Brownout (aviation)
Encyclopedia
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:
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. Another phenomenon observed at night is the Kopp-Etchells Effect caused by small particles hitting the leading edge of the rotor blades and making tiny sparks, creating a disk-shaped sparkling glow around the rotor. This effect can also produce spatial disorientation in the uninitiated pilot.
The visible effects of sand rotor abrasion have been extensively observed in Afghanistan.
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 Longbows 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.
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
Spatial disorientation
Spatial disorientation is the inability to correctly interpret aircraft attitude, altitude or airspeed, in relation to the Earth or point of reference. Spatial disorientation is a condition in which an aircraft pilot's perception of direction does not agree with reality...
and loss of situational awareness leading to an accident. Pilots have compared landing during brownouts to parallel parking
Parallel parking
thumb|250px|right|Parallel-parked cars in [[Washington, D.C.]]thumb|250px|right|A motorist gets assistance parallel-parkingParallel parking is a method of parking a vehicle in line with other parked cars. Cars parked in parallel are in one line, parallel to the curb, with the front bumper of each...
an automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
with one's eyes closed.
The brownout phenomenon causes accidents during helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...
landing and take-off operations in arid desert terrain. Intense, blinding dust clouds stirred up by the helicopter rotor
Helicopter rotor
A helicopter main rotor or rotor system is a type of fan that is used to generate both the aerodynamic lift force that supports the weight of the helicopter, and thrust which counteracts aerodynamic drag in forward flight...
downwash
Downwash
In aeronautics downwash is the air forced down by the aerodynamic action of a wing or helicopter rotor blade in motion, as part of the process of producing lift....
during near-ground flight causes significant flight safety risks from aircraft and ground obstacle collisions, and dynamic rollover
Dynamic rollover
A helicopter is susceptible to a lateral rolling tendency,called dynamic rollover, when lifting off the surface.For dynamic rollover to occur, some factor has to firstcause the helicopter to roll or pivot around a skid, or...
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:
- rotor disk loadingDisk loadingIn fluid dynamics, disk loading or disc loading is the average pressure change across an actuator disk, such as an airscrew. Airscrews with a relatively low disk loading are typically called rotors, including helicopter main rotors and tail rotors; propellers typically have a higher disk...
- rotor configuration
- soil composition
- wind
- approach speed and angle
Countermeasures to prevent brownout-related accidents include:
- Site preparation
- Pilot technique
- Synthetic visionSynthetic visionA Synthetic Vision System is a computer-mediated reality system for aerial vehicles, that uses 3D to provide pilots with clear and intuitive means of understanding their flying environment....
systems also known as "see and remember" - Upgraded horizontal situation indicatorHorizontal Situation IndicatorThe horizontal situation indicator is an aircraft instrument normally mounted below the artificial horizon in place of a conventional heading indicator. It combines a heading indicator with a VOR/ILS display, reducing pilot workload by lessening the number of elements in the pilot's instrument...
with improved symbology - AerodynamicsAerodynamicsAerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...
such as the "winged rotor" on the AgustaWestland EH101AgustaWestland EH101The AgustaWestland AW101 is a medium-lift helicopter for military applications but also marketed for civil use. The helicopter was developed as a joint venture between Westland Helicopters in the UK and Agusta in Italy... - Non-visual displays of position and orientation data derived from suitable sensors, such as Tactile Situational Awareness Systems (TSAS) providing information to the pilot through the sense of touch using tactors.
Sensory illusions
Blowing sand and dust can cause an illusion of a tilted horizon. A pilot not using the flight instrumentsFlight instruments
Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with information about the flight situation of that aircraft, such as height, speed and altitude...
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. Another phenomenon observed at night is the Kopp-Etchells Effect caused by small particles hitting the leading edge of the rotor blades and making tiny sparks, creating a disk-shaped sparkling glow around the rotor. This effect can also produce spatial disorientation in the uninitiated pilot.
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 WarGulf War
The Persian Gulf War , commonly referred to as simply the Gulf War, was a war waged by a U.N.-authorized coalition force from 34 nations led by the United States, against Iraq in response to Iraq's invasion and annexation of Kuwait.The war is also known under other names, such as the First Gulf...
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
Fort Irwin Military Reservation
Fort Irwin & the National Training Center is a major training area for the United States Military and is a census-designated place located in the Mojave Desert in northern San Bernardino County, California. Fort Irwin sits at an elevation of . The 2010 United States census reported Fort Irwin's...
National Training Center in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, 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 Longbows 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
CH-47 Chinook
The Boeing CH-47 Chinook is an American twin-engine, tandem rotor heavy-lift helicopter. Its top speed of 170 knots is faster than contemporary utility and attack helicopters of the 1960s...
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
Project on Government Oversight
The Project On Government Oversight , founded in 1981, is an independent non-profit organization in the United States which investigates and seeks to expose corruption and other misconduct. POGO assists whistleblowers and investigates federal agencies, Congress, and government contractors...
(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
V-22 Osprey
The Bell Boeing V-22 Osprey is an American multi-mission, military, tiltrotor aircraft with both a vertical takeoff and landing , and short takeoff and landing capability...
tiltrotor
Tiltrotor
A tiltrotor is an aircraft which uses a pair or more of powered rotors mounted on rotating shafts or nacelles at the end of a fixed wing for lift and propulsion, and combines the vertical lift capability of a helicopter with the speed and range of a conventional fixed-wing aircraft...
aircraft, which was deployed for combat in Iraq in September 2007. The high proprotor
Proprotor
A proprotor is a spinning airfoil that is used as both an airplane-style propeller and a helicopter-style rotor during the same flight. Proprotors are typically used on vertical takeoff and landing aircraft....
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.
Partial list of related accidents
Civilian
- August 18, 2001, Vinton, CaliforniaVinton, CaliforniaVinton is an unincorporated community in Plumas County, California. It lies at an elevation of . Vinton is located west of Chilcoot.For census purposes, Vinton is included in the census-designated place of Vinton-Vinton....
, USA — Rocky Mountain Holdings, Aerospatiale AS355F1 (N53LH) — MEDEVACMEDEVACMedical evacuation, often termed Medevac or Medivac, is the timely and efficient movement and en route care provided by medical personnel to the wounded being evacuated from the battlefield or to injured patients being evacuated from the scene of an accident to receiving medical facilities using...
helicopter damaged in dynamic rolloverDynamic rolloverA helicopter is susceptible to a lateral rolling tendency,called dynamic rollover, when lifting off the surface.For dynamic rollover to occur, some factor has to firstcause the helicopter to roll or pivot around a skid, or...
after an aborted takeoff at a remote location, with no injuries. The helicopter was substantially damaged. Pilot experienced brownout after lifting off approximately 3 feet (1 meter) off the ground.
- September 22, 2001, Chico, CaliforniaChico, CaliforniaChico is the most populous city in Butte County, California, United States. The population was 86,187 at the 2010 census, up from 59,954 at the time of the 2000 census...
, USA — Enloe Medical Center Aerospatiale AS350BA (N911NT) — helicopter was destroyed after colliding with trees in an aborted landing at a ballpark killing the pilot and injuring one of two flight nurses on board. Witnesses on the scene reported a brownout cloud obscured their vision of the accident sequence.
- March 21, 2004, Pyote, TexasPyote, TexasPyote is a town in Ward County, Texas, United States. The population was 131 at the 2000 census.-History:Pyote began as a small town. Its fortunes rose with oil, but its population decreased when the railroad was built away from the town. At one time Pyote had 3,500 residents...
, USA — Med-Trans Bell 407Bell 407The Bell 407 is a four-blade, single-engine, civil utility helicopter; a derivative of the Bell 206L-4 LongRanger. The 407 uses the four-blade rotor with composite hub developed for the United States Army's OH-58D Kiowa Warrior instead of the two-blade, semi-rigid rotor of the 206L-4...
(N502MT) — EMS helicopter crashed into terrain while maneuvering in reduced visibility at night while transporting a patient. The pilot, flight paramedic, patient, and patient’s mother were killed, and the flight nurse was seriously injured. Witnesses reported brown-out conditions at the time of the accident.
- June 26, 2004, Cibecue, ArizonaCibecue, ArizonaCibecue is a census-designated place in Navajo County, Arizona, United States. The population was 1,331 at the 2000 census.The current council leaders are Arnold Beach Sr...
, USA — Native American Air Ambulance AS350B3 (N5226R) — MEDEVAC helicopter landed hard on a baseball field in a brownout, damaging the tail boom, but without injuring the crew. The damage was not discovered on a post-flight inspection, or subsequent pre-flight inspections, and was only noticed by a aircraft maintenance technicianAircraft Maintenance TechnicianAircraft maintenance technician, as used in the United States, refers to an individual who holds a mechanic certificate issued by the Federal Aviation Administration; the rules for certification, and for certificate-holders, are detailed in Subpart D of Part 65 of the Federal Aviation Regulations ,...
8 days later.
- August 16, 2005, Donnelly, IdahoDonnelly, IdahoDonnelly is a city in rural Valley County, Idaho, United States. The population was 138 at the 2000 census, and was estimated to be 148 in 2007....
, USA, Heliflite LLC, Hughes 369EHughes H-6The Hughes OH-6 Cayuse is a single-engine light helicopter with a four-bladed main rotor used for personnel transport, escort and attack missions, and observation...
(N500FU), helicopter was substantially damaged when the main rotor blade hit a tree on landing, with no injuries. Recent construction work at the site disturbed the surface, creating unexpected brownout conditions.
Military
- October 19, 2001, DalbandinDalbandinDalbandin is a town and Union council of Balochistan, Pakistan. Dalbandin is famous for fruit orchards.On 19th January, 2011, it was struck by a 7.2 magnitude earthquake. At that time it was a sparsely populated area with a population of 15,000. It is located at 28°52'60N 64°25'0E at an altitude...
, Pakistan — U.S. Army Rangers, Task Force 3/75 MH-60K Black Hawk — As the search and rescueSearch and rescueSearch and rescue is the search for and provision of aid to people who are in distress or imminent danger.The general field of search and rescue includes many specialty sub-fields, mostly based upon terrain considerations...
helicopter approached to land at night, it caused a brownout, obscuring the landing area. The aircraft crashed into a sand dune, killing two rangers on board as passengers, and injuring three others. - December 6, 2001, Forward operating baseForward Operating BaseA forward operating base is any secured forward military position, commonly a military base, that is used to support tactical operations. A FOB may or may not contain an airfield, hospital, or other facilities. The base may be used for an extended period of time. FOBs are traditionally supported...
(FOB), Afghanistan — U.S. Marine Corps, HMM-365, UH-1N — Helicopter inadvertently touched down on takeoff while drifting to the right and rolled over. One member of the crew was ejected, and the other three exited before the aircraft was destroyed by fire. Another nearby helicopter was damaged by flying debris from the rotor. - August 12, 2002, FOB, Operation Enduring Freedom — U.S. Air Force, 347th Rescue Wing, HH-60G Pave Hawk — helicopter departed slowly and had insufficient power to climb out of the dust cloud generated on take-off from its own rotor wash. The pilot tried to land and hit a sand berm. The six aircraft occupants evacuated without serious injury.
- February 13, 2003, near Ali Al Salem Air BaseAli Al Salem Air BaseAli Al Salem Air Base is a military airbase situated in Kuwait, approximately 23 miles from the Iraqi border. The airfield is owned by the Government of Kuwait, and during Operation Southern Watch and Operation Telic / Operation Iraqi Freedom hosted Royal Air Force , United States Air Force and...
, Kuwait — U.S. Air Force, 20th Special Operations Squadron, MH-53M (s/n 10930) — helicopter was badly damaged when crew misjudged a night landing in brownout conditions. Some minor injuries. Aircraft was salvaged. - March 23, 2003, U.S. Army Aviation Base Camp, Central Iraq — U.S. Army 6th Cavalry Regiment, AH-64D Apache Longbow — helicopter crashed on takeoff on the unit’s first day at that base camp.
- March 28, 2003, Iraq — U.S. Army 101st Aviation Regiment, AH-64D Apache — while departing from FOB Shell for a combat mission with approximately 40 other fully loaded helicopters, the helicopter rolled over in severe brownout approximately 4 minutes after the first aircraft took-off.
- March 28, 2003, Iraq — U.S. Army 101st Aviation Regiment, AH-64D Apache (97-5032) — after returning to FOB Shell from a combat mission, the helicopter landed hard in brownout conditions, rolled over, and was severely damaged (though later salvaged and repaired).
- March 31, 2003, Iraq — U.S. Army 103rd Aviation Regiment, AH-64D Apache (99-5104) creates brownout on takeoff for a MEDEVACMEDEVACMedical evacuation, often termed Medevac or Medivac, is the timely and efficient movement and en route care provided by medical personnel to the wounded being evacuated from the battlefield or to injured patients being evacuated from the scene of an accident to receiving medical facilities using...
escort mission, resulting in main rotor strike, rollover, and loss of the aircraft. - April 5, 2003, Camp Thunder Road, KuwaitKuwaitThe State of Kuwait is a sovereign Arab state situated in the north-east of the Arabian Peninsula in Western Asia. It is bordered by Saudi Arabia to the south at Khafji, and Iraq to the north at Basra. It lies on the north-western shore of the Persian Gulf. The name Kuwait is derived from the...
— U.S. Army 101st Aviation Regiment, UH-60 Black Hawk — helicopter collided with a sling load during a pickup attempt in brownout conditions. The three injured crew members pulled the two seriously injured pilots from the burning wreckage before it was destroyed by fire. - April 26, 2004, location not specified — U.S. Marine Corps, HMM-266, CH-46E — Hard landing during brownout. Rotor blades struck terrain, but helicopter remained upright.
- July 27, 2005, Spin Buldak Afghanistan — Royal Netherlands Air Force, 298 Squadron CH-47D ChinookCH-47 ChinookThe Boeing CH-47 Chinook is an American twin-engine, tandem rotor heavy-lift helicopter. Its top speed of 170 knots is faster than contemporary utility and attack helicopters of the 1960s...
(D-105) — helicopter made a "hard landing" due to "brown-out conditions" as the crew was attempting to insert forces on the border between Afghanistan and Pakistan. The aircraft was destroyed by fire but there were no injuries.
See also
- Safety of emergency medical services flightsSafety of emergency medical services flightsThe safety of emergency medical services flights has become a topic of public interest in the United States, with the expansion of emergency medical services aviation operations, such as air ambulance and MEDEVAC, and the increasing frequency of related accidents.-Background:Emergency medical...
- Hazards of helicopter flight