Brownout (aviation)
In aviation, brownout is a restriction of visibility caused by dust or sand that is thrown up by the downwash of aircraft. The range of vision and thus the possibility of orientation by sight can be reduced in such a way that the safe guidance of the aircraft is no longer possible simply by looking outwards.
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The decisive factors for the development and intensity of a brownout are the weight of the aircraft, drive and rotor layout / design, the nature of the ground in the landing zone, wind, approach speed and angle. Classic helicopters with a single rotor design are more affected than tandem designs. The smaller the thrown up particles, the stronger the effect. This is especially true of the powdery dust that often covers the earth in Southwest Asia. During a brownout, the pilot cannot perceive any objects in the vicinity that he needs as reference points for control over the flight close to the ground. When landing under visual flight, brownouts pose considerable dangers for the aircraft. Without orientation about his flight position and altitude, the pilot runs the risk of reacting incorrectly by an apparent tilt or an actual tilting of the aircraft and thus causing an accident. Intense dazzling dust clouds, which are caused by a helicopter's rotor downdraft, also harbor risks for ground personnel and ground stations due to the danger of collisions due to poor visibility.
Enhancement of the brownout effect
During night landings, aircraft and airfield lights can enhance the visual impression of the brownout.
Kopp-Etchells effect
At night there can be a light effect known as the “Kopp-Etchells effect” since 2009. It arises at landing sites with low humidity and unbound fine rock dust. Small mineral particles hit the leading edges of the rotor blades and generate small sparks. Observers also suspect occasional static discharges in flying sparks. This creates a disc-shaped, sparkling glow in the rotor plane. This process can damage the rotor mechanically ( abrasive wear ).
The term was coined by the American reporter and photographer Michel Yon . He wanted to honor the US soldier Benjamin Stephen Kopp (1988–2009) of the United States Army and Corporal Joseph Etchells (1987–2009) of the British Army , who both died in the Helmand Province in Afghanistan.
Incidents caused by brownouts
US military operations between 2001 and 2007 resulted in more than 50 brownout incidents. According to military experts, Brownout caused more helicopter crashes than all other causes of crashes combined.
In total, the US military incurred annual costs of around 100 million US dollars during the Iraq and Afghanistan wars from brownouts alone.
Since most brownout incidents take place near the ground and at low speed, there is an above-average chance of survival compared to other aircraft accidents. Nevertheless, for example, the crash of a Bell CH-146 Griffon of the Canadian Air Force in Afghanistan , in which three of the six occupants were killed, shows the danger of brownouts.
Technical aids and countermeasures
According to experts, promising measures against the risks of brownout are a combination of advanced technical equipment, planning technology and pilot training.
In newer helicopter models such as the AgustaWestland AW101 , the improved aerodynamics of the rotor blades thanks to the blade-shaped ends reduce the risk of brownouts. The sensor-based landing aid (SeLa for short) also leads to a technical improvement for landings in brownout conditions. The system developed by ESG with the support of EADS and the Fraunhofer-Gesellschaft consists of two cameras under the fuselage, two radar altimeters , a GPS receiver, a geomagnetic field probe and a gyro system to record the helicopter's position deviation. The system enables the pilot to steer safely until touchdown, regardless of the external conditions. The system also works to the same extent under whiteout conditions. SeLa was primarily developed for use in the CH53 of the German Air Force.
Appropriate preparation of the landing zone can reduce the dangers of a brownout. Larger machines such as B. the CH53 the pilot can be supported by the on-board attendant during landing. This lies on the open stern ramp and announces to the pilot the last few meters before touchdown via on-board radio. However, there may be situations in which the on-board attendant cannot adequately assess the landing area. In the best case scenario, this leads to an aborted landing maneuver .
The pilots are trained through training flights under simulated brownout conditions. This can be done, for example, during night landings with night vision equipment, the flight instructor interrupting the power supply to the night vision goggles of the pilot to be trained shortly before putting on.
- Examples of a daylight brownout
Brownout of an HC-130 Hercules on an unpaved runway, caused by rotor vortices of an HH-60G Pave Hawk
The downdraft of a Bell Boeing V-22 creates a brownout
Eurocopter EC 135 D-HZSG in brownout
See also
Web links
Individual evidence
- ↑ a b c Photogrammetric Characterization of a Brownout Cloud. (PDF; 3.1 MB) In: in http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110011703_2011011946.pdf . Retrieved November 29, 2012 .
- ↑ a b Procedure for pilot support during landings of helicopters in visual flight under brown-out or white-out conditions. In: European Patent Office. Retrieved January 8, 2013 .
- ↑ a b c d The Military Spin. In: Rotor & Wing Magazine. Retrieved January 9, 2013 .
- ↑ the-kopp-etchells-effect. In: michaelyon-online.com. Retrieved November 28, 2012 .
- ^ Corporal Joseph Etchells killed in Afghanistan. In: gov.uk
- ^ Benjamin Stephen Kopp, Corporal, United States Army. In: arlingtoncemetery.net
- ^ The Kopp-Etchells Effect. In: michaelyon-online.com
- ↑ a b c Owning the Aviation Edge. NVGPID: A Simple Device to Train Crucial Skills. (PDF; 244 kB) (No longer available online.) In: quad-a.org. Formerly in the original ; Retrieved January 9, 2013 . ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ^ Flying Blind in Iraq: US Helicopters Navigate Real Desert Storms. In: popularmechanics.com. Retrieved November 28, 2012 .
- ↑ Brownout Caused Afghan Griffon Crash. (No longer available online.) In: Aviation Week. Archived from the original on January 14, 2013 ; Retrieved November 29, 2012 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ AW101 Multi-Role Maritime Helicopter. In: agustawestland.com. Retrieved January 4, 2013 .
- ↑ Manfred Hägelen: Sensor-based landing aid for helicopters. (PDF) In: Annual Report 2009. Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR, May 2010, pp. 46–47 , accessed on January 10, 2018 : "Reliable landing aid up to ground contact"
- ↑ a b Sensor-supported landing aid ordered for the CH-53GS / GE. In: Flugrevue.de. Retrieved November 29, 2012 .
- ↑ Michael Pössel trains helicopter crews. In: nw-news.de. Retrieved November 29, 2012 .
