Brownout ( aviation ) In aviation , a brownout ( or " brown - out " ) is an in - flight visibility restriction due to dust or sand in the air . In a brownout , the pilot cannot see nearby objects which provide the outside visual references necessary to control the aircraft near the ground . This can cause spatial disorientation and loss of situational awareness leading to an accident . Pilots have compared landing during brownouts to parallel parking an automobile with one ' s eyes closed . The brownout phenomenon causes accidents during helicopter landing and take - off operations in arid desert terrain . Intense , blinding dust clouds stirred up by the helicopter rotor downwash during near - ground flight causes significant flight safety risks from aircraft and ground obstacle collisions , and dynamic rollover due to sloped and uneven terrain . Brownouts have claimed more helicopters in recent military operations than all other threats combined . There are several factors which affect the probability and severity of brownout : Countermeasures to prevent brownout - related accidents include : Sensory illusions . Blowing sand and dust can cause an illusion of a tilted horizon . A pilot not using the flight instruments for reference may instinctively try to level the aircraft with respect to the false horizon , resulting in an accident . Helicopter rotor wash also causes sand to blow around outside the cockpit windows , possibly leading the pilot to experience the vection illusion , where the helicopter appears to be turning when it is actually in a level hover . This can also cause the pilot to make incorrect control inputs , which can quickly lead to disaster when hovering near the ground . In night landings , aircraft lighting can enhance the visual illusions by illuminating the brownout cloud . The visible effects of sand rotor abrasion have been extensively observed in Afghanistan . U . S . military experience . Several coalition military aircraft were lost due to roll - overs while executing dust landings during the Gulf War period of 1990 - 91 . In the decade between then and Operation Enduring Freedom , the U . S . Army recorded over 40 cases of brownout condition accidents during training at the Fort Irwin Military Reservation National Training Center in California , and other various sites . Since 1991 , there have been over 230 cases of aircraft damage and / or injury due to unsuccessful take - offs or landings in a dust environment . Although the majority of the incidents occur during landings , there have been a significant number of incidents occurring during take - offs as well . For the more than 50 brown - out incidents with damage reported to date during Army military operations in the 2001 - 2007 time frame , 80 percent were during landings and 20 percent during takeoffs . Helicopter brownout is a US $ 100 million per year problem for the U . S . Military in Afghanistan and Iraq . The Army cites brownout in three out of every four helicopter accidents there . Brownout accidents occur close to the ground and at low airspeed , giving these accidents a higher survivability than other types . However , there have been deaths in military accidents in Iraq and Afghanistan , and nearly all of those were preventable . Brownout accidents destroyed or severely damaged four AH - 64D Apache Longbow s in the first three weeks of the 2003 Iraq invasion , while only one had been lost in combat in the same time period . The tandem seat Apache has a narrower stance than the UH - 60 Black Hawk , making it more susceptible to rollover if the pilot begins to lose roll attitude control from the brownout . But at night , the Apache ' s infra - red vision system provides improved visibility when dust obscures the moonlight — the Blackhawk ' s night vision goggles only amplify available visible light . The CH - 47 Chinook has had a relatively high frequency of brownout accidents . , nine Chinooks were lost in action in Afghanistan , and at least two were caused by brownout , which likely played a role in several other incidents . According to the Project on Government Oversight ( POGO ) , 12 of 41 U . S . Army brownout accidents between 2002 and 2005 involved CH - 47s . Data compiled by POGO from government sources show the Chinook flew 7 percent of all U . S . Army helicopter flight hours between 2003 and 2005 but accounted for 30 percent of all brownout - related accidents . Brownout is a particular concern for the U . S . V - 22 Osprey tiltrotor aircraft , which was deployed for combat in Iraq in September 2007 . The high proprotor disk loading creates a high - velocity downwash , which stirs up the dust cloud from a much higher altitude . This can be a problem while hovering during personnel insertion and extraction via hoist or rope . Initial operational experience indicates that although the dust cloud is larger with the MV - 22 than it is with the CH - 46 it is replacing , pilots report regaining visibility near the ground , allowing them to use visual references prior to landing .