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On May 11, 2001, approximately 0922 Pacific daylight time, a Robinson R44, N111PH, registered to a private individual and operated by Classic Helicopter Corp., as a 14 CFR Part 91 instructional flight, experienced an in-flight breakup while maneuvering about three miles south of Gorst, Washington. Visual meteorological conditions prevailed at the time and no flight plan was filed. The helicopter was destroyed by impact damage and post-crash fire. Both the flight instructor and private pilot were fatally injured. The flight originated from Boeing Field, Seattle, Washington, about 15 minutes prior to the accident.
Most witnesses were at various locations on the Trophy Lake Golf Course located about one-quarter to one-half mile away. One witness reported that he heard a sound and glanced up to see the helicopter initially traveling toward the golf course, then looked as if forward flight stopped before it made "some radical flight maneuvers." The witness described a sound difference with the main rotors before it lost 75 to 100 feet in altitude. The helicopter then made a "radical snap roll" maneuver before beginning a "cork-screw" dive. Prior to impact, the witness noticed that at about 200 to 250 feet above ground level, the tail rotors separated followed by the tail section separation at about 100 to 150 feet AGL. The witness then lost sight of the helicopter in the trees. Shortly thereafter, the witness heard an explosion and observed smoke. One other witness reported similar circumstances.
Several other witnesses reported hearing a "loud bang," "popping," "coughing," or "rough running" engine noise which brought their attention to the helicopter. Each of the witnesses reported observing the helicopter in a "nose down" or "wobbling" attitude while it spun, nose left, to ground impact. Prior to ground impact, the witnesses observed an object or objects separating from the helicopter.
Personnel at Classic Helicopter reported that the flight instructor was also the Director of Operations for Classic Helicopter. The instructor held flight certificates for commercial and flight instructor instrument operations, and rated in rotorcraft. The flight instructors total flight time in all helicopters was estimated as 11,200 hours, with 252 hours in the make and model helicopter involved in the accident. The instructor held a Class II medical certificate dated 1/31/01, with a limitation to wear corrective lenses. The week prior to the accident, the instructor flew 1.6 hours in a Bell 206, 1.3 hours in a Robinson R22, and 6 hours in another Robinson R44 operated by Classic Helicopter.
The second pilot, seated in the right seat, was receiving instruction and building flight time in preparation for the purchase of his own Robinson R44. At the time of the accident, the second pilot held a private pilot certificate for single-engine land aircraft and helicopter operations. The pilot's total flight time was estimated as 451 hours, with 386 hours in rotorcraft and 65 hours in fixed wing aircraft. The pilot had accumulated 6.5 hours of the company required 10 hours of dual flight time in the R44. The pilot held a Class III medical certificate dated 10/24/00, with a limitation to wear corrective lenses. The last flight logged in the pilot's flight logbook, prior to the accident flight, was on April 26, 2001, in the R44.
The helicopter was manufactured by Robinson Helicopter, Torrance, California, and signed off as meeting the requirements for the certification requested and issued a Standard Airworthiness Certificate dated January 12, 2001, at a total flight time of five hours, and serial number 0972. The helicopter was picked up on January 13, 2001, by the registered owner and accompanied by the flight instructor who was involved in the accident. The helicopter was flown to Boeing Field, arriving on January 15, 2001. The helicopter was maintained and operated by Classic Helicopter for the purposes of rental and instructional flights.
Maintenance records indicated that the helicopter was being maintained in accordance with a 100 hour inspection program. The one and only 100 hour inspection was accomplished on April 4, 2001, at a total flight time of 103.9 hours. The helicopter accumulated a total flight time of approximately 131 hours at the time of the accident.
Air Traffic Control communications obtained from Boeing Field tower indicated that at 0906, the pilot requested departure from pad 1 for a "west steam plant departure." The tower controller approved the departure as requested. There were no other recorded communications from the flight prior to the accident.
Personnel at Classic Helicopter reported that the steam plant departure is for helicopters departing from pad 1 in front of the Classic Helicopter facility. The helicopter fly’s below 100 feet until after crossing the extended runway center line, then climb as necessary.
WRECKAGE AND IMPACT INFORMATION
NTSB personnel arrived at the accident site on May 11, 2001, about 1230. The wreckage was located in an area that was heavily wooded with trees varying in height up to about 100 feet. The relatively level ground was covered with thick underbrush. Accident site coordinates were obtained via a hand held GPS at N47 degrees 28.639' W122 degrees 42.087', and an elevation of approximately 440 feet mean sea level. The surrounding area was sparsely populated with residential housing. South of the accident site about 1/4 to 1/2 miles is the Trophy Lakes Golf Course. A resident with an open horse pasture was to the south, and one of the two Nels Johnson Lakes was about 200 feet north of the main wreckage.
The main wreckage consisting of the fuselage and inboard section of the tail boom, minus the empennage section, were located at the base of an approximate 100 foot tree. About 30 feet up from the base of the tree, an approximate 60 degree deep slash mark (as measured from horizontal) was located, with additional damage to the trunk about 15 feet below. A post-crash fire consumed the cockpit area. The fuselage was positioned with its nose oriented about 320 degrees magnetic. The fuselage was laying on its left side. A 10.5 foot section of the tail boom remained in its respective position to the airframe. The tail rotor drive shaft was pulled partially out of the boom structure. One main rotor blade remained attached to the hub. The blade was severely bowed and displayed heat distress. The other main rotor blade separated. About 20 inches of the blade remained attached to the hub. The engine remained in place and displayed severe heat distress.
A search of the surrounding area located several pieces of the main rotor blades up to and in excess of about 180 feet to the south of the main wreckage. Both tail rotor blades had separated from the tail rotor hub. Damage was consistent with the pitch change link being in place at impact. One blade was found in close proximity to the main wreckage. The other blade had been removed by one of the witnesses, and then later retrieved by NTSB personnel. The witness reported its approximate location which was about 80 feet south of the main wreckage.
The empennage section with the upper and lower vertical stabilizer and the horizontal stabilizer attached was located about 180 feet south of the main wreckage. A 22 inch section of the aft tail boom with the tail rotor drive shaft contained within the structure remained attached. The separated end of the drive shaft was severely twisted. The skin at the separation point was severely deformed and appeared torn. The tail rotor gear box driving gear remained, however, the tail rotor assembly had separated. No leading edge damage was noted to the stabilizers. Slight wrinkling to the skin on the right side of the upper vertical stabilizer was noted. An impact dent was located on the left side of the lower vertical stabilizer just below the root.
The tail rotor assembly was located about a week after the accident with the assistance of several volunteers from the local rotorcraft association and Classic Helicopter. The tail rotor gearbox and shaft were located about 130 feet southwest of the main wreckage. The tail rotor hub had separated from the shaft and was found about 160 feet southwest of the main wreckage. Sections of the tail rotor guard were also found in this area.
The wreckage was recovered from the accident site on May 12, 2001, and transported to a secured facility on Boeing Field. The tail rotor assembly and miscellaneous items were located on May 19, 2001, and transported to Boeing Field. A reconstruction of the structure and engine inspection were performed at this facility.
In the presence of and assisted by the NTSB investigator-in-charge, the Robinson participants reconstructed the wreckage components in their respective locations to further document and verify continuity. Prior to recovery from the accident site, documentation was also performed but somewhat limited due to accessibility of certain components by the wreckage. Excerpts from the Robinson party written report is attached.
Documentation at the accident site confirmed that the cockpit and cabin were destroyed by impact damage and post-crash fire. The tail rotor pedals were found in an approximate neutral position. The majority of the fuel system was destroyed by fire. The throttle was close to the full off position.
The flight controls were reconstructed at the secured hangar. Many of the push pull tubes were destroyed by the fire. The identifiable components were identified with the aid of the applicable section from the Illustrated Parts Catalog (IPC) (see attached). During the reconstruction, there was no evidence found to indicate a pre-impact failure of the flight control system.
The driveline inspection revealed that the drive belts were burned. A small portion of the burned belt material was found around and in the sheave grooves. Impact and fire damage was noted throughout the system. The main rotor gearbox and mast assembly displayed heat distress and impact damage. The main rotor shaft appeared straight. The elastomeric teeter stops were both fire damaged, but in place. The main rotor droop stop tusks were both intact and bent downward slightly. Both stops were intact and in place. The main rotor pitch change bearing housing for one of the main rotor blades was found coned up against the main rotor hub surface. This blade had separated about two feet from the main rotor shaft. On the outboard portion of the blade, only the spar was intact for the outboard 2/3 of the blade. The spar exhibited an upward bend. The second blade exhibited a downward bend about 1/2 way along the span.
MEDICAL AND PATHOLOGICAL INFORMATION
An autopsy was performed on both pilots at the Kitsap County Morgue, Port Orchard, Washington. The Forensic Pathologist reported that the cause of death to both pilots was due to multiple blunt force injuries.
Toxicological samples were sent to the Federal Aviation Administration Civil Aeromedical Institute, Oklahoma City, Oklahoma for analysis.
The right seat pilot tested negative for carbon monoxide, cyanide, ethanol and drugs.
The flight instructor seated in the left seat tested positive for Chlorpheniramine in the blood and urine, Diphenhydramine in the blood and urine, Ephedrine in the blood and urine, Pseudoephedrine in the blood and urine, Phenylpropanolamine in the urine and Acetaminophen in the urine.
The National Transportation Safety Board Medical Officer reviewed the autopsy and toxicology findings and reported that Chlorpheniramine is a sedating antihistamine, commonly used in over-the-counter cold/allergy preparations. In therapeutic doses, the medication commonly results in drowsiness, and has a measurable effect on performance of complex cognitive and motor tasks. The amounts reported (0.02 ug/ml, ug/g) indicate that a normal dose of the drug had been used within the previous two to three hours.
Diphenhydramine (commonly known by the trade name Benadryl) is also a sedating antihistamine. Relatively low doses were detected in the pilot's blood indicating ingestion of a normal dose within the prior 12 hours. Its effects are similar to Chlorpheniramine. Diphenhydramine and Chlorpheniramine are not found together in any preparations.
Ephedrine is sold (as a component of "ephedra" or "Ma-Huang") as a stimulant, weight loss product, or decongestant in many nutritional supplements, and as an asthma medication available over-the-counter. It does not usually result in impairment and has a stimulant effect.
Pseudoephedrine is a common decongestant with a trade name Sudafed that is found in many over-the-counter cold and allergy preparations. It is also a component of "ephedra" and "Ma-Huang." Pseudoephedrine does not usually result in impairment.
Phenylpropanolamine is an over-the-counter decongestant. It is also a metabolite of ephedrine and Pseudoephedrine and does not usually result in impairment and has stimulant effects.
Pseudoephedrine, ephedrine, and Phenylpropanolamine are often utilized specifically for their stimulant effects.
Acetaminophen is an over-the-counter pain-reliever and fever-reducer, often known by the trade name Tylenol. It would not generally be expected to result in impairment.
The Medical Officer reported that the combination of medication detected in the pilot's blood and urine indicated that at least two and likely three different preparations were used to treat upper respiratory symptoms.
TESTS AND RESEARCH
On May 14, 2001, the engine was inspected at Boeing Field. The engine, a Lycoming O-540-F1B5, had accumulated a total time of approximately 131 hours since new. The engine had been exposed to severe heat distress. Both magnetos to include the ignition harness were melted and destroyed. The remainder of the accessories were also destroyed by fire damage. All six cylinders and accessories were removed. Once removed, the crankshaft and camshaft were free to rotate by hand. The cylinders appeared low time and the intake and exhaust valves were in place. The spark plugs were removed and all displayed normal operating signatures. The spin-on oil filter displayed heat distress. The filter was cut open and the paper filter element was fire damaged.
Several components of the aft end of the tail boom were sent to the National Transportation Safety Board Materials Lab, Washington D.C. for examination. The components consisted of four pieces of the aft end of the tail boom with attached aft end of the tail rotor drive shaft, a separate tail rotor drive shaft piece, tail rotor gearbox with attached output shaft and pitch control assembly, tail rotor hub with attached root ends of tail rotor blades, both tail rotor blades, three pieces of the aft end of the tail rotor pitch control rod, two pieces of the tail rotor guard and four miscellaneous skin pieces. The materials engineer reconstructed the components in their respective locations and documented the damage (see attached Materials Laboratory Factual Report). The engineer reported that the four pieces of the tail boom labeled A through D indicated that the fracture surfaces were rough and at a slant angle relative to the outer surface, and displayed features consistent with overstress fracture. Piece B identified sliding marks on the upper side consistent with contact with a main rotor blade moving counterclockwise relative to the tail boom. Additional sliding marks were observed on the exterior of the tail boom from the forward fracture surface aft to tail station (TS) 146.00. Similar sliding marks were also observed on a portion of the interior near the upper fracture surface. Vertical sliding marks were observed on the left side of piece B near the aft fracture, approximately 25.75 inches forward of the tail rotor gearbox mounting surface. The engineer reported that the location and direction of these marks were consistent with tail rotor blade contact. Calculations obtained from the manufacturer indicated that, "with blades held rigid and straight and allowed to teeter beyond their normal stops, the tips of the main rotor blades would contact the upper surface of the tail boom at a location 3.325 inches forward of TS 146.00. The tips of the tail rotor blades would contact the left side of the tail boom at a location 25.724 inches forward of the tail rotor gearbox mounting surface." Sliding marks were also located on piece D located from 20 inches to 24 inches forward of the tail rotor gearbox mounting surface. The tail rotor skin was also dented and fractured in this area.
The tail rotor gearbox attachment bolts were fractured consistent with overstress shear fracture. Sliding contact marks were observed on lower and right sides of the interior of the gearbox housing. These marks were consistent with contact with gear teeth at the aft end of the tail boom. The tail rotor output shaft was bent into an "S" shape. The threaded end of the shaft was fractured consistent with overstress fracture in shear. The hardness and diameter of the shaft measured within design specifications. The pitch change control assembly shaft was fractured consistent with overstress. Contact marks were observed on the pitch change control assembly consistent with contact with the tail rotor hub. The piece of the pitch change control assembly that connected the shaft to the pitch change links was missing. One pitch change link was missing. The other was bent and fractured consistent with overstress.
The tail rotor drive shaft pieces were twisted consistent with overstress fracture in torsion. The features were consistent with normal shaft rotation driven clockwise.
The fracture surfaces of the tail rotor pitch change control rod were rough and at a slant angle relative to the outer surface, features typical of overstress fracture. The rod end fitting was fractured in the threads, and the fracture surface was rough and matte gray with deformation of the threaded region, features consistent with overstress fracture in bending.
The tail rotor hub fracture surfaces were consistent with overstress fracture. The tail rotor blades were labeled "1" and "2". The two bolts connecting blade "1" to the hub were fractured consistent with overstress fracture in shear. Sliding damage was observed on the inboard surface of the hub adjacent to the bolts.
The outboard side of the hub identified a rubbery material on the outboard surface at locations approximately perpendicular to the teeter axis. Inside the hole at the hub axis, a contact mark was observed on the inner surface. The mark was consistent with contact with a thin circular component such as the washer retaining the tail rotor teeter stop bumper. The polymer material found on the outboard hub surface and the washer mark inside the hub axis hole is consistent with the teeter stop being installed at the time of impact.
The tail rotor blades were fractured about 11 inches and 12 inches from the hub center. The deformation of the blades adjacent to the fractures was consistent with the tip piece rotating relative to the root piece. The inboard faces of the blades were wrinkled and deformed with some sliding marks and transferred red paint. The fractured and bent pitch change link was attached to blade "1", and the missing pitch change link was for blade "2". The fracture surface for the bolt that connected the missing pitch change link was smeared consistent with overstress fracture in shear. The outboard side of the pitch change link arm on blade "2" had tension cracks in the paint perpendicular to the length of the arm, and the inboard side was damaged consistent with contact with the tail rotor hub. Damage was consistent with the pitch change link being in place at impact.
The fractures surfaces of the tail rotor guard were consistent with overstress separation. Miscellaneous skin pieces displayed features consistent with overstress fracture.
Radar data provided by Seattle TRACON in Continuous Data Recording (CDR) format was provided for review. The data was submitted to NTSB Office of Research and Engineering, Washington DC for study. The attached Radar Study displays the ground track, altitude and time profile, vertical speed and ground speed profile, and rate of turn profile.
The radar tracking beginning at 0915:23 to 0917:55 indicated the helicopter flying at an altitude of 1,300 to 1,400 feet mean sea level (MSL) at an airspeed of between 114 to 121 knots, traveling in a southerly direction. The helicopter then rapidly descends at 2,700 feet per minute and about 103 knots and drops off radar coverage for 33 seconds. At 0918:51, the helicopter then climbs back up to about 1,300 to 1,500 feet, at an airspeed increasing from 64 knots to about 100 knots. The radar tracking indicated a climbing right turn to a northerly direction, then a left turn to the west, continuing to the south at 1,500 feet msl and about 90 knots. The last radar target indicated the helicopter at 0921:28 at 1,500 feet and about 90 knots.
After the wreckage was moved to the Robinson Helicopter Company, further examination by the manufacturer of the tail rotor blades indicated that "the TR (tail rotor) blades had contacted the tailboom with the blades at the full left-pedal pitch. The blade pitch angle was established by the scoring lines on the tip caps of both blades (photos A,B,C,D), which was consistent with the TR control having full left pedal applied when the blades contacted the tailboom. This was further evident by the heavy scoring on the leading edges of the blade tips with only minimum scoring on the trailing edges (photos D,E,F). Had right pedal been applied the trailing edges would have contacted the tailboom first and would have had more scoring."
On August 1, 2001, Robinson Helicopter Company issued Service Bulletin SB-41, Tail Rotor Rigging. This SB affected R44 helicopter serial numbers 0001 thru 1102 and was to be complied with within the next 25 flight hours or by September 15, 2001. The SB reported that, "Inadvertent abrupt application of full left pedal by the student during a simulated power failure could result in excessive flapping of the tail rotor and possible tail rotor blade contact with the tail boom. To reduce the possibility of that occurring, Safety Notice SN-27 Surprise Power Chops Can Be Deadly has been reissued as a Safety Alert. In addition, this Service Bulletin requires re-rigging the tail rotor to reduce maximum blade angle at the left pedal stop and also requires installation of a harder teeter bumper."
The compliance procedure required the adjustment of the push-pull tube assembly to change the full left pedal mean tail rotor blade angle from 21.5 degrees - 22.0 degrees to 16.5 degrees - 17.0 degrees.
Several components were retained by the NTSB for further examination. Those components not retained were released to the President of Classic Helicopter on May 24, 2001. The wreckage was then moved to Robinson Helicopter Company, Torrance, California. On August 29, 2001, the NTSB was informed by a representative of Pathfinder Indemnity Company, Ltd, Fullerton, California, that Pathfinder Indemnity Company, Ltd., had paid its insured in-full for the loss of N111PH, and was the owner and legal custodian of the aircraft and components thereof. The retained components were sent to Robinson Helicopter Company Technical Investigator on November 29, 2001.