History of Flight
On October 7, 2012, at about 1513 Pacific daylight time, a Garlic Helicopters UH-1H helicopter, registration N1577, experienced a forced landing approximately 4 miles southwest of Shady Cove, Oregon. The commercial pilot, the sole occupant, sustained minor injuries, and the helicopter was substantially damaged. The helicopter was registered to a private individual and operated by Columbia Basin Helicopters under 14 CFR Part 133. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight that departed Merlin (Grants Pass), Oregon, at 1400.
The pilot reported that the purpose of the flight was to long-line buckets of water onto a wildfire. After dropping three loads of water, he began the return to base. During straight and level flight, he heard a loud noise and felt an abrupt jolt and right yaw. He descended into a valley when another loud noise occurred, followed by severe vibrations. The low rotor RPM horn activated; the pilot lowered the collective to maintain RPM and proceeded toward an area of small trees. Slightly above tree level, he raised the collective and descended into the trees. The helicopter impacted the ground and rolled onto its right side before coming to rest.
Personnel Information
The pilot, age 30, held a commercial pilot certificate for helicopters issued on February 9, 2004, and a second-class airman medical certificate issued on December 8, 2011, with the limitation that he must wear corrective lenses. He reported 2,959 total flight hours, including 744 hours in the accident helicopter make and model. He flew 243 hours in the 90 days preceding the accident and 24 hours in the 30 days before the accident.
Aircraft Information
The two-seat helicopter, serial number 65-09577, was manufactured in 1965 and powered by a Honeywell T53-L-13B turboshaft engine (serial number LE-18674). Logbook records showed a 25-hour tail rotor gearbox inspection on September 4, 2012, at a tachometer reading of 6,284.2 hours. A 50-hour inspection, including inspection and cleaning of tail rotor blades, was completed on August 24, 2012, at a reading of 6,258.2 hours. On August 17, 2012, skin on the left side of the vertical fin was replaced due to cracking at lower rivets, and a doubler was added; the tachometer reading was 6,231.2 hours. The pilot reported that the helicopter was due for a 25-hour inspection in about 2 to 5 flight hours.
Meteorological Information
The nearest weather reporting station, Rogue Valley International – Medford Airport (MFR), about 12 miles south of the accident site, reported at 1353: clear skies, wind from 300 degrees at 4 knots, visibility 10 statute miles, temperature 28°C, dew point -3°C, and an altimeter setting of 29.85 inches of mercury.
Wreckage and Impact Information
On-scene examination by a Federal Aviation Administration inspector revealed the helicopter came to rest on its right side in mountainous, tree-covered terrain. The helicopter remained mostly intact. Flight control continuity was established throughout except for the 90-degree gearbox and tail rotor assembly. The 90-degree gearbox, positioned between the tail rotor drive shaft and tail rotor assembly, takes input from the tail rotor drive shaft (via a quill assembly) and transfers energy to the tail rotor assembly. The 90-degree tail rotor gearbox and tail rotor assembly had separated from the input quill assembly and were not located at the accident site. Two of the tail rotor gearbox attachment studs and their nuts remained attached to the input quill mounting flange on the vertical fin side but were fracture-separated on the gearbox side of the mounting flange.
The cargo hook was found open, with the long line and bambi bucket still attached. The long line extended aft into the trees where the bambi bucket came to rest.
Tests and Research
A postaccident engine inspection revealed no visual anomalies. The chip detector showed no debris. The engine oil filter contained some small debris but not enough to block it. The engine was test-cell run at various power settings with no noted mechanical failures or malfunctions.
The tail rotor gearbox input quill assembly, vertical driveshaft clamp, and two remaining gearbox attachment studs were sent to the NTSB Materials Laboratory for examination.
The NTSB Materials Lab reported that both studs exhibited fatigue cracks starting at the root of a thread on one side and extending across the bolt until meeting a smaller crack from the opposite side. The relative size and location indicated initial uniaxial bending fatigue followed by reverse bending fatigue. On one stud, the two fatigue cracks met along a parting line with no overstress region. The second stud had a rough region between the cracks indicative of final overstress fracture.
The input quill mounting flange showed helical rubbing marks around five of six stud holes and a lip of deformed material adjacent to the holes, indicating contact by studs.