On October 6, 2007, about 1335 Pacific daylight time, a Yakovlev YAK-50, N509RA, collided on the ground with a Yakovlev YAK-50, N950MS, at Gillespie Field Airport, El Cajon, California. Both owners were operating their airplanes under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The airline transport pilot flying N509RA was not injured; the airplane sustained minor damage. The airline transport pilot in N950MS was not injured; the airplane sustained substantial damage to the left elevator and rudder. The local flights departed Gillespie Field at 1215. Visual meteorological conditions prevailed, and a visual flight rule (VFR) flight plan had been filed. According to the Federal Aviation Administration (FAA), four airplanes were conducting a formation flight. During the landing roll on runway 27R, the number four airplane (N509RA) struck the number three airplane (N950MS). The number four airplane sustained minor damage, including damage to the propeller and damage to the leading edge of the right wing. The number three airplane sustained substantial damage to the tail section. The pilot of the number four airplane reported that he was landing behind the number three airplane, using a staggered landing pattern. Due to the gusty wind conditions, the number four airplane floated on landing and touched down past the intended landing point on the runway. After landing, the number four airplane slowed to 2-3 miles per hour and began to turn to the left to exit onto taxiway 02. The pilot reported that he was confused because he did not see the other airplane, but decided that the number three airplane had continued further down the runway. The pilot of the number four airplane did not see the number three airplane until the propeller of his airplane impacted the tail section of the number three airplane. In a later conversation between the pilots, the pilot of the number three airplane stated that during his landing he had crossed onto the right side of the runway. The pilot of the number four airplane thought that this was due to the crosswind conditions. The right side of the runway had been designated to the number four airplane. An aviation routine weather report (METAR) for Gillespie Field was issued at 1347. It stated: winds from 260 degrees at 13 knots gusting to 17 knots; visibility 30 miles; skies clear; temperature 22 degrees Celsius; dew point 5 degrees Celsius; altimeter 30.02 inHg.