Landing a helicopter in sandstorms, dust, or snow typically produces a dense cloud that can disorient and blind pilots. In military operations, these treacherous “brownout” conditions often are to blame for costly mishaps.
The Army has for years been pursuing technologies to help pilots see through blowing dust during landings, but no silver bullet has yet emerged.
As early as this fall, the Defense Advanced Research Projects Agency will be testing a new landing system for military helicopters that promises safer flying in brownouts.
The system, known as Sandblaster, seeks to provide helicopter pilots an accurate depiction of the outside world by combining various technologies — sensors, digital terrain data, high-tech displays and advanced helicopter flight controls. It enables the pilot to see through the cloud and guide the helicopter to a preset point or let the helicopter land itself while the pilot watches over the landing zone.
“We’re working to solve the brownout problem in an integrated, affordable, end-to-end system,” says Reggie Brothers,
Sandblaster program manager at DARPA’s strategic technology office.
If Sandblaster performs as expected, it will provide, for the first time, a semi-automated system that would let military pilots land a helicopter, hands off, in brownout conditions.
Pilots currently do make safe brownout landings — employing rolling techniques and relying on crew chiefs looking out the back door. But they’re still vulnerable to rollovers, obstructions, and crash descent rates. The technologies developed so far have been piecemeal successes.
DARPA awarded in May a $16.6 million contract to Sikorsky Aircraft to build, by September 2008, a prototype brownout system for the Army’s new UH-60M Black Hawk. The long-term goal, Brothers says, is to develop a system that can be adapted for any military helicopter.
“It’s far and away the most dangerous thing you can do as a helicopter pilot ... I’m essentially flying a controlled crash into the ground with no outside reference,” says Air Force Pave Low Special Operations pilot Maj. Michael Grub.
Brownout clouds start up to 100 feet above the ground for the heaviest helicopters with the greatest rotor downwash. Drifting in a dust cloud to touchdown makes helicopters prone to lateral rollover or ground collisions.
In just the first year of the war in Iraq, brownout mishaps cost the Army three fatalities, 29 non-fatal injuries, and $60 million in equipment damage, notes the Army Aviation Applied Technology Directorate. One Army Chinook was destroyed and 16 soldiers were injured in Afghanistan when the CH-47D set a landing gear in an irrigation ditch.
A study by the Air Force Research Laboratory categorized mishaps across all the military services from 1985 to 2005, and found the risk of brownout accidents to be several times greater at night than in daylight. The study attributed seven major Pave Low and eight major Pave Hawk accidents to brownout — all of them at night.
Crews who fly with night vision goggles have reduced peripheral vision and can more easily lose situational awareness. “When we went into Iraq for the second time, we saw a real spike in brownout mishaps,” says Col. Peter Mapes, an AFRL physician, pilot and researcher.
The Air Force acknowledged last year that seven of 11 Pave Hawks lost in combat had fallen victim to brownout. Marine Corps rotorcraft, too, fly into the same degraded visual environment as Army and Air Force helicopters. All the services have pursued brownout countermeasures.
Brownout was a known hazard before and during the Persian Gulf War in 1991, but the large number of helicopters and frequency of flights in the current conflicts in Iraq and Afghanistan has underscored the danger. In 2003, the Army classed brownouts as a major safety hazard, particularly for Chinook cargo and Black Hawk utility helicopters. Attack helicopter crews in Afghanistan and Iraq quickly learned to use Apache cockpit hover symbology to make safe brownout landings.
Cargo and utility helicopter program managers asked the Army’s aviation technology directorate at Fort Eustis to put brownout landing cues in the analog cockpits of the Chinook and Black Hawk. In August 2003, the Army also asked Rockwell Collins to adapt the horizontal situation indicator that the company installed in the Army’s more sophisticated special operations aircraft in conventional Chinooks and Black Hawks.
The resulting “brownout situational awareness upgrade” gave utility and cargo helicopter pilots a small liquid crystal display that charted velocity vector, acceleration cues, radar altimeter height and vertical speed. Army engineers also integrated a Honeywell embedded GPS/inertial navigator with the existing radar altimeter on both the UH-60 and CH-47 to generate a precision hover display.
Trials at the dusty Yuma Proving Ground, Ariz., in September 2004 proved that the brownout situational awareness upgrade symbology was usable, but the Army declined to fund kits for older Black Hawks and Chinooks. The symbology derived from the situational awareness kit will nevertheless appear on the Rockwell common avionics architecture system in the new CH-47F and UH-60M. Brownout safety improvements have helped pilots learn how to make rolling landings to keep ahead of the dust cloud.
To provide brownout landing cues, the Air Force Special Operations Command adopted symbology like that in the Army Apache for its MH-53M Pave Low helicopter. The Navy recently tested the laser-based LandSafe system on a Marine Corps CH-53E to provide ground speed and drift, airspeed, altitude, and wind speed and direction on a cockpit hover display. Pending a demonstration report, LandSafe may go aboard the current CH-53E and new CH-53K heavy lift helicopters.
The new Marine Corps MV-22 and Air Force CV-22 Ospreys will give pilots calculated flight path vector displays for manual or automatic brownout landings by using the hover hold function in the tilt rotor flight controls.
To improve the handling qualities of its special operations helicopters, the Air Force Special Operations Command equipped all Pave Low MH-53Ms with an “altitude hold hover stabilization system” capable of near-automatic landings. The system flies the aircraft to a two- to three-foot hover over a programmed point, so the pilot can land safely. The Air Force can begin to phase out the Pave Low fleet, but it has funded the altitude hold hover stabilization technology for the Pave Hawk rescue fleet as it awaits a new combat search-and-rescue helicopter.
Even with precision hover symbology and enhanced flight controls, helicopter pilots want a see-through sensor for brownout conditions. Air Force researchers evaluated sensors for DARPA’s Sandblaster effort and found forward-looking infrared technology nearly blind in brownouts. Imaging laser radar technology can see through dust, but the Army opted to test millimeter wave radar on a Black Hawk as the helicopter’s autonomous landing system. The 94 GHz radar from Sierra Nevada Corp. provides a real-time picture of the landing zone on two cockpit displays and is expected to be tested at Yuma in 2008.
The Air Force Research Laboratory, meanwhile, has tested a see-and-remember photographic landing augmentation system for helicopters on a Pave Low helicopter in simulated sand-dust approaches on the Eglin Range around Hurlburt Field, Fla. It was developed by Applied Minds Inc. and integrated into the MH-53M by Aerospace Integration Corp.
It uses a gimbaled, high-resolution camera with infrared strobe and laser rangefinder to image a landing zone seconds before the helicopter enters the brownout cloud. The crew sees the picture geo-registered on the hidden landing zone with altitude, height above ground, distance from landing zone, speed and heading symbology.
Helpful though it may be, a see-and-remember sensor cannot show real-time hazards that move into the brownout cloud during landing. DARPA’s Sandblaster integrates new see-through sensors with an advanced pilot-vehicle interface, digital terrain database and augmented flight controls.
“It’s an open architecture,” Brothers explains, “so we’re looking at a variety of different sensors. Right now we’ve been looking at radar because it has potentially greater ability to see through sand.”
Laser radar will be tested in dust at Yuma this summer, but whatever the sensor, the Sandblaster technology is intended for the new UH-60M with digital cockpit and fly-by-wire controls.
“We’re developing a system that’s almost sensor-agnostic for the ‘60M,” he adds.
UH-60M maker Sikorsky Aircraft is responsible for integrating the prototype brownout system. Honeywell Aerospace is in charge of developing the pilot-vehicle interface and providing what Sikorsky engineers call a “knowledge fusion evidence grid.” Honeywell’s enhanced ground proximity warning system for civil helicopters and airplanes already uses a stored database to warn pilots of upcoming terrain and obstacles with symbols and audible cues.
The company’s integrated primary flight display generates a three-dimensional graphic display of surrounding terrain annotated with flight symbology. The Sandblaster knowledge grid will use high-resolution digital terrain elevation data to enhance the see-through sensor image pixel by pixel in a synthetic vision display. It will also annotate the combined picture with symbology showing the predicted flight path.
The initial see-through sensor for Sandblaster — the Sierra Nevada millimeter wave radar — is more powerful than the one used in the Army’s helicopter autonomous landing system (HALS), which also is undergoing tests. The 94 GHz radar permits a small antenna with a tight beam to paint upcoming terrain. Sandblaster is expected to provide advanced flight controls to put the helicopter on the ground. Sikorsky is now delivering S-92 search-and-rescue helicopters that are able to fly hands-off to a rescue hover.
Hypothetically, a helicopter will be flown to a hover either manually or automatically and will set itself down automatically without drifting to either side. The crew will see the process on the “pilot vehicle interface” and go around if they see they’re approaching an obstacle in the cloud.
The Army aviation technology directorate demonstrated that the brownout situational awareness upgrade (BSAU) provided precise hover cues so the aircraft didn’t drift and roll over, but the Army didn’t buy the system for existing helicopters. The avionics architecture in the UH-60M and CH-47F will provide the symbology of BSAU.
The downside of BSAU is that it can’t show the landing zone, so the pilot could set down in a shallow ditch or hit a tree stump invisible from higher up, or run into a truck driven into the dust cloud while the pilot is blind.
The Navy’s LandSafe shows precise landing symbology so the aircraft doesn’t drift or land too hard, but provides no real-time view of the world.
The Air Force’s photographic landing augmentation system for helicopters (PhLASH) takes a picture of the landing zone a few seconds before brownout, which provides some guidance, but is not a real-time image that can show a new obstacle that entered the cloud.
Sandblaster integrates the data from see-through sensors, stored terrain elevation, precision altitude and drift (laser and GPS), and precision hands-off flight controls.
Early generations of each technology are in test or in commercial service, but Sandblaster requires more advanced capabilities and has to integrate them all.
The Honeywell enhanced ground proximity warning system, which is found in commercial helicopters, uses a stored database with terrain elevation data to give audible and symbolic collision warnings, but Sandblaster needs higher resolution to augment the radar pseudo-picture.
Sikorsky’s S-92 search-and-rescue aircraft is being delivered to the U.K. Coast Guard with flight controls that can fly hands-off to a hover, but Sandblaster flight controls are supposed to bring the helicopter all the way to the ground.
When asked which technology is more complex to work with, Brothers says, “They are all difficult.”
The current Sandblaster effort has three six-month phases. The first phase, already under way, builds and tests individual components, and includes simulator tests at the Sikorsky facility in Stratford, Conn., and at the Army Aeroflight Dynamics Directorate at Moffett Field, Calif. In the second phase, the four pillars of Sandblaster are tested in simulations. The third phase, at Yuma Proving Ground, will be a live test of the integrated solution on a UH-60M in dusty conditions.
The Army Aviation and Missile Command is the contracting agency for the Sandblaster program. The Air Force Research Laboratory continues to monitor the individual anti-brownout technologies that currently are being developed by all the services.
Brothers says production plans for a Sandblaster system — if it passes critical tests — are still to be formulated, and will include input from the Army Aviation Center, Air Force Special Operations Command and Air Combat Command. “This is such a serious technology issue for the military; we decided this was something we wanted to do,” says Brothers.
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