Refinements making TAWS better suited to helicopter use
The recent increase in fatal helicopter accidents, along with a push by the FAA to standardize the manufacture of helicopter terrain awareness and warning systems (TAWS), has prompted a number of avionics companies to expand their product offerings and make changes to existing systems.
Between FY2002 and FY2008, helicopter emergency medical service (HEMS) and offshore oil rig operators had 33 fatal accidents resulting in 121 deaths; the FAA listed one of the main causes as controlled flight into terrain (CFIT). As a result, the agency issued on December 17 technical standard order (TSO) C-194, which lists the minimum performance standards TAWS must meet for FAA approval. Although the FAA said it “supports the voluntary implementation of TAWS,” it has no immediate plans to mandate its use.
One of the first products to comply with the new TSO is the Sandel Avionics ST3400H helicopter TAWS (HTAWS). The new system, which is based on Sandel’s ST3400 Class A TAWS for Part 25 aircraft, displays traffic when interfaced to an existing TCAS receiver and can be ordered with the company’s Class-B night vision imaging system (NVIS) option. In addition, the product is a single panel-mount, self-contained unit and can be installed in place of an existing radar altimeter indicator. It does not require remote processors or additional displays and requires less modification, less downtime and costs less than other products, the company said. Sandel plans to announce the cost of the product here at Heli-Expo’09.
The defining feature of the new system, according to Sandel president and CEO Gerry Block, is the high-resolution graphic display, which uses a high-brightness 3ATI LED-backlit display engine. “The pilot-friendliness is going to change the way pilots think about TAWS,” said Block. “Right now pilots think of TAWS almost like a black box. This is the opposite of a black box. It’s a very beautiful display technology with a TAWS unit in it.”
Block said the display will be a factor in the number of operators who purchase the system. “It’s a well known fact that TAWS will have an effect on the safety of [helicopter] operations,” Block said. “I don’t know if that’s debatable. The issue for the operators is whether they want it or not. What we’re trying to do is introduce a product that is helpful to the pilots.”
Chelton Flight Systems also offers a TAWS product for helicopters as part of its electronic flight instrument system (EFIS). The company originally certified the system under the FAA’s previous advisory circulars AC 27-1B and 29-2C and is now making “slight modifications to meet the new TSO,” according to Gordon Pratt, vice president of business development for Cobham Avionics, the parent company of Chelton Flight Systems. “There were some minor changes between the advisory circular and the TSO, the verbiage of some points,” Pratt explained. “We’re making those changes and we’re applying for the TSO here shortly.”
The Chelton system is part of a multifunction display that has an integrated moving map and a flight management system (FMS). Because the product is embedded in the EFIS, it is more reliable than other TAWS products, Pratt said. “Other TAWS systems are a separate box that you have to hook up to a separate display. Ours is embedded in the display, so there’s virtually no chance of a failure. If you have single box and the TAWS box fails, you’ve lost your TAWS protection. Our architecture is embedded in each display as a stand-alone function. Even if you were to lose four displays, you would still have full TAWS protection.”
The system also employs a forward-looking view, which is different from other products, Pratt said. “Our HTAWS has a downward-looking view, like other systems, but it’s also forward looking. It’s like looking out the front window,” he said. The system is also NVG compatible and was built for helicopter environmental standards from the beginning. “It’s not a fixed-wing product that was adapted for helicopters.”
To date, Chelton has sold approximately 1,500 units, Pratt said. The equipment proved its worth in Alaska, where the company distributed the systems to fixed-wing aircraft and helicopter operators. “Every commercial operator who wanted one was given one free of charge,” Pratt said. “Prior to the installation of our systems, they had a terrain accident every nine days on average. Since they put our systems in, the aircraft that are equipped haven’t had a single accident in five years.” He added, “I think there’s enormous and overwhelming evidence that TAWS or some sort of terrain-awareness system is effective.”
A third option for helicopter operators is Honeywell’s enhanced ground proximity warning system (EGPWS). The Mark XXI and XXII versions were designed specifically for helicopters and can prevent collisions with ground, water or man-made obstacles, such as towers or high-tension wires.
The Mark XXI is the “basic, inexpensive” version, according to Doug Kult, Honeywell sales director for helicopters and surface systems. It includes an internal GPS card and interfaces to weather radar indicators, multifunction displays and stand- alone displays. The XXII version, on the other hand, exceeds the FAA TSO-C151b Class A requirements and requires a radar altimeter. In addition to terrain awareness, the system also includes features such as excessive descent rate, excessive closure rate, descent after takeoff, insufficient terrain clearance, descent below glide slope, and
altitude callouts for excessive bank angle, tail strike protection and autorotation.
Kult believes the equipment will be especially useful for helicopter pilots flying to oil rigs in the Gulf. “Flight over water has some issues,” he said. “The horizon is not really there because the sky and water sort of blend together. There’s also a problem with the human eye in measuring the altitude over water. More than one pilot has said he was flying along, looked down and the radar altimeter was at zero. Collision with water, which sounds kind of absurd, happens more often than we realize.”
Honeywell plans to introduce this year an integrated hazard awareness system system for helicopters. The single box will include a ground proximity warning system, weather radar and collision awareness system.
“It’s unfortunate that we’re losing so many lives in helicopters,” Kult said. “Honeywell has been saving lives for more than 50 years, and it’s our mission to improve that accident rate. [The products] are not a save-all. You have human beings involved, and you have systems that are subject to vibrations and wear and tear. But certainly, making a pilot more aware of the terrain and conditions around him will make him safer.”