Most accidents involve multiple factors. It follows that knowledge of critical flight circumstances and factors are helpful in avoiding accidents.

Two recent model aircraft accidents and one that occurred a few years ago have common factors. They resulted in considerable damage to the flying aircraft, parked aircraft, and a serious threat to pilots and crews, These accidents happened close to people but fortunately no one was injured. Although these particular accidents were obviously not predictable, the flight circumstances are identifiable for caution to be exercised in conjunction with other factors that may lead to serious flight safety situations.

How often does the wind blow down the runway centerline? Most runways are aligned with prevailing or mean wind direction ... but the wind usually does its own thing. This simply means that most of our takeoffs and landings are made with some cross-wind component. The average pilot can probably make safe takeoffs and landings as long as the crosswind component (an equivalent wind at right angle to the runway heading) is below 5 to 10 M.P.H. Crosswinds above these values pose threats not to be taken lightly, especially where more than a very small number of airplanes and people are involved.

Let us examine the safety factors in crosswind flying. Figure 1 is not to scale but shows the typical field layout. The critical wind direction is from the pilots back as he faces the runway. Assume a fairly steady 15 m.p.h. wind from the southwest with aircraft taking off to the south. What are the factors that could cause an accident? 1. crosswind component tending to turn the airplane toward the pilots. This weathervane characteristic, while on the main gear, is from the wind pushing on the fuselage side and vertical surfaces. 2. The so called torque tending to turn the aircraft to the left as power is applied. The spiraling airflow from the propeller slipstream pushing against the vertical surfaces tending to make the tail go to the right and the nose of the airplane to the left. 3. Initial steering available from nose or tail gear. 4. Subsequent steering using rudder. 5. Roll and pitch control. Factors 1 and 2 oppose in this case tending to make heading control down the runway centerline easier. Factor 1 affects tail draggers and tri-gear airplanes about the same. On a very smooth runway factor 3 may be of small importance. On a rough runway factor 4 comes into play when ground roll is started. Pilot skill and airplane controllability are involved in all five factors. Factors 2, 3 and 4 become more critical if the pilot is experienced on only grass runways and attempts takeoff on a hard surface runway... regardless of crosswind! Factor 5 becomes important when the wheels leave the ground. Premature liftoff, if heading toward the flightline, in attempting to fly over the over the flightline can be especially critical in aircraft that are marginally powered, have a high wing loading, or snap rolls easily.

A 20 M.P.H. northwest wind with airplanes taking off to the north poses a considerably greater threat to flight safety. There were the conditions at the time of the crashes indicated above. Factors 1 and 2 are additive posing a hazardous situation for even the moderately experienced pilot with a relatively controllable airplane. The following is a likely sequence of events in this case resulting in three crashes: a) The airplane was taxied to the south end of the runway and aligned with the runway heading and on the centerline. b) power could have been applied somewhat abruptly add an extra crosswind gust may have occurred resulting in a quick change in the aircraft heading of about 30 to 45 degrees to the left toward the flightline. Factors 1 and 2 are additive wherein more power without much airspeed and without a lot of corrective rudder makes the airplane turn into the wind direction all the faster. c) with a lot of power, not much airspeed, and the airplane heading toward the flightline the pilot uses a lot of elevator and aileron trying to avoid the flightline. This resulted in a stall/snap roll crash into the flightline.

Remember, the most hazardous crosswind takeoff situation regarding pilots and flightline safety is with the wind from behind the pilots and takeoff from right to left. What may be done to minimize this hazard? Avoid this hazardous crosswind situation, if at all possible, by using another runway. If another runway is not available then more distance between the runway and pilots- flightline is prudent. Under this crosswind condition the aircraft could be headed to the right of the runway heading by 10 to 20 degrees. Application of power should be consistent with adequate heading control. The first two or three seconds of ground rolls can be the initial conditions for a subsequent crash. Be prepared to chop power instantly if adequate heading control appears questionable during the first few seconds. Practice this most critical crosswind takeoff situation on a hard surface runway under less critical conditions (lower wind velocity, no spectators, etc.) until you know pilot/airplane limitations. It is possible to adjust throttle trim to the point where minimum stick throttle position will kill the engine for emergency purposes. If in doubt about pilot/airplane limitations under crosswind conditions and especially with spectators or a flightline of aircraft present... DON'T FLY!