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Human Factors: Vision, Scanning, and Judgement

Eyes provide the brain with a visual image of the environment. Each eye acts as a natural and very sophisticated digital camera. Its basic function is to collect light rays reflected from an object, using the lens to focus these rays into an image on a screen (the retina), and then converting this image into electrical signals that are sent via the optic nerve to the brain. This is how you see. The brain matches the image to previously stored data so you recognize (perceive) the object. The connection of the optic nerve to the brain is so close and integral, and the importance of the messages sent to the brain is so dominant, that the eyes can almost be considered an extension of the brain. Today we’ll talk more about vision with an excerpt from our textbook The Pilot’s Manual Volume 2: Ground School (PM-2C).
Scanning by Day
The central (foveal) region of the retina provides the best vision, and in full color but only during reasonable daylight. Objects are best seen by day if you can focus their image on the foveal region, and you do this by looking directly at them. The most effective method of scanning for other aircraft for collision avoidance during daylight hours is to use a series of short, regularly spaced eye movements to search each 10° sector of the sky. Systematically focusing on different segments of the sky for short intervals is a better technique than continuously sweeping the sky. This is sometimes called the saccade/fixation cycle, where the saccade or movement takes about one-third of a second.

Methodical scan.

Methodical scan.

Relative Movement
If there is no apparent relative motion between you and another aircraft, you may be on a collision course, especially if the other aircraft appears to be getting bigger and bigger in the windshield. Due to the lack of movement across your windshield, an aircraft on a collision course with you will be more difficult to spot than one that is not on a collision course.

Any relative movement of an object against its background usually makes it easier to notice in your peripheral vision. The image of the other aircraft may not increase in size much at first, but, shortly before impact, it would rapidly increase in size. The time available for you to avoid a collision may be quite brief, depending upon when you see the other aircraft and the rate of closure.

Constant relative position = collision course.

Constant relative position = collision course.

If you are flying at 100 knots and it is flying at 500 knots in the opposite direction, the rate of closure is 600 knots, i.e. ten nautical miles per minute. If you spot the other aircraft at a distance of one nautical mile, you only have 1/10 of a minute (six seconds) to potential impact. If you are a vigilant pilot and spot it at 3 nautical miles you have eighteen seconds in which to act.

In hazy or low-visibility conditions, your ability to see other aircraft and objects with edges that might be blurred will be diminished and, if you can see them, they may appear to be further away than their actual distance. You might be closer than you think.

Empty-Field Myopia
When trying to search for other aircraft in an empty sky, the natural tendency of a resting eye is to focus at about six feet. Consequently, distant aircraft may not be noticed. To avoid this empty-field myopia, you should focus on any available distant object, such as a cloud or a landmark, to lengthen your focus. If the sky is empty of clouds or other objects, then focus briefly on a relatively distant part of the airplane like a wing tip as a means of lengthening your focus. Having spotted an airplane in an otherwise empty sky, be aware that it could be closer to you than it appears to be, because you have no other object with which to compare its size.

A small, dark image formed on the retina could be a distant aircraft, or it could be a speck of dirt or dust, or an insect spot, on the windshield. Specks, dust particles, a scratch, or an insect on the windshield might be mistaken for a distant airplane. Simply moving your head will allow you to discriminate between marks on the windshield and distant objects.



Scanning by Night
The central (foveal) region of the retina containing mainly cones is not as effective at night, causing an area of reduced visual sensitivity in your central vision. Peripheral vision, provided by the rods in the outer band of the retina, is more effective albeit color blind. An object at night is more readily visible when you are looking to the side of it by ten or twenty degrees, rather than directly at it. Color is not perceived by the rods, and so your night vision will be in shades of gray. Objects will not be as sharply defined (focused) as in daytime foveal vision.

The most effective way to use your eyes during night flight is to scan small sectors of sky more slowly than in daylight to permit off-center viewing of objects in your peripheral vision, and to deliberately focus your perception (mind) a few degrees from your visual center of attention (that is, look at a point but look for objects around it). Since you may not be able to see the aircraft shape at night, you will have to determine its direction of travel making use of its visible lighting:

  • the flashing red beacon;
  • the red navigation light on the left wing tip;
  • the green navigation light on the right wing tip; and
  • a steady white light on the tail.
Position lights.

Position lights.

Visual Judgment on Approach
The eyes and brain use many clues and stored images of known objects to help in judging distance, size and height. The relative size and relative clarity of objects give clues to their relative distances: a bigger object is assumed to be nearer than a smaller one and a more clearly defined object nearer than a blurry one. When the object is near, binocular vision (the slightly different images of a nearby object relative to its background seen by each eye) assists in depth perception.

Texture also assists in depth perception: the more visible the texture, the closer the object appears to be. On final approach as you near the aim point, the surface texture will appear to flow outward in all directions from the point on which you are focused. This is one means by which you can visually maintain the flight path to the aim point: adjust the attitude and heading so that the point from which the texture appears to be moving outward remains the desired aim point.

Aim point.

Aim point.

Texture is also used for the estimation of height; for instance, as you approach flare height for a landing, the actual texture of the runway or the grass passing by the cockpit becomes increasingly noticeable. Relative motion also aids in depth perception. Near objects generally appear to pass by faster than more distant objects. This helps a visual pilot estimate height above the runway before and during the flare: the closer the airplane is to the runway, the faster the runway surface and the surrounding environment appears to pass by.

Depth perception can be difficult in hazy or misty conditions, where edges are blurred, colors are muted, and light rays may be refracted unusually. This gives the impression of greater distance, an impression reinforced by the fact that we often have to look at distant objects through a smoggy or hazy atmosphere. This illusion is referred to as environmental perspective. In hazy conditions, the object might be closer than it seems; in very clear conditions, the object might be further away than it seems. On hazy days, you might touch down earlier than expected; on very clear nights, you might flare a little too soon.

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Weather: Precipitation

We’re seeing rain for the first time in over two months in the Seattle area right now, so how about a refresher on precipitation today on the Learn to Fly Blog? Today’s post is excerpted from Aviation Weather (AC 00-6B).

Precipitation is any of the forms of water particles, whether liquid or solid, that fall from the atmosphere and reach the ground. The precipitation types are: drizzle, rain, snow, snow grains, ice crystals, ice pellets, hail, and small hail and/or snow pellets.

Precipitation formation requires three ingredients: water vapor, sufficient lift to condense the water vapor into clouds, and a growth process that allows cloud droplets to grow large and heavy enough to fall as precipitation. Significant precipitation usually requires clouds to be at least 4,000 feet thick. The heavier the precipitation, the thicker the clouds are likely to be. When arriving or departing from an airport reporting precipitation of light or greater intensity, expect clouds to be more than 4,000 feet thick.

All clouds contain water, but only some produce precipitation. This is because cloud droplets and/or ice crystals are too small and light to fall to the ground as precipitation. Because of their microscopic size, the rate at which cloud droplets fall is incredibly slow. An average cloud droplet falling from a cloud base at 3,300 feet (1,000 meters) would require about 48 hours to reach the ground. It would never complete this journey because it would evaporate within minutes after falling below the cloud base. Two growth processes exist which allow cloud droplets (or ice crystals) to grow large enough to reach the ground as precipitation before they evaporate (or sublimate). One process is called the collision-coalescence, or warm rain process (see Figure 14-1). In this process, collisions occur between cloud droplets of varying size and different fall speeds, sticking together or coalescing to form larger drops. Finally, the drops become too large to be suspended in the air, and they fall to the ground as rain. This is thought to be the primary growth process in warm, tropical air masses where the freezing level is very high.
Figure 14-1. The collision-coalescence or warm rain process. Most cloud droplets are too small and light to fall to the ground as precipitation. However, the larger cloud droplets fall more rapidly and are able to sweep up the smaller ones in their path and grow.

The other process is the ice crystal process. This occurs in colder clouds when both ice crystals and water droplets are present. In this situation, it is easier for water vapor to deposit directly onto the ice crystals so the ice crystals grow at the expense of the water droplets. The crystals eventually become heavy enough to fall. If it is cold near the surface, it may snow; otherwise, the snowflakes may melt to rain. This is thought to be the primary growth process in mid- and high-latitudes.

The vertical distribution of temperature will often determine the type of precipitation that occurs at the surface. Snow occurs when the temperature remains below freezing throughout the entire depth of the atmosphere (see Figure 14-2).
Figure 14-2. Snow temperature environment.

Ice pellets (sleet) occur when there is a shallow layer aloft with above freezing temperatures and with a deep layer of below freezing air based at the surface. As snow falls into the shallow warm layer, the snowflakes partially melt. As the precipitation reenters air that is below freezing, it refreezes into ice pellets (see Figure 14-3).
Figure 14-3. Ice pellets temperature environment.

Freezing rain occurs when there is a deep layer aloft with above freezing temperatures and with a shallow layer of below freezing air at the surface. It can begin as either rain and/or snow, but becomes all rain in the warm layer. The rain falls back into below freezing air, but since the depth is shallow, the rain does not have time to freeze into ice pellets (see Figure 14-4). The drops freeze on contact with the ground or exposed objects.
Figure 14-4. Freezing rain temperature environment.

Rain occurs when there is a deep layer of above freezing air based at the surface (see Figure 14-5).
Figure 14-5. Rain temperature environment.

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Aerodynamics: Descent and Gliding Flight

Our CFI is out enjoying the Reno Air Races this week, so today we’ll share a follow up to Monday’s post with another excerpt from Aerodynamics for Aviators.

Descending a light propeller-driven general aviation aircraft is a fairly simple task. Reduce power to a point where there is more power required than power available, and the basic principle of weight takes over. Under normal flight conditions, descending flight is initiated by the pilot creating a decrement of power (more power required than available). Once the aircraft begins descending, the weight vector can be broken up into two parts, just like with the climb. One component acts perpendicular to the flightpath (down), the other acts forward and parallel to the flightpath, helping accelerate the aircraft.

Gliding flight can be self-induced by bringing the power back to idle, but in most piston aircraft, descents are not conducted at idle power, thus they are called a powered descent. This is because of shock cooling and the possible damage it could cause to the engine. A true gliding descent would be used if the engine fails. Gliding flight can be broken down into two parts, minimum sink and maximum range.

The minimum sink glide is used to prolong the time aloft in the event the engine or engines fail. This is a speed that is not published, but could be useful if you are over your current landing site and wish to stay aloft a little longer. Most light single-engine airplanes will be at (or close to) minimum sink with full aft trim. This is slower than best glide speed. A pilot who elects to use this method should accelerate to best glide once a normal pattern altitude is reached. This will provide a larger margin above stall and the aircraft will have more positive maneuverability. It should be noted that the best glide speed should be used unless the pilot has training and experience flying at the minimum sink glide speed.

The maximum glide range occurs at the speed for maximum range: L/DMAX. This is generally a published speed and is used when the engine stops or fails in flight. Some Airplane Flying Manuals (AFMs) contain glide ratio charts. There are some concerns with these charts:

  1. They do not account for wind.
  2. They are usually calculated in a minimum drag configuration (gear and flaps up).
  3. They are usually calculated with controllable-pitch propellers in the full decrease position (high AOA).
  4. They are usually calculated at maximum gross weight.

Wind is a factor in glide distance and angle. A headwind will decrease glide distance, and the angle of descent will increase (steepen). A tailwind will increase the glide distance and flatten the angle of descent. You experience the effects of both a headwind and a tailwind when you do a power-off approach. On downwind the aircraft has a flatter descent and a higher groundspeed. Turning base to final, the angle of descent steepens and the groundspeed slows.

Weight is also a factor in glide distance if L/DMAX is not maintained. Without an AOA indicator, the only way to maintain a specific AOA at L/DMAX is to vary the airspeed. As weight increases, the airspeed would need to be increased to maintain L/DMAX.

Altitude also affects the airplane’s gliding distance. To understand this we need to step back and look at the effects of altitude on true airspeed. As the aircraft climbs, TAS increases about 2% per 1,000 feet. An aircraft gliding at higher altitudes will have a higher TAS, this means that it will be moving down the slope at a faster rate. This is of particular importance when operating an aircraft at high density altitudes.

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Aerodynamics: Cruise Flight

Cruise flight centers on two basic principles: how far we can fly, and for how long. How far we can fly is defined as the aircraft’s range. How long we can fly is defined as endurance. Today’s post is an excerpt from our textbook Aerodynamics for Aviators.

When flying, we generally consider range in two ways:

  1. Maximizing the distance we fly for a given fuel load.
  2. Traveling a specified distance while burning minimum fuel.

It’s important to understand that range and endurance are not the same. Range relates to distance, endurance relates to time. The formula for endurance is:

endurance = hours ÷ fuel

Hours is simply flight time expressed in whatever units you want: hours, minutes or seconds. Fuel can be expressed in gallons or pounds. A pilot who wants to achieve maximum endurance would slow the aircraft to the minimum power required speed. Figure 5-24 shows the minimum power point being the lowest point in the drag curve.


Figure 5-24. Maximum endurance.

If the aircraft were to slow even further, to point A, drag would increase rapidly, more power would be required, and the engine would burn more fuel. If the aircraft were to accelerate above point B, drag also increases, which increases fuel burn. As you can see, flying at maximum endurance speed is not practical in the real world; you may save fuel but it would take forever to get to the destination. This speed is also not practical for operations such as holding because it is generally close to stall. From a practical standpoint, endurance comes from the selection of a cruise power setting of 55%, 65%, or 75% endurance charts. The point of this type of flying is generally to minimize or eliminate fuel stops (very time consuming) along the route, or to minimize fuel burn for cost purposes—not necessarily to stay aloft for hours on end.

Range can be broken down into two parts: specific range and total range. An easy way to understand the difference is to use a car trip scenario. If I have a car that has a 20 gallon fuel tank and gets 30 miles per gallon, I can travel 600 miles on one tank of gas. The specific range in this example is 30 miles per gallon, and the total range is 600 miles. In an airplane, specific range is how many nautical miles you can travel on one gallon or pound of fuel. The total range is how far the airplane can fly with the remaining fuel load on board the aircraft. The definition for specific range is:

specific range = NM ÷ gallons of fuel (Note: pounds can be inserted for gallons.)

Specific range is affected by three things: (1) aircraft weight, (2) altitude, and (3) configuration. The maximum range of the aircraft can be found at L/DMAX. Unlike endurance, which is found on the drag curve where minimum power is required, maximum range is found where the ratio of speed to power required is the greatest. This is located on the graph by drawing a tangent line from the origin to the power required curve (Figure 5-24). Another way to think about this is that as you move from the origin point along the tangent line toward L/DMAX you increase airspeed at a greater rate than fuel burn (think of the ratio). At L/DMAX, the ratio of fuel to airspeed should be 1. At any speed above L/DMAX, the fuel burn ratio increases at a greater rate than the airspeed. Therefore, L/DMAX is the point where the speed-to-power ratio required is the greatest.

Another aspect of range that we need to examine is the effect of weight on range. Because L/DMAX occurs at a specific angle of attack, and most general aviation airplanes do not have AOA indicators, the airspeed has to be varied as weight changes to maintain a constant AOA. Figure 5-25 illustrates this: as weight increases, the speed must be increased to maintain the AOA. This is because as weight is increased, the AOA must be increased to produce more lift; the only way to lower the AOA is to increase speed. As weight decreases, the speed must decrease. The reasoning is that as the aircraft becomes lighter, the AOA is lowered to compensate for less weight; the only way to increase AOA is to reduce speed (Figure 5-25).


Figure 5-25. The effect of weight on range.

The effect of altitude on range can be seen in Figure 5-26. Flights operating at high altitude require a higher TAS, which will require more power.


Figure 5-26. The effect of altitude on range.

Another aspect of cruise flight relating to range and endurance, one that is often not talked about in textbooks, is cruise performance. From a practical standpoint, the pilot will not fly the aircraft at maximum endurance or range—it is just too slow. In reality, pilots often operate propeller-driven airplanes at 55%, 65%, or 75% best power or endurance.

In order to calculate how to get to your destination as fast as possible, find the highest true airspeed for your aircraft. Most fixed-gear single-engine aircraft that cruise in the 110–130 knot range will have their highest TAS in the 6,000 to 7,000-foot range. This is a good place to start; however, the wind, terrain, and the need for fuel stops will dictate the altitude and speed at which the aircraft ultimately flies.

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Aircraft Performance: Changing Airspeed in Straight-and-Level Flight

Normal cruise involves setting cruise power, holding cruise altitude, and accepting the airspeed that is achieved, which should be close to the figure published in your Pilot’s Operating Handbook. On occasions, however, there is a need to fly at other than normal cruise airspeed. Today, we’ll discuss the basics of changing speeds in straight-and-level flight with an excerpt from The Pilot’s Manual: Instrument Flying (PM-3D).

This requires a different pitch attitude and a different power setting. To slow the airplane, the pilot reduces power and gradually raises the pitch attitude to maintain altitude; to increase airspeed, the pilot increases power, and gradually lowers the pitch attitude to maintain altitude.

Once the desired airspeed is achieved, the pilot adjusts the power to maintain it. The precise power required for steady flight will depend upon the amount of total drag, which, in level flight, varies with angle of attack and airspeed. Higher power will be required for:

  • high speed cruise (when total drag is high mainly due to parasite drag); and
  • low speed cruise (when total drag is high mainly due to induced drag).

Medium power is required for normal cruise. The ASI confirms whether or not correct power is set. The ASI is the primary performance guide to power requirements during level flight if you fly a particular airspeed.

Practicing airspeed changes in cruise is excellent instrument flying practice since pitch, bank (and balance) and power changes must all be coordinated to maintain constant altitude and heading. When the pilot changes power, a single-engined propeller- driven airplane will tend to move around all three axes of movement. If the propeller rotates clockwise as seen from the cockpit (the usual case), adding power will cause the nose to pitch up and yaw left, with a tendency for the airplane to roll left.

The pilot can counteract this by applying forward elevator pressure to prevent the nose pitching up, with right rudder and right aileron pressure to overcome the tendency to yaw and roll left. The converse applies when reducing power, hold the nose up and apply left rudder pressure. Refer to the AI to keep the wings level and hold the pitch attitude, and keep the ball centered.

Some hints on changing cruising speed follow:

  • The attitude indicator gives a direct picture of pitch and bank attitudes.
  • The ball gives a direct indication of coordination.
  • Useful performance instruments are the altimeter and VSI—they ensure altitude is being maintained, and the heading indicator to ensure heading is being maintained.
  • The airspeed indicator indicates the power requirements. If too slow, add more power; if too fast, reduce power.

The pilot’s scan rate of the flight instruments during any power change needs to be reasonably fast to counteract the pitch/yaw effects smoothly and accurately. For this reason, it is good to develop the skill of judging power changes by throttle movement and engine sound, rather than only by observation of the power indicator. This allows the pilot to concentrate on the flight instruments until after the power change has been made, at which time a quick glance at the power indicator for fine adjustment suffices.

When you memorize the approximate power settings necessary to maintain the various cruise speeds, then power handling and airspeed changes become simpler to manage.

Small airspeed changes (say five knots either way) can generally be handled by a single small power change, then allowing the airplane to gradually slow down or accelerate to the desired speed. Large airspeed changes, however, are most efficiently achieved within a few seconds by underpowering on the initial power change for a speed decrease, or overpowering on the initial power change for a speed increase. This allows more rapid deceleration or acceleration to the desired speed, at which time the necessary power to maintain that airspeed is set.

Once the desired airspeed is achieved and suitable power is set, the ASI will indicate if further fine adjustment of power to maintain airspeed is required. In level flight, the ASI is the primary guide to power requirements.

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Regulations: Notices to Airmen

Today, we’ll take a look at NOTAM’s with an excerpt from Bob Gardner’s textbook The Complete Private Pilot (PPT-12). For all of the regulations pertaining to aviation, check out our annual FAR/AIM series.

Information that might affect the safety of a flight, such as a runway closure, Temporary Flight Restriction (TFR), NAVAID outage, lighting system change, etc., is available from your flight service station briefer.

Your briefer has access to NOTAMs. So do you, at PilotWeb. If you use one of the computer flight planning products such as DUATS or the AOPA flight planner, you will also receive current NOTAMS—but be aware that TFRs can pop up without warning. Always check for them with flight service before takeoff to avoid being intercepted by F-16s or Coast Guard helicopters and forced to land.

If you want to know about VOR outages, runway closures, men and equipment on the runway, etc., look for or ask for D NOTAMs. For long cross-countries it is always valuable to call one of the fixed-base operators at the destination airport for last-minute information, such as “the power is out and we can’t pump gas!”

To make it easier for pilots to scan through a list of NOTAMs for information specific to their flight, the FAA uses “key words” in the first line of text. See the figure below—although this FAA document does not include recent additions: ODP, SID, STAR, CHART, DATA, IAP, VFP, ROUTE, SPECIAL, or (O); also, the keyword RAMP will no longer be used. As a VFR pilot, you are definitely interested in Visual Flight Procedure (VFP) and Obstacle Departure Procedure (ODP) NOTAMs which, although intended for instrument pilots, might contain information useful to you.

Every 28 days the FAA releases the Notices to Airmen publication that contains all current NOTAM (D)s and FDC NOTAMs, except for Temporary Flight Restrictions. When a NOTAM is published here (or in the Chart Supplements U.S.) it no longer shows up on the briefer’s screen; if you don’t ask the briefer for any published NOTAMs that will affect your flight, you will never find out about them. You can get this publication online at


Example of FAA NOTAM “key words” (see AIM Table 5-1-1 for more keywords and definitions). (Click to expand)

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Human Factors: Optical Illusions

Of the senses, vision is the most important for safe flight. However, various terrain features and atmospheric conditions can create optical illusions. These illusions are primarily associated with landing. Since pilots must transition from reliance on instruments to visual cues outside the flight deck for landing at the end of an instrument approach, it is imperative that they be aware of the potential problems associated with these illusions and take appropriate corrective action. Today, we’ll take a look at the major illusions leading to landing errors with an excerpt from the Pilot’s Handbook of Aeronautical Knowledge.

Runway Width Illusion
A narrower-than-usual runway can create an illusion that the aircraft is at a higher altitude than it actually is, especially when runway length-to-width relationships are comparable. The pilot who does not recognize this illusion will fly a lower approach, with the risk of striking objects along the approach path or landing short. A wider-thanusual runway can have the opposite effect with the risk of the pilot leveling out the aircraft high and landing hard or overshooting the runway.

Runway and Terrain Slopes Illusion
An upsloping runway, upsloping terrain, or both can create an illusion that the aircraft is at a higher altitude than it actually is. The pilot who does not recognize this illusion will fly a lower approach. Downsloping runways and downsloping approach terrain can have the opposite effect.


(Click to expand)

Featureless Terrain Illusion
An absence of surrounding ground features, as in an overwater approach over darkened areas or terrain made featureless by snow, can create an illusion that the aircraft is at a higher altitude than it actually is. This illusion, sometimes referred to as the “black hole approach,” causes pilots to fly a lower approach than is desired.

Water Refraction
Rain on the windscreen can create an illusion of being at a higher altitude due to the horizon appearing lower than it is. This can result in the pilot flying a lower approach.

Atmospheric haze can create an illusion of being at a greater distance and height from the runway. As a result, the pilot has a tendency to be low on the approach. Conversely, extremely clear air (clear bright conditions of a high attitude airport) can give the pilot the illusion of being closer than he or she actually is, resulting in a high approach that may result in an overshoot or go around. The diffusion of light due to water particles on the windshield can adversely affect depth perception. The lights and terrain features normally used to gauge height during landing become less effective for the pilot.

Flying into fog can create an illusion of pitching up. Pilots who do not recognize this illusion often steepen the approach abruptly.

Ground Lighting Illusions
Lights along a straight path, such as a road or lights on moving trains, can be mistaken for runway and approach lights. Bright runway and approach lighting systems, especially where few lights illuminate the surrounding terrain, may create the illusion of less distance to the runway. The pilot who does not recognize this illusion will often fly a higher approach.

How To Prevent Landing Errors Due to Optical Illusions
To prevent these illusions and their potentially hazardous consequences, pilots can:

  1. Anticipate the possibility of visual illusions during approaches to unfamiliar airports, particularly at night or in adverse weather conditions. Consult airport diagrams and the Chart Supplement U.S. (formerly Airport/Facility Directory) for information on runway slope, terrain, and lighting.
  2. Make frequent reference to the altimeter, especially during all approaches, day and night.
  3. If possible, conduct an aerial visual inspection of unfamiliar airports before landing.
  4. Use Visual Approach Slope Indicator (VASI) or Precision Approach Path Indicator (PAPI) systems for a visual reference, or an electronic glideslope, whenever they are available.
  5. Utilize the visual descent point (VDP) found on many nonprecision instrument approach procedure charts.
  6. Recognize that the chances of being involved in an approach accident increase when an emergency or other activity distracts from usual procedures.
  7. Maintain optimum proficiency in landing procedures.

In addition to the sensory illusions due to misleading inputs to the vestibular system, a pilot may also encounter various visual illusions during flight. Illusions rank among the most common factors cited as contributing to fatal aviation accidents. Sloping cloud formations, an obscured horizon, a dark scene spread with ground lights and stars, and certain geometric patterns of ground light can create illusions of not being aligned correctly with the actual horizon. Various surface features and atmospheric conditions encountered in landing can create illusions of being on the wrong approach path. Landing errors due to these illusions can be prevented by anticipating them during approaches, inspecting unfamiliar airports before landing, using electronic glideslope or VASI systems when available, and maintaining proficiency in landing procedures.

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We’re here at EAA Airventure Oshkosh 2017!

We’re here! Come find us at our booth (2075-2079) in Hangar B, showcasing our current line of training products and pilot supplies along with some new products. Come say hello and get your flight training questions answered by ASA staff.


On Monday, July 24th (tonight!), ASA will be hosting the Collegiate Tailgate Party in Aviation Gateway Park from 5:00-6:30 PM. We had a great time hanging out last year and are looking forward to doing it again. There will be food, music, games, and prizes, so come on out and join us!


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Procedures and Airport Operations: Crosswind Takeoff

Since The Pilot’s Manual: Flight School (PM-1C) is now available in eBook format (from ASA and iTunes), this week we’ll feature another maneuver from the textbook. The fifth edition of Flight School covers everything you need to know in order to fly your airplane through the maneuvers required for certification.

Not all airports have a runway that faces upwind on a given day. For this reason, takeoffs and landings on runways where there is a crosswind component are frequent events. Every airplane type (from the smallest trainer up to the Airbus A340 and Boeing 747) has a maximum crosswind component specified in the flight manual and pilot’s operating handbook. If the actual crosswind component on the runway exceeds the limit for the airplane or what you feel is your own personal limit, then use a different runway (which may even mean proceeding to a different airport).

Takeoff Run
A crosswind blowing under the upwind wing will tend to lift it. Counteract this effect and keep the wings level with aileron; that is, move the control column upwind. While full deflection might be required early in the takeoff run, this can be reduced as the faster airflow increases control effectiveness. You do not have to consciously think of aileron movement; just concentrate on keeping the wings level.

A right crosswind, for example, requires right control column and left rudder (crossed controls). A glance at the wind sock before you open the throttle for the takeoff run will allow you to anticipate this and position the controls correctly.

As speed increases, the amount of aileron and rudder required will reduce until, at liftoff, there will probably be some rudder still applied, but little or no aileron. There is no need to consciously think about this; just:

  • keep straight with rudder; and
  • keep the wings level with the ailerons.

Allow the aircraft to accelerate. Use as much rudder as necessary but avoid braking. In a crosswind takeoff, hold the airplane on the ground during the ground run (with slight forward pressure on the control column) and then lift off cleanly and positively. It may be advisable to delay liftoff until 5 knots or so past the normal rotation speed to achieve a clean (no skip) liftoff.

Drift After Takeoff
As the airplane enters the air mass after liftoff, it will tend to move sideways with it. Any tendency to sink back onto the ground should be resisted to avoid the strong sideways forces that would occur on the landing gear.

Once well clear of the ground, the aircraft will naturally yaw upwind (weathervane) to counteract the drift. Keep the wings level. Any remaining crossed controls are removed once airborne by centralizing the balance ball and keeping the wings level. Climb out normally on the extended centerline of the runway.


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Aircraft Systems: Types of Electricity

Today, we’re featuring an excerpt from our new textbook Practical Electricity for Aviation Maintenance Technicians. As you can tell from the title, this book is geared for new AMT candidates, but it does feature a wealth of information on aircraft electrical systems useful to anyone flying or fixing airplanes.

There are two basic types of electricity: static and current. In static electricity, electrons accumulate on a surface and remain here until they build up a pressure high enough to force their way to another surface or device which has fewer electrons. Static electricity is generally a bother, and steps must be taken to prevent its formation and/or to get rid of it.

Current electricity, on the other hand, is the type most often used. There are two types of current electricity, Direct Current (DC), in which the electrons always flow in the same direction, and Alternating Current (AC), in which the electrons periodically reverse their direction of flow.

Static Electricity
When you slide across the plastic seat covers of an automobile, the friction between your clothing and the seat covers causes your clothes to pick up an excess of electrons from the seat. This is exactly the same thing described earlier when a piece of amber was rubbed with sheep’s wool.

If there is no conductor between your body and the car to make a path for these electrons to leak off, your body holds the extra electrons and is said to be charged because there is an electrically unbalanced condition between it and the car. But as soon as you touch or even come close to a bare metal part of the car, the extra electrons leave and jump to the metal in the form of a spark. This accumulation and holding of electrical charges is called static electricity.

Lightning is just a big spark. Friction of the air moving up and down inside the clouds causes water droplets in the clouds to become charged, and when enough electrons have concentrated in a cloud, the electrical pressure they produce forces them to move through the air. These electrons jump between clouds having different charges or from a cloud to the ground. This is the gigantic spark we call lightning.

As mentioned earlier, an object with an excess of electrons is negatively charged, and an object which has lost its electrons and wants to get them back is positively charged. Two positively charged or two negatively charged objects repel each other, while objects having opposite charges attract. When oppositely charged objects touch, the extra electrons travel from the negative object to the one with the positive charge and they become discharged, or electrically neutral. While static electricity has some uses, it is most often thought of as a nuisance. So a path must be provided to allow the electrons to pass harmlessly from one charged object to another before the charges can build up enough pressure to cause a spark to jump.

In addition to producing a mild shock when you touch the metal part of your car, static electricity can cause radio interference and can damage sensitive electronic components. It is possible, on a dry day, that just taking a few steps on a nylon carpet can build up more than 10,000 volts of static electricity on your body. When you have accumulated this much charge and touch some electronic components, they can be destroyed. When working with sensitive electronic equipment, always wear a grounded wrist strap to bleed off any charge on your body before handling the equipment.

Many airplanes have static discharge points or wicks installed on the trailing edges of the control surfaces. These devices allow the static charges that build up on the control surfaces as air flows over them to discharge harmlessly into the air and not cause static interference in the radio equipment.

Static discharge points are installed on the trailing edge of control surfaces to bleed off the static charges that build up as air flows over the surfaces.

Static discharge points are installed on the trailing edge of control surfaces to bleed off the static charges that build up as air flows over the surfaces.

Static electricity causes a serious fire hazard when aircraft are being fueled or defueled. The flow of gasoline or turbine fuel in the hose produces enough static electricity to cause a spark to jump and ignite explosive fumes.

Current Electricity
Current electricity is the form of electricity that has the most practical applications. A source of electrical energy such as a battery or alternator acts as a pump that forces electrons to flow through conductors. In this study of practical electricity, this flow is called current and because we are considering it to flow from positive to negative, it is positive current.

Aircraft must be electrically grounded before they are fueled. Bonding wires connect the aircraft and the fueling truck or pit together, and both of them are connected to the earth ground so that static charges that build up during fueling can pass harmlessly to ground.

Aircraft must be electrically grounded before they are fueled. Bonding wires connect the aircraft and the fueling truck or pit together, and both of them are connected to the earth ground so that static charges that build up during fueling can pass harmlessly to ground.

For current to flow, there must be a complete path from one terminal of the source back to the other terminal. The figure below shows a complete electrical circuit. The battery is the component in which chemical energy is changed into electrical energy, and current is forced out of the positive terminal, through the switch, the control device, to the lamp. The lamp acts as the load, which changes electrical energy into heat and light. The current then returns to the negative terminal of the battery. Current flows as long as the switch is closed, forming a complete path.

The electrical pressure that forces current through the circuit is measured in volts, with the basic unit of electrical pressure being one volt. Electrical current is measured in amperes or, as we more commonly call it, in amps. One amp is the flow of one coulomb per second, and one coulomb is 6.28 billion billion (6.28 x 1018) electrons. All conductors have some resistance which opposes the flow of electrons in much the same way that friction opposes mechanical movement. The basic unit of electrical resistance is the ohm. One volt of electrical pressure will force 1 amp of current to flow through 1 ohm of resistance.

This is a complete electrical circuit. When the switch is closed, current flows from the positive terminal of the battery through the lamp, where there is enough opposition that the filament gets white hot. After all of the pressure from the battery is dissipated by the lamp, the current returns to the negative terminal of the battery.

This is a complete electrical circuit. When the switch is closed, current flows from the positive terminal of the battery through the lamp, where there is enough opposition that the filament gets white hot. After all of the pressure from the battery is dissipated by the lamp, the current returns to the negative terminal of the battery.

When current flows through a resistor, power is dissipated and voltage is dropped. The voltage across a resistor can be measured with a voltmeter in the same way as the voltage produced by a battery. This voltage is caused by current (I) flowing through the resistor (R), and it is called an IR drop, or a voltage drop. The end of the resistor where the positive current enters is the positive end, and the end where it leaves is the negative end.

A battery is a source of electrical pressure that is also called an EMF, electromotive force, potential, or potential difference. All are measured in volts, and all mean essentially the same thing.

A battery is a source of electrical pressure that is also called an EMF, electromotive force, potential, or potential difference. All are measured in volts, and all mean essentially the same thing.

When current flows through a resistance, power is used, or dissipated, and voltage is dropped. The voltage dropped across a resistor can be measured with a voltmeter in the same way as the voltage produced across the terminals of a battery.

Electrical pressure caused by changing some other form of energy into electrical energy may be called an electromotive force (EMF) a potential difference, or just a potential. Electrical pressure caused by current flowing through a resistance is not a source of electrical energy; it is a drop in the electrical pressure. This voltage is usually called a voltage drop or an IR drop because the amount of drop may be found by multiplying the current (I) by the resistance (R) through which it flows. These terms for voltage are often used interchangeably, and all of them use the volt as the basic unit of measurement.

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