Aeromedical health: Disorientation of chopper pilots

DISORIENTATION OF CHOPPER PILOTS

Some VERY basis concepts for health care practitioners

  • Vibration of a helicopter makes it more difficult to fly as visual referencing is disturbed.
  • Entering of cloud or mist can disorientate pilot in terms of position in space.
  • Vertigo (spacial disorientation) is a whirling sensation. When flying at night and a cloud bank is lit up by the moon, a pilot can experience spacial disorientation if the bottom of the cloud is not parallel to the earth’s surface. One is erroneously inclined to believe that the bottom of a cloud is always parallel to earth’s surface. On erroneously correcting for the “skew” cloudbank, the helicopter will start turning.
  • In bad weather with turbulence attitude changes of up to 20° can take place without the helicopter pilot realising it (that is when there are no visual references). The rolling is undetectable to the balance senses in the ear
  • On entering cloud (with no visual referencing) the helicopter can start banking. The banking leads to a drop in altitude. The banking can be undetectable to the balance senses in the ear, but the pilot suspects it due to the drop in altitude. In reaction the pilot may pull back on the cyclic and increase power which in fact may tighten the turn and worsen the situation. Once the turn has developed the pilot gets the illusion of of turning in the opposite direction when trying to stop the turn, leading to a wrong corrective action. A very dangerous situation develops.
  • Flicker vertigo is caused by the light flickering through the rotor blades of the helicopter. It can lead to nausea, dizzyness, unconsciousness, or an epileptogenic reaction. As soon as the pilot realises this is happening the pilot must reorientate the helicopter so that this flickering does not occur.
  • White-out is when the white sky and snow-covered land surface visually merge. Lack of shadows on snow surfaces makes referencing difficult. Depth perception also dissapears when foreground and background landscapes appear at the same hue of white. White-out is exacerbated during lightsnowfall or percipitation (this is even worse at night).  Glare obscures shadow contrasts even 1/2 meter off the ground. When the pilot approaches he or she may still be able to identify references such as a radio mast but as the helicopter nears the ground, snow powder blown into the air induces white-out.
  • Grey-out is the poor visibility when a helicopter flies over water during bad weather. The grey of the water and the grey of the sky merges and makes visual referencing impossible. It makes the pilot want to fly lower as the horison seems clearer on flying lower. The pilot can then inadvertently put the helicopter in the water.
  • Water effects occur when the helicopter pilot flies over glassy water. The water and the skyline merge and the pilot has to fly using the shoreline as reference.