NTSB Factual Report

HISTORY OF FLIGHT

On January 14, 2003, approximately 0750 Pacific standard time, a Cessna 172K single engine airplane, N1909V, impacted a vehicle during a forced landing near Gig Harbor, Washington. The pilot, his two passengers, and two occupants of the automobile the aircraft collided with were uninjured. The aircraft, which was being flown by its owner, sustained substantial damage. The aircraft was on an instrument flight rules flight plan in instrument meteorological conditions at the time of the power failure that lead to the forced landing. The flight, which was personal in nature, was being operated under 14 CFR Part 91, and originated from the Tacoma Narrows Airport, Tacoma, Washington, at 0740.

On the day of the accident, at 0500, the pilot departed Portland-Hillsboro Airport, Hillsboro, Oregon, on an IFR flight plan to Seattle-Tacoma International Airport, Seattle, Washington. When he was approximately 15 miles south of Seattle-Tacoma Airport, being vectored to the ILS localizer, the pilot heard the engine "sputter." According to the pilot, he did not detected any problems in his engine instruments, and the sputter was of such a duration and nature that his two passengers did not notice it. Although the sputter was only momentary, and did not repeat itself, because the aircraft was about two miles south of Tacoma Narrows Airport at the time, the pilot elected to make a precautionary landing at Tacoma Narrows. After landing, the pilot began looking for a possible cause for the momentary sputter, and while doing so discovered that the aircraft's right fuel tank was empty and the left fuel tank contained 10 gallons. Believing that the sputter may have been caused by a momentary interruption of the fuel flow as the right tank became empty, the pilot had the local fuel provider put 10 gallons of aviation fuel in each wing tank. After the refueling, the pilot received an updated weather briefing and filed for an IFR flight from Tacoma Narrows to Seattle-Tacoma.

When the pilot taxied out for departure, he proceeded to the south end of the field for an expected departure to the north from runway 35. Prior to calling for his clearance, the pilot did a "full and extra long" engine run-up, during which he detected nothing unusual about the way the engine was running or the indications on the engine instruments. He was then instructed to taxi to the north end of the field for a takeoff to the south. After taxing to the approach end of runway 17, the pilot performed another engine run-up with no irregularities detected. He then departed to the south, and turned to climb on the heading he was given in his clearance, entering instrument meteorological conditions (IMC) at about 700 feet above the ground (AGL).

Just after the pilot received a northbound clearance and a climb to 3,000 feet, the aircraft's engine started making "horrible rumbling sounds" and started surging. He therefore immediately declared an emergency and requested vectors for an immediate approach back at Tacoma Narrows. Seattle Approach then turned him toward the ILS localizer for runway 17, but the engine started sounding worse and started loosing power. Although the pilot was initially able to maintain level flight, as the engine continued to loose power, he found it necessary to descend as he flew toward the airport. He eventually broke out of the clouds somewhere between 800 and 1000 feet above the ground and about four miles from the airport. Seeing that he would be unable to make it to the airport, the pilot then elected to land on a small road he saw on the left side of the aircraft. When the aircraft was about 10 to 20 feet in the air, a car pulled in front of the aircraft, and just as it was touching down on the road, the aircraft impacted the rear of the car on the driver's side.

METEOROLOGICAL INFORMATION

At 0753, the weather observation facility at the Tacoma Narrows Airport (located approximately 4 1/2 miles south of the accident site) reported wind 290 degrees at 4 knots, visibility 10 statute miles, broken clouds at 700 feet, overcast clouds at 1,200 feet, temperature 7 degrees C, dew point 6 degrees C, an altimeter of 30.31 inches of Mercury, and remarks indicating ceilings were 400 feet agl variable to 900 feet agl.

WRECKAGE AND IMPACT INFORMATION

Damage to the airplane included the separation of the right landing gear, aft crushing of the outboard section of the right wing, a bent right flap, extensive damage to the right side of the tail section, a bent propeller, and substantial structural damage to the firewall. Initial inspection of the engine revealed that there was a hole in the right forward portion of the crankcase half above the number five cylinder. There was some oil spray on top of the crankcase, but the dipstick indicated approximately seven quarts of oil were still present in the engine.

The engine was removed from the aircraft and submitted to a teardown inspection. All cylinders except the number five cylinder still had what appeared to be the factory lock paste/torque putty on their mounting nuts. The oil screen contained metal shavings, and the teeth and walls of the oil pump were dented and scored. The oil pump would not turn freely. The crankshaft was found to have broken into three sections. One fracture was across the number seven cheek at main journal number three. The second fracture was across cheek number nine near main journal number four. The fracture surface at cheek number seven contained a number of obvious beech/clam shell marks. The fracture surface at cheek number nine was a solid gray granular consistency. All main journals were shinny with no obvious scoring. The number five and six rod journals were severely damaged. There was no evidence of thermal stress on the journals or bearings. The crankshaft counterweights were all still attached. The lobes of the camshaft were inspected and all showed normal wear except for the impact damage present in the area of the number five and six cylinders.

The crankshaft was submitted to the National Transportation Safety Board materials laboratory for further examination. A microscopic examination of the fracture at the number nine cheek (forward fracture) revealed features consistent with a bending overstress separation with no evidence of preexisting progressive fatigue cracking. A majority of the fracture surface at the number seven cheek revealed clam shell markings and arrest lines consistent with fatigue progression. The point of initiation was determined to be about one millimeter (approximately 0.039 inches) below the surface of the forward radius of the number three main bearing journal. The origin was located in the center of the crankshaft cheek near the point where the oil transfer tube passes through the cheek. From the point of initiation, the crack propagated in all directions penetrating the aft face of the crankshaft cheek, but propagating predominately forward at a 45 degree angle toward the center of the crankshaft. At least 75 percent of the fracture surface on the cheek cross section contained fatigue propagation markings. The aft face of the fracture was viewed with a scanning electron microscope, and fatigue beach markings close to the proximity of the origin point were able to be observed, however fracture face recontact damage had obliterated the initiation point itself. No material defects, inclusions, or anomalies were detected at the origin site.

ADDITIONAL DATA AND INFORMATION

A review of the engine log reveled that the number five cylinder was replaced with an overhauled unit on February 8, 2001. According to the log, all new parts except the piston pin were used. A review of the propeller log showed that a "new propeller" had been installed on the engine on December 12, 1985, and an overhauled propeller had been installed on November 12, 1992. A review of the yellow tag associated with the 1992 installation indicated that as part of the overhaul of the propeller one reconditioned blade was installed. A call to the overhauling repair station confirmed that there were no longer work orders or process sheets on file for this overhaul. A review of the aircraft, engine, and propeller logs did not reveal the reason for the propeller replacements.

Teledyne Continental Critical Service Bulletin 96-8 (CSB96-8) calls for the replacement of the original airmelt (Non-VAR) crankshaft in this model engine with a vacuum arc remelt (VAR) crankshaft anytime the engine is overhauled or "... whenever the crankshaft is removed or made accessible by crankcase disassembly." A review of the engine log for this aircraft determined that no overhaul or maintenance action making the crankshaft accessible had taken place since the date of production.

The aircraft, except for the engine, was released to Mr. Drew Vickers, a representative of the owner, at Tacoma Narrows Airport on January 16, 2003. The engine, except for the components sent to the NTSB materials laboratory, were released to Ben Olson, a representative of the owner, at Tacoma Narrows Airport on January 21, 2003. The NTSB materials laboratory advised the Investigator-In-Charge (IIC) that the crankshaft components had been returned directly to Mr. Scoot Bloom, the owner of the aircraft, upon completion of their examination.

NTSB Probable Cause

The loss of engine power in the climb due to the fracture of the number seven engine crankshaft cheek due to the propagation of a fatigue crack initiation point. Factors include a vehicle pulling onto the road that the pilot selected for his forced emergency landing.