Brownout and degraded visual environments, explained

Brownout is the loss of outside visual reference when a helicopter's rotors raise a cloud of dust and sand around it near the ground. A 2005 American Forces Press Service story described brownout as rotors kicking up dust and debris, reducing pilots' vision and making landing dangerous. Brownout is one kind of degraded visual environment (DVE). The U.S. Army Combat Readiness/Safety Center reported in a June 2014 article that 88 of 367 Class A and B accidents since the start of the wars in Afghanistan and Iraq involved DVE, and that 57 percent of those involved brownout. The Army budgeted for DVE technologies from 2011, and in 2023 its work to add one system to the CH-47F was at an early stage.

What brownout and DVE mean

The 2014 safety center article defines DVE as reduced visibility of varying degree in which situational awareness and aircraft control cannot be maintained as fully as in normal visual meteorological conditions. The author, Lt. Col. Mike Higginbotham, then director of the center's Aviation Directorate, calls the definition intentionally broad: smoke, rain, night, dust, haze, brownout, and whiteout all count. The cause can be weather, darkness, or a helicopter's own rotor wash recirculating dust or snow.

The article separates two terms. Spatial disorientation is what happens to the pilot, who fails to sense the aircraft's position, motion, or attitude correctly. DVE is the condition in which the disorientation occurs.

The multiservice sling load manual, TM 4-48.09, dated July 23, 2012, gives the same idea for ground crews: brownout, the loss of vision from blowing sand, presents the same visual and reference problems as whiteout.

The mishap record

Historically, the 2014 article says, about 20 percent of Class A and B mishaps were attributed directly to spatial disorientation or loss of situational awareness in DVE. Class A counts ran two of eight accidents in fiscal year (FY) 2013, five of 18 in FY2012, two of 14 in FY2011, and eight of 21 in FY2010. Over the previous 12 years, DVE accounted for 24 percent of the Army's flight accidents. Of the 88 DVE mishaps since the wars began, 67 percent occurred in combat and 52 percent during the landing phase. The author wrote that the Army had made no progress on this loss factor since the center's accident database began in 1972.

The same article quotes a 1995 Army laboratory survey of helicopter accidents from 1987 to 1992. The survey found brownout, whiteout, or inadvertent entry into instrument conditions in only 25 percent of spatial disorientation accidents, while aircrew distraction was thought to play a part in 44 percent.

Two 2005 Chinook cases show the range. The 2005 story reports that a coalition CH-47 made a hard landing in brownout near Spin Buldak on July 27, 2005; the aircraft was destroyed by fire, and no one was injured. The same story reports the investigation of the April 6, 2005 CH-47D crash near Ghazni that killed 18. That aircraft met a dust storm with winds of more than 45 knots, and the pilots became spatially disoriented while transitioning to instrument flight.

Why the CH-47's rotor wash matters

TM 4-48.09 says large helicopters such as the CH-47 and CH-53 can generate rotor wash in excess of 120 knots, strongest between 20 and 60 feet outside the rotor disc. That wind can make it hard for ground crews to stand and can move unsecured material, and the same recirculating air raises the dust cloud of a brownout.

Ground-side measures appear in ATP 3-04.17, the Army's 2018 publication on forward arming and refueling points, as changed in 2021. The manual says aircraft movement should be limited in desert and snow, where wind and rotor wash may cause brownout or whiteout. The manual stresses hard surfaces for eliminating brownout, found by site surveys, and warns that no single dust palliative suits every situation and that vendor claims are only partially true at best.

The Army's sensors and mitigation programs

An April 2012 Army News Service story traces the modern effort. A Helicopter Survivability Task Force formed in 2009 led to a Program Executive Office Aviation study dated August 11, 2011, which found DVE the greatest threat to Army aircraft. Under an operational needs statement, the Army planned to buy five 94-gigahertz millimeter wave radars called Helicopter Autonomous Landing Systems. Project manager Col. Anthony Potts said the Army had budgeted $226 million for DVE technologies from 2011 to 2015, and that millimeter wave radar best penetrated dust.

A September 2016 army.mil story reports that the Degraded Visual Environment Mitigation program tested an integrated cueing, sensor, and flight control solution in dust and brownout at Yuma Proving Ground, Arizona, on an EH-60L, with a milestone on September 15, 2016. The story attributes to PEO Aviation officials the finding that 80 percent of rotorcraft losses in Iraq and Afghanistan came from combat non-hostile or non-combat factors, including DVE.

For the CH-47F, the work was at an early stage in 2023. An August 11, 2023 army.mil story describes the DVE Pilotage System (DVEPS), which fuses several sensors into a forward-looking image of terrain and obstacles for brownout takeoffs and landings. As of that story, DVEPS was fielded on a limited number of HH-60Ms. Demonstrations at Redstone Army Airfield on July 24-26, 2023 were part of early-stage materiel development to install the system on the CH-47F.

What to check

• Does a DVE figure name its period and source? The 2014 safety center counts end in FY2013.
• Does a claim treat brownout and DVE as the same thing? In the 2014 article, brownout was involved in 57 percent of DVE mishaps, not all of them.
• Does a system claim say whether it is fielded or in development? In August 2023 DVEPS was on limited HH-60Ms, and CH-47F work was early-stage.
• Does a landing zone plan account for CH-47 rotor wash in excess of 120 knots and use hard surfaces where they exist?
• Does a mitigation plan cover training and flight controls as well as sensors? The 2016 tests treated sensors, cueing, and flight controls as complementary.

Azcuna's ELLMENT for the CH-47 puts the Chinook's public technical manuals, the Army sling-load manuals and a unit's own SOPs on a laptop or tablet that answers a repairer's or flight engineer's question with no network and cites the manual and page. Azcuna submitted it as a concept white paper to the Army's xTech|Search 10 competition in October 2026.

Sources

1. 1Army Aviation's enduring challenge · U.S. Army Combat Readiness/Safety Center, via army.mil (June 24, 2014)
2. 2Officials Report on Chinook Incidents in Afghanistan · American Forces Press Service (July 28, 2005), via DVIDS
3. 3TM 4-48.09, Multiservice Helicopter Sling Load: Basic Operations and Equipment · Headquarters, Department of the Army and other services (July 23, 2012)
4. 4ATP 3-04.17, Techniques for Forward Arming and Refueling Points · Headquarters, Department of the Army (June 4, 2018, with Change 1 of May 18, 2021)
5. 5Army acquiring 'brown-out' assistance for helos · Army News Service, via army.mil (April 2012)
6. 6Degraded visual environment researchers conduct milestone testing · AMRDEC and Yuma Proving Ground Public Affairs, via army.mil (September 26, 2016)
7. 7Preparing the Chinook for the Army of 2030 · army.mil (August 11, 2023)

Where this shows up in our work

• ELLMENT for the CH-47 Chinook answers a repairer's or flight engineer's question from the Chinook's manuals and the Army sling-load manuals and cites the page, with no network.
• TRACE, the offline S1000D and IETM viewer opens S1000D, MIL-STD-3001 and PDF technical manuals on a tablet with every marking intact.