Sunday, June 7, 2009

Cross wind landing Techniques

Crosswind Techniques

By Jim VanNamee

It’s summer in the mountains now, and distant afternoon thunderstorms often produce blustery wind speeds above what is usual. The inevitable hangar discussion ensues around crosswind take off and landing techniques. Some questions asked are:• Does one operate where crosswinds exceed the demonstrated limit found in the POH?• Should I use the slip or "kick out" method of landing?• How much flaps does one use in a crosswind?Let’s investigate some of these questions and determine for ourselves our own answers to the above questions based upon our own skill level. But first, how do we derive the crosswind component? "Use the crosswind component chart," says the student to the examiner. Yeah, well, it’s been a long time since you’ve even seen that chart, right? Of course, it’s been a long time since you’ve reviewed the POH, either. That’s where it can be found for some airplanes, but, hey, since we aren’t in doubt, we don’t read the book, do we? So, great aviators that we are, we estimate:
Wind off the Nose 30 degrees50 degrees 70 degrees
Crosswind ComponentHalf the wind speedApprox. 75% of the windApprox. 90% of the wind
Does one fly in crosswinds in excess of the demonstrated limit in the POH? The POH figures were set during certification trials by test pilots flying the airplane in a manner akin to how you might fly. In other words, they try to take into account how the average GA pilot would fly the plane, and not how experienced, high time engineering test pilots take to the air. Federal Aviation Regulation (FAR 23.233) requires that all airplanes certificated after 1962 must be safely handled in a 90-degree crosswind at .2 Vso. This means that if your C-182 has a stall speed of 49 knots it should be able to handle a direct crosswind of 10 knots, or your Turbo-Bonanza with a stall speed of 57 knots must be safe in a 11.5 knot direct crosswind. We know that the POH records higher demonstrated values than 10 or 11.5 knots, respectively. How’d that happen? The figures derived are not the limit’s the plane’s controls can handle in a crosswind, but a conservative value that keeps you out of trouble, and keeps the manufacturer out of court. There is a rule of thumb articulated by an unknown "they" that says "If wind gusts surpass 65 percent of Vs1, don’t take off or land." For a C-182 with a Vs1 of 50 knots, and a Turbo-Bonanza of 64 knots, this means a direct crosswind of 32.5 and 41.6 knots respectively should keep you from operating that day. Most pilots should cower at these crosswind numbers, and rightly so. It’s possible the aforementioned test pilots can handle these crosswinds with great vim and vigor, but the rest of us should probably opt out at a much lower figure. Practice should show you what your limit is. Another rule of thumb – if the local "Vulture’s Row" crowd suddenly appears on the ramp with coat hangers and marshmallows as you taxi out, you may want to return to the tie-down area.Can you fly in higher crosswinds than the airplane’s certification minimums? I would hope so. Can you fly in winds up to the demonstrated limits in the POH? I hope so. Can you fly in higher winds? Maybe. However, I would couch all of these replies with three precautions:1. Wet or snow covered runways change everything. Unless you want to demonstrate your best Olympic skating techniques, it would be best to stay in bed that day. Besides, the French judge won’t appreciate your larking about on the runway, anyway.2. Practice, practice, practice. And, oh, by the way, practice with an instructor who has the skills to handle and demonstrate crosswind landings in these type of conditions, in the airplane you fly. The time to find out that your expertise isn’t up to even certification minimums is not on take off run or in the flare.3. FAR 91.13 (Careless or Reckless Operation) can be used against you if you operate your aerospace vehicle in excess of the POH demonstrated crosswind component. The FAA can violate you and/or a civil suit can be filed should an unpleasant event occur as a result of your actions in a high wind environment.Does one use the slip or "kick out" method of landing in a crosswind? At the moment of touchdown in a crosswind, the airplanes’ fuselage must be heading parallel to its direction of travel, preferably down the center of the runway, with drift under control as well as no lateral movement. Most pilots probably use a slip to accomplish crosswind landings. This is a tactic where a crab on final is established, then at some point (about there looks right) the fuselage is aligned to the runway centerline with rudder, and the upwind wing lowered into the wind to negate drift. The airplane is landed on the upwind wheel. Keep the plane over, and aligned with, the runway centerline and allow the raised (downwind) wing to lower itself to the ground aerodynamically. Continue to maintain rudder and aileron in a cross-controlled condition until coming to a stop. Making a perfect landing on the upwind wheel and then encountering a roll over situation doesn’t make for the best of days. If you can imagine a line drawn from the axle of your main wheels to the axle of your nose wheel, this is the "roll over axis" of a tricycle landing gear airplane. Any more than about ten degrees of cornering angle (angular difference between the heading of the tire and the path it is actually taking – skidding) and your little aerospace vehicle can begin to roll about its roll over axis. Maintain cross-controlled rudder and ailerons to keep the fuselage over and aligned with the runway centerline and drift under control. Even after taxiing off the runway, utilize the POH recommended techniques for taxiing. Rollout and taxiing in high wind conditions can be a precarious period during your flight. Yes "flight." You aren’t through, and shouldn’t relax, until the engine is shut down, gust locks in place, and the airplane tied down.There are some disadvantages to the slip method of landing. You must determine when to set up the airplane for this type of approach. Too early, and your passengers become uncomfortable; too late, and you may not have set up the plane for a safe and successful landing. Because the wind can vary at differing altitudes, even on final, you are constantly making adjustments with aileron and rudder to keep the plane aligned with the centerline of the runway. Since it is a cross-control technique, the rate of descent increases. This, along with an adjustment for gust factor, entails a higher approach speed than normal.Another method of crosswind landing is the "kick out" technique. This was used by pilots of early jet passenger planes because the jet didn’t slip well. This method advocates crabbing the plane on final until in the flare. Just prior to touchdown, the upwind wing is lowered and that tire is "planted" on the runway. The remaining wheels are allowed to lower themselves aerodynamically. Roll out is accomplished the same as the slip method of landing. This technique, also, has disadvantages. If the crab is taken out too early, the pilot must either go around or establish a crosswind slip to landing. If the crab is taken out too late, upon touchdown the airplane can start skidding athwart the pavement and the hapless pilot may soon discover how to enlighten his or her friendly NTSB envoy about the topic of roll over axis. Also, one must be very proficient in this type of modus operandi. Much practice is required for mastery. Notice I didn’t discuss this method very intensely. I’m not ready to spend a successful 3.0 hours of PIC X/C flight time and then exchange that for about 5 seconds of wishful thinking. There are advocates for this type of crosswind landing technique, and I respect their opinion. However, I’m not comfortable with it, and it’s definitely not for weekend warriors.Does one use flaps in a crosswind? This is one question that has a lot of answers – many with stanch opinions. Visit the Google web site, under the group rec.aviation.student, where you will find a plethora of panaceas, opinions, and solutions to this oft-asked query.Flaps allow a pilot to fly a steeper rate of descent without an increase in airspeed. This means flaps are both a lift and drag-producing device. Stall speeds are reduced by the addition of flaps. Up to a point, flaps produce more lift than drag. Ever notice the droop created by the first setting of flaps almost mirrors aileron droop with full throw of the yoke? That setting approximates the flap angle that creates the most lift without the negative consequences of drag. Go beyond that flap setting and drag begins to have a more noticeable affect. This is the area where you get the ability to increase your rate of descent without increasing airspeed.Flaps allow for a slower groundspeed on touchdown. If, for example, full-flap final approach airspeed in your trusty C-182 is 60 knots and the headwind component is 10 knots, then you can still touch down with the same groundspeed – even if you’ve increased your final approach speed for zero flaps and the gust factor. At this point, flaps become a personal preference. Yes, I know stall speed is increased with no flaps extended, but since you fly an airspeed several knots higher than full flap final approach airspeed, you have about the same buffer between Vso and Vs1. More flaps also offer a better opportunity for the airplane to weathervane immediately after touchdown; in a high wing airplane, the upwind wing can be more easily lifted by a gust. My personal preference with a headwind down the runway is 20 degrees of flaps if the wind is 10 knots or less, and 10 degrees of flaps if the wind is 11 to 20 knots. I don’t use full flaps unless I am performing a short or soft field landing. At high density altitudes found in the mountains, most rental and training airplanes available here may not climb during a go around if the flaps fail and we are "heavy, hot, high, and humid." The Turbo-Bonanza? It’s a rock on final with 30 knots of headwind and full flaps – goes around, too. Jim Van Namee lives in Angel Fire, New Mexico, and is a CFI at Taos Aviation Services, Taos Regional Airport, Taos, New Mexico. If you have questions about flying in the Taos or Angel Fire area, he can be reached at

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