What happened
On September 24, 2009, at 1843 mountain standard time, an Eurocopter AS 350 B3, registration N103LN, was performing a landing at the St Mary's Helistop in Tucson, Arizona. The aircraft, operated by Air Methods Corp, was in the final phase of its approach, approximately five feet above the landing pad, when it experienced an uncommanded left yaw.
The pilot attempted to counter the yaw using right anti-torque pedal input, but the maneuver was unsuccessful. In response to the loss of control, the pilot rapidly lowered the collective and rolled the throttle off, resulting in a hard landing. The helicopter came to rest facing the opposite direction from its original approach. There were no injuries to the pilot, flight nurse, medic, or the patient on board. The aircraft sustained substantial damage, including buckled skin on the tail boom approximately two feet aft of the rear structure attachment.
Hospital surveillance footage captured the event, showing the helicopter making a steady approach before pivoting approximately 180 degrees over a four-second period just before touchdown.
The investigation
An inspection by a Federal Aviation Administration (FAA) inspector confirmed that all control linkages were intact and that continuity was established between the anti-torque pedals, cyclic, and collective to the flight control surfaces.
Investigators examined the tail rotor servo actuator (part number SC5072). The component was subjected to a visual examination and a pressurized acceptance test involving 100 extension-retraction cycles at 580 psi. The servo showed no leaks and performed within designed parameters. Additionally, data from the Vehicle and Engine Multifunction Display (VEMD) showed no failure diagnosis pages for the accident flight.