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On March 19, 2000, at 1545 Pacific standard time, a Bell 212 helicopter, N415B, was destroyed after impacting terrain following a loss of control while in cruise flight near Snelling, California. The commercial pilot, who was the sole occupant, received fatal injuries. The aircraft was being operated as a positioning flight by Aviation International Rotors (A.I.R.), Inc., Apple Valley, California, under 14 CFR Part 91 when the accident occurred. The flight originated from Fresno, California, at 1515, and was destined for Sacramento, California. Visual meteorological conditions prevailed at the time and a company visual flight rules (VFR) flight plan had been filed.
The accident helicopter was second in a flight of two en route to Sacramento. Both helicopters departed Apple Valley, made fuel stops in Bakersfield, California, and Fresno before continuing on to their final destination of Sacramento. The lead pilot reported that they were cruising about 800 feet mean sea level (msl), or 400 to 500 feet above ground level (agl), over rolling terrain. The pilot estimated that the accident aircraft was echelon right, and about eight rotor disks to the rear, with cruise airspeed of about 100 knots. Both aircraft were on a common air-to-air frequency and had been communicating previously with no reported difficulties.
As the flight neared the Snelling Highway northeast of Merced, the lead pilot called the accident pilot, asking about his fuel consumption rate. When he did not receive a reply, he turned his helicopter 180 degrees to look for the other helicopter. As he did, he saw a column of black smoke. He flew toward the smoke, and as he neared, he realized the second helicopter had crashed and was nearly engulfed with flames.
He immediately landed his helicopter, deplaned, and approached the burning wreckage to aid the pilot, but was driven back by the heat and flames. Realizing that there was nothing further he could do, he got back into his helicopter and flew to Castle Airport (located in Atwater, California, approximately 11 miles southwest of the accident site), where he reported the accident to authorities and the operator.
The lead pilot reported he had an encounter with a large bird about a mile back along the flight path from the accident site.
The non-instrument rated commercial helicopter pilot had accumulated 6,200 total flight hours, of which approximately 500 hours were in the same make and model as the accident helicopter. He obtained a second-class medical certificate, which was issued on May 11, 1999, with a limitation for corrective lenses, and a waiver for blood pressure.
The pilot underwent surgery in December 1999, to adjust for flat feet. As a result of the surgery, the pilot wore a cast on his right lower leg that extended from just below his knee to his toes.
The pilot did not fly after the surgery until the day of the accident. He received a check-out flight from the pilot of the lead helicopter before they departed on their trip. The purpose of the flight was to see if the cast would inhibit the pilot's ability to fly the helicopter. According to the chief pilot, both the lead and accident pilots determined that the accident pilot would be able to fly.
According to the lead pilot, the accident pilot was mentally ready and excited to fly. The accident pilot assured the lead pilot that his personal doctor had released him to work and he was ready to fly. The check-out flight lasted less than 30 minutes and included operations in the traffic pattern. He reported noting no problems with the accident pilot's ability to fly the helicopter.
The twin-engine helicopter (serial number 30613) was powered by two Pratt & Whitney PT-6-3 engines. The helicopter's main rotor group included a two-blade, semi-rigid type rotor, and a stabilizer bar with dampers. The rotor hub yoke was underslung on its mounting trunnion through two pillow blocks, which provided a flapping axis. The all metal blades were attached through grips, which rotated on yoke spindles to change blade pitch. The helicopter's paint scheme (from the skid crossover tubes to the transmission/engine area) consisted of horizontal bands of red, blue, white, blue, and white.
Review of helicopter maintenance records revealed that the helicopter underwent its last annual inspection on March 15, 2000, at an airframe total time of 15,184.8 hours. According to the maintenance log, the following work was conducted during the annual inspection:
Inspection of Hangar Assemblies
Overhaul of Tail Rotor Hub Assembly
Overhaul Main Drive Shaft
Overhaul Pylon Assembly
Main Rotor Head Strap Change
Overhaul Main Transmission
At the time of the annual inspection, one of the two blades (the white blade, P/N 212015501-115, S/N A-2991) was removed for rework and repair. The total time on the blade since manufacture was 1,861 hours. The Historical Service Record for the blade indicated that on December 20, 1999, it underwent the following actions: "Inspected I.A.W. [in accordance with] 204-099-223 vol. XI, repaired the lower surface skin at station 70 to 74.5 per IAC-8110-0386, repaired the upper and lower surfaces spar doublers at the tip, installed a full chord skin repair on the upper and lower surface at the tip, replaced the abrasion strip, replaced the inboard leading edge splice cover, replaced the forward tip cap, replaced the main attachment bushing, refinished the paint and static balanced per BHT [Bell Helicopter Textron] spec[ifications]." The blade had accumulated 8.3 hours at the time of the accident since its reinstallation.
A mechanic flew with the accident pilot on the Apple Valley to Bakersfield, and Bakersfield to Fresno legs of the flight. According to the mechanic's written statement, he performed the daily preflight inspections along with the pilot on the morning of the accident. The pilot requested approximately 2 cups of oil in the combined gearbox, to which the mechanic complied and added the oil. The mechanic reported they departed for the first leg of flight and during the takeoff climb, the accident pilot radioed the lead pilot alerting him of a torque split of approximately 30 percent. The lead pilot asked if the accident pilot had verified the number 2 throttle was "full open with friction?" The accident pilot responded that he would verify. The mechanic added the lead pilot was correct and the engine torque indications were then "matched perfectly," and they continued to Bakersfield. The mechanic reported the remainder of the flight to Bakersfield, and the flight to Fresno, were uneventful, and the pilot flew "perfectly."
According to the lead pilot, the weather at the time of the accident was described as unlimited visibility, with clear skies, and wind from 330 degrees at 20 knots gusting to 30 knots.
WRECKAGE AND IMPACT INFORMATION
Merced county sheriff's deputies reported when rescue personnel reached the scene, about 2 hours after the crash, the fire had burned itself out. The debris path extended along the approximate route of flight on a bearing of about 300 degrees covering a distance of nearly 1,000 feet. The main wreckage came to rest at 37 degrees 29.182 minutes north latitude and 120 degrees 21.038 west longitude.
One of the first pieces of debris found was a nearly 12-foot section of the honeycomb airfoil from the white blade. Its separation from the blade began outboard of the doublers, ran along the leading edge D-spar, and continued to within about 2 feet of the tip. The skin on the separated upper surface of the blade was rolled back toward the trailing edge. The outboard 2 feet of blade, excluding the leading edge spar, was located further along the debris path, but forward of the main wreckage.
The left skid and left step, with a corresponding ground scar were found early in the debris field (approximately 456 feet prior to the main wreckage area), as were sections of the left cabin and pilot doors, and a section of the nose compartment access door (battery door).
The main rotor hub, with the remaining portion of both blades, was found about 400 feet beyond the main wreckage, and was the last item found in the debris field.
The main fuselage showed evidence of multiple separations on the left side of the aircraft that began near the nose, ran through the floor, extending aft to the engine cowlings. The fuselage showed no evidence of sliding after ground contact. The majority of the fuselage structure sustained severe fire damage. The entire cockpit and cabin surrounding structure was destroyed. The instrument panel, and the left and right seat were in place; however, the left seat sustained substantial deformation in the down direction. The left side collective and cyclic controls were destroyed. The right seat remained intact; however, the seat cushion and cover were destroyed by the fire. The right seat cyclic and collective controls were in place; however, the top portion of the cyclic control was separated and burned. The instrument panel sustained deformation and heat damage. The complete right windscreen was found on the ground just forward of the main fuselage. No evidence of the left windscreen was found.
The underlying transmission and engine support area was compressed and burned to where the transmission was found laying on the ground on the left side of the wreckage and the control deck and engines were approximately waste high.
The nose compartment access door was found separated into two sections. The one section displayed some sooting and the other section, which was found early in the debris path, was clean. The fracture surface appeared to have been cut in a diagonal direction from mid-length on the right side (when viewed from the aft of the helicopter) to mid-length on the leading edge of the door.
The radar dome cover was also found separated from the aircraft and was found along the debris path.
The pilot was found seated in the left front seat. He was reported to have been wearing a flight helmet, which the operator reported that he routinely did not buckle. The helmet was found outside the left side of the main fuselage and there was no apparent damage.
The pilot's helmet and a section of the left door post were retained by the Safety Board for further examination concerning matter found on the door and helmet.
Main Rotor Hub and Blades
Examination of the rotor blades and hub revealed the main rotor hub remained intact. The entire red blade and the white blade's leading edge remained attached to the rotor hub. The white blade drag brace remained in one piece and was attached to a section of blade trailing edge. The red blade drag brace was bent and separated toward the blade's leading edge (as though the drag braced ends had been bent toward each other in the aft direction). The stabilizer bar was fragmented and a majority of its components were found near the main rotor blades. The separation surfaces resembled taffy in their deformation.
The red blade sustained substantial chordwise damage from the root to approximately midspan. The blade remained intact; however, some of the chordwise gouging destroyed the blade skin and underlying honeycomb. The outboard tip of the blade displayed some light scoring and white paint transfers.
The Safety Board retained the white main rotor blade fragments for further examination.
Main Rotor Controls and Mast
The main rotor mast was separated into two sections; the lower section, which stayed with the main wreckage and its transmission, and the upper section, which was separated at the blade stop area and was connected to the main rotor hub. The mast separation area showed evidence of rectangular distortion toward the inside diameter of the mast, directly below the blade stops. The mast fracture surfaces displayed 45-degree shear lips.
Tail Boom and Tail Rotor
Although nearly burned to ash, the tail boom remained in its position relative to the fuselage. The tail stinger did not display any bending or scraping. The tail rotor showed evidence of significant leading edge contact on one blade. A linear ground scar equivalent in length to a tail rotor blade was observed adjacent to the tail rotor section. Several sections of tail rotor drive shaft, which were found adjacent to the main wreckage area, showed evidence of torsional twisting and separation. The tail boom, forward of the 42-degree gearbox, was destroyed by the fire. The elevator spar tube and horn assembly were found in their relative position among the tail boom ash; however, the elevator skins were burned to ash entirely, with the exception of a 1-foot outboard section of the left elevator. It was also found among the debris field and was unburned. The fracture surface of the 1-foot elevator section displayed curved metal in the upward direction on the upper and lower skin, and the spar tube.
The engines were examined at the salvage facility by a technical representative of Pratt & Whitney and the Safety Board. No anomalies with the engines were noted that would have prevented their operation.
The hydraulic system sustained substantial heat damage and was destroyed.
TESTS AND RESEARCH
The doorpost and helmet were sent to the Armed Forces Institute of Pathology (AFIP) in Washington, D.C., in an attempt to determine if a bird had contacted either the helmet or doorpost. According to AFIP, the doorpost and helmet were returned to the wreckage storage facility and a report was sent to the Safety Board; however, the Safety Board has no record of receipt of the AFIP report.
The fractured white blade was examined by the Safety Board Metallurgy Lab and Bell Helicopter metallurgists. It should be noted that blade stations (measurement of inches) are referenced in both reports. The Bell Helicopter report references blade stations from the center of the hub (being zero) to the tip of the blade (being 288). The Safety Board report references blade stations from the root of the blade (being zero) to the tip of the blade (being 264).
According to the report produced by Bell Helicopter metallurgists, approximately 97 percent of the blade was recovered for examination. The leading edge spar was in one piece and had remained attached to the rotor hub at the accident site. The spar was bent downward and was swept forward. The leading edge spar displayed impact damage at stations 78-110, 181-183, and 281-283.5.
A 152.5-inch section of honeycomb, skin, and trailing edge after-body between blade stations 111.5 and 264, was found separated from the spar. This section was found early in the wreckage distribution path. "All of the skin fractures on the top of the blade were adjacent to the spar's aft end." The skin fractures on the bottom side of the blade were either adjacent to or as much as 3 inches from the spar's aft end. All of the fractures of that section "were a result of overload."
The separations of the top skin from the spar between stations 160 and 178.5, and between stations 263 and 279, were examined. The separated surfaces of the spar and skin exhibited "fractured adhesive with a rough texture to the separated surfaces indicating both separated in a cohesive manner as a result of overload."
Both the top and bottom of the blade exhibited spanwise streaks of paint that were transferred from other parts, as well as associated mechanical damage. Red and white paints were the main paint colors transferred. The leading edge abrasion strip, which remained with the spar, had score marks as well as smears of red, white, and yellow colored paint. The smears were spanwise in the outboard direction.
There was heavy chordwise damage to the bottom of the skin and the trailing edge of the blade from impact with an object. One of the strikes was at station 264. The bottom skin and honeycomb, as well as the trailing edge and trim tab structure were torn and fractured due to the impact. The contour of the broken trailing edge had a measured diameter of approximately 1.25 inches.
Energy Dispersive X-ray Analysis of three impact areas on the blade only showed the characteristic elements of the trailing edge extrusion aluminum alloy. The analysis also showed the presence of carbon and oxygen "likely from the adhesive compound used between the skin and trailing edge extrusion."
All of the fractures found on the blade "were a result of overload."
The main rotor blade bolt, the drag brace bolt, and two shims (used between the drag brace clevis and the blade) were examined. The blade bolt and drag brace bolt showed some wear on each shank. The shims were adjustable layered shims, one of which was found in two pieces. Both were worn.
According to the Safety Board report, the general observations were similar to the Bell Helicopter materials report. The Safety Board lab personnel also noted an adhesive layer on both the separated upper skins and on the mating honeycomb core. A portion of the inner surface of the debonded upper skin was examined at high magnification using a scanning electron microscope. No evidence of any rubbing was observed. Regarding the other fracture surfaces, no evidence of fatigue or other progressive crack growth was observed.
The blade disk's angular deviation from its plane of rotation was calculated by a Safety Board investigator to determine what angle would allow the main rotor blades to slice through the battery door and the left elevator. The blade deviation angles to contact the left elevator were calculated as approximately 65 degrees laterally and 22 degrees longitudinally. Blade contact with the battery door would require approximately a 33-degree deviation from its plane of rotation.
An autopsy was conducted on the pilot by the Merced Pathology Medical Group, Inc., Merced, California. According to the autopsy report, the pilot "had no complete coronary artery occlusion;" however, "coronary narrowing was of the severity sometimes found in individuals for whom no other cause of death can be identified and could have been the cause of the accident."
Toxicological tests on the pilot for carbon monoxide, cyanide, volatiles, and drugs were negative.
According to Aviation Supplies and Academics' (ASA) Introduction to Rotary Wing Flight (a training manual which was derived from the U.S. Army's FM1-51 manual), mast bumping is the result of excessive rotor flapping, and "is the violent contact between the static stop and the mast during flight," and can cause mast damage or even separation. Mast bumping and possible rotor mast failure is usually attributed to "inappropriate pilot response to low-G maneuvers, engine failure, and some types of tail rotor failure."