4 Killed, 2 Injured in Separate Wisconsin Aircraft Crashes

Midair collision between a helicopter and gyrocopter killed 2 and injured 2 near Wittman Regional Airport.
Single-engine plane crashed into Lake Winnebago, killing both occupants.
Crashes occurred during Experimental Aircraft Association's annual convention.
Aircraft were privately owned, not part of the airshow performances.
Authorities including NTSB investigating causes of the separate crashes.