BAE Systems has developed Brownout Landing Aid System Technology, or BLAST, to help solve the piloting challenge of landing in Degraded Visual Environments (DVEs). It provides intuitive eyes-out landing guidance on a helmet-mounted display, augmented with a dynamic, cognitive 3-D synthetic view of the landing zone on a multifunction display generated from active scanning millimeter-wave radar.
Examining the nature of U.S. military helicopter losses from 2002-08, BAE identified a very significant proportion of accidents that could have been avoided, or reduced, by using an active scanning radar sensor and new integrated software. During that period, there were 130 events involving 189 fatalities involving combat helicopter operations, but not involving hostile actions. In non-combat operations there were 134 events resulting in 140 fatalities. Looking at the data connected with these figures it was clear that flight in brownout conditions and controlled flight into terrain were the biggest causes of accidents, but the two categories could benefit enormously from a new system solution.
The brownout phenomenon is caused by excessive dust and dirt thrown up when aircraft take off or land. In the case of helicopters, the turning rotors can cause this condition to persist even while idling, waiting to takeoff, or when hovering to attach or drop off under-slung loads, which might be containers or netted supplies. The larger the helicopter, the bigger the downwash and the greater the impact on creating a brownout condition.
Making rolling approaches to a landing site can reduce the dust cloud, but as the helicopter gets lower and slows down the dust cloud will close in and envelop it.
BAE decided that off-the-shelf technology from already-fielded systems would be the quickest and most affordable route to developing the new counter brownout system. The chosen radar sensor combines proven millimeter wave technology with advanced situational awareness capabilities.
Radar monopulse processing added to a 94-GHz sensor gives improved angular accuracy for visual acuity, and an inherent ability to see through the DVE conditions. Small size and weight were vital requirements for helicopter use, with adaptive inertial stabilized scan volume.
The radar sensor for the BLAST trials has been taken from an MBDA Brimstone missile, and an existing Valley View patented terrain morphing algorithm has been used. The radar sensor is small and lightweight with advanced all-weather performance and measurement accuracy. It has narrow beam width in azimuth and elevation with low side lobes. A bonus is the inherent low probability of intercept.
The 94-GHz sensor is mounted on the helicopter nose in a forward-looking position, with an embedded computer with a proprietary monopulse radar-processing algorithm and synthetic terrain-morphing display engine, multifunction displays, a landing zone designation switch, and a tracked helmet-mounted display for each pilot. This combination gives intuitive flight symbology landing guidance augmented with a dynamic cognitive view of the ground in and around the landing zone. The system emulates normal flying operations where the pilot chooses the landing point, and then visually flies to that position using flight instruments and internal and external references.
The solution uses this constant aspect procedure to allow a landing in either brownout or whiteout (powdered snow) conditions. The sensor adaptively scans the designated area. The detected radar signal is digitized and processed using innovative monopulse processing techniques to provide terrain details, including the precise height and width of objects. The terrain-morphing display algorithm uses the sensor data along with the stored terrain database and helicopter state data to continuously update and synthetically render a real-time image on a head-down display to show the landing zone features. This is done in such a way that the terrain model has a sufficiently high resolution to distinguish objects of interest (such as wires, boulders, fences, poles, vehicles and personnel) from the actual terrain.
The pilot is also able to select a 2-D horizontal situational view to improve object awareness in the horizontal plane. A Brownout Symbology Set (BOSS) is optionally overlaid on the head-down display, providing cueing to guide the pilot to the landing point in the absence of a helmet-mounted display with conformal landing symbology.
The BLAST system architecture is scalable and a low-cost development. It can offer a pilot a passive flight guidance via conformal symbology on a helmet display with the option to add active scanning to provide a dynamic cognitive view on a multifunction display during landing. The intuitive and simple-to-use system features keep training costs low. The conformal symbology design reflects years of avionics experience, and the display image is simple to interpret. Production systems can easily be fitted to new aircraft, or retrofitted to in-service helicopters.