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N381MC accident description

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Tail numberN381MC
Accident dateNovember 08, 2007
Aircraft typeHughes 269C
LocationBaker City, OR
Near 44.859167 N, -117.806389 W
Additional details: None

NTSB description

HISTORY OF FLIGHT

On November 8, 2007, approximately 1245 Pacific standard time, a Schweizer 269C helicopter, N381MC, impacted the terrain about one and one-half mile north of Baker City Municipal Airport, Baker City, Oregon. The private pilot, who was the sole occupant, was killed in the accident sequence, and the helicopter, which was owned and operated by Baker Aircraft, was substantially damaged. The 14 CFR Part 91 solo instructional/proficiency flight, which departed Baker City Municipal Airport about five minutes prior to the accident, was being operated in visual meteorological conditions. No flight plan had been filed.

According to witnesses, after departing Baker City Municipal Airport, the helicopter turned to the north, climbed to an altitude that was reported to be as low as 100 above ground level (agl) and as high as 800 feet agl. The helicopter then paralleled Interstate Highway 84 as it proceeded to the north. As it approached Chandler Lane (Highway 203), its tail reportedly lowered, it slowed, rotated or turned slightly to the east, and then descended rapidly toward the terrain. Witnesses reported that near the beginning of the descent, the main rotor blades either slowed their rotation significantly or "stopped turning." One witness stated that almost immediately after observing the change in rotation speed of the main rotor blades, "…the helicopter just dropped out of the sky."

PERSONNEL INFORMATION

The 59-year-old pilot held a commercial pilot certificate with an airplane single engine land (ASEL) rating and an instrument rating for airplanes. His last medical, a Second Class, was issued on March 1, 2007. He had accumulated about 2,050 hours of flight time, with about 62 hours in helicopters, 60 of which were accumulated in the 90 days prior to the accident. According to a representative of Baker Aircraft, the pilot was in the process of developing his proficiency for an upcoming flight check during which he hoped to qualify for a commercial helicopter rating.

According to the pilot’s logbook he flew five flights in N381MC on the day prior to the accident, for a total of 5.8 hours. Four of those flights were during daylight hours, and one, lasting 1.3 hours, was logged as night time. On the morning of the accident, the pilot flew a 1.5-hour dual instructional flight, which ended around 1000.

AIRCRAFT INFORMATION

The accident helicopter, a Schweizer 269C, serial number 1240, was manufactured in 1986. It was owned and operated by Elkhorn Aviation, Inc., doing business as Baker Aircraft. Its last 100-hour inspection was completed on October 28, 2007, and at the time of the accident, it had accumulated 4,324 hours. The helicopter had been flown on two prior flights on the day of the accident. The first was the training flight involving the deceased pilot, and the second was another training flight of 1.5 hours duration. The helicopter’s fuel system was then topped off with 16.65 gallons of aviation fuel prior to the accident flight.

METEOROLOGICAL CONDITIONS

According to the 1253 automated aviation weather surface observation (METAR), the winds were from 230 degrees magnetic at four knots. The sky was clear, with a visibility of eight statute miles. The temperature was 13 degrees Celsius, and the dew point was two degrees Celsius. The altimeter setting was 30.03 inches of mercury. There were no reports of gusting winds or turbulence.

WRECKAGE AND IMPACT INFORMATION

The helicopter impacted flat level open terrain about one-tenth of a mile south of Chandler Lane/Highway 203, and about four-tenths of a mile east of Interstate Highway 84. The altitude of the site was approximately the same as that of the airport, 3,370 feet mean sea level (MSL). The initial ground impact scar consisted of two parallel indentations about 65 inches apart and about 50 inches long. The indentations, both of which were about one inch deep and two inches wide, ran on an east/west magnetic heading. The northerly indentation had created a ridge about one-half inch in height along its northern edge, and near its westerly end was found about the aft 18 inches of the left skid. This portion of the skid was still connected to its lateral support leg and diagonal brace, both of which had separated from the airframe. Lying alongside of the aft portion of the skid was the aft skid oleo/vertical support leg. Another section of the left skid, about 16 inches long, was lying about two feet northeast of the aforementioned section, and the forward oleo/vertical support leg was located about two feet further northeast. The primary wreckage came to rest about 20 feet north of the initial impact point. The only other readily identifiable object located at the initial impact point was the cylindrical body of the fuel gasculator unit, along with its associated wire screen filter.

The primary wreckage, which included the pilot/passenger compartment, right skid, engine/transmission section, and the main rotor shaft and blades, was lying on its right side facing to the east. The bottom of the helicopter’s structure, along with the engine induction and exhaust pipes, had been crushed directly upward into the structure above them. The forward portion of the left skid was found lying about three feet north of the primary wreckage. The Plexiglas pilot/passenger compartment enclosure/bubble had fractured into small pieces, and the instrument pedestal had been thrown forward out of the compartment, and remained only partially attached by its associated electrical wiring. The transmission and main rotor shaft were still attached to the primary structure, but the main rotor shaft housing had fractured just above the flange that attaches it to the transmission housing.

The shroud was removed from the drive belt/clutch pulley system, and it was determined that the arms that support the driven pulley and the tensioner/clutch pulley had fractured. All eight drive belts were still in their respective groves on all three pulleys, and there was no evidence of in-flight slippage of any of the belts. The electrically-driven jackscrew in the actuator that controls the engagement of the driven pulley, by causing the tensioner/clutch pulley to increase tension on the drive belts, was found in the fully retracted (driven pulley fully engaged) position. The clutch engagement toggle switch on the instrument console was found in its center "HOLD" position, with the switch guard open.

The scroll was removed from the induction fan, and circumferential rubbing/scaring was found along about 45 percent of the interior of the scroll structure. In addition, much of the area of the aft (non-attached) end of most of the fan blades had been burnished to a bright shine due to their rotational contact with the scroll.

All three main rotor blades were still attached to the rotor hub, and all three were still attached to their pitch change links. The drag-link dampeners attached to the root of the blades had been pulled out of their housings on two of the blades. The flight control torque tubes were traced from the rotor head to the point where they entered the crushed structure of the pilot/passenger compartment, and no evidence of malfunction, anomaly, or failure was evident in either the tubes or their interconnect ends. One main rotor blade, which suffered very little direct impact damage, was relatively straight along about two-thirds of its span. It then was bent downward about 10 degrees, before bending upward again about 10 degrees, and then continuing relatively straight to its tip. The second blade, which had been ripped open span-wise along its most outboard 18 inches by contact with the terrain, showed the upward curvature and upper skin compression creases consistent with coning along its entire span. The third blade, which had been bent downward about 45 degrees about one foot outboard of the hub by terrain contact, also showed signatures consistent with coning along its entire span.

The tail boom had been torn from the fuselage, and was located about 10 feet west of the primary wreckage. The two tail boom support arms had torn loose of the fittings that attach them to the undercarriage structure. The tail rotor drive shaft had separated from its junction just aft of the upper (driven) pulley assembly. The tail rotor gearbox remained attached to the aft end of the boom, but one of the tail rotor blades had separated from the tail rotor shaft at its root. The separated blade was found lying about 25 feet west of the primary wreckage. The tail rotor pitch change links showed no signs of malfunction or anomaly. The vertical stabilizer, which normally sticks straight down from the boom, had been crushed upward and folded up and around the right/starboard side of the boom structure by contact with the terrain. The horizontal stabilizer, which normally angles diagonally up and to the right, had flexed downward about 60 degrees. The tail rotor drive shaft had come in contact with the tail boom root internal structure. The drive shaft was dented inward, with no circumferential scaring of its surface. The impact damage to the drive shaft was consistent with the drive shaft contacting the boom structure after its rotation had been stopped by the tail rotor contact with the terrain.

An on-scene inspection of the engine determined that the fuel servo, fuel pump, and left magneto had broken loose from their mounts. Before removing the helicopter from the field, fuel was confirmed at the boost pump, and a borescope inspection was performed on all cylinders, with no anomalies noted. In addition, the top spark plug from each cylinder was examined, and no damage, unusual wear, or contamination was noted.

The helicopter, except for the fuel injection servo, was recovered to SP Aircraft, of Boise, Idaho, where, on December 13, 2007, it underwent a further teardown inspection directed by the Federal Aviation Administration (FAA). During that inspection the magnetos were determined to produce spark at all of their leads when rotated by hand, and the remaining four spark plugs were determined to have normal wear with no damage or contamination. Continuity was visually established from the crankshaft, through the camshaft, accessory section and the valve train. The valves were removed, and no evidence of valve sticking or blow-by was observed. The fuel nozzles were found free of debris.

During the engine teardown the following three anomalies were noted:

1. One cylinder base nut on the bottom portion of the number two cylinder base flange was found to be missing. 2. The number three and number four connecting rod bearings, along with the center crankshaft main bearing, were found worn through the Babbitt material. All other main and connecting rod bearings showed varying degrees of wear. 3. Copper material was found in both the oil filter and the oil pickup screen.

No evidence was found that would indicate the missing cylinder base nut affected the ability of the engine to produce full power, and there was no indication that the worn Babbitt material had produced any damage to the crankshaft journals, the crankshaft bearing saddles, or the connection rods. At the completion of the teardown examination, it was determined that nothing had been discovered that would have lead to an in-flight loss of power or engine failure during the accident flight.

Further discussions with the helicopter’s owner determined that there had been a couple of recent flights during which the individual who had added oil had inadvertently failed to reinstall the oil filler cap after adding oil. According to this individual, "A couple of quarts of oil were lost during each of these flights."

During the investigation, the Investigator-In-Charge (IIC) reviewed the results of a series of oil analysis performed by Aviation Oil Analysis (AOA), of Phoenix, Arizona, since the engine’s last overhaul. All results received by the owner prior to the accident indicated "normal values," with a copper concentration between 2.3 and 7.4 units. A sample taken on October 19 and processed by AOA on October 25, but not received by the owner until after the accident, indicated results that were consistent with the wearing of the bearing Babbitt material (copper concentration of 34.9 units). The AOA codes for this sample read as follows:

Code 178 -- Copper increased for oil time. Code 108 – Check oil filter for chips. Code 158 – Resample 15 to 20 hours to monitor wear trend.

The fuel injection servo that had separated from the engine upon impact was taken to Precision Airmotive, of Marysville, Washington, where it underwent an NTSB-monitored flow check and teardown inspection. The servo flows were within service flow limits at all six standard flow test settings, and the teardown inspection did not reveal any anomaly that would have contributed to an in-flight loss of power.

MEDICAL AND PATHOLOGICAL INFORMATION

An autopsy was performed on the pilot in Clackamas, Oregon, on November 10, 2007. According to that autopsy, the cause of death was "Massive blunt force injuries," and the manner of death was by "Accident."

The FAA’s Forensic Toxicology Research Team performed a toxicology examination on specimens taken from the pilot. The results were negative for ethanol in the Vitreous, and the standard test for carbon monoxide and cyanide were not performed. The results of the toxicological drug screen were as follows:

0.016 ug/ml, ug/g TEMAZEPAM detected in blood 7.702 ug/ml, ug/g TEMAZEPAM detected in urine 0.234 ug/ml, ug/g OXAZEPAM detected in urine OXAZEPAM not detected in blood OMEPRAZOLE present in urine NAPROXEN detected in urine

(c) 2009-2011 Lee C. Baker. For informational purposes only.