Getting Helicopter TAWS Right

By John Croft
Source: Business & Commercial Aviation

“Up until recently, we started out with normal standard modes. There was a cockpit switch to activate a low-altitude mode to desensitize the alerting when flying low and in the mountains,” says Ishihara. “The approach was to just make one HTAWS to fit everyone's needs, but after talking to operators, we realized that operations are so wide, the one-system-fits-all-approach may not be suitable.”

That led to a software update with a search and rescue (SAR) mode and an offshore mode for the Mark XXII. “There was already a low-altitude mode function, but because [SAR] operations are very specific to low altitudes, we had to customize or tailor some of the low-altitude mode functions so SAR pilots could operate without any terrain calls,” says Ishihara.

He says offshore operators were having similar issues, particularly in the North Sea where the weather is challenging, making nuisance alerts all the more bothersome.

One area where Honeywell is focusing much effort for the future is in HTAWS functionality in 3-D on the PFD as part of a synthetic vision system (SVS) for helicopters. Though no product has officially been launched, the company recently tested a group of pilots with a primary flight display showing fused SVS and infrared camera video in its AW139 helicopter in the New York metropolitan area. Along with 3-D representation of terrain and obstacles, and the accompanying caution and alert warnings, the system included a wire database. Results were presented in a paper at the recent Avionics Europe conference. Both Honeywell and Rockwell Collins are working on advanced vision systems that fuse synthetic vision, infrared sensors and radar, typically under contracts to the U.S. military.

One area where Honeywell is not looking to make changes on the civilian side is with the 6 arcsecond (610 ft.) resolution of its H-EGPWS database, a resolution a factor of two or more less than its competitors now have.

“Based on our initial flight tests in mountainous areas looking at 1 arcsec or 3 arcsec resolution, we find that the higher resolution may give some benefits where mountainous features aren't exactly straight, but even if you have a fraction of an arcsec, it doesn't make cost-benefit case,” he says, noting that increasing the terrain resolution from 6 arcsec to 3 arcsec requires four times more data. “Our database can support that, but our studies show 6 arcsec is adequate,” says Ishihara.

Like Sandel, Garmin opted for more resolution and incorporated a 2.5 arcsecond (254 ft.) terrain database in its latest GTN series GPS, navigation and communications radio for helicopters.

Revealed at the HAI's Heli-Expo in Las Vegas in March, the helicopter GTN, which follows a fixed-wing version already in production, has a touchscreen interface and reduced protection mode designed to minimize nuisance alerts at low altitudes while keeping terrain and obstacle protection intact. The company says it has already received a TSO for the helicopter-specific GTN hardware upgrades and expected to receive software TSO in March while pursuing STCs for installations in “several popular helicopter models.” Garmin also offers HTAWS for legacy systems including the GNS 430W/530W, G500H, G1000H and as part of the G5000H suite for the new Bell 525 Relentless. Several of the models have synthetic vision capability.

The new GTN carries three databases — terrain, obstacles and airports/heliports. Garmin builds the high-resolution terrain database from NASA space shuttle radar topography missions, Japanese advanced spaceborne thermal emission and reflectivity radiometer data and “numerous” other sources, says Bill Stone, Garmin's avionics product manager. “The high-resolution data improves terrain alerting by reducing nuisance alerts when operating at low levels.”


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