History of Flight
On November 25, 2017, about 1455 central standard time, a Cessna 172N airplane, N739KW, sustained substantial damage following a partial loss of engine power and forced landing about two miles south of Oloh, Mississippi. The private pilot in the left front seat and the passenger in the front right seat sustained no injury, and the passenger in the left rear seat sustained minor injuries. The airplane was registered to a private individual and was operated by the pilot as a Title 14 Code of Federal Regulations Part 91 visual flight rules personal flight. Day visual meteorological conditions were present at the time of the accident, and no flight plan was filed. The airplane departed from the McComb-Pike County Airport (MCB), McComb, Mississippi, about 1405.
The pilot reported the purpose of the flight was for sightseeing with two passengers. The airplane departed with 40 gallons of 100 low lead fuel. After departing MCB, the pilot was flying en route to the Hattiesburg Bobby L. Chain Airport (HBG), Hattiesburg, Mississippi. At 3,500 ft above mean sea level with the power at about 85 percent, the mixture leaned out slightly, and with the engine gas temperatures observed at normal, the engine produced a "very rapid metallic banging/clanging noise" along with an instant loss of engine RPM. The pilot immediately applied the carburetor heat and checked the engine oil pressure, engine oil temperature, and engine gas temperature, and noticed all gauges were in the normal operating range.
According to the pilot, the engine was creating a "violent shaking" of the entire airframe. After about 20 seconds of carburetor heat application, the pilot applied full mixture and started adjusting the throttle to see if he could obtain more power. He reported that with more power applied, the shaking became more violent along with a loss of engine RPM. The pilot realized that the power the engine was producing at this point was not sufficient to hold altitude. He then reduced the power, and the shaking subsequently reduced, but it did not stop.
The pilot assessed his current location and the distance from the destination airport and determined that the airplane would be unable to glide the full distance. He also assessed turning back to another airport and determined the airplane would be unable to make this distance. The pilot decided to conduct a landing to a nearby open field. He reported that at this point, the engine was just above idle but still not producing sufficient power to hold existing altitude or assist in gliding to an airport.
As the pilot was deciding which field to land in, he made wide, slow turns holding as much altitude as possible. He selected a flat field and steepened his turn for an emergency landing profile. Once the airplane descended and the pilot was committed to landing at the field, he realized there were large power lines traversing across the approach end of the field. Once over the power lines, the pilot "slipped" the airplane to lose altitude as quickly as possible. He reported the slip got the airplane on the ground faster but also increased airspeed.
Once on the ground, the pilot attempted to apply the brakes on the damp grass but realized the airplane was going too fast and was not going to stop by the end of the field. At the end of the field, the pilot observed various trees and a small driveway-size opening. Using the rudder authority he had left, the pilot maneuvered the airplane to the right, placing the fuselage into the opening. As the airplane skidded toward the tree line, it traveled through a barbed wire fence, and the right wing impacted a tree, turning the airplane to the right about 90°. The left wing dug into the ground, stopping the forward movement. The airplane came to rest on the nose wheel and the left main landing gear, with the empennage elevated in the air. The pilot performed a shutdown, and the three occupants egressed without further incident.
Aircraft Information
An examination of the airplane's maintenance records revealed no evidence of uncorrected mechanical discrepancies with the airframe, engine, and propeller. No evidence of a 400-hour inspection or an overhaul being conducted on the engine during its service history was found listed in the engine maintenance records. On October 8, 2004, the number 3 cylinder was replaced with an unknown overhauled cylinder. On November 16, 2004, the number 3 cylinder was replaced with a new cylinder from Lycoming Engines. During these two maintenance procedures, it was undetermined if the number 3 valve keys (intake and exhaust) or the number 3 valve stem cap (exhaust) were replaced or remained the original parts installed by the manufacturer.
Wreckage and Impact Information
The wreckage was transported to a secure location, and an airframe and engine examination was conducted under the direction of the National Transportation Safety Board investigator-in-charge. No preimpact mechanical malfunctions or failures were noted with the airframe and propeller. All engine accessories were present. The engine case was intact. All engine controls displayed a full range of motion with no binding.
Engine continuity was established by rotating the propeller and observing rocker assembly movement and gear rotation in the rear of the engine. Thumb compression readings were established for cylinders 1, 2, and 4; the number 3 cylinder did not produce compression. The top four spark plugs were removed for examination with a lighted digital borescope. The number 3 piston area displayed internal impact marks from the piston impacting the exhaust valve. The number 3 exhaust valve was open and displayed impact marks from contact with the piston.
The rocker arm cover was removed on the number 3 cylinder, and it was observed that fractured pieces of the valve key (exhaust) and valve stem cap (exhaust) were lying on the bottom of the rocker area of the cylinder head. The number 3 valve spring seat (upper exhaust) had impact damage. The number 3 exhaust valve assembly moved freely inside the valve seats and was contacting the top of the piston.
Additional Information
A Federal Aviation Administration (FAA) aviation safety inspector responded to the accident site. During a postaccident on-scene inspection, a fuel sample was obtained, and no contamination was found. The FAA ASI reported that both fuel cells in each wing remained intact with no ruptures observed, and the fuel quantity was unable to be verified due to the extreme positioning of both wings. The airplane sustained substantial damage to both wings and the fuselage.