N8457J – Robinson Helicopter Company R22 – 1998-02-26 NTSB Accident Report

HISTORY OF FLIGHT

On February 26, 1998, at 1318 hours Pacific standard time, a Robinson R22, N8457J, impacted terrain in a ravine near Littlerock, California. The aircraft was destroyed and the commercial pilot/owner, the sole occupant, suffered fatal injuries. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The aircraft was being operated under 14 CFR Part 91 as a personal flight, and originated from a private airport at Adelanto, California, at 1300.

The right-hand cockpit door of the helicopter and pieces of the windshield Plexiglas were found in a debris field approximately 1/4 mile east of the main wreckage. Witnesses reported that winds at the time of the accident were westerly at 20 to 25 knots. One witness reported he heard a loud "schwapp-like" noise followed shortly by engine silence, and then saw the helicopter disappear from view in a near vertical descent.

The pilot of a sheriff's department helicopter located the wreckage, landed nearby, and was the first person on scene. He reported that the surface winds were from the west at 20 -25 knots and that it was "bumpy and turbulent" in the area when he arrived. He also said that there was the smell of fuel in proximity of the fuel tank and he noted that the cap from the fuel tank had been ejected and was laying on the ground opposite the tank, about 15 feet upslope. The citizen who had called in the report of the accident arrived at the scene and said he had seen the aircraft roll to the left and fall.

A friend of the pilot, who is a student helicopter pilot, reported that on the day of the accident, the pilot flew the accident helicopter from Whiteman to the friend's hangar at Adelanto private airport and back. He did not refuel. They were going to fly the friend's Rotorway helicopter; however, the friend said that the wind was blowing about 15 knots and he was experiencing translational lift in hover which made him uneasy so he landed and put the helicopter away. They then got in the car and drove around the airport for 3 or 4 hours before the pilot departed for home. The friend said that he had frequently flown in the R22 with the pilot and that he cruised at 21 inches manifold pressure, which gave about an 80-knot indicated airspeed. The pilot also had told him to slow down in turbulence but not below 60 knots.

Another friend, also a helicopter rated pilot, characterized the pilot as a "very conservative, better than average" pilot whom "always wanted to learn more." He had "good ability for a man his age." The two men had attended a CFI renewal conference at the HAI convention in February (1998) where low-g flight and mast bumping were discussed. The friend said "he was well aware of it."

This friend recalled two instances when they had encountered turbulence while flying up to the desert from Whiteman in the R22. He said he was alarmed by the amount of [acoustic] blade slap in the turbulence. They turned around and went home. When asked about airspeeds flown, the friend recalled that the pilot was always "very conservative in cruise setting, a little below recommended."

PERSONNEL INFORMATION

The pilot's wife reported that he maintained two logbooks, one for fixed wing flight hours and another for rotary wing flight hours. After the accident only the rotary wing logbook was located. The pilot's wife said, however, that he had flown rotary wing aircraft exclusively for at least the last 2 years. On November 8, 1994, when the pilot applied for his airplane, single engine sea rating checkride, he reported having 1,450 fixed wing hours.

According to the aircraft manufacturer, the pilot completed the factory pilot training course in the aircraft in 1994, 1995, and in February 1997. In the 1995 and 1997 training, the company records indicate that the pilot's proficiency was rated "below average."

AIRCRAFT INFORMATION

Robinson Helicopter Company recommends that the R22 helicopter is overhauled (engine and airframe) at 2,000-flight hours or 10-year intervals, whichever comes first. The accident aircraft was last overhauled at the Robinson factory in December 1987, and had accumulated 907 flight hours since overhaul.

According to the aircraft maintenance records, main rotor blades (serial numbers 3011 and 3017) were installed during the 1987 overhaul and were new at that time. They have a 2,000-hour service life.

RADAR DATA

A replay of recorded radar data at High Desert TRACON showed a VFR aircraft (transponder code 1200) flying from east to west at 3,800 feet (msl) which disappeared from radar at the accident location at 13:11:42 hours. High Desert TRACON has a REHOST radar system that does not output recorded data. On March 6, 1998, a Safety Board investigator viewed a replay of the data on a display at the High Desert facility and manually recorded the data (attached). According to system specialists at TRACON, the scan rate of the antenna results in a target return (update) approximately every 4.5 seconds and ground speeds displayed are rounded to the nearest 10 knots using conventional arithmetic rounding (e.g. 75 to 84 knots is displayed as 80 knots). The ground speed displayed is determined from the distance traveled and elapsed time since the last radar return.

At 13:06:23, an arbitrary start time, the radar displayed the aircraft approximately 7 miles east of the accident location at 3,800 feet msl, tracking 255 degrees magnetic, at 80 knots ground speed. In the next 5 minutes the target continued westbound on approximately a 255-degree magnetic course at displayed ground speed of 80 knots, or occasionally 90 knots, at altitudes of 3,700, 3,800, or 3,900 feet. At 13:11:13, the aircraft was 0.7 miles east of the accident site at 3,900 feet with ground speed of 90 knots. At 13:11:17, while still at 3,900 feet, the ground speed increased to 130 knots. In the two subsequent returns, while remaining at 3,900 feet, the ground speeds displayed were 140 and 120 knots. At 13:11:31, the altitude increased to 4,000 feet and the ground speed decreased to 100 knots and then, at 13:11:36, slowed to 80 knots. At 13:11:40, the radar return indicates that the aircraft reached 4,100 feet at 70 knots ground speed, and this is the last return from the aircraft. A tabulation of the radar data is attached to this report.

A systems performance specialist at TRACON speculated that the ground speed increase at 13:11:17 might have been due to an anomaly in the REHOST display software. The display is comprised of a mosaic of radar maps and the aircraft was crossing a boundary from one map to another at that time. Several replays of the data showed the aircraft westbound with equal distance traveled between radar returns. At 13:11:13 the target moved an inordinate distance west, and then at 13:11:17, moved back eastward near the prior return. The specialist was otherwise unable to explain this return. The reference barometric pressure, used to decode the aircraft's mode C return, was 29.92 for the east map and 29.93 for the west map.

METEOROLOGICAL INFORMATION

According to the Quality Assurance Office at the Federal Aviation Administration (FAA) Western Region headquarters, there was no record of any weather briefing given to the pilot.

A meteorology factual report prepared by the Safety Board staff meteorologist is attached. The meteorologist reported that surface observations near the time of the accident from surrounding stations reported westerly to northwesterly surface winds at 10 to 30 knots. Winds aloft from the accident elevation to 10,000 feet were northwesterly from 6 knots increasing to 40 knots, and several pilots reported moderate to severe turbulence below 8,000 feet with winds aloft of up to 50 knots and updrafts and downdrafts near the mountains.

AIRMET TANGO 3 was valid at the time of the accident for occasional moderate turbulence below 12,000 feet (msl). The AIRMET was for the area from Beatty, Nevada, to 30 miles southeast of San Diego, to 50 miles west of Santa Barbara, and then back to Beatty.

WRECKAGE AND IMPACT INFORMATION

The aircraft wreckage was located in a shallow ravine in a desert area of low rolling terrain. The location is in the northern foothills of the San Gabriel Mountains at latitude 34 degrees 30.49 minutes north and longitude 117 degrees 59.94 minutes west (GPS). The elevation is approximately 3,100 feet msl. To the north and northeast of the accident site the terrain slopes downward onto the Mojave Desert and, to south of the site, rises into the mountains. There was no fire.

All of the aircraft was present at the wreckage location except the windshield Plexiglas, the windshield center bow, the right-hand entry door, a portable fire extinguisher, the AFM holder bracket and some loose paper items. The Plexiglas and other loose items were located in a fan-shaped debris field over approximately a 1/4-mile area east and east-northeast of the main wreckage location.

The fuselage was lying on its left side oriented approximately 340 degrees magnetic. The left side exhibited crushing damage through approximately 40 percent of the fuselage width. When viewed from the rear, the plane of the crushing was from approximately 11 o'clock to 6 o'clock. When the fuselage was lifted, there was a depression approximately 1-foot deep in the soft soil. There was a vertical indentation in the wrinkled cockpit floor structure that extended from the nose of the aircraft aft to the forward landing skid crosstube. The indentation was approximately at the lateral center of the left seat and exhibited the shape and size of the leading edge radius of the main rotor blade. A similar impact mark was present in the bracket used to stow the aircraft flight manual at this location. The bracket was found in the debris field approximately 150 feet northeast of the main wreckage. The rotor blade exhibited scratch marks at approximately the midspan location corresponding to the distance from the rotor attachment at the mast to the indentation in the fuselage frame. There was also an indentation in the forward face of the left arm of the cyclic control, the radius of which approximately equaled the radius of the main rotor leading edge. The mark on the cyclic control was aligned with the mark in the fuselage frame on an exemplar R22 helicopter and corresponded approximately to the full left cyclic control position.

The fuel tank was crushed and the fuel tank cap was approximately 25 feet upslope from the tank. The engine remained with the fuselage and the left-hand cylinders exhibited impact damage. One of the two power transmission belts was off the pulley at the drive shaft, however, the belt was undamaged. The engine cooling fan and shroud did not exhibit any circumferential scrape marks. The right-hand landing skid remained attached to the fuselage although both attachments at the fuselage were fractured. The left-hand skid, broken at the forward strut and both fuselage attachments, was imbedded in the dirt below the right-hand skid. A loose 5-gallon plastic fuel container was found in the cockpit trapped under the left seat; although ruptured, it still contained aviation gasoline.

The tail boom, broken at three stations, remained attached to the fuselage by the tail rotor drive shaft and antitorque control linkage. The empennage control surfaces were separated from the tail boom and were located about 25 feet southwest. The tail rotor assembly was broken from the 90-degree gearbox where the shaft support casting attaches to the gearbox. The tail rotor hub with one blade and the root of the second blade attached, was located 25 feet west of the fuselage. The second tail rotor blade, severed outboard of the root reinforcement area, was located approximately 6 feet east of the fuselage. The tail rotor shaft and shaft support housing, broken from the 90-degree gearbox, remained attached to the hub assembly. The tail rotor blades were bent to the side, inboard toward the tail boom, and did not exhibit any chordwise striations or leading edge damage.

The main rotor hub, with both rotor blades attached, was severed from the main rotor drive shaft at the base of the hub and was on the ground approximately 1 foot from the main rotor mast. One blade (s/n 3017) was laying on the surface, leading edge down, and had several small compression wrinkles in the trailing edge. The other main rotor blade (s/n 3011) was lying under the fuselage, passing under the cockpit, trailing edge up. The tip of the second rotor was bent approximately 90 degrees down, about 10 inches inboard of the tip. The tips of both main rotor blades did not exhibit any chordwise striations or leading edge damage. At the drive shaft break, the shaft exhibited a flattened shape over half its circumference and a circular shape over the other half. The flattened half was on the same side of the hub as the blade, which was under the fuselage.

The cyclic controls were displaced full left and forward of neutral. The left antitorque pedal was full forward and the collective was full down. The rotor brake switch was off, the governor switch was on, and the clutch switch was engaged. The lateral cyclic right trim control was pushed in.

The Safety Board examined the aircraft on March 4, 1998, at Aircraft Recovery Services in Compton, California. The flight control linkages were continuous between the cockpit and the swash plate attachments. The rod end failures at the swash plate were accompanied by bending in the threaded area. The antitorque pedals were trapped at impact in the full left pedal position. The filaments in the cockpit annunciator light bulbs for LOW RPM, MR CHIP, TR CHIP, and MR TEMP were evenly spaced and did not exhibit any lateral or longitudinal distortion. The glass envelope of the LOW FUEL annunciator light bulb was broken, however, the filament remained intact and exhibited modest irregular stretching of the filament winding accompanied by lateral (sideways) deformation. The glass envelope of the CLUTCH annunciator light bulb was also broken and the filament supports were bent. A small fragment of the remaining filament exhibited tight, uniform winding.

The fragments of Plexiglas recovered from the debris field were mated in a "jigsaw puzzle" manner over an exemplar intact windshield assembly. The larger pieces of Plexiglas constituted the majority of the right-hand windshield. Approximately 50 percent of the left-hand windshield Plexiglas comprising the center area was not recovered.

The main rotor and tail rotor transmissions were opened for examination and no abnormalities were noted. The magnetic plug in the main transmission was free of metal.

The throttle governor computer and servo were tested at Robinson Helicopter Company on March 11, 1998. The computer tested within limits for in-service units and the servo tested within specifications for new units.

The engine and Spragg clutch were examined at Aircraft Recovery Service on March 13, 1998. The engine exhibited impact damage on the left-hand side and the cooling baffles, intake and exhaust pipes, and ignition wires on the number 1 and 3 cylinders were destroyed. The right magneto and the carburetor were broken from the engine at there mounting bases. The engine air path was free of obstructions from the intake and air filter to the muffler and the interior of the exhaust pipe was gray.

The engine was mechanically continuous from the output shaft to the accessory case. The crankshaft and camshaft bearings were bright and shiny and the camshaft lobes were normal. The tappets were shiny and unspalled. The accessory drive gears were intact. The cylinders, valves, and pistons exhibited normal coloration and combustion deposits.

The left and right magnetos were timed to the engine at 25 and 23 degrees, respectively, and both magnetos sparked an electrode when rotated by hand. The ignition circuit (P-leads) tested open from the magneto lead to the ignition switch. The spark plugs were free of fouling and were light gray in color.

The carburetor was broken from the engine sump at its base through the throttle plate shaft. The throttle, mixture, and accelerator pump linkages were intact. There was no fuel in the carburetor, however, the float lobe nearest the left-hand side of the aircraft exhibited implosion on the outboard side.

The Spragg clutch between the engine and the transmission drive shaft was disassembled and the inner (driven) race exhibited galling. All of the Telatemp tapes on drive train components were normal.

ADDITIONAL INFORMATION

In January 1996, airworthiness directive (AD) 95-26-04 was issued to owners of R22 helicopters requiring additions to the aircraft flight manual (AFM).

In part the amendments add to the Normal Procedures Section:

"Until the FAA completes its research into the conditions and aircraft characteristics that lead to main rotor blade/fuselage contact accidents, and corrective type design changes and operating limitations are identified, Model R22 pilots are strongly urged to become familiar with the following information and comply with these recommended procedures.

Main Rotor Stall: Many factors may contribute to main rotor stall and pilots should be familiar with them. Any flight condition that creates excessive angle of attack on the main rotor blades can produce a stall. Low main rotor RPM, aggressive maneuvering, high collective angle (often the result of high-density altitude, over-pitching [exceeding power available] during climb, or high forward airspeed) and slow response to the low main rotor RPM warning horn and light may result in main rotor stall. The effect of these conditions can be amplified in turbulence. Main rotor stall can ultimately result in contact between the main rotor and airframe. [...]

Mast Bumping: Mast bumping may occur with a teetering rotor system when excessive main rotor flapping results from low "G" (load factor below 1.0) or abrupt control input. A low "G" flight condition can result from an abrupt cyclic pushover in forward flight. High forward airspeed, turbulence, and excessive sideslip can accentuate the adverse effects of these control movements. The excessive flapping results in the main rotor hub assembly striking the main rotor mast with subsequent main rotor system separation from the helicopter.

To avoid these conditions, pilots are strongly urged to follow these recommendations:

(1) Maintain cruise airspeeds between 60 KIAS and less that 0.9 Vne, but no lower than 57 KIAS.

(2) Use maximum "power-on" rpm at all times during powered flight.

(3) Avoid sideslip during flight. Maintain in-trim flight at all times.

(4) Avoid large, rapid forward cyclic inputs in forward flight, and abrupt control inputs in turbulence."

In the Emergency Procedures Section the following were added:

(1) RIGHT ROLL IN LOW "G" CONDITION

Gradually apply aft cyclic to restore positive "G" forces and main rotor thrust. Do not apply lateral cyclic until positive forces have been established.

(2) UNCOMMANDED PITCH, ROLL, OR YAW RESULTING FROM FLIGHT IN TURBULENCE.

Gradually apply controls to maintain rotor rpm, positive "G" forces, and to eliminate sideslip. Minimize cyclic control inputs in turbulence; do not overcontrol.

(3) INADVERTENT ENCOUNTER WITH MODERATE, SEVERE OR EXTREME TURBULENCE.

If the area of turbulence is isolated, depart the area; otherwise, land the helicopter as soon as practical. [...]

A copy of the airworthiness directive is attached. Additionally, Robinson Helicopter Company has issued Safety Notices SN-10, SN-11, SN-24, SN-29 and SN-32 regarding low rotor rpm (main rotor stall), low "G" conditions, and flight in high winds and turbulence. The Safety Notices are also attached.

Safety Notice SN-32 was issued in March 1998, after the accident, regarding flight in high winds or turbulence as follows:

HIGH WINDS OR TURBULENCE

Flying in high winds or turbulence should be avoided but if unexpected turbulence is encountered, the following procedures are recommended:

1) Reduce airspeed to between 60 or 70 KIAS.

2) Tighten seat belt and firmly rest forearm on right leg to prevent unintentional control inputs.

3) Do not overcontrol. Avoid large or abrupt control movements. Allow aircraft to go with the turbulence, then restore level flight with smooth gentle control inputs.

4) Leave governor on and do not chase RPM or airspeed. Momentary rpm or airspeed excursions are to be expected.

5) Avoid flying on the downwind side of hills, ridges, or tall buildings where the turbulence will likely be most severe.

6) Never fly into a blind or box canyon during high winds.

RELEASE AND TOX

The Los Angeles County, Department of Coroner performed an autopsy and the FAA's Civil Aeromedical Institute performed a toxicological analysis.

The aircraft wreckage was released to the pilot's estate on March 13, 1998.