Bell 206 B3 N204PA accident near Seward, Alaska

Probable cause

The pilot's failure to maintain clearance from snow-covered terrain during hover in deteriorating weather and flat light conditions, which resulted in a tail rotor strike.

NTSB analysis

The commercial helicopter pilot, with two passengers aboard, was supporting a snow survey crew atop an expansive, smooth, featureless, and snow-covered glacial ice field. This operation required brief stops at various predetermined sites along a prearranged route. When the pilot departed from one site en route to the next predetermined site, deteriorating weather conditions coupled with flat light conditions hampered his ability to see the topographical features of the ice field below. As the pilot slowed the helicopter to make a precautionary landing, the helicopter “touched down early.” After the initial touchdown, the pilot hover-taxied the helicopter to an area about 20 or 30 yards beyond the initial touchdown point, then he landed the helicopter in the deep snow. After landing, the helicopter tipped backwards as the aft portion of the skids settled into the deep snow, and the tail rotor blades subsequently struck the snow. The operator reported no preaccident mechanical problems with the helicopter.

Before the helicopter could be ferried from the site, a maintenance technician inspected the helicopter for damage. Finding no apparent damage, the helicopter was started, ground run, and then hovered. While hovering, a tail rotor driveshaft coupling separated, and the pilot did a hovering autorotation back to the snow-covered ice field. As a result of the tail rotor driveshaft coupling separation, the helicopter sustained substantial damage to the tail rotor drive shaft assembly. The damage to the tail rotor drive shaft occurred as the helicopter was being ferried from the site, not during the original event. Most likely the drive shaft was degraded during the first landing, but it did not separate until the ferry flight.

Text from the NTSB. Open the NTSB docket for ANC11TA110 for the full record.