Upgrading Your ELT |
Upgrading from the 121.5 MHz Emergency Locator Transmitter (ELT) to the 406 MHz ELT| |
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 (121.5 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 Technical 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 121.5 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 launching 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...