Home

Aviation News

Flight Training

Aviation History

Theory Of Flight

Airframes

Powerplants

Civilian Aircraft

Military Aircraft

Aviation Wallpapers

Aviation Links

Contact


 

 

 

Contents

Wind
An airplane moves in an air mass whose movement affects the ground speed of the aircraft. The ground track of an aircraft is the result of a combination of aircraft speed and direction as influenced by air mass speed and direction. An airplane is capable of moving in six different directions. The three rotational moves are controllable by the pilot while the other three are influences from the air mass around the aircraft.

In every landing the pilot should be aware that airspeed and ground speed are not the same. Regardless of groundspeed the required airspeed must be flown. The landing ground speed in a 90 degree 30 knot crosswind will closely approximate that of a calm wind landing. Regardless of the wind direction and velocity a minimal ground contact speed is desirable. The pilot must exercise his best judgment in consideration of conditions, POH recommendations and his own abilities in deciding how to apply flaps. If you are undecided or affected by unfamiliarity, turbulence etc, get further instruction to improve your decision-making ability. As with any landing, do not add flaps within 200' of the ground. Configuration changes are likely to have significant influence on your airspeed control. The removal of flaps should only be incorporated into a go-around.

Wind often is very stressful to the pilot. Takeoffs and landing techniques require greater skill under the influence of wind. even the light and variable wind adds complexities that are difficult to plan for. Having specific wind information can either add to or subtract from a pilot's stress. Runway selection is primarily based on wind direction except where noise abatement rules prevail. Acquiring wind judgment skills is a prime reason for flying in different conditions. A pilot has no way of knowing how the wind will be on a particular leg, at a particular runway, at a particular time or how it will change without notice. You must always fly in anticipation of the wind never being as forecast, stated or expected. Use the wind to stretch your skill limits.

With experience a pilot learns to read winds from water, dust, DME, GPS, the windsock and weather forecasts. Regarding the latter, one thing you can be certain of is that the winds will NOT be as forecast. It is not a good idea to read the wind from a tetrahedron. Most tetrahedrons have locks that allow them to be positioned for the preferred runway without regard to wind direction. The windsock is the best wind indicator at an airport and should be noted on downwind and especially on final. The AWOS at an uncontrolled airport is up-dated every minute.  Scheduled ATIS changes are once an hour at about 45-minutes after the hour.  When conditions change rapidly or significantly the ATIS may be updated. What you see on downwind will enable you to make a wind adjusted pattern. A disproportionate number of landing accidents are caused by a pilot's failure to adjust the pattern for wind direction and velocity.

The FAA wind cone (sock) can be of several colors but usually orange and either 8 or 12 feet long. Windsocks are fully extended in 15-knot winds. I make a practice of having students practice reading windsocks by comparing ATIS or tower wind directions and velocities with their guesses from the windsock. At one time Concord, CA had five windsocks. It was not unusual to have them all showing different direction and velocity. There is no record of the first windsock, however, the first lighted windsock was sold in 1928 by the Heath company.

When winds are gusting and shifting it is best to add one-half the gust value to your approach speed to protect against shear-induced changes in airspeed. Wind shear on approach causes turbulent eddies that can cause real and illusionary changed in the flight path. An aircraft on glide path can develop sink rates that con only be arrested with full power. This sink is because of loss of lift caused by a headwind component becoming a tail wind in a matter of seconds. Aircraft failing to make adequate correction will land short. A go-around is the option.

Item:
The setting sun is already below the horizon. Refraction causes the illusion.

Item:
. Perhaps the easiest way to remember is that any verbal wind direction by ATC is given magnetic.

The Calm Wind Approach
One of the most difficult patterns to fly well is the one required by a calm wind. In a calm wind situation a student pilot anticipates that landings should be easier. Not so. It is the calm condition at an airport that creates problems. It is not usual in calm wind conditions to have winds of differing velocities as you descend on final. During calm wind landings I suggest that you allow a slightly larger pattern to allow for such variations. If you use the standard landing procedures, suggested elsewhere, you will probably be high on final in calm wind conditions. The airplane is configured for a steep approach but does not come down. Even with full flaps, power off, and short field approach speed the airplane does not come down as expected. Even a well-planned approach under calm surface wind conditions can result in a go around. A second approach may have the same result. The fact is that the calm wind at the surface may well be a tail wind 500' above the ground.

If you experience such an approach, advise the tower to consider changing runways. Even at tower airports it is not unusual to have a wind shift occur well before the runway is changed. Sometimes the runway will be retained because of local noise-abatement requirements.

Light Wind Patterns
Last week, as I walked up to the plane, I momentarily stopped and felt the wind. It was very light but could be perceived as a tail wind for the noise abatement runway currently in use. I had my student, sitting in the plane, get out and asked him to feel the wind. What followed was an analysis of what happens when a wind is classified as "calm". Even more importantly, we covered all the effects for the even greater probability that the wind would be "light and variable". We did some watching of aircraft making their landings. Landings were consistently long on the 5000' runway. Also, the landings were usually off to the side of the centerline.

On average, landings are made into runways with the twelve-knot relatively constant velocity and direction winds. Most of our practice and landings are into such winds plus or minus a knot or two. This experience has taught us to make the adjustments to the pattern and aircraft configuration required producing a satisfactory landing. "Calm winds" which are more likely to 'light and variable do not provide the clues the inexperienced pilot has come to expect.

The light tail wind will increase the ground speed and shallow the approach angle. The usual changes in flaps, power, and airspeed fail to produce the desired results. This is caused by the fact that, while the tail wind may exist from 600 feet down to 100 feet the winds higher and lower will be from different directions and velocities. Even the tail wind will vary in velocity on final. The momentary truly calm wind compounds the difficulties.

The solution I offered my student was to extend the down wind leg of the pattern by twenty to thirty seconds any time the ATIS, wind sock, or AWOS indicates a calm wind condition. This adjustment allowed for the more shallow approach angle caused by the increased ground speed. The student was on a good approach but a new "calm wind" problem arose. In the flare the aircraft would begin a barely perceptible drift off the centerline.

It seems that the intensity of the landing itself often so focuses the attention of the student that he/she is completely unaware of drift unless it is either pronounced or occurring just before touchdown. The likelihood or probability of this drift condition occurring must be pre-registered into the mind of the pilot any time the "calm" condition exists. With the runway out of sight in a proper flare the pilot must get his clues from the peripheral vision and the horizon. This takes both practice and experience especially in calm conditions. A failure to correct even the slightest side load on the landing gear is potentially very harmful to the aircraft since this is the weakest area of landing gear geometry. The instructor who does not foresee this area of landing difficulty is not properly anticipating an area of difficulty. It is best to teach every landing as though it has a cross wind.

Strong Wind Patterns
A few day prior to this flight another student and I had winds at 23 knots with higher gusts 40 degrees off the runway heading. Once again I proceeded to talk and walk through the headings for both left and right traffic that would produce an appropriate pattern. Just to get into the plane and start doing landings in these conditions would have been most inappropriate. We were transitioning the student from a C-150 to a C-172. This was his third C-172 flight but his first since getting his license.

In the pattern walk through, I gave the student the needed opportunity to see that some operational adjustments would be required. The initial takeoff would cause us to gain altitude over less distance so that our crosswind would need to be flown angled well into the wind and extended somewhat to create a wider downwind. The turn downwind would need to be angled away from the runway since it was necessary to fly a somewhat wider downwind leg both because of being in right traffic and because the wind direction would produce a an effectively shorter base leg due to a higher ground speed. The power reduction would begin before the numbers and even more angle into the wind would be taken to counter the increased wind effect at a slower airspeed. The wider downwind would give us a base leg sufficiently long to allow adjustments in the length and height of our final approach. The instructional emphasis here is that the pilot's control over the final approach must begin on the downwind leg if not sooner.

Under these or similar conditions the landing must be considered an option not a necessity. The go-around is the first choice option if the stabilized final approach cannot be established.

Flying the same runway in left-hand traffic in the same wind conditions requires the pilot to make a shorter crosswind to help counter the wind's efforts to drift the aircraft away from the runway. The downwind leg must be angled toward the runway. The base leg again must be sufficient to allow adjustments to the height and length of the final approach course.

The instructional process for landings is not complete unless it exposes the student to the wind conditions described above. The opportunity to fly both left and right patterns in the same crosswind conditions is essential. Going to controlled airports with multiple runways can create variety of pattern and conditions. ATC will honor requests for crosswind runways and different patterns when traffic conditions allow. Changing the time of day is a good way to obtain varied wind velocity.

Continue To Next Page

 


Copyright 2003-Now www.airman.us All rights reserved. Reproduction in any form is prohibited.