Describe conditions which can lead to the creation of a false horizon.
Sloping layers of cloud by day, angled lines on the ground or areas of light at night can produce a false horizon
This can mislead and result in the pilot selecting false attitudes and receiving conflicting information
Explain the see and avoid method of avoiding mid-air collisions.
To understand the time factor in seeing / avoiding, we must first look at the time taken for each individual part
Looking – 0.1 – 0.2 secs
Seeing – 0.2 – 0.3 secs
Recognising – 0.7 – 1.0 secs
Evaluating / deciding – 2.0 – 3.0 secs
Physical action – 2.0 – 3.0 secs
Total time – 5- 7.5 secs
By the time we see a potential threat, and conduct an evasive maneuver, the time passes is around the 5 – 7.5 seconds. It is vital we maintain a good lookout to see potential threats as soon as possible.
Explain the following visual illusions, and describe methods of managing this:
Autokinesis
A single light source at night can appear to “dance” and move even though it is stationary
This is the autokinetic effect
More likely if only one light source
The brain has difficulty making sense of the single pinpoint of light and will move it around to try to find a pattern / make some sort of sense out of it
Stroboscopic illumination illusion / flicker vertigo
Occurs when there is a bright light source in the visual field that is being interrupted intermittently and rapidly
Eg propellor / rotor blades
The bright flickering effect can cause dizziness and feeling unwell
Sometimes convulsions seizures can occur
If encountered pilot should alter their gaze , use a sunshade or re-position the aircraft to avoid the flicker
Break off phenomenon
Flight is in conditions of very little visual, mental or physical stimulation with low workload
Break-off phenomenon is where the pilot feels psychologically detached from surroundings
May feel as if they are outside the cockpit looking in
Aircraft may feel as though balancing on a pinhead and about to fall off
Not serious or long lasting
Can occur inn altitude or hazy flight conditions
Considered normal response to low visual stimulus
How to deal with this
Black hole phenomenon
Serious disorientation can occur with a pilot at night when there is no horizon and no outside visual references on the ground
Visual judgement of height above the ground is impossible as there is no depth perception
This is a black hole phenomena
Must fly on instruments only and ignore all body sensations
Empty Visual Field Blindness
Also known as Low Visual Stimulus Shortsightedness
Occurs where the visual field looks the same in all directions and is unbroken
For example in haze or over a smooth sea surface
When the eye is un stimulated it takes up it’s natural relaxed focal length which is 3-4 metres
Gives a false impression that the pilot is doing a good lookout
This can be overcome by
-the pilot anticipating likely conditions for it to occur
-consciously stretching the focal length of the eyes eg by looking outside at the wingtip
-periodically gazing far out to a distant cloud or other feature
Explain effective visual search techniques.
When scanning the sky for other aircraft, it is vital we conduct a good lookout procedure
Divide the area ahead into 20 degree sectors and scan
Take into account the time it takes to recognise what the eyes are seeing – at least 1.5 seconds
To account for glare and other factors make the time 2 seconds
Describe the visual system resting state focus and its effects on object detection.
With normal vision the lens focuses an inverted image onto the rear of the eyeball – Retina.
The lens shape changes to focus the object according to it’s distance
Describe the effects of hypoxia on vision.
When one is hypoxic, you can suffer from symptoms such as:
Describe the factors associated with the selection of suitable sunglasses for flying.
Should be impact resistant
Should transmit 10-15% of light
Should filter out UV rays
Should not be worn in decreased light
Preferably should not be polarised
Describe the following visual conditions:
Short sightedness
Distant objects are blurred and near objects are clear
When the eye is relaxed and the cornea and the lens focus the rays in front of the retina
Presbyopia
Occurs naturally in people over 40 yrs
Long-sightedness caused by the lens material losing some of its flexibility
Muscles are less able to increase the curvature
Astigmatism
The curvature of the cornea is not perfectly round
Causes uneven refraction of the light
Causes distorted images
Identify precautionary actions to protect night vision adaptation.
Ensure that if using usual visual references on takeoff at night – make sure the eyes are adequately night adapted (30 mins)
Use only red and UV cockpit lighting to preserve night adaptation
State the normal time for full night vision adaptation.
For full night adaptation, this will take 30 minutes
Half night adaptation takes 10 minutes