Obstacle detection options abound for helo operators

Aviation International News » March 2008
February 27, 2008, 8:32 AM

Equipment manufacturers are striving to provide effective, reliable obstacle detection, as collisions with obstacles, notably wires, account for a significant portion of helicopter accidents. Offerings vary from expensive laser radars that benefit situational awareness to lower-cost systems with more limited functionality.

Germany-based EADS Defence and Security’s Helicopter Laser Radar (Hellas) scans the area in front of the helicopter with a laser beam that is not harmful to the human eye. It detects even thin wires at distances of up to 3,300 feet. The system can detect obstacles that include poles, isolated trees, windmills, cables and telephone lines, according to the company.

Two versions are available. The one most likely to be installed on a civil helicopter is Hellas-W/HR (Warning/High Risk). It alerts the pilots to obstacles through warning indicators (both aural and visual) and/or the multifunction display (MFD). On an MFD, the pilot sees a depth and grayscale image of the terrain in front of the helicopter.
Obstacles are displayed in red. Power consumption is about 150W. Detection range is greater than 1,970 feet for wires with diameters of more than 10 mm.

The other variant, Hellas-A, displays obstacle information on a helmet-mounted display. It was developed for a military helicopter (the NH-90 transport) “but if a civil helicopter has a helmet-mounted display it is possible to use it also for civil applications,” an EADS spokesman told AIN. Detection range is greater than 2,460 feet for wires with a diameter of 5 mm or more. Obstacles are categorized as wires, poles or trees. Power consumption is approximately 150W.

The EADS spokesman pointed out that Hellas is the only in-service obstacle warning system on the civil market. Among the first customers are the German Federal Police, which uses Hellas on 43 Eurocopter EC 135s. Hellas-W/HR is approved by the EASA under a German-delivered JTSO (joint technical standard order).

Italian-based Selex Communications, meanwhile, is offering its laser obstacle avoidance and monitoring system (LOAM). It has been fitted to six AgustaWestland search-and-rescue EH-101s for the Danish Air Force. It is said to be suitable for civil applications, including light singles.

The LOAM system can detect wires down to a diameter of 5 mm. “We could detect even smaller diameters but, below five millimeters, a wire can be cut [by cable-cutting passive devices],” Luca Taverni, navigation and optoelectronic system engineer at Selex, told AIN.

The LOAM operates on a similar principle as Hellas. A laser beam periodically scans the area around the flight path. Analyzing the returned echo, it identifies possible obstacles and provides the crew with information and warning.

The main difference is in the scanning technique. “Rather than raster scanning, we use Palmer scanning, which is more circular,” Taverni told AIN. The result is a smaller blind area and easier-to-recognize obstacles.

Thanks to second-generation processing capability, the system can classify obstacles between wires, pylons and buildings. Each category should be viewed as a family. A tree or other vertical obstacle will be highlighted as a pylon, a hill as a building or other extended obstacle, and so on.

Obstacles can be highlighted on the video or infrared image (supplied by the LOAM sensor unit) on a specific display or MFD. If an escape maneuver is required, the system would give the crew guidance cues. “The pilot just has to overlay the flight vector onto the cue,” Taverni said.

If a flight path vector cannot be displayed, a separate warning unit is offered. It also gives escape guidance via four directional arrows.

Selex claims the LOAM has a field of vision of 40 degrees horizontally and 30 degrees vertically. The advertised maximum detection range is 6,500 feet, while the minimum is 160 feet. Obstacle detection probability is said to be greater than 99.5 percent, and the false alarm rate is said to be smaller than one per two hours.
The 53-pound system consists of a sensor, a control panel and the warning unit. “It is never as light as we want it but it is fine with a Eurocopter EC 130 [the testbed for the system],” Taverni said.

Certification remains an issue for civil applications, according to Taverni. Only STCs seem possible in the near future because the “the FAA and the EASA have no document to certify this class of equipment,” he explained.

Taverni declined to provide a price estimate, citing variations due to options, installation, quantities and so on. But he insisted that the system is affordable for small private operators of EMS helicopters in the two- to three-metric-ton-mtow range. The Finmeccanica subsidiary has flown its system on an AB212, among others.

In the U.S., Selex is partnering with Lockheed Martin Systems Integration-Owego to market the system.

Not every operator can afford such sophisticated systems. For those operators, U.S.-based SafeFlight offers a different detector in the $20,000 to $30,000 range. Available for a few years already in the U.S. and recently certified in Europe,
the powerline detection system (PDS) detects the electromagnetic field radiated by a power line. In addition to its low price, its weight–less than one pound–is a great advantage over the other systems.

When the helicopter is approaching a live powerline, a red light flashes on the instrument panel. Simultaneously, an aural signal, sounding like a Geiger counter, warns the pilot of the line’s proximity. Frequency increases as the helicopter gets closer to the line. Wire strikes account for two-thirds of helicopter crashes, a PDS demo pilot told AIN.

System sensitivity is adjustable. However, one limitation is the system’s inability to provide a direction to the source of the warning. Another is the fact that it can detect only live power lines. Ski-lift cables, for example, cannot be detected.
In Europe, SafeFlight distributor Trans Hélicoptère Service has negotiated with at least one insurance company a 20- to 25-percent premium discount for helicopters fitted with the PDS.  

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