NTSB Factual Report

HISTORY OF FLIGHT

On August 17, 2014, about 1105 central daylight time, a Cessna 172N, N734YW, sustained substantial damage when it hit trees and impacted the terrain after a partial loss of engine power during the initial climb from the Natchitoches Regional Airport (IER), Natchitoches, Louisiana. The pilot received serious injuries, and the sport pilot rated passenger was fatally injured. The airplane was registered to and operated by Cane River Aviation, Inc., under the provisions of the 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed at the time of the flight, which was operating without a flight plan. The airplane departed IER about 1102 on a local flight.

The pilot reported that he conducted the preflight and engine run-up with no anomalies noted. During takeoff, he rotated the airplane about 70 kts and the climb out was normal. About 300 ft above ground level (agl), the engine suddenly lost power and shook violently. The pilot scanned for potential emergency landing areas and decided to attempt to land in a soybean field that was about 135 degrees to his left. The airplane overflew the soybean field that was about 4,600 ft in length and impacted a line of trees at the end of the field.

Security cameras located about 0.4 miles east of the departure end of runway 17 recorded much of the accident flight. One camera recorded the accident airplane during its initial climb after departing from runway 17. The airplane can be seen as it climbed to 300 - 400 ft agl and headed south of the airport. Another camera recorded the airplane as it appeared to level off with black smoke trailing from the airplane. The airplane turned to the left as it continued to trail black smoke. A third camera recorded the airplane as it turned left to a heading of about 030 degrees. No black smoke could be seen, but the airplane was losing altitude for about 1 nm before it impacted a tree line. No S-turns or side slips were observed on the video. The accident site was located about 0.65 nm from the approach end of runway 25 on a 290 degree bearing.

PERSONNEL INFORMATION

The 80 year-old pilot held a private pilot certificate with a single-engine land rating. He reported that he had 1,991 total hours of flight time with 1,632 hours in make and model. He held a third class medical certificate that was issued on April 16, 2013, with the following limitation: Must wear corrective lenses.

The 82 year-old sport pilot rated passenger's last Federal Aviation Administration (FAA) medical exam was conducted on September 20, 2005. At that time, he indicated that his flight experience included 60 total hours of flight time and 0 hours with in the last six months. The pilot's FAA medical certificate expired on September 30, 2007.

AIRCRAFT INFORMATION

The airplane was a single-engine Cessna 172N, serial number 17269230, manufactured in 1977. It was equipped with a Lycoming 160-horsepower O-320-H2AD engine, serial number L-3942-76. The last annual maintenance inspection was conducted on December 13, 2013, with a total airframe time of 2,408.2 hours and an engine time of 940.2 hours since the last overhaul, which was accomplished on May 26, 1990, over 24 years before the date of the accident.

Lycoming recommends that engines that have not accumulated the recommended hourly time between overhauls be overhauled during the 12th year after the last overhaul. The engine had accumulated 958.1 hours of time in service since the last overhaul.

Lycoming issued a Mandatory Service Bulletin (SB) 412B, on March 10, 1978, concerning the security of the intake and exhaust valve rocker arm retaining studs and proper valve train operation, and procedures for rocker stud replacement. The serial numbers identified in the SB did not include the accident engine's serial number. In section 5 of the SB, it states:

"To identify this change, metal stamp the cylinder heads with the letter T in the milled channel half way between the two rocker arm retaining studs. Current production engine and replacement cylinders which are already in compliance with this bulletin are identified in the same location by the letters L and LO and are not subject to the requirements of this bulletin."

The FAA issued Airworthiness Directive (AD) 77-20-07 on August 31, 1978, to prevent hazards in flight associated with loose rocker arm retaining studs and failure of the hydraulic tappets. The serial numbers identified in AD 77-20-07 did not include the accident engine's serial number.

On May 25, 2006, Lycoming issued SB 240T, which concerned the mandatory parts replacement at normal overhaul and during repair or normal maintenance. The SB stated: "During overhaul of any Lycoming reciprocating engine, it is mandatory that the following parts be replaced regardless of their apparent condition." Rocker arms and fulcrums (O-320-H, O, LO, TO, LTO-360-E series) were required to be replaced during an overhaul.

METEOROLOGICAL INFORMATION

At 1035, the surface weather observation at IER was: wind 250 degrees at 6 knots; visibility 10 miles; scattered clouds at 2,600 feet; scattered clouds at 3,300 feet, temperature 31 degrees C; dew point 24 degrees C, and altimeter 30.02 inches of mercury.

WRECKAGE AND IMPACT INFORMATION

The airplane hit the top branches of a 50-ft willow tree and impacted the terrain in a bean field. The initial impact point was about 150 feet from the willow tree on a heading of 320 degrees. The cut through the willow tree was consistent with about a 45-degree left wing low attitude. The left wing's red navigation lens was found in the debris field before the initial impact point. The main wreckage was located about 15 ft from the initial impact point, and it came to rest heading 120 degrees.

The front section of the airplane, which included the instrument panel, was partially separated from rest of the fuselage forward of the wing strut fuselage attach points. The hour meter indicated 2,339.3 hours and the tachometer gauge indicated 2,426.1 hours of operation. The engine and propeller exhibited minimal impact damage. The propeller remained attached to the engine crankshaft flange and was bent slightly aft, but both propeller blades were straight with no leading edge damage or chordwise scratching. The propeller spinner was crushed and deflected upwards. The nose gear separated from the fuselage, but the main landing gear remained intact.

Both wings remained intact, but the leading edge of the left wing exhibited aft crushing along its entire span. The right wing had leading edge crush damage on the outboard section of the wing. The ailerons and flaps remained attached to both wings. The flaps were in the up position. Additionally, the flap handle, flap indicator, and the flap actuator were found in the up position. The left and right fuel tanks remained intact and both fuel caps were secure. The empennage remained largely intact. The vertical stabilizer and rudder had minimal damage. The left and right horizontal stabilizers exhibited aft crushing and leading edge damage. Flight control cable continuity was confirmed from the flight controls to their respective attach points on the flight control surfaces.

The left front seat remained attached to the seat track and was latched in the fourth hole from the front of the seat track. The left front seat belt was observed unlatched with the shoulder harness remaining attached to the fitting. The right front seat was observed separated from the seat tracks and outside the aircraft. The right front seat belt shoulder harness was found attached to the fitting.

The engine was removed from the firewall and transported to an empty hangar at the airport where it was suspended from a lift and examined. When the No. 1 cylinder rocker box cover was removed, the exhaust valve rotator cap was found loose in the rocker box. The exhaust valve rocker retaining stud was observed backed out of the cylinder head threads by about 5 threads, or about 1/4 inch, and the valve rocker and pushrod were loose. The clearance between the valve rocker and the valve stem was too great to allow the exhaust valve to open as the engine rotated.

The engine was rotated by turning the propeller and continuity of the crankshaft to the rear gears was confirmed. Valve train continuity was confirmed to all valves except the No. 1 cylinder exhaust valve. Compression and suction were observed from all four cylinders. The interiors of the cylinders were examined using a lighted borescope and no damage was noted.

The No. 1 cylinder was removed and no damage to the piston or the interior of the cylinder was noted. The exhaust valve rocker retaining stud was removed using finger pressure only. No damage to the stud threads or the corresponding threads in the cylinder head was noted. Two shims were observed on the stud. No damage was noted to the lower shim. The hole in the upper shim was elongated and one side of the shim was bent upward and distorted. The fulcrum exhibited wear. The exhaust valve rocker arm retaining stud did not have markings indicating that it was an oversized stud. Numerous letters and numbers were stamped onto the cylinder head in the milled channel between the two rocker arm retaining studs, including the letters L and T. Fretting damage was noted to the cylinder head in the area of the exhaust valve rocker attachment.

MEDICAL AND PATHOLOGICAL INFORMATION

There was no toxicological report associated with the accident pilot.

TESTS AND RESEARCH

The exhaust valve rocker retaining stud was sent to the National Transportation Safety Board's (NTSB) Materials Laboratory for examination to determine if thread locker had been used on the stud and if the stud threads had sustained any damage.

The stud threads were examined and an amber-colored, semi-soft solid deposit was found during the visual examination. The deposit was removed and examined. The examination revealed that the material was consistent with several carbohydrates similar to starch and dextrin. Materials like these are often used as binders in adhesives and resins; however, the origin of this deposit could not be determined. There was no evidence that thread locker was present on the stud. No damage was found to the threads and aside from the small deposit described above, no other material was found.

NTSB Probable Cause

The partial loss of engine power due to the exhaust valve rocker retaining stud backing out of the cylinder head, which resulted in the exhaust valve being stuck in the closed position. Contributing to the accident was the pilot’s failure to configure the airplane and fly it in a manner that would allow him to make the emergency landing in the field rather than overfly it, and the pilot’s failure to have the engine overhauled according to the recommended overhaul interval.