MD Helicopters MD 900, Mesa, Ariz., Sept. 8, 2004–The NTSB attributes the accident during the test flight to the fracture of a tension-torsion strap in the fan because of progressive fiber failure of the composite material from compression and/or transverse shear stresses with repeated manipulation of the antitorque control pedals without the fan operating at full rpm. A factor was the manufacturer’s inadequate fatigue and load testing on the strap.
Taking off from Boeing Heliport, the MD 900 had a Notar fan failure and landed hard. When the helicopter started vibrating, at about 30 to 40 feet agl, the pilot lowered the collective to the full-down position and touched down at about 30 to 40 knots groundspeed.
The pilot was uninjured.