A light single-engine turbine helicopter buzzes a lake and pulls up to strafe the nearby craggy mountain peaks on moonless January night. Conditions that might otherwise be ingredients of an all-too-familiar chain of events leading to a crash site, on this particular night were rendered harmless by the 3-in., brightly colored back-lit display on the bottom right side of N547SA's panel.

The differentiating instrument on the Eurocopter AS350B2 in this case was a Sandel ST3400H “HeliTAWS” terrain awareness and warning system. HeliTAWS shows the location of terrain, obstacles and power lines relative to the helicopter's position on a color-coded 2-D moving map display. Perhaps more importantly, pilots with the retrofitted instrument can concentrate on flying, secure that the technology will give them 10-20 seconds warning via cockpit lights and urgent-sounding voices before the helicopter's path is projected to hit terrain or obstacles. The technology is similar to fixed-wing TAWS, which has been widely adapted for commercial aircraft by regulation starting in the 1970s, but must also work properly in the low-altitude regimes where helicopters tend to live.

While HTAWS is not new — some helicopters have been carrying the equipment since 1997 — what is new is that avionics providers are enhancing the databases and logic in the units both for the alerts and 2-D maps, and in some cases, for 3-D versions of terrain and obstacle alerts with synthetic vision. The action is being driven in part by a continued problem with controlled-flight into terrain (CFIT) accidents but also by customer requests for HTAWS that will allow them to do specialized work without unnecessary terrain alerts, aka nuisance alerts. Regulators are also driving the changes by progressively tightening guidance materials to cut down on nuisance alerts and increase the reliability of the systems, which some say is thwarting installations on low-end helicopters due to excessive costs.

My night demonstration flight on January 10 with Sandel's HeliTAWS test pilot, Gary Roesink, who's day job is chief pilot for San Diego-based Corporate Helicopters, showed off Sandel's trademark approach to heightened situational awareness without nuisance alerts in the rugged Lake Hodges area north of San Diego. By definition, a nuisance alert is an alert “that occurs when there is no threat or is unnecessary for the intended operation,” says the FAA. In practice, pilots tend to disable systems that generate too many nuisance alerts, a result that could have deadly consequences when those warnings are real.

These days, Sandel uses N547SA for demonstration flights, but the aircraft several years ago was the testbed for HeliTAWS development work, for which the company received a Technical Standard Order (TSO) approval in August 2010. Sandel followed the TSO with supplemental type certificates (STCs) to install the ST3400H in the Eurocopter AS350B2 and Bell 412EP. The company won't say how many HeliTAWS units it has in the field since first offering the ST3400H two years ago. For the fixed-wing world, Sandel builds compact integrated display systems, including primary flight displays and TAWS units, for customers in the business aviation, airline and regional airline sectors.

An FAA HTAWS advisory circular (AC 27-1B) update likely to come out later this year will raise the bar for gaining STC approval, in part by recommending a pilot-controlled reduced-protection mode for low-altitude operations and off-airport landings to reduce nuisance alerts. The AC will also recommend that FAA inspectors test the reduced-protection mode inflight.

“Applicants should consider providing a mode that will account for off-airfield operations that will still provide the pilot with essential alerts regarding terrain without nuisances alerts,” says the FAA. “Without a reduced protection or similar mode, nuisance alerts may lead to pilots ignoring or inhibiting the HTAWS at inappropriate times.”

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.

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.”

“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.”

The helicopter-specific obstacle database for the GTN includes 30,000 additional low-altitude threats compared to the fixed-wing version. When asked if Garmin is considering including wires in its obstacle database, Stone says “I don't know if we can comment.”

What he can comment on is the drop in HTAWS retrofits for lower-end helicopters has seen due to the FAA's move in 2012 to require STCs for all HTAWS aftermarket installations, where previously the less complicated field installation process (Form 337) was accepted. Honeywell's Ishihara has seen the change as well, noting that Mark XXI units, previously installed with a 337, now require STCs.

Stone says the aircraft downtime required to earn an STC versus Form 337 is “much greater” particularly when the FAA is understaffed and projects often go into “sequencing” for three to six months before the needed government engineers or inspectors become available. “It's a huge impact to put [the helicopter] down for months to go through the STC process,” says Stone. “It's a barrier that can prohibit, financially, getting the technology on the aircraft.”

Under the sequencing process, which the FAA started in 2005, the agency evaluates each STC project at its regional certification offices. Those that will require more than 40 man-hours of engineering or inspector time are put into sequencing, says Stone. “The initial phase is 90 days,” he says. “At the end of 90 days, the FAA reevaluates their workload to see if they can assign inspectors and engineers to work on the project. If not, application goes back into sequencing.”

“There can be significant downtime without clarity of when the resources might be available,” says Stone.

The FAA tells BCA it now requires STCs for all installations because HTAWS units meeting TSO C-194 “have an appreciable effect on the airworthiness of rotorcraft and must be accomplished via STC.”

The benefit will likely be worth the wait for operators with a genuine need for HTAWS, particularly if purchasing a system tailored to the particular environment where the helicopters do their work. “Accidents are caused by pilot distractions,” says Sandel's Block. “That's why true alerts are important. It's not about pilot skill, but about helping them out in a situation where they have other things to pay attention to.” BCA