 continuously and notify air traffic control of their positions when they hear an ELT signal. Participation isn’t mandatory and you must remember that pilots have requirements to monitor other frequencies as well. How do I inspect my ELT? ELT inspections should be done by a certificated mechanic or avionics shop. That being said, FAR 91. 207 is the guide for inspecting the ELT. Every 12 calendar months the ELT must be inspected. The mechanic must verify that the ELT is placed as far aft in the fuselage or tail as practical. If the ELT has been used/activated for more than one hour (cumulative) the batteries must be replaced. The battery must also be replaced if the expiration date has passed. Some newer TSO-C91a ELTs use standard â€Å"D† batteries. If they are installed you need to check for a date label. If there isn’t a manufacture â€Å"Good Until† date on the batteries they must be replaced with batteries having a date. Other inspection items include; checking for proper installation of mounting brackets, security of coax, and security of the antenna. Check the batteries and battery box for corrosion. Check the inertia (G) switch. Remember this activates the ELT. You should only test the inertia switch at 5 minutes past the hour. You can also activate the ELT with the remote switch, so if its 1405 hours and the tower hears a tone and it only lasts a few seconds they’ll assume, and correctly so, that someone was testing their ELT. When you’re testing a new 406 MHz ELT don’t leave it on for more than 60 seconds, because after 60 seconds it transmits GPS coordinates and aircraft data to SARSAT. Then you have to explain your false alarm. You’ll also need to check the operation of the remote switch. When you turn it on did you get a light in the switch? Your old TSO-C91 ELT fails inspection. What now? Your mechanic comes to you and says â€Å"I’m sorry but your ELT failed the Inertial switch test and needs to be replaced† After you’ve finished bemoaning the cost of replacement parts and sausage fingered mechanics you ask yourself; Do I have to upgrade to the newer TSO-91a model? Well the answer is no, if you can find a replacement ELT that is the exact part number of your old one, you can use it. It can be new or used. Actually there are companies still making direct replacement ELTs for these older ones. Remember if you purchase a used ELT it must be inspected and tested before being installed. Remember â€Å"direct replacement† If you can’t find it, you have to upgrade. After looking around and find that you can’t locate a direct replacement you take your mechanics advice and purchase a new TSO-C91a, 406 MHz ELT with GPS interface. When you get you bill for the annual inspection your mechanic hands you a piece of paper that says Official 406 MHz ELT Registration Form† telling you that you should fill this out and fax it in to the number listed on the top of the form Registering your new 406MHz ELT Your next step is to register your new 406 MHz ELT. While you certainly don’t have to register your new ELT why go to all the trouble of upgrading to the best technology available and not register it? There’s no subscription service and ità ¢â‚¬â„¢s free. Every new 406 MHz ELT has its own unique hexadecimal code (or ID). When the ELT is installed, the aircraft owner/operator notifies NOAA of the install by going to NOAA’s website at, https://beaconredistration. oaa. gov, or by filling out NOAAs â€Å"Official 406 MHz ELT Registration Form† and faxing or mailing it to NOAA’s office in Suitland MD. On both the online and hand written form you’ll be ask to enter the new beacons ID number and create a password for that beacon. You’ll also assign a security question in case you forget your password. When you click the submit button the NOAA computer will cross check the beacon ID you supplied against a master list of beacon IDs provided by the manufacture. If your beacon checks out, meaning that it’s not already registered to another aircraft, you’ll be prompted to provide owner/operator information (address, telephone number, email address), aircraft information (registration â€Å"N† number, type, make, model, color, seating capacity, survival equipment, and home airport), and lastly emergency contact information (the name and phone numbers for a primary and alternate contact) Hit the submit button and in 7 to 10 days you’ll receive a registration sticker in the mail. Affix the sticker to the ELT and you’re registered. Comparing the 406 MHz Beacon to the 121. 5 MHz Beacon Beacons transmitting on 121. 5 MHz are anonymous beacons. Search and Rescue responses can take from 4 to 6 hours or as much as 12 hours to sort out the validity of the beacon. Resources must be sent out to determine who is in trouble. The 121. 5 MHz signal is also ground based. 406 MHz beacons are registered. If a 406 MHz beacon signal is received the MCC knows immediately who’s in trouble. A 406 MHz beacon can also transmit its location using GPS coordinates (Latitude and Longitude). The delays are greatly reduced in determining if a 406 MHz alert is a false alarm. All alerts form 406 MHz beacons come from beacons. For the 121. 5 MHz beacons only about 1 out of 5 alerts originate from beacons (remember the pizza ovens? ). 121. 5 MHz beacon detection is accurate to within 15 nautical miles. 406 MHz beacon detection is accurate to within 3 nautical miles (with position calculated by Doppler shift) and less than 100 yards if using GPS positioning. The 406 MHz Beacon will also transmit on 121. 5 MHz to assist with search operations. To reiterate the 121. 5 MHz frequency is not tracked by SARSAT. 121. 5 MHz beacons transmit at 0. 1 watt. 406 MHz beacons transmit at 5. 0 watts. ELT cost is the final factor to be considered in our comparison. The low end cost of a new 121. 5 / 243. 5 ELT is about $200. 00 uninstalled. The cost of a new 406MHz ELT ranges from about $900. 00 dollars for a non GPS/FMS interface unit with a whip antenna to about $4,000. 00 uninstalled for a unit with GPS/FMS interface and high speed blade antenna. In accordance with Federal Aviation Regulation part 91. 207 all US registered civil aircraft must have attached an approved automatic type ELT that is in operable condition. After June 21 1995, in accordance with the FAAs new TSO-C91a, ELTs meeting the requirements of the old TSO-C91 may not be installed in new aircraft. . Resources a. Federal Aviation Administration; Technical Standard Order TSO-C91, Emergency Locator Transmitter Equipment, 1971 b. Federal Aviation Administration; Technical Standard Order TSO-C91a, Emergency Locator Transmitter Equipment, April 29, 1985 c. Federal Aviation Administration, Federal Register; April 2, 1990, Volume 55, Number 63, Page 12316 d. Federal Aviation Administration, Federal Register; September 21, 1971, Volume 36, Number 183, Page 18716 e. Electronic Code of Federal Regulations; Title 14, Aeronautics and Space, Volume 2 and 3n part 91, 121, 135 f. AOPA On-line Regulatory Brief; Emergency Locator Transmitters. ttp://www. aopa. org/whatsnew/regulatory/elt. html g. COSPAS SARSAT Information Bulletin; Issue 22 February 2010, By Daniel Levesque, Head of Secretariat International Cospas-Sarsat Program. h. Washington State Department of Transportation; Emergency Locator Transmitters, December 29, 1970. www. wsdot. wa. gov/aviation/sar/elt_history. htm i. I Fly America; ELT Update, Limit Your Testing Time, By H. Dean Chamberlain, June 2010. www. iflyamerica. org/elt. asp j. NOAA Satellite and Information Service; Search and Rescue Satellite-aided tracking. www. sarsat. noaa. gov/emerbcns. html