Friday, 13 October 2017
Acknowledgements: FAA Safety Team (FAAST)
What Is It?
Sight, supported by other senses, allows a pilot to maintain orientation while flying. However, when visibility is restricted (i.e., no visual reference to the horizon or surface detected) the body’s supporting senses can conflict with what is seen.
When this spatial disorientation occurs, sensory conflicts and optical illusions often make it difficult for a pilot to tell which way is up.
Contributing to these phenomena are the various types of sensory stimuli: visual, vestibular (organs of equilibrium located in the inner ear), and proprioceptive (receptors located in the skin, muscles, tendons and joints). Changes in linear acceleration, angular acceleration, and gravity are detected by the vestibular system and the proprioceptive receptors, and then compared in the brain with visual information.
In a flight environment, these stimuli can vary in magnitude, direction, and frequency, resulting in a “sensory mismatch” which can produce illusions and lead to spatial disorientation. Some of these illusions can lure pilots in to making poor decisions or improper control inputs.
For example, aerial perspective illusions may make you increase or decrease the slope of your final approach. They are caused by runways with different widths, up-sloping or down-sloping runways, and up-sloping or down-sloping final approach terrain.
NTSB accident data suggests that spatial disorientation may be a precursor to many general aviation accidents - particularly in night or limited visibility weather conditions. Instrument and VFR pilots are both vulnerable to spatial disorientation and optical illusions which may cause loss of aircraft control.
An auto-kinetic illusion gives you the impression that a stationary object is moving in front of the airplane’s path; it is caused by staring at a fixed single point of light (ground light or a star) in a totally dark and featureless background. This illusion can cause a misperception that such a light is on a collision course with your aircraft.
False visual reference illusions may cause you to orient your aircraft in relation to a false horizon; these illusions are caused by flying over a banked cloud, night flying over featureless terrain with ground lights that are indistinguishable from a dark sky with stars, or night flying over a featureless terrain with a clearly defined pattern of ground lights and a dark, starless sky.
How to Prevent Spatial Disorientation
You, the pilot, should understand the elements contributing to spatial disorientation so as to prevent loss of aircraft control if these conditions are inadvertently encountered.
The following steps should help prevent spatial disorientation:
· Before you fly with less than 3 miles of visibility, obtain training and maintain proficiency at flying by instruments.
· At night, or with reduced visibility, use and rely on your flight instruments. Be sure to test your flight instruments before each flight as well during your pre-flight and taxi.
· Maintain night currency if you intend to fly at night. Include cross-country and local operations at different airports.
· Study and become familiar with unique geographical conditions in areas in which you plan to operate.
· Check weather forecasts before departure, en-route, and at destination. Be alert for weather deterioration.
· Do not attempt VFR flight when there is the possibility of getting trapped in deteriorating weather.
· If you experience a visual illusion during flight (most pilots do at one me or another), have confidence in your instruments and ignore all conflicting signals your body gives you. Accidents usually happen as a result of a pilot’s indecision over relying on the instruments.
· If you are one of two pilots in an aircraft and you begin to experience a visual illusion, transfer control of the aircraft to the other pilot, since pilots seldom experience visual illusions at the same me.
· If you fly single-engine IFR frequently, consider investment in an alternate vacuum system or electric standby attitude indicator. By being knowledgeable, relying on experience, and trusting your instruments, you will be contributing to keeping the skies safe for everyone.
Thursday, 12 October 2017
Acknowledgements: FAA Safety Team (FAAST)
The GAJSC has determined that a significant number of general aviation accidents could be avoided if pilots were to establish personal minimums for flight in windy conditions. Identifying and adhering to personal wind limitations can significantly reduce the number of wind-related aircraft accidents.
Wind socks must withstand wind speeds of up to 75 knots. They must be fully extended in 15 knot winds and must rotate to indicate wind direction in winds of 3 knots or greater.
But the big question is, how much wind can you handle? There are at least two factors to consider before answering that ques on and neither one is straight forward.
· How much wind can the airplane handle?
The pilot handbook for airplanes manufactured from 1975 to the present will contain a Maximum Cross Wind Component or Velocity in the Normal Operations section. This is not a limitation but rather the maximum cross wind experienced in the course of flight testing for certification. Could the airplane be controllable in more wind? Possibly. But you won’t know without conducting some tests of your own.
What we do know is that the airplane will be controllable with less cross wind. FAA Type Certification Rules require that airplanes must handle safely on the ground in a 90-degree cross wind of 0.2 Vso (e.g., an airplane which stalls at 49 knots will be controllable on the ground with just under 10 knots of wind). Will it handle more? Possibly. But for sure it will be controllable with less.
· How much wind can the pilot handle?
Pilot performance varies considerably from day to day and even hour to hour. Some of the factors include:
· Total pilot experience
· Experience in aircraft type
· Mission imperative
· Stress, hunger and fatigue.
Establish a Baseline
We need to establish a pilot performance baseline - your personal, documented, demonstration of performance - in order to establish personal minimums. We suggest you document your wind performance at least once a year with a CFI.
Try to pick a day when you can experience actual cross-wind conditions in the airplane you usually fly, loaded to your typical mission weight.
Select an airfield that’s typical for the missions you fly.
Prepare a log of the flight to record aircraft used, gross actual weight, departure & destination location, elevation, density altitude, wind direction & speed, cross-wind computation, take-off flap setting, rotation speed, rotation speed x 70%, distance to rotation, distance to 50 feet, available landing distance.
Once you’ve completed the log you’ll have a performance baseline to work with. You can then adjust your performance expectations on the day to compensate for any of the human factors mentioned earlier, and you can thereafter adjust your baseline as you gain experience and skill; and with a CFI on board you can get an objective assessment of your capabilities. A flight instructor may offer suggestions and instruction for improving your baseline performance.
Devote some time and money to practice your piloting skills in actual windy conditions. Concentrate on flying as precisely as you can, compensating for wind and predicting your performance.Work toward flying a base to final turn that aligns you perfectly with the runway and maintain that alignment all the way through the approach, landing and roll out.
Be aware that many airports are subject to local wind challenges including wind shear and turbulence. Mountain airports in particular require careful planning and prior knowledge to ensure safe operations. Consult a local CFI or experienced pilot before flying to unfamiliar mountain or back country fields.
You should consider adjusting your personal minimums to compensate for fields with wind shear potential. Local knowledge is key to avoiding nasty surprises. If you’re flying to desert des nations, planning for arrivals before noon will definitely make for a smoother flight with less turbulence and fewer thunderstorms to deal with.