DEN02GA085

the pilot's abrupt collective input during water application to a forest fire. Contributing factors were encountering a vortex ring state, the inadvertent settling with power, the low altitude, and the mountainous terrain.

The helicopter was engaged in fire suppression activities. As the pilot made an approach for a water drop, witnesses said the engine made a "high-pitch whine," there was "a loud pop," they saw the rotor blades "slowing down," and heard the blades making a "thump, thump, thump" sound. The pilot was heard to say he was "going down." Witnesses reported seeing purple or blue flames shooting 2 to 3 feet from the exhaust stack. After the helicopter struck the ground and rolled over, witnesses heard the engine spooling down and saw flames coming from the engine "like a blowtorch." A post-impact ground fire, confined to the cockpit area, was quickly extinguished. An examination of the helicopter engine revealed evidence of heat distress aft of the labyrinth seal. The turbine section had a "corn cob" appearance. The first and second stage nozzles showed heat damage. The third stage nozzle was totally destroyed. According to the engine manufacturer, the turbine blades were exposed to "around 1,000 degrees C., about 400 degrees C. beyond the normal operating temperature over a short period of time." According to "Helicopter Aerodynamics," if the rate of descent exceeds 1/4 of the hover induced velocity, the flow conditions are such that the air is going both up and down through and around the rotor in a disorganized and unsteady manner. This is called vortex ring state. It exists until the helicopter is descending at about twice the hover-induced velocity. In the vortex ring state, the helicopter pilot may find himself in the unusual situation where pulling up the collective pitch does not slow the rate of descent. This is known as settling with power. The pilot has entered "a flight condition where the required power is more than the available power." According to the Artouste IIIB Training Manual, engine rotation (nominal) speed is 33,500 rpm, plus or minus 200 rpm. The fuel control unit maintains this speed. If a load is placed on the engine, the fuel-metering valve opens, fuel flow increases, and engine torque increases. Variation from this speed must not exceed 1,000 rpm. The time it takes to return from a speed variation to the nominal engine rotation speed is less than 4 seconds.

HISTORY OF FLIGHT On July 30, 2002, at 1843 mountain daylight time, an Aerospatiale SA315B, N3978Y, registered to Roberts Aircraft Co., Granite Canyon, Wyoming, and operated by Geo-Seis Helicopters, Inc., Fort Collins, Colorado, was destroyed when it struck terrain while maneuvering 6 miles southeast of Estes Park, Colorado. The commercial pilot, the sole occupant aboard, was fatally injured. Visual meteorological conditions prevailed at the time, and no flight plan had been filed. The flight originated from a staging area near Estes Park approximately 1840. The helicopter was engaged in fire suppression activities at the Big Elk fire near the Rocky Mountain National Park. According to the U.S. Forest Service (USFS), several large unburned "islands," approximately 400 acres in size, were in the northwest section of Division B. Due to the abundance of fuel and topography, this area had the greatest potential for the fire to spread towards Estes Park. According to the USFS, the pilot's day began at 0745 when he was dispatched to the Big Elk Helibase, arriving there about 0800. After being briefed, the pilot began making water drop missions. At 1530, he transported fire managers and reconnoitered a fire area. It was determined that additional water bucket drops would be necessary to cool down certain areas, and pre-treat unburned areas. For the next two hours the pilot made a number of water drops. The pilot returned to the helibase about 1800 and the helicopter was refueled. The pilot took off approximately 1820 and made two additional water drops. According to witnesses, as the pilot made his approach for a third water drop, they heard engine sounds described as the "engine screaming"; like a "car was in neutral and the engine was running fast"; a "high-pitch whine"; a "high-pitch noise"; a "strange noise" like the engine was "under strain" or "bogging down"; "Rrrrrr"; and an "electronic sound with grinding metal." Some witnesses heard "a loud pop," or a "snap." Witnesses said the rotor blades were "still turning" or "slowing" or "winding down." One witness said the "rotor sound was gone." Many reported hearing the rotor blades making a "thump, thump, thump," or "whoop, whoop, whoop" sound. Witnesses monitoring the helicopter's radio frequency reported hearing the pilot say, "Hey guys, I'm having trouble, I'm going down"; "I'm having trouble here"; "Helicopter going down"; "Going down, going down"; "Boat down," or words to that effect. Witnesses on the ground saw purple or blue flames coming from the exhaust stack. One witness said they were "pinkish-colored." Another witness said the flames "took on a flame-thrower effect, " shooting flames two to three feet out the exhaust stack. Another witness reported seeing the helicopter falling "skid down." Another witness said that hitting the ground and rolling over, they heard the engine spooling down. Flames were seen "coming from the engine after impact" and it "sounded like a blowtorch." A postimpact ground fire, confined to the cockpit area, was quickly extinguished. Witnesses agreed that when they heard the noises and saw the flames coming from the tailpipe, the water bucket --- although low --- was above the trees. The accident occurred during the hours of daylight at a location of 40 degrees, 17.99' north latitude, and 105 degrees, 26.94' west longitude, or about 6 miles southwest of Estes Park, Colorado, near Rocky Mountain National Park. CREW INFORMATION The pilot held a commercial pilot certificate, dated May 3, 1974, with rotary wing-helicopter, instrument-helicopter, and airplane single-engine land ratings. He also held a second class airman medical certificate, dated May 23, 2002, with the restriction, "Must have available glasses for near vision." When he applied for this certificate, he estimated his total flight time at 8,000 hours, 50 hours of which were accrued in the previous six months. The USFS reported that the pilot had 7,730 hours of total time, 900 hours in the Aerospatiale SA315B, and over 7000 hours in rotorcraft. The pilot had 200 hours of flight time within the previous 90 days, 100 hours within the previous 30 days, and 8.7 hours within the previous 24 hours before the accident. According to FAA Civil Aeromedical Institute (CAMI), a review of his medical file disclosed "no major medical problems." AIRCRAFT INFORMATION N3978Y (s/n 2520), a model SA315B Llama, was manufactured by Aerospatiale in 1978. It was equipped with a Turbomeca Artouste IIIB turboshaft engine (s/n 815), rated at 858 shaft horsepower. It was owned by and registered to Roberts Aircraft Company of Granite Canyon, Wyoming, operated by Geo-Seis Helicopters, Inc., of Fort Collins, Colorado, and under contract to the Rocky Mountain Interagency Helitack. It was equipped with a 100-foot long line. One end was attached to a quick-release on the bottom of the helicopter, and the other end was attached to a 144-gallon "Bambi" bucket. Opening the bucket and dropping its contents was pilot-controlled by activating a cockpit release, either manually or electrically. According to the helicopter maintenance records, the last inspection was performed on May 10, 2002. The airframe had accrued 202 hours since this inspection, and had a total time-in-service of 3,709 hours at the time of the accident. The turbine nozzle guide vanes had accumulated 4,707 total hours and were original equipment. According to Turbomeca, the nozzles are not cycle-limited. According to FAA Special Airworthiness Information Bulletin (SAIB) No. NE-03-30, dated March 13, 2003, the French Military Services had previously sold surplus Aerospatiale Alouette and Lama helicopters, powered by Turbomeca Artouste II, III, and Astazou XIV engines, to the public. The Bulletin noted that the helicopters "may not have been maintained within the framework of a civil regime and their configuration may not conform to the type definition approved by the Civil Aviation Authority." The French Direction Generale de l'Aviation Civile (DGAC) issued various airworthiness directives to mandate the proper actions to be taken, prior to the next flight, for authorized use of these engines for civil operation. "The FAA, however, does not recognize these surplus foreign military engines as eligible for installation on any civil aircraft having an Airworthiness Certificate other than 'Experimental'. We will not issue an Airworthiness Certificate other than 'Experimental' for aircraft and engines released as surplus by a foreign military service, even if these products have been subsequently resold by a manufacturer, owner/operator, repair facility, or part supplier, due to the lack of historical fleet records. This data is essential to verify the modification standards, the applied repair solutions, the scheduled and unscheduled maintenance practices, and in particular, the life cycle remaining for the critical parts. Without complete knowledge of the previous operational usage and all the aspects of its quality system for maintaining the engines, we cannot find the appropriate level of continued airworthiness for safe operation" as required by Title 14 CFR Part 21.29. These "aircraft and engines cannot be used for civil operation in the US, other than as 'experimental' category aircraft. You cannot presume that their accessories, spare parts, whether new, used or parted out, are eligible for installation of FAA type certificated products used for civil operation." Turbomeca Service Bulletin No. 218 72 0094 (originally issued August 16, 1995, and most recently updated on August 9, 1997), applicable to Artouste IIIB and B1 engines, outlined the procedures to be taken to convert former military engines to civilian use. The Bulletin required an "engine Airworthiness statement" containing "(1) the knowledge of the engine configuration and of the compliance with the maintenance instructions defined by Turbomeca (periodic inspections, general ov