N3276TBell UH-1H · 1941

On April 24, 2020, about 1600 mountain standard time, a Bell UH-1H helicopter, N3276T, was substantially damaged when it was involved in an accident in Mesa, Arizona. The pilot was fatally injured, and the second pilot was seriously injured. The helicopter operated as a Title 14 Code of Federal Regulations (CFR) Part 91 relocation flight.

The surviving pilot stated he does not recall the accident sequence. Witnesses reported they observed the helicopter flying low toward Falcon Field Airport (FFZ), Mesa, Arizona, with white smoke emitting from the tail rotor area. Suddenly, the tail rotor separated from the helicopter and landed in a dirt lot below. The helicopter continued northeast as it started to spin and impacted the ground.

The flight track indicated that the helicopter took off from Jacqueline Cochran Regional Airport (TRM), Palm Springs, California, about 1324 Pacific daylight time and turned eastbound seemingly along Interstate I-10 toward the Phoenix area. The flight track was intermittent due to the helicopter going in and out of coverage for about 2 hours before passing just north of Buckeye Municipal Airport (BXK) Buckeye, Arizona. The helicopter then turned right and tracked southeast for about 10 minutes and turned left traveling east over a mountain chain and continuing until reaching Stellar Airpark (P19), Chandler, Arizona. The helicopter performed one left hand 360° turn just west of the field before continuing across the airport and turning northeast directly toward FFZ. The helicopter continued along that heading until just before crossing Highway 60 when it began to simultaneously descend and lose ground speed. After crossing the highway, it entered a right descending turn until track data were lost about 1556.

According to aircraft records, the accident helicopter’s tail rotor gearbox (also known as the 90-degree gearbox) was removed from a different helicopter in September 2012 due to failing serviceability checks caused by metal accumulation. In November 2012, it was repaired by replacing the main input seal, painted, and installed onto the accident helicopter, about 228 flight hours prior to the accident. There was no other information regarding this installation.

In January 2019, the helicopter’s tail boom, upper portion of the vertical stabilizer, and elevators were painted. Photographs from this painting activity showed that the tail boom, tail rotor gearbox, and tail rotor assembly remained installed during the painting process. The tail rotor assembly and tail rotor gearbox were masked during the painting process. The fuselage and lower tail boom were painted a white color, and the upper portion of the tail boom was painted black. The vertical stabilizer was painted black on the upper and lower portions, with a blue stripe in the middle. The elevators were removed from the tail boom and painted separately; they were painted a blue color.

In April 2019, about 39 flight hours prior to the accident, the tail rotor gearbox was removed from the vertical stabilizer for a corrosion inspection; no defects were noted in the maintenance logs. The United States Army technical manuals, cited by the type certificate holder for maintenance of this helicopter, do not require a retorque and/or torque stabilization check of gearbox retaining nuts a certain number of flight hours after installation.

In December 2019, about 7 hours prior to the accident, oil was drained from the tail rotor gearbox due to discoloration and samples were sent for oil analysis. The oil analysis report indicated abnormal copper and aluminum wear particles within the tail rotor gearbox oil. While no corrective action was recommended at that time, a resample was recommended at the next service interval. The accident occurred before the next oil sample was taken.

According to aircraft records, the accident helicopter’s tail rotor gearbox (also known as the 90-degree gearbox) was removed from a different helicopter in September 2012 due to failing serviceability checks caused by metal accumulation. In November 2012, it was repaired by replacing the main input seal, painted, and installed onto the accident helicopter, about 228 flight hours prior to the accident. There was no other information regarding this installation.

In January 2019, the helicopter’s tail boom, upper portion of the vertical stabilizer, and elevators were painted. Photographs from this painting activity showed that the tail boom, tail rotor gearbox, and tail rotor assembly remained installed during the painting process. The tail rotor assembly and tail rotor gearbox were masked during the painting process. The fuselage and lower tail boom were painted a white color, and the upper portion of the tail boom was painted black. The vertical stabilizer was painted black on the upper and lower portions, with a blue stripe in the middle. The elevators were removed from the tail boom and painted separately; they were painted a blue color.

In April 2019, about 39 flight hours prior to the accident, the tail rotor gearbox was removed from the vertical stabilizer for a corrosion inspection; no defects were noted in the maintenance logs. The United States Army technical manuals, cited by the type certificate holder for maintenance of this helicopter, do not require a retorque and/or torque stabilization check of gearbox retaining nuts a certain number of flight hours after installation.

In December 2019, about 7 hours prior to the accident, oil was drained from the tail rotor gearbox due to discoloration and samples were sent for oil analysis. The oil analysis report indicated abnormal copper and aluminum wear particles within the tail rotor gearbox oil. While no corrective action was recommended at that time, a resample was recommended at the next service interval. The accident occurred before the next oil sample was taken.

On scene examination by a Federal Aviation Administration inspector indicated that the debris field was about 1/2 mile long, extending along a generally northeast direction. The first identified pieces of debris were fragments of glass, which were consistent with a vertical stabilizer navigation light. About 200 yards further northeast were the tail rotor assembly and the input quill assembly. The rest of the helicopter came to rest about ½ mile further northeast in an open, slightly sloped field. The first pieces of debris in the field were the vertical stabilizer and a large portion of the right elevator. Next were two long and narrow ground strikes, consistent with main rotor blade strikes. Immediately following this area was the main wreckage; the helicopter came to rest slightly nose- and left-side low, along a heading of about 49°. The helicopter exhibited upward crushing throughout the cabin and fuselage, most extensively on the left side of the fuselage. The mast and the main transmission were displaced forward and to the left. The main rotor assembly was fracture separated and located about 20 yards northeast of the main wreckage; it was the last major piece of debris.

Postaccident examination of the helicopter’s engine did not reveal any anomalies that would have precluded normal operation. Flight control continuity was mostly established throughout the airframe; some areas were inaccessible due to airframe deformation. The tail boom had been removed for recovery purposes. The vertical stabilizer was fracture-separated, consistent with main rotor blade impact. The tail rotor gearbox was fracture-separated at the attachment studs, and four of the fractured attachment stud pieces were found loose within the vertical stabilizer. A fifth stud piece remained stuck in the vertical stabilizer support casting, and the nut end of the sixth stud piece was not located. The chip detector was removed from the tail rotor gearbox and metallic debris was present. The tail rotor assembly was mostly whole and intact. The linkages and tail rotor blades remained secured in place. The tail rotor blades were damaged at the leading edges near the blade tips and had multiple dents along the span of the blades.

The top of the vertical stabilizer, tail rotor assembly, tail rotor gearbox, input quill assembly, and mounting studs were all packaged and sent to the National Transportation Safety Board materials laboratory for further examination. Progressive crack growth was noted on the mounting studs within the tail rotor gearbox housing. The fracture surfaces were relatively rough, consistent with low-cycle fatigue or cyclic overstress crack growth under relatively high cyclic stresses. Additionally, multiple layers of primer, paint, and sealant were observed on the input quill assembly, including beige-tinted white paint on the flange clamping surface where it had mated to the vertical stabilizer. Beige-tinted white paint was also observed on the vertical stabilizer support casting where it had mated to the input quill as well as the washers for the tail rotor gearbox attachment hardware.

The United States Army Depot Maintenance Work Requirement No. 55-1560-127 contains instructions for painting the tail rotor gearbox. The instructions contain a step to “mask the top part of the outer flange of input quill sleeve and also the entire studs.”

Toxicology testing on the deceased pilot performed by NMS Labs at the request of the Maricopa County Medical Examiner identified oxycodone at 140 ng/ml and its psychoactive metabolite oxymorphone at 10 ng/ml in femoral blood.

Oxycodone is an opioid pain medication available by prescription as a Schedule II controlled substance (high potential for addiction and abuse). It is often sold as a combination product with acetaminophen (Tylenol) under the names Percocet, Roxicet, and Endocet. When sold as a solo drug, the most common name is Oxycontin. In all these forms, it carries a boxed warning about the potential for addiction, abuse, and misuse, and a specific warning that the drug, “may impair the mental or physical abilities needed to perform potentially hazardous activities such as driving a car or operating machinery. Warn patients not to drive or operate dangerous machinery unless they are tolerant to the effects of oxycodone and acetaminophen tables and know how they will react to the medication.” In novice users, usual drug levels where desired effects are likely but toxic effects are unlikely are between 13 and 99 ng/ml. However, with regular use, patients become tolerated to the effects and may appear to be functioning at much higher blood levels.

In 2013, a FAA hotline complaint was filed against the pilot. He was evaluated by an FAA consultant and diagnosed with cocaine and alcohol dependance, both in remission since November 11, 2014. In 2015, the pilot was evaluated and placed in the Human Intervention Motivational Study program to continue his recovery from alcohol and cocaine addiction. With continued evaluation and treatment, the pilot eventually obtained a special issuance first class medical certificate in December 2016. He remained in this program, which requires periodic evaluations and drug testing, until October 29, 2019. During the pilot’s last medical on December 16, 2019, he reported no other chronic conditions and only reported the use of sildenafil (Viagra).

On July 15, 2008, about 1530 mountain daylight time, a Bell UH-1H, N3276T, made a forced landing on sloped terrain after experiencing a loss of engine power in a forested area near Rock Springs, Wyoming. Leading Edge Aviation operated the helicopter under the provisions of 14 Code of Federal Regulations (CFR) Part 133 as a long-line operation. The certificated commercial pilot sustained minor injuries; the helicopter sustained substantial damage. The local flight departed from the accident area at 1330. Visual meteorological conditions prevailed, and a visual flight rules (VFR) company flight plan had been filed.

In a written report, the pilot stated that the helicopter was being used to reposition and set a seismic drill rig in a remote area utilizing a 100-foot-long line. The pilot had moved the drill approximately 100 yards uphill and set it down. The pilot reported that the drill was 1,700 pounds. He also indicated that the helicopter was in a stabilized hover about 100 feet over the drill when the event occurred. The driller notified the pilot that he did not like the drill location, and wanted it repositioned a couple of feet away. While initially beginning to lift the drill, the pilot reported that he added power and heard loud pops, followed by a series of compressor stalls. The pilot detached the cable and pointed the helicopter downhill, away from the drill and ground personnel. The pilot stated that the helicopter touched down on uneven terrain on the skids, which broke away. The helicopter rolled onto the left side, which caused substantial damage to the helicopter.

According to the ground witnesses, the pilot was relocating the drill when the driller noticed a "bad set on terrain," and signaled to the pilot to lift back up and reposition the drill. The rear legs lifted off the ground and then came back down, with the long line becoming slack. The witnesses looked up and saw that the helicopter was "listing," with a trail of fire, about 10 to 15 feet in length emanating from the rear of the engine. They also heard "knocking" noises as the helicopter continued to list, and then watched the helicopter descend and impact the ground.

The accident helicopter was a 1969 Bell UH-1H, serial number 69-15911, originally owned and operated by the United States Army. According to the helicopter maintenance logbook, the last 50-hour inspection was performed on July 14, 2008. Aircraft maintenance and flight records filled out for the day of the accident reported the airframe total time as 11,702.8 hours, with 5.9 hours flown on the day of the accident.

The helicopter was powered by a Honeywell T53-L-703 turboshaft engine, serial number LE-09126Z. A review of the engine logbooks revealed that the No. 1 bearing was originally installed in 1991, at an engine total time of 1,295.00 hours. The engine was then installed on a UH-1H and operated for a total time of 83 hours between September 2000 and July 2002. When the engine was removed it had a total time of 1,378.00 hours. The engine was then installed on another UH-1H and operated from October 2002 until March 2006. Recorded total time at the time of engine removal was 2,544.00 hours. The reason for removal was due to metal contamination and vibration; maintenance was performed in May 2006. Maintenance personnel indicated the source of the metal contamination was the No. 2 bearing, and the vibration was caused by the exhaust diffuser and bearing housing contact. In July of 2006, the engine was installed in the accident helicopter. At the time of the accident, the engine total time was 2,817.8 hours. The total time on the No. 1 bearing at the time of the accident was 1,522.8 hours.

During a visual examination of the engine at the owner's facilities, investigators noted no movement of the power turbine and small metal pieces were found in the exhaust. The compressor blades were damaged, as well as the inlet guide vane trailing edges. The engine was boxed and shipped to Honeywell facilities in Phoenix, Arizona, for further examination.

An engine inspection was performed by Honeywell personnel under the auspices of the Safety Board. Honeywell personnel reported metallic debris on the engine chip detector, and that fuel was present in the fuel line between the fuel control unit and the fuel flow divider; a sample was collected and submitted for material analysis. An oil sample was collected from the aft gearbox and submitted for analysis. There were no discrepancies noted with either the fuel sample or oil sample that were submitted for analysis (Honeywell's complete test analysis are attached as an appendix to this report).

During the external examination of the engine, Honeywell personnel noted oil in the exhaust duct of the engine. The fuel sensing lines remained attached with fuel present in the lines. They were not able to manually rotate the power turbine shaft, and with considerable effort they were able to manually rotate the high speed spool via the starter gear. The reduction gearbox was not disassembled; however, it was free to rotate with debris noted on the oil wetted surfaces. Black debris was also located on the lower most oil transfer tube screen of the planet gear shaft.

The accessory drive carrier assembly was intact and undamaged with all gears and bearings free to rotate. The inlet housing assembly was intact with some debris on the oil wetted surfaces. The power shaft bearing retainer assembly was also intact and undamaged. Honeywell personnel checked the No. 1 bearing oil supply nozzle, and verified that the passage was not blocked. Honeywell reported that the No. 1 ball bearing had failed and resulted in the loss of engine power. The degradation of the No. 1 bearing resulted in the inability to maintain axial position of the gas generator spool.

The damage to the impeller shroud showed that the high speed spool moved forward, which reduced the clearance between the impeller and the shroud until they made contact. The impeller wore through the shroud wall in two places. The holes in the shroud exposed the flow-path to ambient outside air, which compromised the compressor efficiency and overall engine performance.

According to Honeywell, the degradation of the No. 1 bearing along with the decreased engine performance, eventually led to a lower power condition and inability to maintain power turbine speed. Honeywell reported that pieces of bearing cage lying loose at bottom of the reduction gearbox cavity, and balls of the bearings were grouped to one side and smeared over.