Fairchild Hiller FH 1100 N4035G

Summary

On 6 October 2016 at about 21:45 local time, a Fairchild Hiller FH 1100 registered N4035G was involved in an accident near Lino Lakes, Minnesota, United States. 2 people were on board and 2 died. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

6 October 2016 at 21:45

Classification

Accident

Location

Lino Lakes, Minnesota, United States

Coordinates

45.1933, -93.1378

Aircraft

Fairchild Hiller FH 1100

Registration

N4035G

Category

Helicopter

Year built

1982

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Minneapolis → Minneapolis

Aircraft damage

Destroyed

Weather

VMC

Light

Day

NTSB number

CEN17FA012

2 people died.

The separation of the main rotor assembly due to mast bumping.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The airline transport pilot was conducting a local flight with one passenger. The accident flight was the pilot's third flight in the helicopter on the day of the accident; before that day, he had not flown the helicopter in nearly one year. One witness stated that he saw the helicopter rocking back and forth before it "spun sideways" and "a bunch of parts" departed the airframe. Some reported hearing a "clunk" sound, and others reported hearing a "pop" sound. Another witness saw the main rotor blades "seize," then "snap off," followed by the tail rotor departing the helicopter. The witness stated that the helicopter then "dropped out of the sky." The fuselage impacted in an open field, and a postcrash fire erupted. The separated main rotor blades and hub were found in a pond about 500 ft south of the main wreckage. Examination of the rotor mast showed deformation and fractures consistent with overstress under bending and torsion loads but no evidence of preexisting cracks or corrosion. The observed deformation of the mast was consistent with a mast bumping event. Mast bumping can occur in low acceleration of gravity (G) flight conditions, causing the rotor blade to exceed its flapping limits and resulting in the main rotor hub bumping into the rotor shaft. This often results in structural failure of the rotor shaft and a subsequent separation of the main rotor. Due to the extensive thermal damage to the wreckage, only a limited examination could be conducted; however, no mechanical malfunctions or anomalies were noted that would have precluded normal operation. The pilot had accumulated about 15,000 flight hours in airplanes but only had about 55 hours flight time in helicopters, most of which were accumulated more than 1 year before the accident. Although the pilot had received instruction on how to avoid mast bumping, given his low helicopter experience relative to his airplane experience, it is possible that he made a large, abrupt flight control input that resulted in a low-G flight condition and led to the observed mast bumping. However, the pilot's control inputs are unknown, and the initiating event for the mast bumping could not be determined.

Quoted verbatim from the NTSB record.