Safford, AZ, USA
N6259N
WSK PZL Mielec M-18A
The engine lost power while the pilot was turning the airplane onto the base leg of a simulated fire retardant drop pattern. Thereafter, the airplane stalled and collided with the ground while in an uncontrolled descent. The accident occurred during a public-use firefighting training flight supervised by the Department of Interior, Bureau of Land Management (BLM). During the flight the pilot was practicing dropping fire retardant in a designated area on a simulated wildland fire. A witness reported hearing the engine surge several times, after which the airplane's bank increased and it descended. The airplane impacted the ground in a near-vertical, nose-down pitch attitude. The airframe and engine were examined and no evidence of any preimpact mechanical malfunction was found. The airplane was dispatched with adequate fuel for the planned flight. In the airplane's flight manual, the manufacturer provided guidance regarding equalizing unbalanced wing tank fuel quantity levels to avoid fuel starvation from unequal consumption of fuel in the tanks. During the accident investigation, no fuel was found in either the left wing or header tanks, which had retained their integrity. The right wing tank was found ruptured. The pilot operated valve that allows fuel to flow between the main fuel tanks to equalize the amount of fuel in each tank was found in the closed position. The airplane was not equipped with optional low-fuel warning lights in the cockpit. In addition, the examination determined that the AW-2-30 propeller certificated for the airplane had been replaced with the larger, unapproved AW-2 propeller and that the airplane’s propeller logbook did not reflect this change.
HISTORY OF FLIGHT On March 16, 2004, about 0935 mountain standard time, a Wsk PZL Mielec, M-18A, (aka "Dromader") N6259N, collided with terrain following a loss of engine power while maneuvering about 12 nautical miles east-northeast of the Safford Regional Airport, near Safford, Arizona. The commercial certificated pilot was fatally injured, and the airplane was destroyed. During the accident flight, the single-engine air tanker (SEAT) airplane was under the operational control of the Bureau of Land Management (BLM), U.S. Department of the Interior (DOI). The pilot was a non-government employee of the contractor, and he was the sole occupant in the airplane. The airplane was operated with a restricted category Federal Aviation Administration (FAA) airworthiness certificate. The purpose of the public-use training flight was to practice a simulated fire retardant drop in a designated area. The flight was performed under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed, and a BLM approved flight plan had been filed for the local area flight. Following BLM's supervised training program, at 0815, the pilot began the day's flight operation from Safford by performing an initial mission over a designated area. The pilot completed the mission and returned to Safford to reload for another training mission. Reportedly, the airplane was not refueled because it contained adequate fuel for the next flight. The pilot took off about 0915. According to BLM personnel, once airborne the pilot's destination was changed in accordance with the training syllabus. The pilot was diverted to a new area, which required him to reprogram both the global positioning satellite (GPS) receiver and communication radios, and to contact and coordinate his actions with the new fire incident commander (IC). The specific maneuvers (circling vs. straight and level flying with periodic course reversals) undertaken by the pilot while setting up for the new destination were not determined. The diversion exercise took several minutes. The pilot successfully diverted to the new location. A BLM employee, simulating the role of a fire IC, described the training scenario as "operations normal" as the pilot maneuvered the airplane on the downwind leg of the flight pattern. The pilot transmitted a request to the IC to perform a "dry run" prior to dropping his load of water on the simulated wildland fire. During the practice maneuver, the pilot was observed to extend his downwind leg. While turning left to the base leg, the airplane's engine was heard to "surge" two or three times. A witness stated that the airplane assumed an "unusual attitude" with "the right wing up and the nose down" until he lost sight of the airplane as it descended behind a ridgeline. PERSONNEL INFORMATION The pilot held a commercial pilot certificate with the following ratings: airplane single engine land, airplane multiengine land, instrument airplane, rotorcraft-helicopter, and glider. Also, he held a certified flight instructor certificate for airplane single and multiengine, and glider. On January 26, 2002, the pilot filed a report with the DOI in which he indicated his flying experience. In part, the pilot reported that his total pilot-in-command (airplane) flying time was 16,500 hours, and his experience flying the accident model of airplane was 461 hours. On February 4, 2004, the pilot filed another report with the DOI and indicated that his total pilot-in-command (airplane) flying time was 17,150 hours. His experience flying the accident model of airplane was 600 hours. AIRCRAFT INFORMATION The airplane had a carburated radial engine that produced about 967 horsepower. The airplane's maximum gross weight was 11,700 pounds. Weight and Balance. DOI personnel reported to the National Transporation Safety Board investigator that a review was performed of the airplane's flight manual (AFM) and weight and balance data. During the accident flight, the airplane was operated within the appropriate gross weight and center of gravity limits. Fuel System Design. The following description of the airplane's fuel system was included in the AFM: The airplane is equipped with two wing tanks of 94 US gallons. The wing tanks are connected to a header tank of 3.7 US gallons, located in the central part of the centerwing section. The supply lines from the wing tanks to the header tank contain "non-return" valves to "eliminate the possibility of fuel flowing from one tank to the other." The pilot can open an "overflow line" which connects the two wing tanks to equalize the fuel between the two tanks. In the Normal Procedures section of the AFM, there was a warning against allowing an imbalance in fuel quantity between the right and left fuel tanks. The airplane was not equipped with optional low-fuel warning lights in the cockpit. Fuel Balance and Warning Statement. The AFM describes a design characteristic that allows fuel to crossfeed from one wing tank to the other, uncommanded by the pilot. The following information was provided in the AFM's Normal Procedures section: (a) Watch the fuel quantity in the left and right tanks during flight; (b) If unequal fuel quantity is found, open the fuel overflow valve and recover the airplane to level flight or even bank it slightly toward the wing with less fuel to quickly equalize the fuel level in both tanks; and (c) When equal fuel levels have stabilized in both tanks, close the overflow valve. The Emergency Procedures section warns pilots to keep the fuel balanced between the wing tanks to avoid a fuel starvation induced engine failure. Specifically, the following warning was provided: (a) Pay special attention not to allow fuel to be completely consumed from any of the wing tanks according to the fuel gauge or low fuel level warning lights (if installed); and (b) After having noticed unequal fuel consumption from the wing tanks open the fuel overflow valve and recover the airplane to level flight or bank the airplane toward the wing with less fuel to quickly equalize the fuel level in both tanks. METEOROLOGICAL INFORMATION The closest aviation weather observation station to the accident site is located at the Safford Airport. In pertinent part, at 0850 the surface wind was calm, the visibility was 10 miles, and the sky condition was clear. The temperature and dew point were 14 and 1 degrees Celsius, respectively. COMMUNICATIONS The FAA Western-Pacific Region quality assurance staff reported that no communications were recorded from the accident airplane by FAA facilities during the accident flight. No FAA services were being provided to the pilot. WRECKAGE AND IMPACT INFORMATION The accident occurred at the following GPS coordinates: 32 degrees 52.01 minutes north latitude by 109 degrees 23.55 minutes west longitude. The approximate elevation was 4,150 feet mean sea level. The ground was near level and sparsely vegetated. A post impact fire developed in the vicinity of the engine's number 1 cylinder. The first responders extinguished the fire using handheld fire extinguishers and dirt. Under the direction of the Safety Board investigator, DOI personnel examined the accident site and airplane wreckage. The physical evidence indicated that the airplane impacted the ground in a near vertical, nose-low attitude. Terrain and native vegetation a few yards from the impact crater were undisturbed. The forward portion of the fuselage was crushed in an aft direction. The leading edge of the right wing was observed accordioned in an aft direction to the spar. The aft crush was nearly perpendicular to the airplane's longitudinal axis. The leading edge of the left wing was impact damaged, and the outboard portion was bent upward. The engine was found about 22 feet forward of the fuselage. The entire airframe structure was found with the wreckage. The airplane was recovered from the accident site and was examined. DOI personnel reported that it found no evidence of any preimpact mechanical defects with the airplane. MEDICAL AND PATHOLOGICAL INFORMATION The pilot's last aviation medical certificate was issued in April 2003. It bore the limitation that corrective lenses be worn. Several witnesses observed the pilot prior to his departure. None reported observing the pilot manifest abnormal behavior or appearance. The FAA Bioaeronautical Sciences Research Laboratory performed toxicology tests on the pilot. The laboratory manager reported finding no evidence of carbon monoxide, cyanide, ethanol, or any screened drugs. The Ameritox Laboratory, Midland, Texas, on behalf of the Graham County Coroner, also performed toxicology tests on the pilot. The results were also negative for all screened drugs. On March 18, 2004, an autopsy was performed on the pilot by the Forensic Science Center, 2825 E. District Street, Tucson, Arizona 85714. TESTS AND RESEARCH Fuel Balance Pilot Reports. A pilot who had flown the accident airplane a week prior to the crash reported that the airplane used more fuel out of its left tank than out of the right tank. Also, a pilot reported that if the airplane was trimmed out correctly, the fuel could be balanced. Fuel On Board Accident Flight. A reconstruction of the fuel in the tanks was undertaken. Dispatch logs, witness statements, and fueling records were reviewed to ascertain the approximate quantity of fuel on board at takeoff for the accident flight. According to DOI personnel, the evidence indicates that the airplane had been operated between 1.5 and 1.8 hours since it was last refueled. Approximately half of the airplane's total fuel quantity should have been available during the accident flight. The distribution of fuel between the tanks could not be ascertained. Fuel System Examination. Initial responders to the accident site recalled smelling fuel. The BLM's subsequent on-site inspection of the right and left fuel tanks via the fuel filler caps and fuel drains revealed no fuel present. The header tank, which is fed by both main fuel tanks, also contained no fuel. Investigators reported that impact damage was most severe to the right wing with the right wing's fuel tank appearing to have been ruptured during impact. The left wing fuel tank and the header tank showed no obvious signs of rupture. Investigators tested and confirmed the integrity of the left wing fuel tank and the header fuel tank by filling them with water. The only leaks observed during this testing were from fuel lines broken during the impact or from fuel lines that were disconnected after the accident. During the examination of the wreckage, it was noted that the airplane was not equipped with the optional low fuel level warning lights. Also, the handle for the "overflow fuel valve," which allows fuel to crossfeed between the tanks, was found to be in the down (closed) position. Airframe Examination. Inspection of the flight control system in the cockpit confirmed continuity to the rudder and elevator. The flight control linkages from the cockpit to the ailerons were found severed in impact-damaged areas of the airframe. Engine and Propeller Examinations. The engine was torn down under the supervision of DOI personnel, and an examination was performed for evidence of preimpact internal engine damage. No such evidence was detected. The propeller blades were also examined. According to the DOI's investigation report, the deformation and marks observed on the propeller blades were consistent with a windmilling propeller at impact. The examination also determined that the AW-2-30 propeller certificated for the airplane had been replaced with the larger, unapproved AW-2 propeller, and that the airplane’s propeller logbook did not reflect this change. The AW-2-30 propeller has four 3.3-meter blades with square blade tips. The AW-2 propeller has four 3.6-meter blades with rounded tips. Although PZL Mielec had flight tested the AW-2 propeller on the M-18A Dromader airplane, it was not certified for use on the airplane for several reasons, according to a November 19, 2007, e-mail from the manufacturer provided to the NTSB during a follow-on investigation. In the e-mail, the PZL Mielec M-18 chief designer stated that the AW-2 propeller was not certified for the M-18A Dromader because “during test flights pilots reported problem with airplane stability.” The chief designer added that the “gap between the blade tip and the ground (with deflated tires) was too low, [and that the] propeller has not fulfilled FAA requirements in that regard.” He stated that tests were discontinued thereafter. In a September 10, 2009, e-mail to an NTSB engine specialist, the PZL Mielec chief designer stated that during the flight tests of the M-18A Dromader with the AW-2 propeller, fuel consumption was not measured. However, the chief designer added that test personnel involved in those flight tests all confirmed that fuel consumption was slightly higher with the AW-2 propeller, although they could not provide a quantifiable amount. ADDITIONAL INFORMATION. Additional investigative facts, including interview statements and photographs, are included in the accident report received from the DOI. The DOI's report is included in the Safety Board's docket. The wreckage was released to its owner's assigned insurance adjuster on September 7, 2004. No parts were retained.
A loss of engine power due to fuel starvation and at least one ensuing engine power surge, which caused the airplane to pitch up abruptly into a stall at an altitude too low for recovery. Contributing to the accident were the pilot's mismanagement of the fuel supply, his failure to adhere to prescribed flight manual procedures for equalizing the fuel quantity distribution between the fuel tanks, and his failure to maintain adequate airspeed after the power loss.
Source: NTSB Aviation Accident Database
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