Getting Helicopter TAWS Right

By John Croft
Source: Business & Commercial Aviation

The FAA tells BCA that the AC update will follow the issuance of final rules for helicopter emergency medical services operators (HEMS) expected to be published later this year. The preliminary version of the HEMS rule, which the FAA published in 2010 in response to a large number of fatal accidents in the sector, called on operators to equip with HTAWS and radio altimeters to cut down on controlled flight into terrain (CFIT) crashes. Similar problems in the fixed wing sector prompted mandatory installation of TAWS for airlines in the 1970s. As of 2002, all new U.S. registered turbine-powered aircraft manufactured with six or more passenger seats are required to carry TAWS.

For helicopters, terrain and obstacles —including high-voltage power lines — can be a persistent CFIT threat throughout a flight due to the low altitudes involved. A special feature of the Sandel HeliTAWS is a powerline database called WireWatch that shows the location of power lines (carrying 69kV or more) at altitudes of 100 ft. or more AGL, a nod to wire strikes as a frequent ingredient in fatal helicopter crashes. Competing aftermarket HTAWS providers Honeywell and Garmin do not currently have power lines in their databases. As an aside, Safe Flight offers a power line detection system that alerts based on real-time sensing of the electromagnetic fields around live wires, but the system is not part of a TAWS offering.

The International Helicopter Safety Team lists wire strikes as the fourth of its five “most predominant” occurrences for fatal crashes, preceded by loss-of-control, visibility issues and fire. The fifth most common occurrence is system component failure. CFIT is listed under “other frequent occurrences” in the IHST findings, though the ranking can be deceiving.

“An accident that is classified as a pilot's inability to maintain VFR may have ended up as a CFIT,” says Matt Zuccaro, president of the Helicopter Association International. In those circumstances, it is possible TAWS may have helped assuming the pilot was able to maintain control of the helicopter.

“[HTAWS] is a valuable piece of technology,” Zuccaro says. “We're happy to see that it's being refined for helicopters and manufacturers are recognizing the actual environment helicopters fly in.”

Zuccaro cautions that a one-size-fits-all approach does not work for rotorcraft the way it does for fixed-wing aircraft, however. “We see the advantages in the right application. Any safety initiative has to be mission-specific to achieve the real value,” he says. “Do we put HTAWS on every helicopter that flies? At night, HTAWS has a greater than value than during the day. If you're a day VFR operation flying tourists over the same routes, you may not need HTAWS. We're very sensitive to right application of the advancements.”

Mission-specific enhancements are what Sandel, Honeywell, Garmin, the three main U.S.-based providers of retrofit HTAWS, are bringing to market to improve their products, independent of new guidance and rules from the FAA.

In normal mode, HeliTAWS issues an aural and visual caution alert when the helicopter is projected to hit terrain, obstacles in 20 sec. time at the present heading and speed. If the path continues, the system issues an aural and visual warning 10 sec. before impact, requiring immediate action by the pilot.

As we swooped in low over Lake Hodges during our nighttime demonstration, Sandel test pilot Roesink had his HeliTAWS set to “low-sensitivity,” one of four pilot selectable options to suit low-altitude operations. In low-sensitivity mode, Sandel reduces the caution and warning time “allowing the aircraft to get closer to terrain and obstacles,” the company notes in the ST3400H Pilot's Guide.

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