Figure 10.12 A visual illusion caused by a layer of water on the windscreen

Snow Coverage

Not only does snow lead to false height judgements it is often difficult to decide where the surface ends and the sky begins due to the absence of visual and focal clues. It is easy to mistake snow-covered mountains for clouds with catastrophic results.

Whiteout can be caused either by blowing snow, when visibility is reduced to zero and even taxiing is impossible or by extended exposure to the reflected glare of snow. The second cause can be most alarming since it manifests itself in the inability to distinguish ground features. The landscape appears to be a flat, smooth plane of white and accurate height assessment is rendered impossible. There is the added danger that snow may not reflect radar pulses so the high ground will not appear on the weather radar screen.

Fog, Haze, Pollution and LowVisibility

As a result of fog, haze or pollution, runway lights appear dim giving the impression that the runway is further away than it is which gives rise to steeper approaches than normal.

Runway Lights

The intensity of runway lights will also lead to errors. Their brightness or dimness will either give the false impression of the runway being either closer or more distant than it is. Thus incorrect approach angles and judgement of closing speeds are likely.

Spatial Orientation in Flight and the “Seat-of-the-pants”

As we saw in Chapter 4, the vestibular apparatus detects the orientation and movements only of the head. It is therefore essential that the nervous centres also receive information depicting the spatial orientation of the head with respect to the body as well as the spatial orientation of the different parts of the body with respect to each other. This information is transmitted by the proprioceptors which are components of the nervous system and are located under the skin (subcutaneous) in the neck and the major parts of the body. A pilot relying on these inputs is sometimes referred to as flying by the “seat-of-the-pants”.

The most important sense with regards to spatial orientation is sight. Even without the inputs from the vestibular apparatus, a person can still use his/her visual images of the outside world to maintain spatial orientation.

Cognition in Aviation 10

Aviation in Cognition 10

Under instrument conditions a pilot loses this vital visual input. For example, if the aircraft goes into a descent it will accelerate and this acceleration, via the otoliths, will inform the pilot that the aircraft is in the climb. The proprioceptors will also detect a climb because of the g-forces resulting from the somatogravic effect.

Thus these proprioceptive stimuli are completely unreliable when visual contact with the ground is lost or when flying IMC and must be ignored.

CROSS CHECK AND BELIEVE THE INSTRUMENTS

Oculogravic and Oculogyral Illusions

Whereas there are various differing definitions of these two illusions, it has been confirmed that the following (extracted from Fundamentals of Aerospace Medicine by R.L. Dehart), are accepted:

Oculogyral Illusion

Whereas a somatogyral illusion is a false sensation, or lack of sensation, experienced by a pilot undergoing angular motion, an oculogyral illusion is a false sensation of visual movement of an object viewed by a pilot. It is the visual sister to the somatogyral illusion. Thus the pilot experiencing an oculogyral illusion will see objects in front of him/her to be moving in the opposite direction. A very real danger is created when the somatogyral illusion is combined with the oculogyral illusion. In this case the pilot not only has the sensation of turning in the opposite direction due to the somatogravic illusion but this feeling is confirmed by his/her visual inputs - the very human sense that is known to be the most important as far as spatial orientation is concerned and therefore to be trusted.

Oculogravic Illusion

The oculogravic illusion occurs under the same conditions as the somatogravic illusion and is the direct visual result of linear acceleration. For example, a pilot subjected to deceleration experiences a nose-down pitch sensation because of the somatogravic illusion. Simultaneously, he/she observes the instrument panel to move downwards, confirming his/her sensation of tilting forward. Thus the oculogravic illusion is the visually apparent movement of an object in front of the observer that is actually in a fixed position relative to him/her.

Questions

Questions

1.If a runway slopes downwards, how does this affect the pilots’ approach?

a.It is likely to be too high

b.It is likely to be too low

c.It is likely to be too fast

d.It is likely to be too slow

2.If a runway slopes upwards, how does this affect the pilots’ approach?

a.It is likely to be too high

b.It is likely to be too low

c.It is likely to be too fast

d.It is likely to be too slow

3.What is the likely effect of a runway which is wider than expected?

a.Flaring too late and damaging the aircraft

b.Flaring too soon and causing a heavy landing

c.Approach speed much too high

d.Approach speed higher than usual

4.What approach conditions cause the “black hole effect”?

a.Landing at night in sleet or heavy rain

b.Landing at night with a partially lit runway

c.Landing at night with the cockpit instruments turned up too high

d.Landing at night when there are no lights between the aircraft and the runway

5.How does the “black hole effect” alter the pilots’ judgement of the approach?

a.Overestimation of height

b.Underestimation of height

c.Tends to make the approach much too fast

d.Tends to make the approach faster than normal

6.What are the main visual cues for rounding out?

a.Round out height and speed

b.Confirmation of decision height and closing speed

c.Closing speed and height check

d.Apparent speed of ground objects increases and texture of ground changes.

7.How do misty/foggy conditions affect the pilots judgement on the approach?

a.Underestimating range due to illusionary effect through cockpit glass

b.Underestimating range due to the lights appearing dim

c.Underestimating range due to illusionary effect through cockpit glass

d.Overestimating range due to the lights appearing dim

10

Questions 10

Questions 10

8.If two aircraft are on a line of constant bearing, what is the likely outcome?

a.Depends whether by day or by night

b.They will collide

c.There will be a near miss

d.It is quite safe and they will pass well clear of each other

9.How will an oncoming aircraft on a line of constant bearing appear visually?

a.There will be no relative movement and it will appear to be very small until seconds before the collision

b.There will be no relative movement and it will appear to be very small until seconds before the aircraft passes close by

c.There will be no relative movement and it will appear to be very small until seconds before the aircraft passes above

d.There will be no relative movement and it will appear to be very small until seconds before the aircraft passes well clear

10.What is the duration of a saccade and rest period?

a.0.3 seconds

b.0.5 seconds

c.0.013 seconds

d.1 second

11.What visual technique should be used when searching for an aircraft?

a.Sweep from side to side with the eyes covering the whole field of vision

b.Search the sky portion by portion starting on the left

c.Pinpoint 10° segments of the sky and confirm before passing onto another

d.Use a succession of small and rapid eye movements

12.Refraction, due to rain on the windscreen, makes the approach:

a.steeper

b.shallower

c.faster

d.slower

13.Expectation can affect perception.

a.True

b.False

14.The blooming effect of rain makes:

a.the runway appear closer

b.the runway appear further away

c.does not effect runway perception

d.the instruments difficult to read

15.What are the laws that the Gestalt Theory propose?

a.The laws of Perception

b.The laws of Perceptual Illusions

c.The laws of Perceptual Reception

d.The laws of Perceptual Organization

16.A visual scan should cover the sky in overlapping sections of:

a.5°

b.10°

c.15°

d.20°

17.The scanning technique should differ by day and night.

a.True

b.False

18.A distant aircraft is identified and remains on a constant relative bearing. You should:

a.wait until the aircraft appears to grow larger before taking avoiding action

b.take avoiding action if you do not have right of way

c.take immediate avoiding action

d.wait two seconds to reidentify and then take avoiding action

19.Another name for the illusion associated with acceleration is:

a.the somatogyral illusion

b.the somatogravic illusion

c.motion sickness

d.air sickness

20.If an illusion is known to be possible at a particular aerodrome, as Captain of the aircraft, you should:

a.say nothing as it might frighten the crew

b.ensure you brief the crew

c.report the fact to operations so that other crews are aware of the danger

d.report the fact to your operator so that other crews are aware of the danger

Questions 10