N334DFBeech S35 · 1964

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 the provisions of Title 14 Code of Federal Regulations Part 91.

A friend of the pilot stated that the purpose of the flight was to relocate the airplane to 0J4, located 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 to the accident, but upon arrival at the airport, he found that the airplane would not start. Attempts to jump-start the airplane were unsuccessful, and the pilot requested that a mechanic at the fixed-base operator troubleshoot and repair the airplane so that the flight could be completed the next day. The morning of the accident, the mechanic serviced the airplane's battery with fluid, placed it on a charger, and reinstalled it in the airplane. The mechanic then successfully started the engine and performed a run-up check.

A lineman reported that the pilot arrived at CEW between 1400 and 1430 on the day of the accident. He observed as the pilot boarded the airplane, started the engine, and taxied the airplane to the runway for takeoff. He heard the pilot perform a pre-takeoff engine run-up, which he described as unusually long, and stated that typically, the pilot would "hop in and go."

There was no record of the pilot having contacted air traffic control at any time during the accident flight. However, radar data from the Federal Aviation Administration showed a target correlated to be the accident airplane, depart CEW to the north about 1450 and climb to an altitude about 1,600 feet mean sea level. About 1451, the airplane began a left turn to the west and descended to an altitude of 900 feet as it conducted a 360-degree turn in the vicinity of his home. About 1454, the airplane resumed its northeasterly track and climbed to an altitude about 1,400 feet. About 1 minute later, the airplane turned to an easterly heading as it continued to climb, and about 1457, resumed its northeasterly heading and climbed to an altitude about 2,400 feet. About 1459, the airplane began a descending right turn. The last four radar targets, at 1459:45, 14:59:49, 14:59:59, and 15:00:04, placed the airplane about 1.25 nautical miles southeast of the accident site at an altitude about 1,400 feet, and on an approximate magnetic heading of 285 degrees.

A witness located near the accident site observed the airplane circling over his home and stated that the engine sounded as though it was revving up and down. As the airplane descended and flew towards a nearby field, he heard the engine "popping" and saw it trailing smoke. After watching the airplane descend into trees and impact the ground, he drove to the accident site to render assistance. He observed a pillar of black smoke rising from the wreckage and noted that the cockpit was filled with smoke. As he approached the airplane, he stated that it "exploded," and subsequently exploded a second time before first responders arrived.

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, at which time he reported 3,300 total hours of flight experience, with 0 hours in the previous 6 months. No personal flight logs were recovered, and no determination could be made as to the pilot's recent flight experience or his experience in the accident airplane. An autopsy was conducted by the Office of the Medical Examiner, District I, Florida. The cause of death was listed as inhalation of products of combustion. Toxicological testing was performed by the FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma. Testing was positive for carbon monoxide in blood; diphenhydramine in blood, urine, and tissue (0.021 ug/ml); pheniramine in urine and blood; and zolpidem in urine and blood. Diphenhydramine is a sedating antihistamine used to treat allergy symptoms and as a sleep aid. Pheniramine is a sedating antihistamine used in cold and allergy products. Zolpidem is a sleep aid marketed under the brand name Ambien. All detected drugs were below therapeutic levels.

The airplane was manufactured in 1964, and was equipped with a Continental Motors IO-520-BA6B, 285 hp reciprocating engine. The airplane was registered to the pilot in April 1998. No maintenance records were located, however, several work orders dating to September 2011 were provided by local maintenance facilities. In March 2012, an annual inspection was performed at a total aircraft time of 5,047.50 hours. During this inspection, the #3 cylinder was removed and repaired due to a failed compression test and burnt valve. The cylinder was reinstalled and the airplane was returned to service in May 2012. In September 2013, an annual inspection was performed at a total aircraft time of 5,048.02 hours. The mechanic who serviced the battery prior to the accident flight stated that, at the conclusion of the engine run up he performed, the airplane's tachometer read 5,049.08.

Review of work orders from the March 2012 annual inspection revealed a discrepancy stating, "Engine monitor has 2 cylinders that have no CHT reading." This discrepancy was marked as "deferred" and no corrective action was taken. Review of FAA airworthiness records did not indicate any supplemental type certificate (STC) for installation of an aftermarket engine monitor. The airplane was originally equipped with an engine cylinder head temperature (CHT) gauge, which was removed and replaced in November 2013. This gauge displayed CHT information from one cylinder only.

The investigation was not able to determine when or where the airplane was last serviced with fuel, as review of records from the fuel provider at CEW indicated that the pilot had not obtained fuel there since September 2012.

The 1453 automated weather observation at CEW included winds from 300 degrees at 5 knots, 10 miles visibility, scattered clouds at 7,000 feet and 8,500 feet, temperature 37 degrees C, dew point 22 degrees C, and an altimeter setting of 29.95 inches of mercury.

The airplane was manufactured in 1964, and was equipped with a Continental Motors IO-520-BA6B, 285 hp reciprocating engine. The airplane was registered to the pilot in April 1998. No maintenance records were located, however, several work orders dating to September 2011 were provided by local maintenance facilities. In March 2012, an annual inspection was performed at a total aircraft time of 5,047.50 hours. During this inspection, the #3 cylinder was removed and repaired due to a failed compression test and burnt valve. The cylinder was reinstalled and the airplane was returned to service in May 2012. In September 2013, an annual inspection was performed at a total aircraft time of 5,048.02 hours. The mechanic who serviced the battery prior to the accident flight stated that, at the conclusion of the engine run up he performed, the airplane's tachometer read 5,049.08.

Review of work orders from the March 2012 annual inspection revealed a discrepancy stating, "Engine monitor has 2 cylinders that have no CHT reading." This discrepancy was marked as "deferred" and no corrective action was taken. Review of FAA airworthiness records did not indicate any supplemental type certificate (STC) for installation of an aftermarket engine monitor. The airplane was originally equipped with an engine cylinder head temperature (CHT) gauge, which was removed and replaced in November 2013. This gauge displayed CHT information from one cylinder only.

The investigation was not able to determine when or where the airplane was last serviced with fuel, as review of records from the fuel provider at CEW indicated that the pilot had not obtained fuel there since September 2012.

The initial impact point (IIP) was identified as a tree about 80 feet in height, located at 30 degrees, 55.542 minutes north latitude, 86 degrees, 26.103 minutes west longitude, about halfway between CEW and 0J4. The wreckage path extended on a heading of about 310 degrees, with the outboard portion of the right wing located in a tree about 90 feet past the initial impact point. The outboard portion of the left wing came to rest near the base of the tree. A ground scar containing the propeller, which had separated from the engine at the propeller flange, was located about 110 feet beyond the IIP. The main wreckage came to rest upright on a heading of about 145 degrees about 125 feet past the IIP, and consisted of the fuselage, empennage, and the inboard portions of the wings. The fuselage was completely consumed by post-impact fire. Control continuity was established from the ruddervators and trim tabs to the cabin area, and aileron control cable continuity was established from the cabin area to the left and right bellcranks.

The engine came to rest upright and displayed significant thermal damage. The three-bladed propeller was separated from the engine at the flange and located about 5 feet forward of the engine. The propeller blades exhibited 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 observed near the #2 and #4 cylinders. Visual examination revealed that the #2 and #4 connecting rods were fractured.

The Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A), states, "Detonation is an uncontrolled, explosive ignition of the fuel/air mixture within the cylinder's combustion chamber. It causes excessive temperatures and pressures which, if not corrected, can quickly lead to a failure of the piston, cylinder, or valves. In less severe cases, detonation causes engine overheating, roughness, or loss of power." The handbook also states, "Preignition occurs when the fuel/air mixture ignites prior to the engine's normal ignition event. Premature burning is usually caused by a residual hot spot in the combustion chamber, often created by a small carbon deposit on a spark plug, a cracked spark plug insulator, or other damage to the cylinder that causes a part to heat sufficiently to ignite the fuel/air charge."

The same publication, in Chapter 17, "Aeronautical Decision Making," describes several operational pitfalls or behavioral tendencies that pilots may encounter as they develop flight experience. One of these tendencies is "Get-there-it is;" defined as a disposition that "impairs pilot judgment through a fixation on the original goal or destination, combined with a disregard for any alternative course of action."

A detailed examination of the engine was conducted at the manufacturer's facility on August 26, 2014. The left magneto was separated from its mount, but remained attached to the engine by its ignition harness. Due to thermal damage to the distributor gear, the magneto drive shaft could not be rotated. The right magneto was destroyed. The sparkplugs were removed and displayed normal wear and sooting consistent with the post-crash fire. The #6 bottom spark plug was covered in oil and re-solidified splattered metal.

The oil pump drive was intact. The oil pump cavity and gear teeth exhibited normal operating signatures. The oil pressure relief valve displayed corrosion, and the seat was covered with corrosion and debris. The oil cooler remained attached to the engine and exhibited no anomalies. The oil filter remained safety-wired in place on the oil filter adapter. No anomalies were observed. The oil sump drain plug was safety-wired. The aft right end of the oil sump was thermally damaged, exposing the inside of the sump. The sump was removed from the engine and thick, dark residual oil remained, along with fragments of connecting rod bolts, bearing metal, piston material, piston ring segments, and debris. The oil pick-up tube was undamaged, and the oil suction screen was free of obstruction.

The cylinders were disassembled and examined. The #1, #3, and #5 cylinders, pistons, and intake and exhaust valve heads revealed signatures of normal wear. The #2 cylinder combustion chamber was coated with oil and debris. The valve heads exhibited normal operating signatures. The piston face displayed normal combustion deposits that were covered with oil, as well as two semi-circular impressions consistent with valve strikes. The piston skirt was fractured. The #4 cylinder combustion chamber contained oil and debris. The valve heads exhibited normal operating signatures, and the piston face exhibited no anomalies. The piston skirt was fractured and mechanically damaged. The #6 cylinder combustion chamber contained oil and debris. The cylinder head displayed re-solidified, splattered metal around the sparkplug holes, valves, and valve seats; a feature consistent with pre-ignition and/or detonation. The splattering was more prevalent on the bottom side of the cylinder. The top side of the piston face was also covered in the splattered metal, and the bottom side displayed deep pitting and erosion of the face. The piston skirt displayed signatures of thermal expansion, scoring, and material transfer.

The crankshaft and counterweight assembly exhibited lubrication distress, thermal damage, and mechanical damage concentrated at the #2, #3, and #4 connecting rod journals. The crankshaft cluster gear was intact and exhibited normal operating signatures. The gear bolts were secure, and the gear teeth were undamaged. The crankshaft main bearing journals were intact and exhibited normal operating signatures. Both rear and forward sets of counterweight assemblies were intact and free to move on the hanger blades. All of the connecting rod journals exhibited thermal distress and scoring consistent with a lack of lubrication; the most damaged being the #2, #3, and #4 journals. The oil transfer collar was intact and undamaged, and the oil transfer plug was secure.

The connecting rods exhibited significant thermal and mechanical damage, and the #2, #3, and #4 connecting rods were fractured at the journal end. Fragments of connecting rod cap exhibited thermal and mechanical damage. Fragments of connecting rod bolts and nuts exhibited mechanical damage and overload signatures. Fragments of the #2, #3, and #4 connecting rods displayed signatures consistent with lack of lubrication and thermal distress, and were found throughout the engine and in the oil sump. The remaining three intact connecting rod bearings exhibited signatures of lubrication distress and thermal smearing of the surface babbit, exposing the copper layer. The camshaft was thermally damaged, but otherwise displayed no anomalies.

The crankcase displayed extensive thermal damage. The left side displayed holes above the #2 and #4 cylinder mounting pads. The crankcase interior displayed thermal damage toward the rear of the engine, with dark black sooting noted in the front of the engine. Mechanical damage was noted around the #3 and #5 cylinder bays. None of the main bearing support mating surfaces displayed any signs of fretting or bearing lock tab elongation. Soot, ash, and fractured engine components were found throughout the crankcase.

On January 26, 2016, additional examination of the #6 cylinder was performed. The cylinder head was cut from the barrel, and re-solidified material was removed from the bottom spark plug hole to facilitate inspection of the spark plug helicoil. The helicoil did not display any anomalies.