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Operating in bright sunshine beneath a scattered cloud layer, Flights 290 and 671 collided at 10:36:47 a.m. CDT over Wisconsin's Lake Winnebago about six nautical miles (6.9 mi; 11 km) south of Appleton and 2.5 nautical miles (2.9 mi; 4.6 km) east of Neenah, Wisconsin, at an altitude of about 2,500 feet (762 m). The left wing of Flight 671 hit the left wing of Flight 290. The collision resulted in an explosion which tore off most of the Twin Otter's wing, and around a quarter of the CV-580's left wing. The collision left both aircraft uncontrollable resulting in both crashing into Lake Winnebago around two nautical miles (3.7 km; 2.3 mi) east of Neenah Light.

The National Transportation Safety Board noted that the North Central crew would have had to look toward the sun to see the approaching Air Wisconsin plane and concluded that they took no evasive action. Some eyewitnesses believed that the Air Wisconsin Twin Otter began a turn seconds before the collision, but the NTSB did not find sufficient evidence to conclude that the Air Wisconsin crew took evasive action. The rate of closure during the final five seconds before the collision was 688 ft/s (469 mph; 755 km/h).

The North Central aircraft involved, N50858, had been completed as a Convair CV-340/440 on May 25, 1953; it later was converted to CV-580 standard. The Air Wisconsin Twin Otter had been completed on October 6, 1966. Both aircraft were destroyed by the collision and subsequent water impact. Their wreckage was found on the lake bottom scattered over an area roughly one mile (1.6 km) long by one-half mile (0.8 km) wide.

The North Central plane had two passengers and a crew of three (Captain James Cuzzort, First Officer Alton Laabs, and Flight Attendant Frances Rabb) on board, while the Air Wisconsin flight was carrying six passengers and a crew of two (Captain David Jacobs and First Officer Michael Gaffin). All 13 people aboard the two planes died in the collision and subsequent crash, and the NTSB observed that the accident was not survivable.

The National Transportation Safety Board released its report on the accident on April 25, 1973. It was "unable to determine why each crew failed to see and avoid the other aircraft," and concluded that the crash resulted from "the failure of both flight crews to detect visually the other aircraft in sufficient time to initiate evasive action," and stated that it believed "that the ability of both crews to detect the other aircraft in time to avoid a collision was reduced because of the atmospheric conditions and human visual limitations." The NTSB speculated that both flight crews could have been scanning instruments in preparation for descent to their respective destinations at the time of the collision, and this could have reduced their chances of spotting one another. The report also noted that the decision by both flight crews to fly under VFR rather than IFR and the fact that neither captain requested in-flight advisories deprived both aircraft of air traffic control support, and that such support to even one of the aircraft would have ensured sufficient separation to avoid a collision.

The NTSB recommended that the Federal Aviation Administration create a standardized method for training and grading flight crews in visual search techniques and time-sharing between instrument checks and visual searches, and that the FAA expedite the development of anticollision systems.

• Aviation Safety Network: ASN Aircraft accident Convair CV-580 N90858 Appleton, WI
• National Transportation Safety Board Report Number NTSB-AAR-73-09 "Aircraft Accident Report North Central Airlines, Inc., Allison Convair 340/440 (CV-580), N90858, and Air Wisconsin, Inc., DHC-6, N4043B, Near Appleton, Wisconsin, June 29, 1972," adopted April 25, 1973