History of Flight
On August 23, 2014, at 1500 central daylight time, a Beech S35, N334DF, was destroyed during impact with terrain and a subsequent post-impact fire near Laurel Hill, Florida. The commercial pilot was fatally injured. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which departed Bob Sikes Airport (CEW), Crestview, Florida, about 1450, and was destined for Florala Municipal Airport (0J4), Florala, Alabama. The personal flight was operated under 14 CFR Part 91.
A friend of the pilot stated that the purpose of the flight was to relocate the airplane to 0J4, about 19 miles northeast of CEW, where it could be stored in a hangar while the pilot traveled overseas. The pilot attempted to complete the flight the day prior, but the airplane would not start. After unsuccessful jump-start attempts, a mechanic serviced the battery the morning of the accident, started the engine, and performed a run-up check.
A lineman reported that the pilot arrived between 1400 and 1430, boarded, started the engine, and taxied to the runway. The pre-takeoff run-up was unusually long, as the pilot would typically "hop in and go." Radar data showed the airplane depart CEW north about 1450, climb to 1,600 feet mean sea level, then perform a left turn and 360-degree turn near the pilot's home. The flight later resumed a northeasterly track, climbed to about 2,400 feet, and began a descending right turn around 1459. The last four radar targets placed the airplane about 1.25 nautical miles southeast of the accident site at about 1,400 feet on a heading of 285 degrees.
A witness near the accident site saw the airplane circling overhead; the engine sounded like it was revving up and down. As it descended toward a field, the witness heard engine "popping" and saw trailing smoke. After the airplane descended into trees and impacted the ground, the witness drove to the site and observed a pillar of black smoke. The cockpit was filled with smoke, and the airplane "exploded" twice before first responders arrived.
Pilot Information
The pilot held a commercial pilot certificate with ratings for airplane single-engine land and instrument airplane. His most recent FAA second-class medical certificate was issued in March 2014, reporting 3,300 total hours of flight experience, with 0 hours in the previous 6 months. No personal flight logs were recovered. An autopsy listed the cause of death as inhalation of products of combustion. Toxicological testing was positive for carbon monoxide in blood; diphenhydramine, pheniramine, and zolpidem in urine and blood, all below therapeutic levels.
Aircraft Information
The airplane, manufactured in 1964, was equipped with a Continental Motors IO-520-BA6B, 285 hp reciprocating engine. It was registered to the pilot in April 1998. No maintenance records were located, but work orders from September 2011 were provided. In March 2012, an annual inspection was performed at 5,047.50 total aircraft time; the #3 cylinder was removed and repaired due to a failed compression test and burnt valve. In September 2013, another annual inspection was performed at 5,048.02 hours. The mechanic who serviced the battery noted the tachometer read 5,049.08 after his run-up.
Work orders from the March 2012 inspection noted: "Engine monitor has 2 cylinders that have no CHT reading." This was marked as deferred with no corrective action. FAA records did not indicate an STC for an aftermarket engine monitor. The original CHT gauge was removed and replaced in November 2013, displaying CHT from one cylinder only. The investigation could not determine when or where the airplane was last fueled, as records showed no fuel purchased at CEW since September 2012.
Meteorological Information
The 1453 automated weather observation at CEW included winds from 300 degrees at 5 knots, 10 miles visibility, scattered clouds at 7,000 and 8,500 feet, temperature 37°C, dew point 22°C, and altimeter setting 29.95 inches of mercury.
Wreckage and Impact Information
The initial impact point was a tree about 80 feet high at 30°55.542′N, 86°26.103′W, about halfway between CEW and 0J4. The wreckage path extended on a heading of about 310 degrees. The outboard right wing was in a tree about 90 feet past the IIP; the outboard left wing came to rest near the tree base. A ground scar with the propeller, separated at the flange, was about 110 feet beyond the IIP. The main wreckage, upright on a heading of about 145 degrees about 125 feet past the IIP, consisted of the fuselage, empennage, and inboard wing portions. The fuselage was completely consumed by post-impact fire. Control continuity was established from ruddervators and trim tabs to the cabin area, and aileron control cables from the cabin area to left and right bellcranks.
The engine came to rest upright with significant thermal damage. The three-bladed propeller separated at the flange, about 5 feet forward of the engine, with no leading edge gouging, chordwise scratching, or s-bending. The crankshaft displayed multiple cracks aft of the propeller flange. Two breaches of the engine case were near the #2 and #4 cylinders; visual examination revealed fractured #2 and #4 connecting rods.
Additional Information
The Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A) defines detonation as uncontrolled explosive ignition of the fuel/air mixture causing excessive temperatures and pressures, potentially leading to failure of piston, cylinder, or valves. It also defines preignition as premature ignition often caused by a residual hot spot in the combustion chamber, such as a carbon deposit or cracked spark plug insulator.
Tests and Research
A detailed engine examination was conducted on August 26, 2014. The left magneto was separated but remained attached by ignition harness; due to thermal damage, the distributor gear could not be rotated. The right magneto was destroyed. Spark plugs displayed normal wear and sooting consistent with post-crash fire; the #6 bottom spark plug was covered in oil and re-solidified splattered metal.
The oil pump drive was intact with normal operating signatures. The oil pressure relief valve displayed corrosion with debris on the seat. The oil cooler and filter exhibited no anomalies. The oil sump drain plug was safety-wired; the aft right end of the sump was thermally damaged. Thick, dark residual oil in the sump contained fragments of connecting rod bolts, bearing metal, piston material, piston ring segments, and debris.
Cylinders were disassembled and examined. #1, #3, and #5 cylinders showed normal wear. The #2 cylinder combustion chamber was coated with oil and debris; the piston face had two semi-circular impressions consistent with valve strikes, and the piston skirt was fractured. The #4 cylinder contained oil and debris; the piston skirt was fractured and mechanically damaged. The #6 cylinder combustion chamber contained oil and debris; the cylinder head had re-solidified splattered metal around sparkplug holes, valves, and valve seats, consistent with pre-ignition and/or detonation. The piston face was covered in splattered metal, and the bottom side had deep pitting and erosion; the piston skirt displayed thermal expansion, scoring, and material transfer.
The crankshaft and counterweight assembly exhibited lubrication distress, thermal damage, and mechanical damage at #2, #3, and #4 connecting rod journals. All connecting rod journals showed thermal distress and scoring consistent with lack of lubrication, with #2, #3, and #4 most damaged. The connecting rods had significant thermal and mechanical damage; #2, #3, and #4 were fractured at the journal end. Fragments of connecting rod caps and bolts exhibited overload signatures. The remaining three intact connecting rod bearings showed lubrication distress and thermal smearing. The crankcase had extensive thermal damage with holes above #2 and #4 cylinder mounting pads. Soot, ash, and fractured components were found throughout.
On January 26, 2016, additional examination of the #6 cylinder revealed no anomalies in the spark plug helicoil after removal of re-solidified material.