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DALLAS — Just before a midair collision that killed six at a Dallas air show, a group of historic fighter planes was told to fly ahead of a formation of bombers without any prior plan for coordinating altitude, according to a federal report released Wednesday. The report did not give a cause of the crash.

A P-63 Kingcobra fighter was banking left when it struck a B-17 Flying Fortress bomber behind the left wing during the Nov. 12 air show featuring World War II-era planes, the National Transportation Safety Board said in its preliminary findings. All six people aboard the planes — the pilot of the fighter and the bomber’s pilot, co-pilot and three crew members — died as both aircraft broke apart in flight, with the bomber catching fire and then exploding on impact.

There had been no coordination of altitudes in briefings before the flight or while the planes were in the air, the NTSB said. The report said the Kingcobra was third in a formation of three fighters and the B-17 was the lead of a five-ship bomber formation.

Eric…