Since almost one third of helicopter accidents with fatal casualties are caused by impact with obstacles and cables, developing and improving anti-collision systems against low-visibility obstacles is clearly a key objective for avionics specialists. Finmeccanica’s Selex Communications has had success with various military users of its laser obstacle avoidance and monitoring (LOAM) system since introducing it in 2000.
With a view to broadening its applications into civil applications, the Italian company has continued to develop the system with the aim of reducing the LOAM’s weight. As a result, its sensor head unit (SHU) structure, which is located in the aircraft nose, now weighs just over 47 pounds, some five pounds less than previously, while maintaining the same dimensions, center of gravity and performance. The improvement was achieved through an analysis of the rigidity needed to maintain a stable optical path for the electro-optic components.
The 320- by 239- by 419-mm LOAM SHU contains a 1.55-mm wavelength Class IV laser emitter with a 10-kW pulse power, but thanks to its pulse duration of 3 to 5 nanoseconds, its repetition frequency of 60 kHz and a laser beam that scans the area around the flight path twice per second, it becomes a Class I equipment–that is, fully eye-safe. With a field of view (FOV) of 30 degrees in elevation and 40 degrees in azimuth and its capability to tilt automatically, as well as the FOV centerline of around 20 degrees both in azimuth and elevation according to flight data to adapt the scanned area to the flight situation, the LOAM can guarantee to “look-into-turn” during demanding maneuvers at high speeds and elevated bank angles.
The SHU also includes a swash mirror, which rotates at a constant speed around its axis reflecting the laser beam and draws a pseudo-ellipse in the airspace, while the turret periodically sweeps the FOV in azimuth. The combination of these two movements generates the required pseudo-elliptical scan pattern that Selex considers best suited to detecting wire-like obstacles while maintaining an inherent high capacity to keep the detected obstacle shape unaffected by the helicopter motion, allowing it to reconstruct the obstacle shape. False echo reduction, sun cancellation and sensitivity optimization systems are all incorporated into the LOAM sensor.
The first aircraft to receive the latest version of the LOAM with the lighter SHU will be the ICH-47F Chinook helicopter, 16 of which have been ordered for the Italian army (plus four options). The same equipment should be installed on eight Italian navy EH 101s in the amphibious support configuration.
A LOAM system also has been installed on a Bell UH-1H helicopter belonging to Lockheed Martin. This sensor has been operating since 2006 and is part of a sensor package that Lockheed Martin is evaluating for a possible proposal within the degraded visual environment program aimed at the U.S. military helicopter fleet.
At the same time, Selex is looking at future markets, such as light and medium corporate helicopters needing a smaller, lighter and less expensive system. This could function with a lower level of performance to military requirements. For instance, while the current system can detect a 5-mm diameter cable (less than quarter of an inch) from a distance of around 800 yards with an optical visibility of about a mile and a quarter, a detection range of about 550 yards would be sufficient for a helicopter flying at a lower speed. This would provide a similar warning time while not only decreasing the physical constraints of the equipment but also reducing system, integration and qualification costs.
