Extended rotary-wing operations in Iraq and Afghanistan have brought the problems of “brown-out” sharply into focus. There have been numerous accidents as helicopters attempt to land when visibility has been severely impaired by billowing dust and sand. Recognizing the problem, both U.S. and UK defense officials have launched programs to find solutions.
In the U.S. the Defense Advanced Research Projects Agency (DARPA) is running a program called Sandblaster. The first phase was to conduct a series of trials to characterize the nature of “brown-out” clouds. A variety of current U.S. helicopter types were used to create dust clouds, which were then measured for cloud geometry, particle density and particle size. Data from these trials allowed cloud characteristics to be emulated in laboratories for tests of sensors such as LADAR, infrared and millimeter-wave radar.
Subsequent phases of Sandblaster moved from the laboratory to the real world. In February this year Honeywell completed a series of trials with a specially equipped UH-60 Black Hawk. The helicopter made a series of approaches to landing zones to demonstrate the system in a variety of terrain and obstacles. During the trials the pilot used the synthetic-vision system to pick a safe landing site. No actual landings were made due to restrictions.
Under the auspices of Sandblaster, Honeywell was selected by Sikorsky in 2007 to design, integrate and demonstrate the avionics processor that hosts synthetic-vision and sensor-fusion capabilities. The system integrates radar-based sensor information with terrain and obstacle information from a 3-D database.
Information about the aircraft’s current and predicted flight path is displayed using advanced symbology on a head-down synthetic display. The radar sensor not only assesses the desired landing area for potential obstacles, but also determines whether the slope of the terrain is within aircraft limits.
A similar program to Sandblaster known as Low-Visibility Landing (LVL) is running in the UK. It is being conducted by AgustaWestland on behalf of the Ministry of Defence, with the aim of assessing and trialing technologies and proposals from a variety of companies. In the interim, there have been trials involving Chinooks to mitigate some of the problems by adopting faster approach profiles, allowing the aircraft to stay ahead of the dust cloud as they land.
LVL is seeking a solution in which information about the landing zone is provided to the pilot, ultimately to be displayed on head-up or helmet-mounted displays. Like Sandblaster, LVL is based on data fusion techniques, combining laser, radar or IR sensor data with a terrain/obstacle database.
Among the companies partaking in LVL is Atlantic Inertial Systems (formerly BAE Systems Inertial Products), makers of the TERPROM terrain-referencing system. AIS has evolved the initial fast-jet TERPROM system with features specific to the rotary-wing world. This could form an important building block of the ultimate LVL solution.
AIS has undertaken a number of trials in connection with LVL work, involving integration of TERPROM with active sensors, such as the BAE Systems Eagle Owl and Selex LOAM laser obstacle detectors. The company has also demonstrated the extra precision gained from using higher resolution terrain data. A series of flights using digital terrain elevation data (DTED) level 4 confirmed a significant improvement in the horizontal accuracy of terrain-referenced navigation compared with the standard DTED level 1.
In a potential LVL system, TERPROM could be used to give accurate positional data that is referenced to the actual terrain, removing map errors. It also works in areas of GPS degradation or denial. As the pilot approaches the landing area, he could designate a desired landing point, with the TERPROM system providing accurate ranging data and warning of potential hazards. Integrating terrain data with active sensors provides a complete and current picture of the landing zone prior to entering “brown-out” conditions. The system provides continuous cues in the synthetic-vision system to allow the pilot to land the helicopter.
In both the U.S. and UK particular emphasis is being placed on rapid development and affordability, so that solutions can be quickly applied to the in-service fleets.