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N113CF accident description

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Tail numberN113CF
Accident dateJune 03, 1996
Aircraft typeRobinson R-22 MARINER
LocationMekoryuk, AK
Additional details: None

NTSB description

History of the Flight

On June 3, 1996, about 1600 Alaska daylight time, a float equipped Robinson R-22 Mariner helicopter, N113CF, crashed on the surface of a small lake about 32 miles southeast of Mekoryuk, Alaska, located on Nunivak Island. The helicopter was being operated as a visual flight rules (VFR) local area business flight under Title 14 CFR Part 91 when the accident occurred. The helicopter, registered to and operated by Bearing Sea Reindeer Products, was destroyed. The certificated commercial pilot, the sole occupant, received fatal injuries. The flight originated at Mekoryuk about 1500.

A company representative reported that the pilot departed for Cape Corwin located on the southeast corner of the island to pick up a company worker. The helicopter did not arrive and did not return to Mekoryuk. The flight was reported overdue at 2313. Search airplanes located the wreckage on June 4, 1996, about 1300, along the south edge of a small lake, about 1/2 mile north of the coastline.

The accident occurred during the hours of daylight at latitude 59 degrees, 54.170 minutes north and longitude 165 degrees, 43.614 minutes west.

Crew Information

The pilot held a commercial pilot certificate with airplane single engine land, airplane multi-engine land, instrument airplane, and rotorcraft helicopter ratings. The most recent second-class medical certificate was issued to the pilot on May 9, 1996, and contained the limitation that the pilot must wear corrective lenses.

According to the pilot's logbook and aircraft logs, his total aeronautical experience consisted of about 1,411.6 hours, of which 890.4 were accrued in helicopters. In the preceding 90 and 30 days prior to the accident, the logs lists a total of 24.5 and 35.3 hours respectively.

On April 14, 1995, the pilot received a biennial flight review that included Robinson R22/R44 Helicopter Awareness Training specified in Special Federal Aviation Regulation (SFAR) 71.

Aircraft Information

The helicopter and engine had accumulated a total time of 1094.3 service hours. The most recent annual inspection of the engine and airframe was accomplished on April 13, 1996, 29.2 service hours before the accident. During the annual inspection, the number 4 engine cylinder was replaced. The helicopter airframe and engine logbooks and daily log sheets found in the helicopter were examined. The maintenance records indicated that on May 14, 1996, ignition noise filters were installed on both engine magnetos. On the same date, an emergency locator transmitter (ELT) was installed and included a remote activation switch installed on the instrument panel.

On May 28, 1996, a certified airframe and powerplant mechanic inspected and repaired the left magneto. In an interview with the National Transportation Safety Board (NTSB) investigator-in charge (IIC), he reported that the pilot called him and requested his services due to a drop in engine RPM. The mechanic indicated that he found the left magneto "P" lead disconnected. The exposed end of the wire was covered by a piece of black tape. He replaced the left magneto's timing gear, points, and coil. He re-timed the engine, performed an engine run-up, and the helicopter was test flown. The mechanic also stated that on June 1, 1996, he called the pilot to check on the status of the helicopter. The pilot informed him that the engine had "lots of power". The mechanic did not make any notation in the engine logbook concerning his work on the magneto. He did produce an invoice that detailed his work. Written on the invoice was "permanete aircraft record". On May 29. 1996, 4.8 hours before the accident, the helicopter daily log sheet noted that the engine oil was changed.

No records of fueling for the helicopter were located. The Executive Officer of the IRA Council, Native Village of Mekoryuk, reported that the helicopter was last fueled before the accident flight from a 50 gallon barrel of 100LL octane aviation fuel. The pilot normally obtained fuel from barrels that are shipped to Mekoryuk by air cargo or barge. Fuel is then hand pumped from the barrels into the helicopter. The hand pump has a spin-on filter and a water separator installed between the pump and the delivery hose. Examination of the water separator revealed water and sediment in the filter bowl.

The operator indicated that the company's supply of fuel had been exhausted. Fuel for the accident flight was obtained from reserve supplies maintained on the island by the U.S. Fish and Wildlife. The specific barrel that the helicopter was fueled from was not initially located during the examination of the wreckage.

Meteorological Information

The closest official weather observation station is Mekoryuk, Alaska, which is located 32 nautical miles northwest of the accident site. At 1600, an automated weather observation system (AWOS) was reporting, in part: Sky condition and ceiling, measured 400 feet overcast; visibility, 3 1/2 miles; temperature, 38 degrees F; dew point, 34 degrees F; wind, 320 degrees at 13 knots; altimeter, 30.54 inHg.

The company worker that the pilot was planning to pickup from the area of the accident reported that the weather conditions on the afternoon of June 3, 1996, were clear without any strong winds.

On the morning of June 4, 1996, the 0655 AWOS observation at Mekoryuk was reporting, in part: Sky condition and ceiling, partially obscured, ceiling measured 100 feet overcast; visibility, 2 miles; temperature, 34 degrees F; dew point, 32 degrees F; wind, 330 degrees at 13 knots; altimeter, 30.45 inHg.

When the Alaska State Trooper arrived at the accident scene on June 4, 1996, at 2100, he indicated that the weather was clear, temperature 58 degrees F, and the wind was from 310 degrees at 17 knots. He indicated that a thick fog bank was located about 20 miles to the north of the accident site.

Wreckage and Impact Information

The NTSB IIC examined the airplane wreckage at the accident site on June 5, 1996. The helicopter was resting on its landing gear floats, partially submerged, against the south shore of a small lake. The nose of the helicopter at the point of rest was observed on a magnetic heading of 238 degrees. The helicopter was floating with the right side about 15 degrees lower than the left. (All heading/bearings noted in this report are oriented toward magnetic north.)

All of the helicopter's major components were found at the point of rest. The float assembly consists of 4 chambers enclosed in a cylindrical tube. The left gear skid assembly was bent in an upward direction at the forward and aft upper attach points. The left float assembly was attached to the skid tube and the internal float chamber adjacent to the left door was punctured. The right gear skid assembly was also bent upward at the upper attach points. The float assembly remained attached to the skid tube and the two interior chambers adjacent to the right door and engine compartment were punctured. The aft section of each landing gear skid tube was bent upward about 10 degrees at their respective aft cross tube attach points.

The helicopter had external cargo racks installed on each side and were mounted between the fuselage and the floats. The racks were buckled in an upward direction and a vertical/diagonal brace at the aft edge of each rack was buckled in an outward direction. Wooden platforms that formed the bottom portion of each rack were found floating in the water near the helicopter.

The cockpit was crushed in a downward direction. The main rotor mast was displaced slightly forward and the forward edge of the mast fairing was wrinkled adjacent to the upper cabin roof. The floor, forward and aft of the front lateral landing gear cross tube assembly, was displaced in a downward direction. The front windshield bow, dividing the left and right sides of the forward windshield, was separated at its upper attach point with the cabin. The windshield Plexiglas was broken out of the frame and only one small portion of the windshield was present at the wreckage point of rest. The forward cabin door posts are both buckled about mid-height in a forward and outward direction. The left and right doors were broken at their respective lower attach points. Both door latch mechanisms were in the latched position but not retained in the airframe latch points. The outer portions of the cabin, below the left and right door sills, were crushed and distorted in a upward direction.

The collective control friction is adjusted by tightening a toggle lever against a vertical metal tab. The lever is installed through the collective handle near the aft end. The friction was found loose and the collective handle was found to be raised about 1/2 inch from full down as measured by the position of the lever against the metal tab.

The tail boom was attached to its appropriate attach points. Minor wrinkling was noted at the tail boom attach point with the cabin. The vertical stabilizer displayed a slight twist to the right with a wrinkle noted beginning just forward of the tail rotor gear box attach point, oriented on about a 45 degree angle from the top of the tail boom toward the right side of the tail boom and progressing in a forward direction. The tail rotor assembly and tail rotor blades were undamaged. The right side of the horizontal stabilizer located on the lower end of the vertical stabilizer was broken and missing. A white paint smear was noted on the top, aft end of the tail boom, just forward of the top tail rotor gearbox bolt, on the top of the bolt and, and also on the top of the tail rotor gearbox.

The main rotor blades were attached to the mast. One rotor blade displayed a small, upward indentation on the underside of the blade at the blade tip. No scratching or gouging of the paint was evident at the dent. The blade also displayed trailing edge wrinkling about mid-span. The second main rotor blade appeared undamaged. The main drive belts from the engine to the main transmission sheeve were tight. The belt tensioner was extended about 1 1/2 inches. Hand rotation of the main rotor blades in the direction of normal rotation established drive train continuity to the tail rotor. Hand movement of the blades opposite of normal rotation resulted in a locking of the freewheeling unit. The main rotor blade "elephant tusks" were undamaged. One droop stop and its retaining bolt was sheared off. The second droop stop was undamaged. The main rotor blade static stop retainers were broken on both sides of the mast and the stops were missing. A slight indentation was noted on one side of the main rotor mast adjacent to the bottom edge of the rotor hub. The swash plate was raised about 1 1/2 inches between the bottom edge of the sliding uniball assembly and the top of the static mast.

The engine fuel valve was found in the "on" position. The left seat belt/shoulder harness was secured in the latched position. The bottom seat support for both seats is crushed downward at the rear portion of the support. The aft, vertical bulkhead of the cabin is bulged slightly in a forward direction between the left and right seats. Visual examination of the annunciator light bulb filaments revealed that all of the filaments were unbroken and tightly coiled with the exception of the "low rotor" RPM bulb. It displayed slight elongation of the filament at each attach point. The filament portion between the support posts remained tightly coiled.

The helicopter wreckage remained partially submerged in the lake until was retrieved by the operator and transported by boat to the Village of Mekoryuk. On July 8, 1996, the parties noted in this report participated in an examination of the wreckage in Mekoryuk.

Due to the impact and distortion of the airframe, the flight controls could not be moved by their respective control mechanisms. Fractures of the flight control push-pull tubes displayed 45 degrees fracture surfaces and flight control continuity was established throughout the airframe. The collective mounted throttle arm was found in the full open position.

The bottom portion of the engine cooling scroll was cracked and broken and deformed upward into the cooling fan. The deformed portion of engine scroll did not display any rotational scoring signatures from the cooling fan. A rotational scoring mark was noted on the inside metal edge of the bottom half of the scroll. The mark extended about 1/4 of the total radius of the scroll half. The crankshaft could be rotated by hand. Gear and valve train continuity was established and thumb compression in each cylinder was noted when the crankshaft was rotated.

The right magneto's "P" lead was spliced together with a screw and nut joining two "eye" connectors and wrapped in black electrical tape. The left magneto's "P" lead contained a condenser spliced into the lead.

The sparks plugs exhibited corrosion on the electrodes. About 1 cup of water was drained from each engine cylinder when the bottom spark plugs were removed.

The carburetor appeared undamaged. The mixture cable was attached and was found in the "full rich" position. The throttle cable was attached and was found in the mid-range position. The carburetor heat valve was found in the "cold" position. The engine fuel gascolator contained a small amount of water. The internal screen contained small particles of contamination.

The engine was removed from the airframe and shipped to a test facility in Anchorage, Alaska. Prior to shipping, the engine oil was drained. About 3 gallons was water was drained from the engine before any oil was collected.

Medical and Pathological Information

A postmortem examination of the pilot was conducted under the authority of the Alaska State Medical Examiner, 5700 E. Tudor, Anchorage, Alaska, on June 6, 1996.

Tests and Research

On July 10, 1996, an engine examination was conducted at Sea Air Inc., Anchorage, Alaska. The engine exhibited external and internal corrosion. The oil pressure and oil suction screens were free of contaminants. The carburetor was removed and the bowl contained a small amount of water. The carburetor inlet screen was free of contaminants. The metal float and venturi appeared undamaged. The engine timing was verified and both magnetos were set to 25 degrees before top dead center (BTC). The magnetos were opened and compressed air, electrical contact spray cleaner, and a heat gun were utilized to dry the internal components. The engine was then placed on a test stand and started.

The engine ran from an idle at 650 RPM to full power at 2,450 RPM. After about 3 minutes, a magneto check was performed at 1,800 RPM and a drop of 120 RPM was noted on each magneto. The engine was again advanced to 2,450 RPM and after about 1 minute, began to run rough and lost about 300 RPM. A magneto check revealed that the left magneto had an excessive RPM drop. The engine was stopped and 4 new spark plugs were installed in the bottom cylinders but the excessive RPM dropped persisted. A compression test revealed the following: cylinder #1, 72/80 PSI; Cylinder #2, 78/80 PSI; cylinder #3, 70/80 PSI; cylinder #4, 75/80 PSI.

Following the engine examination, the engine magnetos were inspected by the Accessory Shop, Anchorage, Alaska, on July 11, 1996. The examination revealed that the left magneto did not produce spark. It displayed heavy corrosion. The condenser and coil tested within specifications. The points were timed correctly but were corroded. The running points were replaced and the magneto then produced spark. The right magneto produced spark. The condenser was out of limits and the coil was within specifications. The internal timing was incorrect and the wrong tooth was marked on the distributor gear.

On July 19, 1996, the operator located and gathered a fuel sample from the barrel used to fuel the helicopter. The sample was sent to the NTSB IIC and was submitted for testing. The test revealed that the sample contained 27.1 milligrams per gallon of particulate contamination. A microscopic examination of the contamination revealed that 80 percent of the particulates were varnish, 15 percent were silicates,

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