Emergency Location Transmitters (ELT) Emergency Position Indication Rescue Beacons (EPIRB) Sun May 8 00:05:05 1994 Message : #13121876 From: Brent Chapman Address : bchapman@netcom.com Group : Usenet.rec.backcountry Subject : Re: Rescue Transmitters Org. : Great Circle Associates; Mountain View, CA cwild@magnus.acs.ohio-state.edu (Charles F Wild) writes: >I recently received information from NFS about backcountry travel in >the remote northern Wind River Range (Shoshone National Forest) in which was >described a system for signalling for help in the event of an accident. >It is based on the hikers carrying what was called a down pilot emergency >radio which they would use to communicate with overflying aircraft which >would relay the emergency call to a nearby search and rescue team. This would be a standard aviation ELT (Emergency Locator Transmitter) or nautical EPIRB (Emergency Position Indicating Response Beacon, or some such). I spend a fair bit of my spare time (probably about 10-20 hours/month) tracking these puppies down when they go off: I'm a search mission coordinator, search pilot, and ground team member for the Civil Air Patrol, the volunteer civilian auxiliary of the U.S. Air Force that handles the vast majority of ELT/EPIRB searches in the continental U.S. ELTs and EPIRBs operate on the same general principles; they both transmit an distinctive audible AM signal (a "whoop, whoop, whoop"; hard to describe, but very easy to recognize once you've heard it) on the international emergency frequency of 121.5 MHz. Some units also transmit on 243.0 MHz, but those units are primarily used by the military. The primary difference between ELTs and EPIRBs is how they are automatically activated: an ELT is automatically activated when it is subjected to a sudden physical shock (i.e., during a plane crash), and an EPIRB is automatically activated when it is inverted (i.e., when a boat capsizes) or gets wet (i.e., when a boat sinks). Both types of units can also be triggered manually. Both types of units range in size from a few ounces and about the size of a pack of cigarettes on up to the weight and size of a large brick; the bigger units tend to be more rugged and have a more powerful transmitter and longer battery life. Some of the units are designed to be worn by air or ship crews as part of their personal survival gear, and can only be triggered by hand. Some of the units (particularly the larger ones) give you the ability to transmit and receive voice on the emergency frequency, in addition to transmitting the emergency signal. When an ELT or EPIRB is activated, there are essentially two ways for a response to be initiated: either someone hears it, or it is heard by an orbiting satellite. Someone hearing it (typically an aircraft flying overhead or someone working at an airport) reports it to the nearest Flight Service Station (operated by the Federal Aviation Administration), who will start the ball in motion to locate the signal; they contact the U.S. Air Force Rescue Coordination Center (AFRCC) at Langley AFB, Virginia, who is responsible for the search. AFRCC typically makes a few phone calls to local airports and harbors to see if the ELT/EPIRB can be traced that way to a particular facility, and then if necessary calls the Civil Air Patrol (CAP) or other local search agency to locate the ELT/EPIRB. The satellites are monitored by the AFRCC directly. There are, I think, something like 20 satellites that carry a SARSAT package; some are satellites solely for that purpose, and others are weather satellites that carry a SARSAT package as a secondary function. Any given spot is overflown by one of the satellites an average of once every couple of hours, though the period between passes over a given spot is highly variable because of the particular satellite orbits; it might be ten minutes between one pass and the next, then 4 hours until the one after that. Once a signal has been detected and CAP (or other local search agency; CAP does the majority of these searches, though) has been activated, air and ground teams use direction-finding radios to triangulate the source until it is located and shut down. We prosecute all signals agressively, because we can only hear one signal on the frequency at a time; a strong false alarm can keep us from hearing a weak signal indicating genuine distress. Unfortunately, the system has an incredibly high false alarm rate, and a disappointingly low success rate in real distress situations. According to the latest figures I've seen, the false positive rate (when an ELT or EPIRB goes off, but there is no distress situation) is something like 97%; that is, of 100 ELT/EPIRB activations, all but 3 of them will be false alarms. The false negative rate (where there is a distress situation, such as a plane crash or boat capsize, but the ELT or EPIRB does NOT go off) is something like 50%. Successive satellite passes can generally locate an ELT/EPIRB to within 10 or 20 miles. Our aircraft can further locate it to within a mile or less. Our ground teams track it from there. If an ELT/EPIRB signal appears to be coming from "the middle of nowhere", where there are no airstrips or boat harbors, it definitely gets our attention and we wonder if this is one of the 3% of "real" distress signals. We chase all ELT/EPIRB signals agressively, but it's disappointing to know that it's almost certainly going to be another false alarm. The fact that 3% of them _aren't_ false alarms, and lead us to people in distress, keeps us going. We wish the system were more reliable, but we don't let that get in our way. -Brent -- Brent Chapman Great Circle Associates Brent@GreatCircle.COM 1057 West Dana Street +1 415 962 0841 Mountain View, CA 94041 ------------------------ *** Emergency Locator Transmitter (ELT) Use *** Tue Mar 21 10:44:40 1995 Message : #23673578 From: B. Douglas Reeves Address : dreeves@ese.ogi.edu Subject : Re: Where to rent emergency signal beacons Org. : Oregon Grad. Inst. - Dept. Env. Sci & Eng. |> |>EPIRB's are monitored (In the US) by the US Coast Guard, and indeed it is |>against the law to use one inland "except in an emergency" Even so, you |>would have to be close to a CG unit, and there aint too many of those in |>the hills. The USAF and the USN have monitoring stations for them too, |>but military EPRIB's use a different freq than the civilian ones, I |>believe. |> | |Emergency Locator Transmitters are required equipment on all aircraft |(other than ultralights, balloons, etc.) and are monitored by satellites. |The false alarm rate is very high. It used to be illegal to use an ELT |except in an aircraft or boat. Has this changed? | |-- Bob Mills No, it has not. If you activate an ELT (or EPIRB which works only on 121.5 MHz), recievers on several satellites will notice this signal and forward data to the Air Force Rescue Coordination Center (AFRCC). If the signal is in the same place for two or three satelite passes (a few hours apart), then they will attempt to try and find it. Often, they will use local law enforcement or SAR team or the Civil Air Patrol who will attempt to find the ELT using direction finding equipment on a light aircraft (aka Cessna :-). If they find you, they will send in a ground team, often made up of local cops, SAR volunteers or Forest Service folks. It is illegal to use an ELT or EPIRB outside of an aircraft or boat. However, you must decide if the consequences outweigh the benifits or being rescued. However, being one of those folks who is likely to come looking for that ELT, I would suggest you not use it unless you really have to. (Disclaimer: I am not suggesting you do anything illegal like use an ELT or EPIRB outside of an approved vehicle, such as a boat). Please note that this coverage is worldwide and not just costal. Both US DoD and the Russians have shelled out lots of $ for this system and it works reasonably well... except that 95%+ of the signals are false alarms. This is why AFRCC wants several "hits" on the same signal before calling a search. There are many amazing stories about ELTs in strange places and ones that move too. But please don't be like the person who last year turned it on to see if anybody would come looking for them. For more information on airborne SAR, try the Civil Air Patrol www page at http://capwww.au.af.mil or reply to me. D. Reeves -- |B. Douglas Reeves Env. Sci.& Eng. Oregon Graduate Institute| |N6XHW 146.90 PDX (503)833-8504 World dreeves@ese.ogi.edu Net| |"School is Hell, but it beats working"-M. Groening "Blarg!"-P.Lee| (B. Douglas Reeves) ----------------------