Voir Wikipedia en anglais sur http://en.wikipedia.org/wiki/Brownout_(aviation)
Brownout par analogie à whiteout voir http://en.wikipedia.org/wiki/Whiteout_(weather)
Le “brownout” a été la principale cause de pertes d’hélicoptères en Irak et en Afghanistan.
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.