THE HELISTAT, A HYBRID A/C WITH 4 H-34 MAIN FUSELAGES ATTACHED TO A FRAME ALONG WITH A ZPG-2 HELIUM FILLED ENVELOPE HAD JUST COMPLETED IT FIRST HOVER TEST FLT SUCCESSFULLY AND LANDED. A PWR LOSS WAS NOTED ON THE NO. 3 HELICOPTER AND THE TEST WAS TERMINATED AND THE MOORING MAST CALLED FOR. PRIOR TO RE-MOORING A WIND SHIFT CAUSED AN UNCOMMANDED LEFT TURN WHICH THE PILOT COULD NOT CONTROL WITH THE FLT CONTROLS. WITH A TAILWIND, NO WHEEL BRAKES OR GND STEERING A TAKEOFF WAS ATTEMPTED. THE 4 MAIN LANDING GEAR WHICH HAD NO SHIMMY DAMPNERS STARTED TO SHIMMY. THE FOUR HELICOPTERS STARTED TO REACT TO THE SHIMMY WITH GROUND RESONANCE. AS THE HELISTAT FINALLY LIFTED OFF, THE FOUR INDIVIDUAL HELICOPTERS BROKE OFF AND FELL TO THE GROUND. ONE PILOT RECEIVED FATAL INJURIES, 3 RECEIVED SERIOUS INJURIES AND ONE MINOR INJURIES. THE HELISTAT WAS DESTROYED. THE PRW LOSS ON THE NO. 3 HELICOPTER WAS TRACED TO A MISSING THROTTLE LINKAGE CORRELATION PIN. WHY THE PIN WAS MISSING WAS NOT DETERMINED.
https://www.ntsb.gov/investigations/...13X34293&key=1
Surprised anyone survived.