DEN93FA038

While in cruise flight at an altitude of 150 to 200 feet AGL, the surviving passenger heard abnormal sounds from the helicopter which then began a descending right bank into trees. Examination of the helicopter disclosed fatigue failure of the lower mixing unit and a fatigue crack in the upper mixing unit on the flight control system.

History of flight

On April 1, 1993, at approximately 1615 mountain standard time, an Aerospatiale SA316B, N3153R, impacted terrain at 12,000 feet MSL in the Willow Creek Wilderness Area, approximately 15 miles south southwest of Aspen, Colorado. The pilot and two passengers received fatal injuries and one passenger received serious injuries. The helicopter was destroyed. The flight was being conducted under 14 CFR Part 135 to transport persons from a lodge in the vicinity of Crested Butte, Colorado, to Aspen when the accident occurred. Visual meteorological conditions prevailed and no flight plan was filed.

The helicopter was reported missing on the evening of April 1. On the morning of April 2nd, the survivor walked out to a ranch approximately 11 miles from the accident site. On April 4, the bodies of the fatally injured were recovered.

Examination and recovery of the wreckage was delayed due to heavy snow cover at the accident site.

Personnel information

According to available information, the pilot was an experienced mountain pilot, had flown in the accident site region on many previous flights. A review of FAA records did not indicate any abnormal operational history. Details of the pilot's flight experience may be found on page 3 of this document.

Meteorological information

Accident site weather was reported by the survivor who was not aviation oriented, but was an experienced back country ski instructor. His observations are recorded on pages 3 and 4 of this document.

Wreckage and impact information

According to information provided by the survivor, the flight had been airborne approximately 20 minutes and had just passed through a gap known as Schofield Pass. He further reported that the flight was proceeding down a canyon at 150 to 200 feet above ground level when he heard a sound like something under tension broke. This was accompanied by negative 'g' forces and a change in engine noise. The helicopter then descended into 50 to 60 foot high pine trees in a shallow right turn. According to the survivor, there was no communication from the pilot during this time.

The main rotor, main gear box, engine, and aft portion of the tail boom, and the tail rotor assembly were found separated from the helicopter. The helicopter collided with other trees and the cabin top and nose section also separated. The helicopter came to rest upright facing opposite the direction of travel.

According to the survivor, the pilot remained in his seat, the person occupying the left front seat was thrown clear of the helicopter, the person in the left rear seat remained in the helicopter, and he remained in the helicopter. Trained in emergency first aid, the survivor checked for vital signs in the other three occupants after extricating himself. No vital signs were found.

Medical and pathological information

An autopsy was performed at the Valley View Hospital in Glenwood Springs, Colorado. Toxicological test results are enclosed and were negative.

Tests and research

Following examination of the helicopter in the field, and more detailed examination after the aircraft was removed to storage, the following parts were removed for examination by the National Transportation Safety Board Materials Laboratory:

1. Flight control lower mixing unit,

2. Flight control upper mixing unit, and

3. Fore and aft servo.

Examination of the above components revealed a fatigue fracture in the lower mixing unit and fatigue cracking in the upper mixing unit. Details of the examinations are contained in the attached Metallurgists' Factual Report.

A review of aircraft records revealed that the mixing units had been inspected when the helicopter was acquired by the operator approximately 200 flight hours prior to the accident flight.

Additional data

The wreckage was released to Mr. Dennis Jason of Jason and Associates on December 15, 1993.