Getting Helicopter TAWS Right

By John Croft
Source: Business & Commercial Aviation

The other modes are normal, tactical and obstacles-only. There is also an off-airport mode which pilots can use with any of the four selectable sensitivity options. Normal mode is set up for a design cruise altitude (DCA) of 500 ft. AGL; low-sensitivity for a DCA of 300 ft., and tactical is designed for a DCA of 150 ft. with alerts provided but no cautions. Off-airport mode, which suppresses alerts under the assumption that the pilots want to land off-airport, is useful for operations like HEMS.

“We are a successful supplier of fixed-wing TAWS retrofits, and we went back and redesigned it for helicopters based on what we learned from the fixed-wing experience,” says Gerry Block, president and CEO of Sandel. “Helicopters had a CFIT problem, and we could do 10-times the performance and alert properly without nuisance alerts compared to Honeywell and Garmin,” he says.

Block is no fan of Honeywell, having lived through a six-plus-year patent infringement case that Honeywell brought against Sandel and others over Honeywell's patented enhanced ground proximity warning system (EGPWS) technology, the first TAWS product to market. Sandel ultimately won a jury trial that finished in 2008. Two years, later Sandel had its TSO for the ST3400H, several STCs for retrofits, and is a supplier of forward-fit HeliTAWS systems to Sikorsky for the International S70i Black Hawk and terrain alert software for fixed- and rotary-wing aircraft to Rockwell Collins and others.

Sandel uses a 3 arcsecond (height measurements every 305 ft.) terrain and obstacle database from Jeppesen. Wire data comes from proprietary sources for the U.S. market, says Block, and generally from foreign governments for non-U.S. databases. Block says a “good percentage” of the 50 engineering and manufacturing employees at the Vista, Calif.-based company work on helicopter databases.

“We want to continue to improve the wire data,” says Block. “In the minds of most helicopter pilots, that's the thing that worries them the most. CFIT is part of the safety equation, and wires are part of CFIT.”

Honeywell senior principal research and development scientist, Yasuo Ishihara, says “there's been a discussion” at Honeywell about incorporating a wire database in its higher end Mark XXII helicopter EGPWS, but that is just one of many areas where the company is looking to improve its trademark safety tool.

In the more than 10 years since it has been building HTAWS systems, Honeywell has shipped approximately 1,650 of its lower-cost Mark XXI and Mark XXII systems for the worldwide helicopter fleet, including for all factory built Sikorsky civil helicopters.

Ishihara was one of the original designers of the H-EGPWS in 2002 under the tutelage of Honeywell inventor Don Bateman, holder of the patent for the first ground proximity warning system concept in 1975. He was also co-chairman of an RTCA committee that came together in 2006 to develop helicopter-specific minimum operational performance standards (MOPS), recommendations that in 2008 became part of the FAA's HTAWS TSO-C194. Before that guidance came out, Ishihara says “some very proactive” helicopter operators were installing fixed-wing TAWS “because it was available,” leading to issues. “The primary job of a fixed-wing TAWS is to alert you if you are not landing or taking off at an airport,” he says. “That does not work for helicopters.”

He says Honeywell is focused on “advancing and enhancing” its HTAWS capabilities based on feedback from end users and indentifying areas where the company can make further enhancements from real operations. “As an engineer, it's relatively simple to design a system,” he says, “but it's important for us to know how the system works in real operations.”

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