Terrain avoidance system from Sandel enables helicopter pilots to fly in low terrain in poor visibility

SAN DIEGO, 20 May 2010. There are few things more dangerous for a pilot than trying to fly a helicopter close to the ground over uneven terrain in poor visibility conditions with only a global positioning system (GPS) to guide him.

Pennwell web 120 37

Pennwell web 120 37By John McHale

SAN DIEGO, 20 May 2010. There are few things more dangerous for a pilot than trying to fly a helicopter close to the ground over uneven terrain in poor visibility conditions with only a global positioning system (GPS) to guide him.

Currently "most helicopters have no true terrain avoidance system now and depend completely on VFR conditions to avoid CFIT (Controlled Flight Into Terrain)," says Jerry Henry, director of sales for Sandel Avionics in San Diego. "At best they may have a moving map with terrain data in the background but no true alerting system and no TSO C-194 certification. These are terrain awareness only."

Engineers at Sandel Avionicsare developing technology named HeliTAWS to enhance raw GPS position with moving maps and highly detailed terrain and obstacle graphics that show the pilot when he is close to a tower, mountain, or other structures "along with guidance on what action needs to be take to avoid an impact as far as 20 miles in advance."

Sandel will be speaking about and showcasing their technology during the Avionics USA conference and exhibition on June 3-4 at the San Diego Convention Center.

"The technology is already being tested by the FAA and in its final phases of certification," Henry says. The potential applications go well beyond civil airspace however as HeliTAWS would improve military search and rescue missions in hostile terrain, high fog and dust operations, and nighttime missions, he adds.

During a demonstration for Avionics Intelligence editors a former San Diego Police Department pilot flew the helicopter near towers and performed off runway landings on rough terrain. The graphics on the Sandel display were easy enough for the non-engineers and non-pilots on board to follow.

When the aircraft flew too close to a particular obstacle it showed up as red on the display if the helicopter AGL was below the height of the obstacle, while the safe path over terrain was lit up in green-- to allow for a save evasive maneuver and -- everything in between was yellow. All the pilot had to do was follow the green or black path and he would be fine.

The system also shouted out a caution followed shortly after by a warning to the pilot when he approached the red zone. Mountains and hills are color coded black, green, yellow, or red depending on the proximity to the helicopters AGL and towers and other manmade structures circled by yellow for a caution and red for a warning, Henry says. The pilot also has the ability to mute the alerts if he chooses, he adds.

The system shows the terrain in relationship to the helicopter and has pilot selectable range settings of one half to 20 miles, Henry says. The map will show not only mountains hills, and terrain but airports, heliports, towers, GPS Flight Plan etc., he adds.

The terrain and obstacle data within the system comes from Jeppesen, says Daniel Weisz, certification and documentation manager at Sandel.

"We have two data bases that will be able to be updated periodically, terrain and obstacles," Henry says. "We are still determining how frequently this data will be made available but initially since terrain doesn't change hardly at all, an annual update on that will satisfy most clients unless we have another Mt St. Helens episode. Obstacle data changes more frequently and probably should be updated quarterly."

Sandel certifies their software to RTCA/DO-178B software level C, Henry says.

The Sandel device is installed in the place of an existing radar altimeter indicator, he says. The easy installation translates into less maintenance and down time, which cuts down on cost, Henry adds.

"The Sandel ST3400H allows the display of TAS or TCAS on the same display as HTAWS and radar altimeter which in most cases eliminates the need for any instrument panel modification," he says.

Military use

"Currently in very high end military helicopters there are real-time imaging systems being installed that are completely cost prohibitive and weight restricted for older ships in their fleets," Henry says. "Three main technologies are used in this select group of military helicopters -- digital terrain elevation data integration (DTED) and sensor fusion, millimeter wave radar (MMWR) with scanning antenna and laser detection and ranging (LADAR). Combined they exceed the value of most helicopters and weight far more then most airframes will allot.

"For older helicopters in their fleets, a passive system such as the Sandel ST3400H is the perfect solution for cost, weight and ease of installation," Henry continus. "The need in the military is very similar to that of civilian operators and only their specific mission may be different. The ability to fly safely near terrain and obstacles remains much the same."

Other system specifications

HeliTAWS is based on the industry standard ST3400 Part 25 Class-A TAWS and designed specifically for helicopters, according to the Sandel data sheet.

HeliTAWS combines an advanced HTAWS computer with Sandel's display technology in a 3ATI format to provide a single panel-mount, self-contained solution.

"3 ATI is an ARINC standard measurement for the size of the hole needed in the instrument panel to mount this instrument," Henry says. "3 ATI Square turns into a square hole cut in the instrument panel that measures just over 3 by 3 inches. It’s closer to 3.17 inches square."

HeliTAWS also has a night vision option. Henry notes that the Sandel night vision solution maintains its brightness in daylight operations.

According to the Sandel data sheet, the HeliTAWS differs from its fixed-wing counterpart with the following features specifically for helicopters:

- ultra-high resolution 3 arc-second (300 foot) terrain grid;

- one-foot vertical obstacle resolution;

- high-resolution obstacle database;

- on-screen obstacle depiction;

- nuisance alert reduction tailored for helicopter operations; and

- is tested to DO-160F helicopter vibration standards.

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