ERA13LA366

The airplane departed as the fifth airplane in a formation of six airplanes during an airshow demonstration and was about 75 feet to the trailing right of the preceding airplane during the takeoff and initial climb. The pilot reported that, about 10 feet above ground level (agl), the airplane drifted right of the runway centerline and that he then realigned the airplane with the centerline. About 35 feet agl, he encountered "severe turbulence," and the airplane banked left uncontrollably. He attempted to regain control of the airplane; however, it stalled and subsequently impacted the ground in a nose-low attitude. A left crosswind of about 3 knots existed at the time of the accident. According to Advisory Circular 90-23F, "Aircraft Wake Turbulence," "a crosswind will decrease the lateral movement of the upwind vortex." Postaccident examination revealed that the pitch trim was set in an almost full nose-up position. The pilot likely did not comply with the before takeoff checklist and confirm that the trim setting was at 0 before takeoff. In addition, the airplane likely encountered wake turbulence from the preceding airplane. The pilot reported no mechanical malfunction or abnormality that would have precluded normal operation.

Advisory Circular (AC) 90-23F "Aircraft Wake Turbulence", Section 7 "Vortex Behavior" which states in part "A crosswind will decrease the lateral movement of the upwind vortex and increase the movement of the downwind vortex. Thus, a light wind with a cross-runway component of 1 to 5 knots (depending on conditions) could result in the upwind vortex remaining in the touchdown zone for a period of time and hasten the drift of the downwind vortex toward another runway. Similarly, a tailwind condition can move the vortices of the preceding aircraft forward into the touchdown zone. The light quartering tailwind requires maximum caution. Pilots should be alert to larger aircraft upwind from their approach and takeoff flight paths." According to the Aeronautical Information Manual, "government and industry groups are making concerted efforts to minimize or eliminate the hazards of trailing vortices. However, the flight disciplines necessary to ensure vortex avoidance during VFR [visual flight rules] operations must be exercised by the pilot using the same degree of concern as in collision avoidance." According to the Pilot's Flight Operating Instructions T.O. No. 01-160LA-1 Section 8. "TAKE-OFF" which states in part: b. The airplane is taken off in the conventional manner (1) Mixture Control at full RICH position (2) Carburetor air heat at COLD position, unless icing conditions prevail (3) The elevator trim tab at ZERO (4) Check that fuel selector valve is set on LEFT tank position (5) For normal sized fields flaps may be up The two-seat, high-wing, tailwheel airplane, was manufactured in 1943. It was powered by a PZL-Franklin 4ACG199H3, 113-hp engine. According to the airframe maintenance records the most recent annual inspection was completed April 13, 2013, and had a recorded airframe total time of 892.4 hours. The airport was a publically owned airport and at the time of the accident had an operating control tower. The airport was equipped with two runways designated as runway 8/26 and 13/31. The runways were reported as "in good condition" at the time of the accident. Runway 8/26 was a 6,933-foot-long by 150-foot-wide runway and runway 13/31 was a 4,102-foot-long by 100-foot-wide runway. The airport was about 403 feet above mean sea level. On August 17, 2013, about 1335 eastern daylight time, an Interstate S-1B1, N46336, was substantially damaged after it impacted the runway shortly after takeoff at the Lancaster Airport (LNS), Lititz, Pennsylvania. The commercial pilot was not injured. The airplane was registered to American Airpower Heritage Flying Museum and operated by the Commemorative Air Force Delaware Valley Wing under the provisions of Title 14 Code of Federal Regulations Part 91 as an airshow flight. Visual meteorological conditions prevailed and no flight plan had been filed. According to the pilot, he was number 5 in a formation takeoff of 6 airplanes, all of which were vintage military "spotter" aircraft. He was about 75 feet behindthe preceding airplane and slightly offset to the right, during the takeoff and initial climb. The formation flight had departed from runway 13. About 10 feet above ground level (agl), the pilot noticed the airplane had drifted to the right of the runway centerline, which he immediately corrected. He further reported about 35 feet agl he encountered "severe turbulence" and the airplane abruptly rolled to the left. Unable to regain control, the airplane impacted the runway with the left main landing gear and came to a rest. The 1353 recorded weather observation at LNS, included wind from 070 degrees at 4 knots, 10 miles visibility, clear sky, temperature 26 degrees C, dew point 12 degrees C, and a barometric altimeter setting of 30.23 inches of mercury. The pilot, age 52, held a commercial pilot certificate for airplane single-engine land, and a second-class airman medical certificate issued July 11, 2013. The pilot reported 1,626 total flight hours with 15 of those flight hours in the accident aircraft make and model. Initial examination by a Federal Aviation Administration inspector revealed that the airplane came to rest on the paved portion of the runway about 30 feet past the initial impact point and the left wing tip was resting on the ground. The left wing leading edge spar was cracked beginning at the wing tip and proceeding inward about 4 feet, the left main landing gear was collapsed, the fuselage was resting on the ground, and the right main landing gear strut was bent. Photographic examination of the cockpit revealed that the trim wheel was set to almost the "full nose up" trim position.