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On May 22, 2002, at 1506 pacific daylight time, a Robinson R22 Beta single-engine helicopter, N7194J, was destroyed when it impacted trees and rising mountainous terrain during climb to cruise near Mammoth Lakes, California. The private pilot and his certified flight instructor (CFI) sustained fatal injuries. The helicopter was registered to and operated by the private pilot and another private individual. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 personal flight. The cross-country flight departed the Mammoth Yosemite Airport (MMH), Mammoth Lakes, approximately 1500, and was destined for the San Luis County Regional Airport (SBP), near San Luis Obispo, California.
During a telephone interview conducted by the NTSB investigator-in-charge (IIC), an employee of the pilot reported the pilot and his passenger departed SBP approximately 0930, on the morning of the accident and flew to Mammoth Lakes on a pleasure flight.
Employees of Hot Creek Aviation, a MMH fixed base operator (FBO), reported the helicopter arrived at MMH approximately 1350. The pilot and his passenger had lunch at the FBO, stated this was their first time flying into MMH, and requested the helicopter's fuel tanks be topped off with fuel. Line personnel fueled the helicopter with 20.0 gallons of 100LL aviation grade fuel. At 1445, the line personnel observed the private pilot enter the right side, and the passenger enter the left side of the helicopter.
The witnesses reported the helicopter's engine start was "normal." The engine idled for approximately two minutes, then the engine rpm increased to "full power," the helicopter lifted off the ground "approximately 3 to 4 feet, and then set down very controlled." The engine rpm decreased for a few seconds, then was brought back to "full power." The helicopter lifted off the ground, turned to the west, and moved about 30 feet to "the yellow X [a closed taxiway], and set down very hard." One witness stated, "[it] seemed like they had difficulty trying to get off the ground." After a few seconds, the helicopter lifted off again, dragging the forward portion of the skids on the taxiway. The helicopter departed to the west, and "did not gain a lot of altitude." The witnesses observed the helicopter fly toward Mammoth Mountain until they lost sight of it behind the west hangars.
A pilot-rated witness, who was located at his mountainside residence between the accident site and the airport, reported that at the time of the accident, the wind was gusting to 30 knots. Based on previous flight experience in the area of the accident site, the witness stated he often "encountered high turbulence and strong downdrafts" near the top of the mountain pass.
At 1605, the Mammoth Lakes Police Department was notified that two hikers located the wreckage of a helicopter in an area near Lake Mary Road, approximately 7.8 nautical miles southwest of MMH, at an elevation of 8,750 feet mean sea level (msl).
During a telephone interview conducted by the NTSB IIC, the co-owner of the helicopter stated that this was the pilot's first flight in the accident helicopter to MMH. The co-owner stated the pilot had the CFI accompany him for "high altitude" flying.
The pilot received a private pilot certificate with an airplane single-engine land rating on July 17, 1976, and an airplane multi-engine land rating was added on May 6, 1999. He received a private rotorcraft helicopter rating on April 7, 2001. The pilot was issued a second-class medical certificate on September 25, 2001, with the limitation "MUST POSSESS GLASSES WHICH CORRECT FOR NEAR VISION." According to the pilot's logbook, he had accumulated 203.3 flight hours in helicopters of which 201.4 flight hours were in the accident helicopter make and model. Of those 201.4 hours, 112.7 flight hours were accumulated in the accident helicopter. The last logbook entry was dated May 18, 2002.
The flight instructor received a private pilot certificate with an airplane single-engine land rating on October 8, 1985, a private rotorcraft helicopter rating on March 25, 1987, and an airplane multi-engine land rating on October 25, 1987. He obtained a commercial rotorcraft helicopter rating on April 19, 1988, and a helicopter CFI rating on February 1, 1991. The pilot was issued a second class medical certificate on December 3, 2001, with no restrictions or limitations. According to the pilot's logbooks, as of May 19, 2002, he had accumulated a total of 5,973.8 flight hours of which 5,115.6 hours were accumulated in helicopters, 4,273.2 hours were accumulated in the accident helicopter make and model, and 3,516.2 flight hours were accumulated as a CFI. In addition, the pilot had logged 2.5 flight hours as "mountain flying." The pilot completed the Robinson Helicopter Company (RHC) Safety Course on June 12, 2001, and the pilot's logbooks indicated that the pilot had completed the RHC Safety Course on several previous occasions.
The flight instructor was the owner of Heloman Helicopters, of San Luis Obispo. Heloman Helicopter's services included flight instruction, aerial photography, aircraft rental, and aircraft charters.
The two-bladed, two seat, black and white Robinson helicopter, serial number 3198, was issued a standard airworthiness certificate on March 22, 2001, and was registered to the pilot and co-owner on December 19, 2001. The helicopter was powered by a 180-horsepower Lycoming O-360-J2A engine, de-rated to 131-horsepower (serial number L-37992-36A). The most recent annual inspection was completed on December 1, 2001, at which time, the airframe and engine had accumulated a total of 500.0 hours. On February 27, 2001, the altimeter, static system, and automatic altitude reporting system were tested to 16,000 feet msl.
The helicopter was equipped with main and auxiliary fuel tanks. The main fuel tank total capacity was 19.8 gallons (19.2 gallons usable), and the auxiliary fuel tank total capacity was 10.9 gallons (10.5 gallons usable).
The basic empty weight, and longitudinal and lateral centers of gravity (CG) for the helicopter, were calculated on March 7, 2001, and were found to be 873.85 pounds (lbs), 103.8 inches and -0.1 inches, respectively. The calculations were based on the actual weights and moment arms from the helicopter equipment list.
According to the approved rotorcraft flight manual, the maximum allowable gross weight for the accident helicopter was 1,370 lbs, with a longitudinal CG range between the 96.5 inch forward limit and the 100.0 inch aft limit (measurements are referenced to the datum point, which located 100 inches forward of the rotor centerline). The lateral CG range was between the 2.20 inch left limit and the right limit of 2.60 inches (measurements are referenced to the centerline of the mast: - is left, + is right).
Considering the occupants, miscellaneous baggage, and full of fuel, the helicopter's gross weight at the time of departure was 1,459.25 lbs with the calculated longitudinal CG at 97.56 inches, and the lateral CG at +0.06 inches. The following weights were used for the weight and balance calculation: pilot (right seat) - 218 lbs, flight instructor (left seat) - 180 lbs, miscellaneous baggage - 10 lbs, and fuel - 178.2 lbs (29.7 gallons total / 6 lbs per gallon). The weights of the occupants were obtained from their most recent pilot medical certificates, and the miscellaneous baggage was weighed at the salvage facility after the helicopter was recovered.
According to the approved rotorcraft flight manual, the maximum operating DA for the accident helicopter was 14,000 feet msl.
According to the approved rotorcraft flight manual section 5, "PERFORMANCE", the in-ground-effect (IGE) hover ceiling versus gross weight, and the out-of-ground-effect (OGE) hover ceiling versus gross weight performance limits were not available beyond 1,370 lbs. gross weight. The performance specifications had been approved up to the maximum allowable gross weight.
At 1501, the MMH AWOS reported the wind from 290 degrees at 14 knots, gusting to 19 knots, clear sky below 12,000 feet msl, 10 statute miles visibility, temperature 59 degrees Fahrenheit, dew point 16 degrees Fahrenheit, an altimeter setting of 30.03 inches of Mercury. The calculated DA was 8,702 feet.
At 1601, the MMH AWOS reported the wind from 270 degrees at 13, gusting to 19 knots, clear sky below 12,000 feet msl, 10 statute miles visibility, temperature 58 degrees Fahrenheit, dew point 20 degrees Fahrenheit, an altimeter setting of 30.02 inches of Mercury. The calculated DA was 8,593 feet.
The density altitude (DA) at MMH and the accident site was calculated by the NTSB IIC to 8,702 feet and 10,681 feet, respectively. The DA calculations were based on the MMH automated weather observing system (AWOS) report recorded at 1501, the airport/facilities directory (A/FD) published airport elevation of 7,128 feet msl, and the accident site elevation, recorded with a global positioning satellite (GPS) receiver, of 8,750 feet msl.
The Mammoth Yosemite Airport, MMH, is a public uncontrolled airport located 6 miles east of the city of Mammoth Lakes, California, at 37 degrees 37 minutes north latitude, and 118 degrees 50 minutes west longitude, at a surveyed elevation of 7,128 feet msl. The airport features a single asphalt runway, runway 9/27, which is 7,000 feet long and 100 feet wide. According to the A/FD's airport remarks, "the airport is located in mountainous terrain with occasional strong winds and turbulence. The airport has a lighted windsock available at runway ends and at the center of the airfield. Pilots could experience southerly crosswinds in excess of 10 to 15 knots, turbulence, and possible windshear along first 3000 feet of runway 27."
WRECKAGE AND IMPACT INFORMATION
The accident site was located at 37 degrees 36.980 minutes north latitude, 119 degrees 0.022 minutes west longitude. The helicopter came to rest on the side of a road on a magnetic heading of 050 degrees in a heavily wooded area. Numerous severed tree limbs and branches, which displayed fresh cuts, were located within a 40-foot diameter of the helicopter. Three trees, located 31 feet, 36 feet, and 35 feet from the helicopter, with an average height of 100 feet, displayed severed branches and limbs at their tops. The outboard 36 inches of one main rotor blade and outboard 42 inches of the other main rotor blade were separated and located 56 feet and 90 feet from the helicopter, respectively. The helicopter came to rest on its right side, and there were no ground scars except for the scars located beneath the helicopter.
The right skid was separated from the forward and aft crossover tubes, and the right forward crossover tube was separated from the fuselage. The right side of the cabin was crushed inward and aft into the instrument console. The instrument console was separated from its mounting structure. The right cyclic grip was separated and not found. The upper and lower right seat cushions were separated, and the right seat structure was crushed on the right side. Local authorities reported that when they arrived on scene, fuel was leaking from the helicopter and they turned the fuel selector to the OFF position. The throttle and mixture control levers were found in the mid-range and full rich positions, respectively. The manifold pressure gauge indicated 28 inches, the altimeter indicated an altitude of 9,200 feet with the Kollsman Window set at 30.02 inches of Mercury, and the Hobbs meter displayed 543.1 hours. The left and right cabin doors were separated from their respective hinge points, and the door lock pins were engaged on both doors.
The flight control tubes and bell crank assemblies had fracture points throughout the system. Flight control continuity was established by moving the flight controls at either side of the fracture points. All the fracture points exhibited physical evidence consistent with overload failure.
The engine remained attached to the airframe; however, the upper mounts were cracked. The engine accessories remained attached to their respective mounts. The exhaust system remained intact. The battery was found dislodged from the battery box. The throttle and mixture control settings at the carburetor were found in the full open and full rich positions, respectively. The upper sheave pulley displayed rotational signatures. The engine to transmission drive belts were intact and displayed signatures consistent with rubbing. Fuel was found in the system lines and gascolator, and approximately 4 gallons of fuel were drained from the main and auxiliary tanks during the recovery. The integrity of the main fuel tank was compromised on the interior wall above the fuel sending unit, and the fuel cap was secured. The integrity of the auxiliary fuel tank was compromised on the interior wall, and the fuel cap was secured.
The main rotor assembly, with its remaining main rotor blades (MRBs), remained attached to the transmission. The main rotor transmission housing was fractured at the right forward mount, and the transmission mounts were attached and secure. The main rotor drive shaft was intact and displayed signatures consistent with rubbing on the outboard edge of the sheave. Continuity between the engine and the main rotor system was established. The clutch assembly was intact and operational.
The MRBs were identified and marked by the manufacturer as red and blue. The red MRB was bent upward approximately 10 degrees from the rotor head to the blade tip, and the trailing edge displayed several compression wrinkles along the entire blade. The MRB's pitch horn was bent, the droop tusk was intact, and the blade boot was intact. The outboard 3 feet of the MRB was separated, and the tip weight was installed and intact on the separated section.
The blue MRB was bent upward approximately 60 degrees from the rotor head to the blade tip, and the trailing edge displayed several compression wrinkles along the entire blade. The MRB's pitch horn and droop tusk were intact, and the blade boot was torn and damaged. The outboard 3.5 feet of the MRB was separated. The tip weight was installed and intact on the separated section.
The tailboom was partially separated and bent at the fuselage attach point and at the 3rd and 4th tailboom bays. The tail rotor pitch change shaft and drive shaft were bent at the corresponding tailboom separation points. The intermediate flex coupling was intact. The tail rotor gearbox remained attached to the tailboom and rotated freely by hand. One tail rotor blade was not damaged, and the other tail rotor blade was bent outward approximately 20 degrees. The outboard 8 inches of the horizontal stabilizer was bent down, and the bottom of the vertical stabilizer was bent to the left. There was no evidence that the main rotor blades contacted the tailboom.
Both pilot autopsies were performed by the Mono County Coroner's Office, Bridgeport, California, on May 23, 2002. Toxicological tests performed by the FAA's Civil Aeromedical's Institute (CAMI) Forensic Toxicological and Accident Research Center were negative for both pilots.
Both seatbelts were found buckled and were cut during the rescue operation. The pilot and passenger shoulder harness inertia reels were intact and were functionally tested with no anomalies noted.
The helicopter was not equipped with an emergency locator transmitter (ELT).
TEST AND RESEARCH
On May 25, 2002, at the facilities of Plain Parts, Pleasant Grove, California, under the supervision of the NTSB IIC, the engine was examined and an engine test run was completed with the engine still installed on the helicopter. Prior to the engine test run, the engine manufacturer representative removed the right bottom spark plugs and approximately 1 to 1 1/2 cups of engine oil was drained from the #2 and #4 cylinders. The spark plugs were cleaned and reinstalled. The engine oil dipstick was checked and indicated that the engine contained 5 quarts of oil. A slave battery was connected to the starter. The transmission drive belts were cut and removed from the engine driven pulley. Fuel was added to the main fuel tank, and the fuel selector was turned to the ON position. The master switch was turned ON, and the engine was started using the broken key in the ignition switch. After the engine was warmed-up, the engine was test run at various power settings (idle to full power of 104 percent rpm) for approximately 5 minutes. During the engine test run, the magnetos were checked, and the temperature and oil pressure gauges were operational. No anomalies or discrepancies were noted during the engine test run.
A Garmin GPS GNC 420 unit was recovered from the accident helicopter and tested by the manufacturer, GARMIN International, Inc., Olathe, Kansas, on June 7, 2002. According to GARMIN, "damage from the accident to the internal circuitry has prevented us from being able to review any stored data."
According to the FAA's Basic Helicopter Handbook (Advisory Circular 61-13B), "High altitude pilot technique" section, "Of the three major factors limiting helicopter performance at high altitudes (gross weight, density altitude, and wind), only gross weight can be controlled by the pilot of a helicopter that is equipped with an unsupercharged engine. At the expense of range, smaller amounts of fuel may be carried to improve performance..."
In addition, the handbook states, "When the wind blows over large obstructions such as mountain ridges...it is a much more disturbed condition. The wind blowing up the slope on the windward side is usually relatively smooth. However, on the leeward side the wind spills rapidly down the slope...setting up strong downdrafts and causing air to be turbulent. The downdrafts can be very violent and cause aircraft to strike the sides of mountains. Therefore, when approaching mountain ridges against the wind, it is sound practice to make an extra altitude allowance to assure safe terrain clearance. Where pronounced mountain ridges and strong winds are present, a clearance of 2,000 or 3,000 feet above the terrain is considered a desirable minimum. Also, it is advisable to climb to the crossing altitude well before reaching the mountains to avoid having to make the climb in a persistent downdraft."
The helicopter was release to the owner's representative on June 13, 2002.