Downed aircraft location

Flight Operations

Downed Aircraft Location by

Barney

Green

Rescue units are hesitant to launch a search mission unless secondary confirmation of a crash has been verified. This sometimes delays the rescue process as much as 24 hours. Other problems with the ELT system include the fact that some ELTs do not survive the crash, and others are not activated by a crash. (A recent review of fatal aeromedical helicopter accidents revealed that most ELTs were not activated by the crash). Then there are pilot reports of searchers chasing vague, often intermittent ELT signals for a week or more without finding the accident site. Recognizing the need to provide a technologically-advanced system to counter the failures of the ELT concept, ARNAV Systems Inc. of

In the 75 year history of aviation, many people involved in remote area aircraft crashes have died from injuries and/or exposure who might otherwise have been saved by early location, rescue and treatment. The introduction of the ELT (Emergency Locator Transmitter) beacon brought high hopes that such technology would provide the early alarm and location, information to lead rescuers directly to the crash site for fast attention and treatment for the injured. For the most part, however, the ELT has not lived up to early expectations. A recent analysis of the ELT concept has revealed that some )7-986 of all ELT transmissions are false alarms. As a result, Search and

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The ELT from a downed aircraft sends a distress signal picked up by the SARSAT satellite. The message is relayed to a rescue coordination center via a ground station. Air and land rescue vehicles are then dispatched to the scene. (Diagram courtesy Glatzer Industries Corp., New Rochelle, NY) 30

HOSPITAL AVIATION, OCTOBER 1986

Portland, OR developed a better way to provide missing aircraft location information. Their product, dubbed an emergency location system (ELS), provides more than just the ELT beacon alone. In addition to the standard ELT whooping tone, the ARNAV ELT broadcasts a "plane talk" voice message via a digital voice synthesizer. When an RS-232 interface is used to couple the ELT with ARNAV's R-21 panel-mounted Loran C unit, the longitude/latitude coordinates are also broadcast, with accuracy expectations to within 30-40 meters. Current technology provides downed aircraft location position determination by two or more satellites. These satellites, located at several fixed positions over the earth, provide directional information which, when plotted, show the location of the activated beacon. The same information can be obtained by two aircraft approaching the crash site from two different directions. While the new system still allows such positioning, it also provides the lat/long coordinates, negating the need for positioning by triangulation. Tuning into the VHF aircraft emergency frequency of 121.5 MHz following a crash, a searchers will hear the ELS emergency tone, punctuated every few minutes by "This is Bell LongRanger helicopter N 42 Kilo Mike, running zero hours threetwo minutes, Latitude North 37 degrees, 22 minutes, ten seconds; Longitude West 121 degrees, 14 minutes, 38 seconds." The last position recorded by the Loran-C prior to its failure in the crash will be broadcast over the ELT. "At 200 milliwatts of power, the range should be at least 100 miles, but it's line-of-sight so it might be less," said Charlie Armiger, ARNAV's National Sales Manager. "But, with satellite relay, it's unlimited." In addition to the standard emergency whooping tone and the synthesized voice broadcasts that are designed to catch the attention of area listeners, the system also transmits a tone encoded signal of higher power

Flight Operations (2.0 watts, and ten times the normal output) which is picked up by satellite. Through relays and decoding, the message goes from satellite to mission control center to rescue coordination center to search & rescue squad, all in a very short period of time. "It's the best of both worlds," said Armiger. "It leads Search and Rescue people directly to a crash site and there's little or no chance of a false alarm." ARNAV is proud of its system for minimizing or eliminating false alarms, and much of this security is built into the ELT beacon. "It's the first of its kind and the first to pass TSO C91-A (the FAA's new Technical Standard Order setting standards for ELT beacon design)," said Armiger. "One of the requirements is a special 'G' switch that activates upon crash and has safeguards against accidental activation. It has a very narrow tolerance and will only activate over a duration of time and in a specific direction. Our switch is called the 'Delta V'." The TSO also requires the ELT to (a) withstand a 500 G impact (like driving a car into a concrete wall at 60 mph), (b) be connected to aircraft power, (c) have a panelmounted test switch and light, and (d) sense the time of activation as well as the impact force. "The ELS-10/RS-232 Interface/R-21 Loran C unit is not a flight follower," Armiger emphasized. "It's a very sophisticated ELT. Its position is continually updated by the Loran. It transmits nothing until it is needed in an emergency and then begins transmitting upon crash impact or when someone turns on the switch." Another Oregon company, II Morrow (pronounced Tomorrow), of Salem, Oregon, also offers an advanced design ELT system similar to ARNAV's. Its system does offer an advanced, computerized flight following system (which will be discussed in the November issue of

Leigh/Sharc-7 ELTs or the DEFT ELTs, all manufactured by affiliate companies of Glatzer Industries Corporation (GIC) of New Rochelle, NY," said Dick Thomas, II Morrow's Advertising Manager. "GIC and its Emergency Beacon Corporation and ELT's Unlimited Inc. affiliates have been working with II Morrow to develop this new ELT." Unlike the ARNAV system, this system broadcasts an encoded message including a Mayday signal, the aircraft ID, the survivor status, and lat/long coordinates. The system has not received TSO C91-A certification because no applications have been made or are likely to be made. Steve Glatzer of GIC went into considerable detail in explaining to Hospital Aviation the intricacies and compromises that went into the organizing of TSO C91-A. "In meetings called to draw up

standards such as these, each manufacturer wants standards that will allow him to put his product on the market," said Glatzero "People like Search and Rescue want something better, and it becomes give and take, a compromise session. "We do not like some of the compromises that were included in TSO C91-A and we feel our methods are better. For example, we encapsulate (pack in plastic) our beacons to make them waterproof and to withstand much higher impact loads than what C91-A requires. We feel the waterproofing and higher G load capacity are critically important features the TSO did not adequately emphasize. All features of our beacons are built to the highest standards. But, we do it our way." Next month, Hospital Aviation will present another use of Loran-C: automatic flight following.

THE LEADING FiRM iN HELIPORT FACiLiTiES:

Hospital Aviation). II Morrow's crash locator system uses the Appollo Loran C "Flybrary" (which II Morrow manufactures), RS-232 interfaced with Emergency Beacon Corporation's model EBC-302 series ELT. However, an ELT already installed in an aircraft may be converted to the II Morrow locator system. "A system can be retrofitted on any of the EBC ELT's or any of the

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HOSPITAL AVIATION, OCTOBER 1986

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