The DF-430 direction finder allows rescue aircraft to home in on beacon signals with greater accuracy
It started 10 years ago with a promise to one fisherman’s mother. Her son’s boat, the F/V Still Crazy V, had started taking on water on a cold, calm, clear February morning on Winyah Bay off Georgetown, S.C. Capt. Tony Culler, a grouper and snapper fisherman, went below to try to stanch the flood.
He couldn’t, and when he came back up soaking wet he probably was already hypothermic. As the bilge filled, Culler activated his EPIRB, and he and crewman Tim Hamm launched a raft, climbed aboard it, and waited for help.
“He was in his life raft shivering to death and holding on to his EPIRB,” says Greg Johnson, the Coast Guard’s commercial fishing vessel safety examiner in Charleston, S.C. The pair could see the helicopters flying search patterns looking for them. Rescuers knew they were there, but couldn’t pinpoint where.
“The good news is they made it back, and they’re still fishing,” Johnson says.
A rescue helicopter found them, but Culler’s worried mom wanted to know why it didn’t find him straight away. Her son had activated his EPIRB, so why couldn’t the helicopters follow its signal right to him?
Johnson promised he would find out. A retired Coast Guardsman and grandson of a California tuna fisherman, Johnson, 59, has spent the last 16 years as a Coast Guard civilian working with fishermen to make their jobs safer. “As a kid, I knew people who didn’t make it back [from fishing],” he says. “This Coast Guard thing is real for me.”
That helps explain why Johnson has spent the last 10 years fulfilling that promise to a fisherman’s mother. He has collected data. He has analyzed EPIRB rescues — just about every one during the last decade. He has interviewed survivors and air-rescue crews. And he helped find a more reliable piece of equipment for homing in on 406 MHz EPIRBs from the air.
It is the Rockwell Collins DF-430, a direction-finder that homes in on the EPIRB’s 121.5 homing signal and its 406 MHz alert signal. As a homing device, the DF-430 is vastly superior to the old direction-finders that picked up the 121.5 signal only, says Johnson’s boss, Larry Yarbrough.
The 406 signal — a half-second pulse emitted every 52 seconds — is 200 times more powerful than the 121.5, so with new technology that can lock on to a pulse, the 406 is much easier for aircraft to home in on and from much greater distances.
“With a DF-430, we get lock-ons [to a 406] at 150 miles sometimes,” Yarbrough says. “An aircraft that is locked on knows where you are. The pilot has a needle to steer by. That’s a big step forward in rescuing you in a timely manner.”
The 121.5, by contrast, works only as a homing signal at short range — often less than five miles, according to a Coast Guard Office of Search and Rescue report delivered at the 2008 beacon manufacturers’ workshop in San Diego.
Starting with $2.6 million from its Integrated Deepwater System Program for modernizing aircraft and vessels, the Coast Guard began equipping its C-130Hs and Falcons with 406 MHz homing equipment in December 2006. Now it is installing the gear on its helicopters. Eventually all of its aircraft will have DF-430s.
This is a game-changer, says Yarbrough, 62, a retired Coast Guard captain in charge of the agency’s fishing vessel safety program in the Southeast and Caribbean. “Most of the aircraft we launch on search-and-rescue cases have it now.”
Aircraft equipped with 406 MHz direction-finding capabilities find boats that planes or helicopters equipped with older technology don’t. Here are two cases in point:
• On April 11, 2007, Paradox, a 35-foot catamaran en route from Isla Mujeres, Mexico, to Anclote on Florida’s west coast, capsized in a 48-knot squall 175 miles southwest of Tampa in the Gulf of Mexico. The capsize activated the vessel’s 406 MHz EPIRB. Tom and Stanna Galbraith of Durango, Colo., hunkered down in the overturned hull, and Tom used a battery-powered saw to cut a hole in the bottom so they could crawl out when rescuers arrived. A Falcon jet equipped with the old direction-finder couldn’t find Paradox, but a prototype C-130 with the new 406 direction-finder located the catamaran, and a helicopter rescued them.
• Early Jan. 25, 2009, the crew of the sailboat Audrey issued a mayday over VHF radio after their boat lost power and shredded its sails 37 miles southeast of Cape Fear, N.C. Because of the boat’s distance offshore, radio communication was erratic and difficult to use to triangulate its position, but the two people aboard also were carrying a 406 MHz EPIRB with GPS, which they activated. The EPIRB gave the Coast Guard Audrey’s position, and a helicopter with 406 direction-finding gear homed right in on the boat. Audrey’s actual position turned out to be about 40 miles from the location that had been triangulated using the broken-up mayday.
The DF-430 has helped save or assist 47 boaters in 26 months, says Cmdr. Joseph Deer, a C-130 pilot and head of the DF-430 project for fixed-wing aircraft. “As a pilot, I’ve used it,” he says. He has locked on to a signal from 60 miles at an altitude of 5,500 feet. At 20,000 feet, aircraft lock on from more than 100 miles away. The higher the aircraft flies, the farther away it can lock on.
“These are sci-fi numbers,” he says. “We’ve never done this before.”
Deer says the DF-430 homing device ratchets up the efficiency and effectiveness of airborne search and rescue, but he stresses it won’t help unless boaters carry a 406 MHz EPIRB or personal locator beacon. In the best of all possible worlds, a boater will be carrying a 406 MHz with GPS, which sends rescuers the disabled vessel’s GPS-derived position with the distress signal.
An EPIRB with GPS on a disabled boat working together with a DF-430 on a rescue aircraft can shave minutes, hours, even days off rescue operations in which minutes sometimes make the difference between rescuing a grateful survivor and recovering a victim.
“You can go nearly anywhere on the planet and turn this on, and rescue resources will detect it,” says Deer.
And they’ll find you because the technology for alerting rescuers and leading them to a distressed boater just keeps getting better, Johnson says.
The 121.5 signal is a carryover from when EPIRBs transmitted emergency alert signals at 121.5 or 243 MHz. As of Feb. 1, the International Cospas-Sarsat System, which detects alerts via satellite and sends them on to the Coast Guard, no longer monitors either of those frequencies, only 406. The 406 EPIRB still uses 121.5 as a homing signal, but it isn’t as effective as it once was. As an alert signal, 121.5 originally transmitted at 75 milliwatts, powerful enough for Coast Guard direction-finding gear to home in on the signal pretty efficiently. But the Federal Communications Commission cut the signal strength to 25 milliwatts when it became a homing signal so it wouldn’t interfere with aircraft rescue frequencies, according to the workshop report. That reduced its range and made a “huge difference in the instability of the signal and our ability to find it,” Yarbrough says.
The 121.5 is an inherently bad signal for direction-finding anyway, according to Yarbrough. It is easily absorbed and deflected by obstacles. If boaters hold an EPIRB close, their bodies can block the signal and prevent it from reaching an aircraft behind them. The signal also can be blocked if a boat turns turtle with the EPIRB trapped inside. And when a 121.5 MHz signal is deflected, Yarbrough says, rescuers sometimes find themselves chasing it in the wrong direction.
One advantage of 121.5 for homing is its continuity. The 406 is a pulse signal, and until DF-430 arrived it couldn’t be used for homing. “The technology didn’t exist to home in on it because the pulse was so short,” Deer says.
Now airborne searchers lock on to the 406 as far out as they can to guide them to a disabled boat, then home in on the continuous 121.5 when they get in close.
Yarbrough says the Coast Guard plans to install 406 direction-finders on its landside Rescue 21 communications towers to augment the VHF radio
direction-finders its watchstanders use at coastal stations to triangulate the position of a VHF mayday source. It also is acquiring portable 406 direction-finders to put on its rescue boats so boats can home in on 406 alert signals, too.
“We’ll be able to send help [to a boat] right from the station,” and it will be able to lock on to the 406 signal, he says. “We won’t have to send a helicopter.”
Most rescues occur within 20 miles of shore, a compelling reason for even inshore boaters to carry a 406 EPIRB. “I wouldn’t go out on Biscayne Bay without an EPIRB,” Yarbrough says. “I understand what a terrific piece of safety equipment that is.”
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This article originally appeared in the August 2009 issue.