The Low-Level Pilot’s New Best Friend

Tuesday, February 16, 2010 - Dan Megna, Vertical Online

In the business of operating helicopters low-level there exists a very real and ever present danger. Terrain and obstacles, both naturally occurring and man-made, clutter the environment. Unfortunately, pilot tasking, distractions and weather conditions all contribute to the risk of these hazards going undetected.

I recently wrapped up 18 years as a pilot and crewman flying light and medium helicopters in the public safety arena. Our missions were pretty typical for a public operation: law enforcement, search and rescue, and fire fighting. Most were conducted low-level, in accordance with visual flight rules during the day and on night vision goggles at night, in hilly and mountainous terrain, at altitudes ranging from sea level to over 6,000 feet.

Flying above a dam, the ST3400H display clearly
shows terrain contours and elevation changes
on both sides of the aircraft.

As a matter of survival, I learned techniques and tactics that I believed provided the safety margins needed to work in the low-level environment. But I'll admit: my toes still make a fist in my boots at the thought of instances where terrain or obstacles snuck up and surprised me. Thankfully I was never flying faster than my guardian angels.

So, imagine my enthusiasm when I was presented the opportunity to fly along and evaluate a new terrain awareness and warning system (TAWS) specifically designed for helicopters. Sandel Avionics recently introduced the ST3400H: a compact, self-contained unit that far exceeds the requirements of TSO-C194, the United States Federal Aviation Administration's newly published technical standard order that sets the minimum HTAWS standards.

“The ST3400H is not just another black box,” said Jerry Henry, Sandel's director of sales. “It's a self-contained HTAWS computer with three separate databases for 3 arc-second terrain, man-made obstacles and user-defined waypoints or obstacles, with a built-in, high-resolution terrain display with tremendous safety benefits to the pilot.” The unit is a passive system that requires an interface with a WAAS (Wide Area Augmentation System) GPS to provide highly accurate position and altitude information.

Henry explained that Sandel took the requirements outlined in TSO-C194 and used them as just a starting point. “The end result of our creative development will be a revolutionary self-contained safety system.”

In our test aircraft, a Eurocopter AS 350B2, the ST3400H was cleanly mounted in the panel, directly in front of the pilot, replacing a radar altimeter indicator. Sandel claims that because the unit can replace most popular radar altimeter indicators, installation time is minimal, and, in most cases, requires no panel modifications. The ST3400H can also act as the primary display for TAS (traffic advisory system), TCAD (traffic alert and collision avoidance device), and TCAS (traffic alert and collision avoidance system) traffic warning systems, as well as depicting flight plan waypoints and direct-to commands from the GPS.

In flight, pilots can select the range of coverage (from 10 miles to one mile) and mode of sensitivity with the push of a button. The unit can be set for high-altitude, en route flight, or all the way down to a mode designed for low-level, visual flight rules (VFR), off-airport operations —all without aggravating nuisance alerts. According to Sandel founder Gerry Block, the ability to suppress false alerts during normal operations, including low-level operations, is part of “pursuing our mission on HTAWS [that] have no compromises in performance.”

The ST3400H display is color-coded to indicate
the varying levels of danger posed by
surrounding terrain.

The colorfully detailed, high-resolution, night-vision-goggle-friendly display is easy to read and interpret. An icon at the bottom of the display represents the helicopter. Black indicates the aircraft is clear of all terrain and obstructions. Green patterns show rising terrain that does not present a danger. Yellow and red represent terrain and obstacles that are near, at or above the helicopter's current altitude. Published obstacles such as communications towers are depicted by their own distinguishable icons.

Flying through a narrow canyon with the ST3400H set in VFR low mode and a coverage range of one mile, I was impressed with how the display accurately depicted the terrain contours and elevation changes on both sides of the aircraft. The serpentine route ahead of me through the bottom of the canyon was clearly depicted as a black pattern sandwiched between splashes of green, yellow and red.

Sandel claims that, in VFR low mode, the ST3400H will give no alerts unless you aim the nose of the aircraft toward hazardous terrain. To demonstrate this, we initiated a shallow bank toward terrain. When the unit calculated impact within 20 seconds, a female voice announced a caution and the hazard was indicated on the display with a yellow circle. If we failed to take corrective action and impact was calculated at 10 seconds, a male voice announced “warning terrain” or “warning obstacle” and the display indicated a prominent red circle around the hazard.

Climbing out of the canyon, we set a course toward rising terrain and maintained it at about 500 feet above ground level (AGL). The display was a sea of black with occasional splotches of green indicating we were clear of all terrain and obstacles. Our heading, altitude above ground level and pilot-selected minimum altitude were digitally displayed as well.

As we flew toward a prominent mountain peak topped with antennas and radio repeaters, we changed the coverage range to three miles. As we closed to within three miles, the ST3400H clearly depicted the peak and the antennas with ominous patterns and icons of yellow and red. Closing on the peak, we received the aural and visual warnings of a potential impact.

The ST3400H alerts low-flying pilots to hazards such as towers.

With the advanced HTWAS processor, comprehensive databases and high-resolution display all in one 3-ATI instrument, Henry said, “This system only gets more capable as you bring more inputs into it.” The ST3400H will accommodate inputs to satisfy not only the minimal requirements of TSO-C194, but also those required for all modes of ground proximity warning systems.

Turning back toward the airport, we set the ST3400H to the en route mode and a 10-mile coverage range, then climbed up to 1,000 feet AGL. The display turned black, except for small blotches of green and yellow several miles away, well clear of our intended course. Thinking back on the demonstration, I couldn't help but consider how this unit could have aided me during my parapublic flying days, by providing highly accurate, real-time graphical data while operating in the low-level environment. I think my guardian angels would have appreciated the help, as well.

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