History of Flight
On July 16, 2013, about 0955 mountain daylight time, a Tamarack UH-1H helicopter, registration N775AR, was substantially damaged after a loss of control and ground impact near Dove Creek, Colorado. The pilot, the sole occupant, was fatally injured. The helicopter was registered to BVDS Incorporated and operated by Billings Flying Service under 14 Code of Federal Regulations Part 133 during a seismic survey operation. Visual meteorological conditions prevailed for the local flight, which departed without a flight plan from a staging area near Dove Creek, Colorado, about 0953.
Ground witnesses at the survey location reported that the pilot flew inbound from the left seat, hoisting a basket load with a long line rope. The pilot overshot the intended drop site, and the basket load impacted the ground, followed immediately by the 150-foot long line falling straight down onto the basket load. At about the same time, the helicopter entered a right bank, then a left bank, and subsequently impacted the ground in a steep left bank.
Personnel Information
The pilot, age 27, held a commercial pilot certificate with airplane single and multiengine land, airplane instrument, and rotorcraft-helicopter ratings, as well as a flight instructor certificate with similar ratings and a mechanic airframe and power plant certificate. On June 24, 2013, the pilot was issued a Class 2 medical certificate with no restrictions. The pilot had logged over 5,000 hours total flight time, with over 1,800 hours in the make and model of the accident helicopter. In the seven days prior to the accident, the pilot had flown the accident helicopter about 15 flight hours.
Aircraft Information
The helicopter, originally manufactured in 1965 by Bell Helicopter, Inc., was equipped with a Lycoming T53-L-13B engine, composite main rotor blades, and BLR Aerodynamic Solutions Tailboom Strakes and Fast Fin System. The FAA issued a restricted type certificate to Tamarack Helicopters, Inc., authorizing agricultural, forest/wildlife, and external load operations, and certified the helicopter to be flown from the left seat. Following extensive maintenance and refurbishment by Billings Flying Service, the helicopter was released for maintenance test flights on June 5, 2013. At the time of the accident, the helicopter had flown a total of 14,798 hours, including 41 hours after completion of the refurbishment.
The helicopter was operating about 700 pounds below performance limit capability for a 50-foot out-of-ground-effect (OGE) hover. The basic helicopter weight was 5,240 lbs; total weight was about 8,000 lbs, based on an estimated 2,000 lbs basket load, 500 lbs fuel, 180 lbs pilot, and 80 lbs tools and personal gear. The FAA-approved operator manual supplement hover chart indicated a maximum weight of about 8,700 lbs for a 50-foot OGE hover.
Meteorological Information
The weather observation station at Cortez Municipal Airport (KCEZ), about 21 miles south of the accident site, reported at 0953: wind 300 degrees at 4 knots, visibility 10 miles, overcast clouds at 8,500 feet, temperature 21°C, dew point 12°C, altimeter 30.25. Density altitude at the accident site was about 9,500 feet, based on an elevation of 7,630 feet and a standard temperature lapse rate from KCEZ.
Wreckage and Impact Information
The helicopter impacted into relatively flat, bush-covered terrain and came to rest on its left side. The main fuselage had significant crushing to the nose and left side. The skids exhibited bending to the left forward crosstube, consistent with a left bank nose-down attitude at impact.
Both composite main rotor blades were attached to the hub with blade bolts and drag braces; each blade showed damage consistent with ground contact while rotating. The main rotor hub was intact except that the pitch horn from one blade had separated from its grip, consistent with impact forces. The mast remained attached to the hub and transmission. The main transmission chip detector had no debris. No pre-impact anomalies were observed with the main rotor hub, blades, or mast.
The flight controls and hydraulics system exhibited extensive impact damage. The helicopter had dual flight controls; the pilot was flying from the left seat, with instrumentation on the left pilot door for external load operations. The pilot's cyclic and collective sticks exhibited overload fractures near their mountings. Rotating controls had continuity to the stabilizer bar and each pitch change link and pitch horn. The hydraulic pump was removed from the drive quill; the splined driveshaft was intact and rotated with minimal resistance.
Engine examination revealed compressor shroud metal spray on the aft side of the 2nd stage power turbine, consistent with operation at impact. Evidence of engine rotation included rotational scoring and tearing on the particle separator housing and first stage axial compressor blades that were either broken or showed rotational scoring and leading edge damage.
A follow-on airframe examination at the salvage location found the left and right hydraulic servos intact with frame mounts exhibiting overload fractures. Many hydraulic lines were fractured due to overload. No chafed hydraulic lines were observed. The hydraulic switch was in the ON position; this switch is located on the far right side of the center pedestal, out of immediate reach for a pilot flying from the left seat.
Light bulb filaments from the cockpit annunciator panel were examined for filament stretch. The hydraulic pressure annunciator light and the auxiliary master caution light had stretched filaments, confirmed by Bell Helicopter engineering laboratory. Other filaments were not stretched.
Several hydraulic fluid drips were observed on lines. A hydraulic check valve near the tail rotor control actuator servo could be rotated by hand between solid lines and fittings; it was intact and connected to undistorted walls in the aft belly compartment. In that compartment, several rags were found soaked with hydraulic oil.
The external cargo hook responded to electrical and mechanical release commands. The cargo hook electrical switch and manual release could not be tested due to damage.
Medical and Pathological Information
An autopsy on July 27, 2013, attributed the cause of death to blunt force injuries. The FAA's Civil Aeromedical Institute performed toxicology tests; no carbon monoxide, ethanol, or drugs were detected. The pilot wore a headset, not a helmet. The left seat was equipped with a seat belt and shoulder harness. The seat belt right side attachment fitting was fractured. The shoulder harness was not connected to the seat belt, and the straps were not restrained within the guide at the top of the seat.
Tests and Research
Hydraulic system components were examined and tested at the Bell Helicopter engineering laboratory. Bench testing revealed that the right cyclic, left cyclic, and collective hydraulic servos operated normally and did not exhibit evidence that would preclude normal operation prior to the accident. Testing of the hydraulic control panel, filter, and pump revealed no anomalies or leakage. Of the various fixed lines and flexible hoses tested, leakages were observed in two components: a hydraulic return line near the transmission, and a hydraulic check valve/pressure line to the tail rotor control actuator servo near bulkhead station 211.
The hydraulic return line near the transmission had 45-degree shear laps in the flareless fitting due to removed tubing material that allowed the sleeve to lap over itself during tightening. It could not be determined if ground impact opened one of the sleeve laps, or if a noticeable 10-degree bend in the tube adjacent to the leak was impact-related.
The hydraulic check valve exhibited longitudinal cracks at both threaded ends, a result of stress corrosion cracking, as evidenced by intergranular features, crack branching, and corrosion. No material discrepancies were noted. Evidence of Teflon tape was present at the outlet end of the threads. Teflon tape is commonly used in plumbing to seal threads but is not an approved material for use with the hydraulic system.
The hydraulic line containing the check valve near the tail rotor servo was pressure tested. The check valve exhibited a leak rate of about 100 cc per minute at both 850 psig and 1,000 psig. At 1,000 psig, when the line was slightly cocked, the valve exhibited a leakage rate of about 300 cc in 45 seconds. The hydraulic system has a total capacity of about 8 pints, with the reservoir capacity about 5.3 pints (one pint equals about 473 cc).
Test Flight Information
In July 1988, US Army Aviation Engineering Flight Activity completed an airworthiness and flight characteristics evaluation report for the UH-1H with composite main rotor blades (CMRB). The report concluded: "Hydraulic system failure characteristics were qualitatively and quantitatively evaluated … during approaches to running landings. A slight nose-down pitching moment upon failure was controlled by an approximate 15 pound aft longitudinal force. Increased right lateral control forces coupled with the onset of some control feedback required moderate pilot compensation to prevent pilot-induced oscillation (PIO) tendencies, causing an increase in control activity." The report also stated: "The hydraulic system failure characteristics of the UH-1H helicopter with the hub spring and CMRB installed are acceptable; however, high altitude operations could be compromised due to the high collective control force encountered without hydraulics assist, thereby restricting control travel."
Following the accident, without FAA or NTSB awareness, two pilots from Billings Flying Service conducted an informal UH-1H flight test at high altitude. The flying pilot notified the NTSB of his findings during an interview. During a simulated long line profile with the hydraulics system turned off, the flying pilot observed a high amount of force was required to apply collective. While making a "hard pull" of the collective with his left arm, the pilot observed that he had a tendency to "brace" himself and push the cyclic to the right, causing a right bank. This tendency to bank right was not immediately recognized, since he was leaning left to simulate sighting for a long line operation. As he attempted to return to a level attitude, he overcorrected and entered into nearly 90 degrees of left bank. The pilot was very startled and immediately directed the other pilot in the right seat to restore hydraulics system pressure to assist with recovery.
Maintenance Information
The helicopter mechanic stated that hydraulic leaks had been a long-term challenge with the accident helicopter and that most of the hydraulic lines had been replaced as the helicopter was rebuilt and brought up to certification standards. While deployed to the Dove Creek location, a hydraulic line had been replaced six days prior to the accident due to a leak near the transmission filter.
The mechanic, director of maintenance, and accident pilot were aware of a slow, "weeping" hydraulic leak in the aft belly of the fuselage but did not foresee it causing a significant issue. Replacement components for the hydraulic system near the leak, including lines, fittings, and a check valve, had been requested from home station and were expected to arrive within days of the accident. Information concerning this leak was not entered into the maintenance records.
On the day prior to the accident, the pilot told the mechanic that the cyclic appeared "notchy," as if it would "bump" a little during movement. The pilot thought it might be associated with winds. The mechanic inspected for loose hardware, the main rotor hub, main rotor dampeners, and pitch change linkages near the swashplate, and observed no anomalies.
The mechanic stated that he added one or two cups of hydraulic fluid to the reservoir within a day or two of the accident. On the morning of the accident, the mechanic noticed the check valve fitting was not tight. He tightened several fittings in the surrounding area, used Teflon tape in an attempt to help the check valve fittings 'grab' more effectively, and used rags to soak up hydraulic fluid in the aft belly.
Additional Information
Billings Flying Service personnel described the operating environment at the Dove Creek survey location as 'tense'. About three days prior to the accident, an owner of Billings Flying Service terminated a contract pilot after the accident pilot informed the owner of this pilot's aggressive flying at the location. Following the termination, the accident pilot informed the owner that survey personnel were dissatisfied with losing the other pilot and blamed the accident pilot for the termination. According to the owner and mechanic, survey personnel had 'timed' how long the accident pilot was taking to perform long line operations. A survey supervisor had informed the owner that the accident pilot was taking "50% longer" than the terminated pilot. The owner stated that the accident pilot was very concerned with losing the survey contract and told him the work environment felt hostile. The mechanic stated that he also felt pressure to ensure flights were completed. The director of maintenance stated that the accident pilot and mechanic were concerned that any "maintenance down time" would result in a contract penalty.