CEN14FA143

The pilot’s inadequate emergency response to a runaway propeller and his failure to maintain airspeed, which resulted in the airplane exceeding its critical angle-of-attack and stalling. The cause of the runaway propeller was undetermined.

After several hours of ground instruction and one solo flight, the private pilot was making only his second takeoff in a single-seat Hawker Sea Fury airplane. Two witnesses standing at midfield reported hearing abnormal engine and propeller sounds during takeoff, and the airplane's speed seemed to be slower than normal. Another witness, who had pilot experience in the Hawker Sea Fury, did not see the takeoff but reported that he could clearly hear the engine "screaming," and he knew at that moment that the accident pilot was experiencing a propeller overspeed. A flight instructor was conducting a formation takeoff in trail behind the accident airplane to observe the flight. After his takeoff, he joined in on the right side of the accident airplane and he heard the accident pilot make a radio transmission that he had an overspeed and the airplane's rpm was at 3,500. The instructor reported that the maximum takeoff power was about 2,900 rpm. No further transmissions from the accident pilot were heard. The instructor kept repeating for the pilot to pull the power back and keep the nose down. Both airplanes climbed to about 1,000 ft above ground level, and the accident airplane began a slow turn to the left. The flight instructor continued to fly in formation with the accident airplane and continued to transmit instructions to the accident pilot to lower the nose and reduce the throttle. However, the accident airplane continued to slow and fly in a nose-up attitude until it stalled and rolled to the right. It then entered a vertical nose-down dive and impacted terrain. The flight instructor and witnesses reported that there was an immediate explosion and postimpact fire. The witnesses' description of abnormal engine and propeller sounds and the accident pilot's report of 3,500 rpm are indicative of a runaway propeller. The Hawker Sea Fury emergency checklist indicated that recovery from a runaway propeller was possible when following the procedures listed in the checklist, which include reducing the throttle, decreasing the propeller angle, and maintaining an airspeed of 140 knots. A postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. A laboratory examination of the impact- and thermally damaged propeller regulator did not show any obvious evidence of preimpact mechanical malfunction or abnormalities. The cause of the runaway propeller could not be undetermined.

The Unicom radio frequency at BKD was not recorded. The FAA Airport/ Facility Directory, South Central U. S., indicated that BKD was a non-towered airport with a field elevation of 1,284 feet mean sea level (msl). The longest runway was 17-35, which was an asphalt runway 4,997 feet long by 100 feet wide. Runway 17 was oriented to 180 degrees true and 173 degrees magnetic. Records show that runway 17 had a 0.5 percent upslope gradient to the south. Other shorter runways at BKD were also listed. The propeller regulator, including the control input rod ends, mechanical controller, internal hydraulic gear pump assembly, and the drive gear were removed from the wreckage and were examined at the NTSB Materials Laboratory in Washington, D. C. Examination of the broken control input connecting rod showed the fracture surfaces were consistent with fracture from bending overstress. The drive gear had deformation which was consistent with twisting and bending. Four of the gear teeth contained smear marks on their aft faces which was consistent with teeth-shaped witness marks on the forward face of the hydraulic gear pump housing. A 0.5 inch long radial tear exhibited characteristics consistent with overstress fracture. A key inside the circumferential face of the gear bore was still in place in the gear slot and exhibited smearing and deformation consistent with impact with an adjacent part and corresponded with similar marks on the inner face of the drive gear bore. The hydraulic gear pump was still attached to the surrounding propeller housing that had fractured and separated from the rest of the airplane. The fracture surfaces were consistent with overstress fracture. The pump assembly was removed from the fractured housing. Two of the three bolts were still fixed with safety wire attached. The inboard faces of the pump exhibited darkening and soot consistent with fire exposure. The right inboard side of the forward face of the pump exhibited four teeth-shaped impressions. Those witness marks corresponded with the smear marks on the drive gear teeth. The shape of the gear marks was consistent with the drive gear rotating clockwise (forward looking aft). The rear and sides of the housing exhibited a few indications of damage. The most notable area was one of the side flanges with a bolt hole that had been worn away. The four bolts in the aft of the pump were still in place, with the safety wire affixed. The hydraulic pump was disassembled and examined. The surfaces were covered in a gelatinous substance consistent with dried hydraulic fluid which left gear teeth impressions on the surfaces, consistent with the position of the gears at the time of the accident. The cylindrical surfaces exhibited longitudinal marks consistent with the positions of the internal gear teeth crests. Ferrous corrosion product was present in the housing interior. However, this corrosion product was confined to the corners of each gear recess. The pattern of corrosion was consistent with pooled water after the accident. There were no indications of excessive wear or smearing on the interior housing surfaces. None of the channels for hydraulic fluid flow contained any indications of blockage. An examination of the hydraulic pump gears after removal from the pump showed that they were relatively undamaged and were able to be rotated about their shafts. The exterior faces of the gear teeth exhibited some rotational wear marks, consistent with typical service wear. The teeth exhibited some ferrous corrosion product, which was limited to four of the forward teeth faces and two gear teeth valleys on each gear. This corrosion was consistent with pooled water incurred after the accident. The laboratory examination of the impact damaged and thermally damaged propeller regulator and other parts revealed no evidence of preimpact mechanical malfunctions or failures that would have precluded normal operation. According to the Checklist for the Hawker Sea Fury: the Emergency Checklist procedure for "Runaway Propeller" on page 36 states: "Failure of the governor to operate properly may result in a runaway propeller. A runaway propeller goes to full low pitch and may result in an engine rpm of 3600 or more. When such a failure occurs, the only method of reducing rpm is to pull the throttle back and decrease airspeed. In doing this, it is highly important to reduce airspeed in order to maintain the maximum horsepower available. The following procedure is recommended: Throttle . . . . . . . . . . .REDUCED (2900 RPM) Propeller . . . . . . . . . .DECREASE Note: In case of an overspeed, moving the propeller control lever toward DECREASE may bring the propeller under control. Airspeed . . . . . . . . . .140 KNOTS Raise the nose to lose speed and then return to level flight attitude keeping IAS at approximately 140 knots. When over a landing area, lower the gear and make an approach at normal landing speed. Caution: If engine rpm cannot be kept within limits, expect the engine to quit or seize at any time". Land . . . . . . . . . . . . . .ASAP" According to the Department of Energy Handbook DOE-HDBK-1081-94, December 1994 Magnesium Properties – on pages 20 through 22, and page 34 states: "The ignition temperature of massive magnesium is very close to its melting point of 1,202 degrees Fahrenheit (F). Solid metal ignition of magnesium can occur at 1,153 degrees F. Metal marketed under different trade names and commonly referred to as magnesium may be one of a large number of different alloys containing magnesium, but also significant percentages of aluminum, manganese, and zinc. Some of these alloys have ignition temperatures considerably lower than pure magnesium, and certain magnesium alloys will ignite at temperatures as low as (800 degrees F). Flame temperatures of magnesium and magnesium alloys can reach (2,500 degrees F)." "The more massive a piece of magnesium, the more difficult it is to ignite, but once ignited, magnesium burns intensely and is difficult to extinguish". According to "Civil Pilot Accident Experience With High Performance Military Surplus Type Aircraft" (1967); R. G. Snyder: The study of one particular type of military type aircraft during a 26 month period showed that, of the 80 operational airplanes of that type, 25 of the airplanes were involved in aircraft accidents which resulted in 12 fatalities and 4 serious injuries. The conclusions on page 32 noted that the "major cause of these accidents was overwhelmingly pilot experience". An autopsy was performed on the pilot by the Tarrant County Office of the Chief Medical Examiner in Fort Worth, Texas. Forensic toxicology was performed on specimens from the pilot by the FAA Civil Aerospace Medical Institute (CAMI), Oklahoma City, Oklahoma. The toxicology report stated that tests for carbon monoxide and for cyanide were not performed, ethanol was not detected in vitreous, and no listed drugs were detected in blood. The wreckage was located on dirt and rocky terrain in a remote wooded area at an estimated elevation of about 1,250 feet msl about 1 mile southeast from BKD. Evidence at the scene showed the airplane impacted in a nearly vertical nose-down attitude. There was evidence of a postimpact fire which thermally damaged most of the vegetation within a diameter of more than 100 feet. The initial impact crater was about 1 foot deep and about 5 feet in diameter. The completely separated front section of the engine was found upright on the southeast edge of the impact crater. The propeller hub remained attached to the engine's propeller shaft and two blades of the propeller remained attached to the propeller hub. The other two blades were completely impact separated from the hub, but were found adjacent to the engine and impact crater. The propeller blades showed evidence of leading edge impact damage and showed evidence of chordwise smearing on the blade faces. Bro