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Monday, August 1, 2005

Adding to the Arsenal

SEARCH-AND-RESCUE CREWS ARE benefiting from ongoing advancements in communications and navigation technology and now stand to get a little more help with a less exotic but critical item on their equipment lists--their aircraft hoists.

The growing use of personal locator beacons continue to transform search-and-rescue operations around the world, with the more capable waveform of the 406-MHz. units permitting greater relay of information from persons in distress and the satellite network they use supporting speedier location of the lost and troubled.

The greater utility of the 406-MHz. system, combined with the design limitations of the 121.5 and 243 MHz. units means that the latter are steadily marching toward obsolescence. Given the rate of false alarms from 121.5-MHz. units, the inability to compare signals to a database of registered users and the lesser capability of the units, Cospas-Sarsat--the international SAR satellite system coordinated by the United States, Russian, Canada and France will stop supporting 121.5-/243-MHz. service on Feb. 1, 2009.

The 406-MHz. units make fuller use of the low Earth orbit and geosynchronous satellite constellations that detect and relay their signals. The low satellites orbit about 600 mi. (967 km.) above us, which gives them a period--or time to complete a full orbit--or about 100 min. That means it takes one of these satellites about 15 min. to rise above the horizon, pass over you and drop below the opposite horizon. The frequency and speed of these passes allow sensors on these satellites to determine the location of a 406-MHz. signal (using Doppler-shift calculations) to within about 3 mi. (4.8 km.) (The accuracy is about 12 mi. (19 km.) for 121.5-/243-MHz. signals.)

Because they are relatively close to the Earth, these satellites can only "see" a swath of the surface about 4,000 mi. (6,437 km.), which means it may take several passes for the low constellation to detect a distress signal.

Enter the geosynchronous satellites, which orbit 22,300 mi. (35,888 km.) from Earth. At that distance, they stay in the same spot over the surface. Because there is no relative movement, they can't determine location as accurately as their low counterparts. But with four of these birds in place above the equator, virtually all of the Earth's surface between 80 deg. N. and 80. deg. S. Lat. is constantly observed.

That means a distress signal is detected almost immediately. (They only detect 406-MHz. signals.) The geosynchronous satellites' coverage of the polar regions, above 80 deg. Lat. is limited, however.

Because the geosynchronous satellites can't accurately determine the location of a signal, protocols for 406-MHz. units embed position data derived from the GPS constellation in their distress signal. The signal also includes information on the identity of the registered user.

Techtest, Ltd., part of the H R Smith Group of Companies, is among the vendors offering advanced personal locator beacons. Techtest's Series 500-27 GPS beacon recently was tested by the U.S. Coast Guard for the COSPAS-SARSAT Joint Committee to assess overall system performance, accuracy, availability and timeliness. According to Barry Thrower, Business Development Manager for the H R Smith Group, the tests showed that 500-27 beacon gave 100-percent message availability and delivered a 90-percent success rate in transmitting positional data to within 0.6 mi. (1 km.) accuracy.

It also achieved a 100-percent success rate in determining accuracy within 3 mi. (5 km.). In addition, the beacon was consistently in the top grouping for a range of land and sea trials which included varying degrees of GPS visibility. Of particular note, the Techtest beacon was the only product to successfully penetrate a high-density tree canopy.

As for the less exotic equipment, hoists tend to evolve slowly. Goodrich, for instance, is promoting is A.C.-powered and translating-drum hoists, and is looking at prospects for installed embedded hoists, a la the V-22 configuration, on new aircraft in development. On the V-22, the hoist is built into the aircraft, with its cable fed along a boom over the hatch.

Both Breeze-Eastern and Goodrich are focusing in the near term on improving their customer service by stocking up on spare hoists and parts, moving toward around-the-clock availability of field technicians and tech support and reducing turn-around time on units sent in for repairs.

Goodrich also is looking at a number of options for new installations of its hoists. It is working with the Los Angeles County Fire Dept. on development of a "plug-and-play" configuration in which a Goodrich hoist would interface with the system control and power connections for a Breeze-Eastern unit.

The company also is working on adapting its hoist installation on Eurocopter's EC135 for use on AS350 B3's operated by the San Bernadino County, Calif. Sheriff's Dept. That department was to display an aircraft in the configuration at last month's Airborne Law Enforcement Assn. annual meeting in Reno, Nev.

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