Visual Illusions Awareness
Page 7
Summary of key points
The following critical keypoints need to be emphasized:
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Awareness of weather factors;
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Awareness of surrounding terrain and obstacles;
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Awareness and assessment of approach hazards (i.e., conditions that may result in visual illusions, such as “black hole”);
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Adherence to defined PF/PNF task sharing for acquisition of visual references and for flying the visual segment; this includes:
. monitoring by PF of outside visual cues while transiently referring to instruments to support and monitor the flight path during the visual segment; and,
. monitoring by PNF of headdown cues for effective cross-check and back-up (i.e., for calling any excessive-parameter-deviation).
Associated Briefing Notes
The following Briefing Notes complement the above discussion on the acquisition of visual references and on visual illusions:
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1.6 – Approach and Go-around Briefings.
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5.2 – Terrain Awareness – When and How ?
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7.3 – Acquisition of Visual References.
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7.4 – Flying Visual Approaches.
Regulatory References
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ICAO – Preparation of an Operations Manual (Doc 9376).
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FAR 91.175 – Takeoff and landing under IFR – Paragraph (b), Loss of visual references.
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JAR-OPS 1 – Subpart E – All Weather Operations - 1.1430 – Aerodrome Operating Minima.
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JAR-OPS 1 – Subpart E – All Weather Operations - 1.435 - Terminology.
Visual Illusions Awareness
Page 8
Introduction
Flight crew awareness and alertness are key factors in the successful application of wind shear avoidance and escape / recovery techniques.
This Briefing Note provides an overview of operational recommendations and training guidelines for aircraft operation in forecast or suspected wind shear or downburst conditions.
Statistical Data
Adverse weather (other than low visibility and runway condition) is a circumstantial factor in nearly 40 % of approach-and-landing accidents.
Adverse wind conditions (i.e., strong cross winds, tailwind and wind shear) are involved in more than 30 % of approach-and-landing accidents and in 15 % of events involving CFIT.
Wind shear is the primary causal factor in 4 % of approach-and-landing accidents and is the 9th cause of fatalities.
These statistical data are summarized in Table 1.
% of Events
Adverse weather 40 %
Adverse wind (all conditions) 33 %
Wind shear 4 %
Table 1
Weather factors in Approach-and-Landing Accidents
Defining Wind Shear
Wind shear is defined as a sudden change of wind velocity and/or direction.
Two types wind shear can be encountered:
. Vertical wind shear:
. vertical variations of the horizontal wind component, resulting in turbulence that may affect the aircraft airspeed when climbing or descending through the wind shear layer;
. vertical variations of the horizontal wind component of 20 kt-per-1000 ft to 30 kt-per-1000 ft are typical values, but a vertical wind shear may reach up to 10 kt-per-100 ft.
. Horizontal wind shear:
. horizontal variations of the wind component (e.g., decreasing head wind or increasing tail wind, or a shift from a head wind to a tail wind), may affect the aircraft in level flight or while climbing or descending;
. horizontal variations of wind component may reach up to 100 kt-per-nautical mile.
Wind shear conditions usually are associated with the following weather situations:
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