Fatal Erie helicopter crash caused by rotor system failure

The 2015 crash of a helicopter at the Erie airport, which left two people dead, was caused by an inflight break-up of the aircraft’s rotor system prompted by undetected fatigue cracking, the National Transportation Safety Board says.

Specifically, federal investigators zeroed in on the chopper’s No. 2 main rotor spindle — an integral part of the rotor system that buoys the blades of the helicopter — as the primary culprit.

In its final report on the crash, released late last month, the NTSB also cited the Enstrom 280FX’s design as a contributing factor to the helicopter’s crash.

Helicopter flight instructor Alex Viola, a 23year-old from Arkansas City, Kan., and student Amy Wood, 25, of Boulder, died in the Jan. 26, 2015, crash. The helicopter was registered to New Course Aviation Company and operated by Mountain One Helicopters, according to the NTSB.

Mountain One Helicopters said after the crash that Viola was an instructor for the company and that Wood was working on getting her private license.

The NTSB said the helicopter — manufactured in 1985 — was on final approach to land when one of the chopper’s three main rotor blades separated, causing the in-flight break up. A witness told investigators she heard a loud “pop” before seeing the helicopter start to rotate as a blade came off the aircraft.

“Metallurgical analysis of the fractured spindle revealed signatures consistent with a fatigue crack initiating from multiple origins that propagated across 92 percent of the spindle cross-section,” the report said. “The remaining 8 percent of the fracture surface exhibited signatures consistent with overload.”

Similar fatigue cracks were also observed stemming from the thread roots on the helicopter’s No. 1 and No. 3 spindles, the NTSB found.

Before the accident, the report said, the spindle was not considered to be subject to wear and was therefore not regularly inspected. Federal investigators said there would have been a “low likelihood of the operator detecting the fatigue fracture within the spindle threads before the accident.”

Since then, the Federal Aviation Administration began requiring inspection of spindles with 1,500 hours or more time in service and Enstrom released a directive bulletin to operators.