N2590KCessna 180K · 1978

On October 12, 2014 about 1250 eastern daylight time, a Cessna 180K; N2590K, was substantially damaged when it nosed over during a forced landing after a loss of engine power in Boca Raton, Florida. The private pilot received minor injuries. The passenger was uninjured. The flight departed from Columbus Airport (CSG), Columbus, Georgia, about 0930, destined for Boca Raton Airport (BCT), Boca Raton, Florida. Visual meteorological conditions prevailed, and an IFR flight plan was filed for the personal flight, conducted under the provisions of 14 Code of Federal Regulations Part 91.

According to the pilot, on the day before the accident occurred, he and his wife had departed Southwest Michigan Regional Airport (BEH), Benton Harbor, Michigan, at approximately 1015 then flew approximately 1.5 hours to Monroe County Airport (BMG), Bloomington, Indiana for fuel. After landing at BMG, they had the airplane refueled, filling the tanks with 24 gallons of fuel and then departed for CSG. After flying 3.2 hours, they landed at CSG. The pilot then had the airplane refueled once again, topping the fuel tanks off with 54.3 gallons of fuel and then checked in to a hotel.

The following morning, the pilot and his wife returned to CSG from the hotel and departed for BCT at approximately 0930. The pilot advised that the flight was very pleasant with some clouds and build up near Sebring, Florida and that he had entered and flown in instrument meteorological conditions for approximately 42 minutes while at their cruising altitude of 5,000 ft. above mean sea level (msl) without any problems. As they were handed off to Palm Beach Approach, they descended to 4,000 ft. msl, and were gradually descended down to 2,000 ft. msl. A little while later after leveling at 2,000 ft. msl they were cleared to 1,000 ft. msl. and were handed off to BCT control tower. Moments later, the airplane began shaking violently, a "loud noise" was heard, and the propeller stopped rotating, and then began windmilling slowly. The engine however, would not produce any power. The tower then cleared them for a visual approach to runway 05.

The pilot realized that they were not going to make the airport and he and his wife began looking for an "undeveloped area" to make an "engine out" landing while he trimmed the airplane and tried to restart the engine. He then spotted what used to be a polo field which was being developed into home sites and turned towards it. He thought it was his only chance to land in an unobstructed area. His wife meanwhile spotted "wires" and advised him of them while he continued to fly the airplane and attempted to restart the engine. Then after clearing the last of the "wires" he turned the airplane to align it with the polo field and landed. The ground was soft and sandy however, and during the landing roll, the airplane nosed over and came to rest inverted. The pilot and his wife then released their safety harnesses and egressed.

According to FAA and pilot records, the pilot held a private pilot certificate with ratings for airplane single-engine land and instrument airplane. His most recent FAA third-class medical certificate was issued on March 31, 2014. He had accrued about 2,649 total hours of flight experience, 2,545 of which, was in the accident airplane make and model.

The accident airplane was a 4-place, single-engine, high-wing monoplane of conventional metal construction. It was equipped with tailwheel type landing gear, and was powered by a normally aspirated, 285-horsepower, air cooled, horizontally opposed, direct drive engine, driving a three-bladed, Hartzell, controllable pitch propeller.

Review of Federal Aviation Administration (FAA) airworthiness records revealed that the engine had been converted from a fuel injected Continental IO-550-F to a O-550-F/TS by Texas Skyways Incorporated under FAA approved Supplemental Type Certificates (STC) by removing the fuel-injection system, replacing the original 8.5:1 compression ratio pistons with 7.5:1 pistons, and installing a carburetor.

According to the STC information, the conversion was applicable for Cessna 180s and 182s that were manufactured from 1953 through 1986.

According to FAA and maintenance records, the airplane was manufactured in 1978.

The engine's most recent major component replacement was on March 21, 2012, at 983.53 hours of operation (46.16 hours prior to the most recent annual inspection), and involved removal, overhaul, and reinstallation, of the No. 3 and No. 4 cylinder assemblies.

Its most recent annual inspection was completed on December 1, 2013. At the time of the inspection, the airplane had accrued 4,545.74 total hours of operation, and the engine had accrued 1,096.43 total hours of operation.

The recorded weather at BCT, located 3 nautical miles northwest of the accident site, at 1153, included: winds 090 at 10 knots, 10 miles visibility, scattered clouds at 2,500 ft, temperature 30° C, dew point 23° C, and an altimeter setting of 30.06 inches of mercury.

The accident airplane was a 4-place, single-engine, high-wing monoplane of conventional metal construction. It was equipped with tailwheel type landing gear, and was powered by a normally aspirated, 285-horsepower, air cooled, horizontally opposed, direct drive engine, driving a three-bladed, Hartzell, controllable pitch propeller.

Review of Federal Aviation Administration (FAA) airworthiness records revealed that the engine had been converted from a fuel injected Continental IO-550-F to a O-550-F/TS by Texas Skyways Incorporated under FAA approved Supplemental Type Certificates (STC) by removing the fuel-injection system, replacing the original 8.5:1 compression ratio pistons with 7.5:1 pistons, and installing a carburetor.

According to the STC information, the conversion was applicable for Cessna 180s and 182s that were manufactured from 1953 through 1986.

According to FAA and maintenance records, the airplane was manufactured in 1978.

The engine's most recent major component replacement was on March 21, 2012, at 983.53 hours of operation (46.16 hours prior to the most recent annual inspection), and involved removal, overhaul, and reinstallation, of the No. 3 and No. 4 cylinder assemblies.

Its most recent annual inspection was completed on December 1, 2013. At the time of the inspection, the airplane had accrued 4,545.74 total hours of operation, and the engine had accrued 1,096.43 total hours of operation.

Airplane Examination

Examination of the airplane revealed that it had been substantially damaged. The engine cowling was bent and dented in several places. One of the propeller blades of the 3-bladed propeller had been bent aft about 15° and a 2nd blade had a visible bend located about 12 inches outboard of the blade clamp.

The left lift strut was bent at a 20° angle near the midspan location, and the left aileron was bent in two places. The upper surface of the left wing displayed wrinkling forward of the wing flap, and at the leading edge, forward of the fence which was mounted between the aileron and wing flap. The tops of the vertical stabilizer and rudder were crushed.

Engine Examination

The engine had remained intact and no impact damage was noted. The externally visible portion of the crankshaft was intact and appeared undamaged. The crankcase was intact; after closer examination, it was noted there was a very small crack near one of the backbone bolts. All the rear accessories remained attached and were undamaged.

The exhaust system displayed normal operating signatures and was undamaged. The induction system also remained attached to the engine and there were no signs of induction leaks.

The left magneto remained attached to its mounting location and was undamaged. It was noted that one of the ignition harness cap screws was missing. The magneto was placed on a test bench and it produced spark on all six posts. The right magneto remained attached to its mounting location and was also undamaged. The magneto was placed on the test bench and it also produced spark on all six posts.

The ignition harness remained intact and undamaged. The spark plugs had remained installed in their cylinders and were undamaged. It was noted that the No. 5 and No. 6 top spark plugs were Autolite spark plugs. All the other spark plugs were manufactured by Champion. All the spark plugs displayed normal operating signatures when compared to Champion Aviation Service Manual AV6-R.

The carburetor was undamaged, and the internal components displayed normal operating signatures. the fuel inlet screen was clear of any contaminates.

The oil sump was intact and undamaged. The oil sump contained multiple metallic components and particles consistent with bearing material, piston material, and one counterweight pin retaining plate and one snap ring. The oil pick-up tube and screen was undamaged, and there was a small amount of metallic particles noted in the screen. The oil pump was intact and undamaged. The oil pump was disassembled, and it was noted that the oil pump housing displayed scoring consistent with hard particle passage. The oil filter remained secure and undamaged. The oil filter housing was cut open and the filter pleats contained a significant amount of metallic material. The oil cooler was secured to its installation point and was undamaged. The oil cooler was removed and there were no anomalies noted.

All the valves were intact and undamaged, and displayed normal operating and combustion signatures. All the rocker arms also remained intact and undamaged, and displayed normal operating and lubrication signatures.

All six cylinders had remained attached to their respective cylinder bays. Examination of the cylinders and pistons revealed that:

- The No. 1 cylinder was undamaged. It was noted that one of the nuts attached to a hold down stud was loose and there was a significant gap between the nut and the cylinder flange. The cylinder, valve heads, and overhead components displayed normal operating signatures. The piston had remained intact and displayed minor mechanical damage to the backside of the piston and the rear piston ring was broken. The piston face displayed normal operating and combustion signatures.

- The No. 2 cylinder was undamaged. It was noted that the breakaway torque on the through bolts was about 200 in-lbs. less than on the rest of the through bolts. The cylinder bore displayed a significant amount of corrosion and the cylinder skirt displayed mechanical damage. The valve heads and overhead components displayed normal operating signatures. The piston displayed a significant amount of mechanical damage to the piston skirt towards the rear of the piston; several large portions of the piston had broken free from the rest of the piston and the rear piston ring was broken. The piston face displayed normal operating and combustion signatures.

- The No. 3 cylinder was undamaged. The cylinder, valve heads, and overhead components displayed normal operating signatures. The piston remained intact and was undamaged. The piston face displayed normal operating and combustion signatures. The rear piston ring was broken during the removal process. The remaining piston rings were intact and capable of normal movement in their grooves.

- The No. 4 cylinder was undamaged. The cylinder, valve heads, and overhead components displayed normal operating signatures. The piston was intact and undamaged. The piston face displayed normal operating and combustion signatures. All the piston rings were intact and were capable of normal movement in their grooves.

- The No. 5 cylinder was undamaged. The cylinder, valve heads, and overhead components displayed normal operating signatures. The piston was intact and undamaged. The piston face displayed normal operating and combustion signatures. All the piston rings were intact and were capable of normal movement in their grooves.

- The No. 6 cylinder was undamaged. It was noted that there was a significant amount of blue staining around the valves and the bottom spark plug hole. The cylinder bore, valve heads, and overhead components displayed normal operating signatures. The piston was intact, and it was noted that have a significant amount of blue staining around the piston. It was noted there was a small semi-circle indentation in the piston face consistent with a valve strike. The piston face displayed normal combustion signatures. All the piston rings were intact and were capable of normal movement in their grooves.

The crankcase displayed damage consistent with mechanical damage in multiple locations inside the crankcase. The No. 2 bearing support displayed damage consistent with a bearing shift event and a spun bearing event. The area around the No. 2 bearing support through bolt holes displayed a significant amount of fretting between the mating surfaces; the No. 1 bearing support mating surfaces also displayed fretting as well as lock tab elongation.

The main bearings:

- The No. 1 main bearings had shifted slightly out of the support and displayed some deformation. The bearing surfaces displayed normal operating and lubrication signatures.

- The No. 2 main bearings displayed bearing shift signatures and had extruded out of the bearing support. Several pieces of the bearing were found in the oil sump.

- The No. 3 main bearings were intact and undamaged. The bearing surfaces displayed normal operating and lubrication signatures.

- The No. 4 main bearings were intact and undamaged. The bearing surfaces displayed normal operating and lubrication signatures.

- The No. 5 main bearings were intact and undamaged. The bearing surfaces displayed normal operating and lubrication signatures.

The crankshaft was fractured at the crankshaft cheek between the No. 2 main journal and the No. 2 connecting rod journal. The No. 2 and the No. 3 connecting rod journals displayed incipient signatures of lubrication distress. The remaining journals displayed normal lubrication signatures. Examination of the crankshaft using a magnaflux booth, also revealed a crack along the bend radius of the No. 1 journal.

One of the counterweights leading edge pins had been found loose in the crankcase and the counterweight pin retaining plate had been found in the oil sump along with a snap ring. Examination of the counterweight revealed that there was no evidence of mechanical damage, and no indication that the engine had been operating with the counterweight being unsecured. The remaining counterweights were found to be secured to their hangers.

Connecting rods and connecting rod bearings:

- The No. 1 connecting rod was secured to is journal and displayed normal operating signatures. The connecting rod bearings displayed normal operating and lubrication signatures.

- The No. 2 connecting rod remained secured to its journal and displayed normal operating signatures. The connecting rod bearings displayed incipient signatures of lubrication distress.

- The No. 3 connecting rod remained secured to its journal and displayed normal operating signatures. The connecting rod bearings displayed normal operating and lubrication signatures.

- The No. 4 connecting rod remained secured to its journal and the connecting rod displayed mechanical damage near the bearing support area. The connecting rod bearings displayed signatures consistent with lubrication distress.

- The No. 5 connecting rod remained secured to its journal and displayed normal operating signatures. The connecting rod bearings displayed normal operating and lubrication signatures.

- The No. 6 connecting rod remained secured to its journal and displayed normal operating signatures. The connecting rod bearings displayed normal operating and lubrication signatures.

According to Continental Motors Service Bulletin SB03-3, cylinder removal regardless of compression should not be done unless a borescope inspection reveals a definite problem.

Removal of a cylinder requires removal of a total of eight-cylinder hold-down nuts that secure the cylinder base flange to the crankcase. Six of these hold-down nuts are threaded onto short deck studs that are mounted in threaded holes in the crankcase. The other two hold-down nuts are threaded onto a pair of through-bolts that pass all the way through the crankcase.

The left and right banks of cylinders are staggered so that each pair of through-bolts run from the front hold-down nuts on a left-bank (even-numbered) cylinder to the rear hold-down nuts on a right-bank (odd-numbered) cylinder. The engine has four pairs of these through-bolts, and they are primarily responsible for holding the two crankcase halves firmly together.

The crankcase contains precisely machined semicircular main bearing saddles that hold the main bearings to support the crankshaft. The main bearings are semicircular shells consisting of steel back plates laminated to bearing surfaces made of a softer material called "babbit" to prevent scratching the crankshaft journals. The main bearing shells have oil supply holes that must line up precisely with oil passages machined into the crankcase halves.

When the engine is assembled, the ends of the main bearing shells stick out slightly above the mating surfaces of the crankcase bearing saddles. As the case halves are mated during engine assembly by torqueing the through bolts, the bearing shells are forced firmly into the crank-case saddles in a process known as "crushing."

If a bearing shifts for any reason, after removal of one or more cylinders, or during replacement of one or more cylinders, the oil holes in the bearing can become misaligned with the oil passages in the crankcase, partially cutting off the oil supply to the bearing. If the engine is then put back into service, the reduced oil supply to the bearing can cause increased heat and friction that can result in the bearing shifting more, further reducing its oil supply. Eventually, the bearing can shift enough to cause the oil supply to be cut off completely, resulting in a catastrophic failure. This is usually referred to as a "spun bearing."

To help prevent a "spun bearing" from occurring, proper cylinder installation requires a multiple step torqueing process. According to Teledyne Continental Motors Service Bulletin SB96-7C, when doing the cylinder torque procedure, the cylinder base stud threads, through bolt threads, and nuts must be lubricated with clean 50 weight aviation oil, and through bolt nuts at cadmium plated washers will require a lower torque value to achieve the same pre-load on the through bolt since the lubricity of the cadmium plating reduces the friction in the fastener joint.

The cylinder torque procedure (in summary) also requires that:

1- The torque cylinder base nuts must first be torqued to 1/2 of the specified torque value for the fastener.

2- The cylinder through bolt nuts and then the cylinder base stud nuts must then be torqued to the specified torque value for the cylinder base stud nuts.

3- The through bolt nuts, must be torqued "on both sides of the engine," to the specified value for the fastener, "even if only one cylinder is being installed."

4- Engines which incorporate the 7th cylinder deck stud, to install the 7th stud cylinder bracket and conical stud nut, and then to torque the stud nut to the value specified for the fastener.

The Service Bulletin warned that: "Failure to torque through bolt nuts on both sides of the engine can result in a loss of main bearing crush with main bearing shift and subsequent engine failure."