Objective

Introduce the student to physiological factors related to instrument flight, especially disorientation and illusions, and review basic aeromedical concepts from private pilot training.

Elements

• hypoxia and hyperventilation
• illusions
• disorientation
• fatigue
• drugs

Schedule

Introduction	05
Main body	30
Application	20
Conclusion	05
Total	1 hour 10 minutes

Equipment

• Instrument Flying Handbook
• AIM

Instructor actions

Describe spatial illusions, possibly using a spinning chair or other physical means. Discuss existing knowledge of visual illusions and other aeromedical factors, evaluating existing student knowledge and building on it.

Student actions

Participate in the lesson actively, taking notes and participating in active examples where appropriate.

Completion standards

The student should be able to identify the causes, and effects, of various spatial and visual illusions. An understanding of aeromedical factors should also be established through quizzing.

Teaching outline

Hypoxia

• Any state of oxygen deficiency which can impair brain or organ function is considered hypoxia
  • histotoxic
  • hypoxic
  • hypemic
  • stagnant
• Can be overcome with the proper usage of oxygen in flight
  • Mask and flow types:
• Sets in slowly and often goes unnoticed
• Experience in an altitude chamber provides an opportunity to recognize effects
• Can affect night vision
  • daytime use: recommended above 10,000 ft
  • nighttime use: recommended above 5,000 ft

Hyperventilation

• Can be thought of as over-breathing
  • too much oxygen, not enough carbon dioxide
• Often has symptoms similar to hypoxia – lightheadedness, drowsiness, tingling
• Treat with application of oxygen and deliberately-slowed breathing
  • Better to compensate with oxygen than assume hyperventilation rather than hypoxia

Spatial disorientation

• Our eyes provide the primary source of information our brain uses for spatial orientation
  • in normal, VMC conditions, our visual input overrides any other, false sensations
• The inner ear also provides significant orientation data
  • Semicircular canals (three per ear, one on each axis) detect angular (rotational) acceleration
  • Otoliths (one per ear) detect linear acceleration
• Without visual cues, the inner ear can provide drastically false information
  • after approximately 20 seconds, the canals stop detecting a constant-rate turn, and indicate an opposite direction turn when the rotation stops
  • if the head is tilted back or forward, the otoliths can indicate acceleration or deceleration (or vice versa)
• Fatigue and illness can increase the prominence of false sensations or the ability to become disoriented

The following illusions can lead to significant spatial disorientation:

• The Leans: slow bank entry can go undetected, while prompt correction can cause the fluid to indicate an opposite-direction turn. The pilot will either make a turn in the original direction, or lean into the turn.
• Coriolis illusion: the turn has been established long enough for the fluid to cease movement relative to the canal; moving the pilot’s head will cause the fluid to move, creating the impression of movement (often tumbling) along a different axis. Correction can lead to extremely unusual attitudes.
• Graveyard Spiral: after extended constant-rate turns, the canals do not detect movement; leveling off causes the pilot to feel an opposite-direction turn and return to the banked condition. Loss of vertical lift will cause a descent; correcting with elevator will tighten the turn, which will continue the descent, resulting in an unrecoverable spiral.
• Somatogravic illusion: rapid acceleration causes the otiliths to indicate a steep nose-up attitude, causing the pilot to dive. Rapid deceleration can have the opposite effect, resulting in sudden power reduction or pitch application and leading to a stall.
• Inversion illusion: abrupt pitch changes from climb to level can cause the otoliths to create a backwards-tumbling sensation; if the pilot reacts with a nose-down pitch attitude, it can intensify the feeling.
• Elevator illusion: updrafts, such as from turbulence, can create an illusion similar to being in a climb. Downdrafts cause an opposite effect.

Optical illusions

• False horizon: sloping cloudbanks, obscured horizon, or patterns of stars or ground lights can create the illusion of an angled horizon. A pilot can improperly align their aircraft along this horizon, resulting in a dangerous or unusual attitude.
• Autokinesis: if a stationary light is focused on in the dark for a short period of time, it appears to move.
• Runway width: narrower-than-usual runways appear lower, while wider runways appear higher. Approach paths can be dangerously low or high, causing a crash short of the runway or an overrun.
• Sloping runway: upsloping runways make the pilot feel higher than usual, while downsloping runways make the pilot feel lower.
• Featureless terrain: a lack of ground features often causes a ‘black hole approach’, resulting in a much lower approach path than normal.
• Water refraction: rain on windows can cause the horizon to appear higher, making the aircraft feel like it is at a higher altitude and resulting in a lower approach.
• Haze: hazy conditions exaggerate distances, while unusually clear air can cause objects to appear much closer. Water particles diffuse light, and make depth perception more difficult.
• Fog: entering fog can create the illusion of pitching up, causing an abrupt, steeper approach.
• Ground lighting: bright runway lights often make distances appear shorter, while ground lighting can create false approach paths or runways.

Other factors

• Illness
• Medication
• Stress
• Alcohol
• Fatigue
• Eating