NTSB Factual Report

On March 8, 2002, at 1005 central standard time, a Cessna 182H, N64AE, operated by Air Evac EMS, sustained substantial damage during a forced landing to a field after a total loss of engine power. The commercial pilot was not injured. The 14 CFR Part 91 business flight departed West Plains Municipal Airport (UNO), West Plains, Missouri, at 0950, en route to Jonesboro Municipal Airport (JBR), Jonesboro, Arkansas. Visual meteorological conditions prevailed and the flight was on a company VFR flight plan.

The pilot reported he was cruising at 3,000 feet msl on a direct course of 134 degrees to JBR. He reported, "Approximately 14 miles from UNO, I heard a loud bang from the engine followed almost immediately by both smoke from beneath the left side panel and excessive vibration from the engine. I immediately pulled the throttle to flight idle, which reduced vibration considerably, and then the engine and the propeller stopped."

The pilot reported he established best glide airspeed and selected a field for a forced landing. He made a MAYDAY call. He reported, "I went to full flaps (40 degrees) in preparation for landing. I touched down on the main gear wheels on fairly rough ground just at the crown of the hill, which appeared to have a relatively flat plateau." He reported that during landing roll out, the nose wheel struck a rock and the nose gear collapsed.

A review of the engine logbooks revealed that on February 21, 2002, the engine received a 100 hour inspection. The total time on the engine was 4,207.4 hours; the time since major overhaul (SMOH) was 1,250.3; and the tach time was 865.4 hours. The compression readings were 78/80, 67/80, 74/80, 66/80, 67/80, and 67/80. The total time on the engine at the time of the accident was 4,216.1 hours, with 8.7 hours since the last 100 hour inspection.

A visual inspection of the engine revealed a hole in the engine case. The engine was shipped to Teledyne Continental Motors (TCM) in Mobile, Alabama, for an engine teardown.

The engine teardown at TCM revealed that the cylinder part numbers were:

#1: 639272 blue band "CN635448EC" on flange

#2: 654961A1 Steel

#3: 649317CE orange band "cermi-chrome"

#4: 649317CE orange band "cermi-chrome"

#5: 649317CE orange band "cermi-chrome"

#6: 654961A1 Steel

The engine teardown at TCM revealed the piston part numbers were:

#1: TCM 648045

#2: AE, MW 130196 casting number

#3: 648044 casting number

#4: 648044 casting number

#5: 648044 casting number

#6: AE MW 130196 casting number

The TCM engine inspection revealed the crankshaft was broken in two pieces at the number 2 cheek. A fatigue fracture was observed on the fracture surfaces of the number 2 cheek. The number 2 piston rod, rod bearing, and rod journal were discolored and exhibited heat distress. The crankshaft fracture surfaces of the number 2 cheek were sent to the National Transportation Safety Board's Materials Laboratory for further examination. (See Teledyne Continental Motors Engine Report)

The NTSB Materials Laboratory conducted an inspection of the crankshaft, forging number 539664, S/N S401, and heat code E99. The inspection revealed that the crankshaft fractured on two planes through the crank cheek between the #1 and #2 rod journals. The report stated, "Both of the fracture surfaces on the smaller section exhibited smooth crack arrest markings typical of fatigue propagation. These fracture surfaces were heat tinted, but there was no evidence of long-term prior heat damage on any of the journal surfaces. The fracture surfaces on the larger section were obscured by post-fracture damage."

The NTSB report further stated, "The superficial hardness measured on the surface of the #1 main bearing journal averaged 58.3 HR30-N. Core hardness measured on a section taken near the origin area of Fracture A averaged 28.3 HRC..…For the accident crankshaft, Teledyne Continental Motors specified the material to be 4340 steel with surface hardness greater than 60 HR30-N and core hardness of 30 to 33 HRC. For crankshafts manufactured under current specifications, Teledyne Continental Motors specifies a surface hardness greater than 68 HR30-N and core hardness between 33 and 39 HRC, with a nitride case depth of 0.020 to 0.040 inches."

The engine was manufactured as an O-470-R and shipped to Cessna Aircraft Company on May 15, 1967, as a new engine. The crankshaft, forging number 539664, S/N S401, and heat code E99, was manufactured in the 1960's. It is unknown if the crankshaft was the original crankshaft as shipped by Continental Motors on May 15, 1967.

The examination of the engine logbooks revealed that on December 23, 1994, the engine was converted to a O-470-50, as a result of an engine Supplemental Type Certificate (STC) #SE4985NM, which changed the cylinders to the same cylinders and pistons used on Continental IO-520 engines. The total time on the engine at the time of the conversion was 2,957.1 hours. The engine logbook indicated the crankshaft had not been replaced since the STC conversion on December 23, 1994. It had accumulated 1,259.0 hours since the STC conversion. The engine logbook indicated that on January 1, 1995, the tach read 0 and the Since Major Overhaul (SMOH) read 0. The engine was installed on Cessna 182H, N1870X. The registration number was later changed to N64AE. The engine logbook entry stated the following information concerning the engine conversion:

"Modified Continental model O-470-R engine, S/N: 133997-R and carburetor P/N 10-4893, S/N: BD 1 1923 in accordance with the P. PONK AVIATION O-470-50 ENGINE REPORT NO. 2 REVISION C, DATED 5-20-92 UNDER STC #SE4985NM. Installed PPA O-470-50 engine data plate S/N: 2038 per drawing number PPA 052 under STC #SE4985NM."

The crankshaft, S/N S401, was a crankshaft type that was originally used on Continental Motors O-470 and IO-470 engines. During the 1970's, Continental Motors changed the design specifications to the crankshafts used on the IO-470 engines. The new design widened the crankshaft cheeks and narrowed the rod journals, and the lightener holes were made smaller. The new design became known as the "heavy" or "narrow" crankshaft and the old design was known as the "light" or "wide-rod" crankshaft. The current crankshafts are manufactured using vacuum arc remelted steel (VAR), whereas the older crankshafts were made from air remelted steel.

The engine teardown revealed that the pistons installed on the engine were 8.5 to 1 compression pistons used on normally aspirated Continental O-520 engines, not the 7.5 to 1 compression pistons used on turbocharged Continental O-520 engines. The P. Ponk Aviation STC SE4985NM specifies that the 7.5 to 1 compression pistons are the proper pistons to use in the engine conversion.

The P. Ponk Aviation web site, dated 8/14/2002, stated the following information concerning the engine conversion:

"To convert a stock Continental O-470 to a O-470-50 SUPER EAGLE several internal changes need to be made to the engine. First, and most obvious is to exchange the O-470 cylinders for O-520 cylinders which increases engine displacement by 50 cubic inches. O-470 models R and S require a new crankshaft. The crankshaft counterweights are reconfigured and case modifications are made. The cylinders are fitted with low compression pistons which are precision balanced to within .5 grams. The carburetor is also modified. All original external accessories are overhauled and used on the O-470-50. The end product is essentially a O-520 which is carbureted and derated to 270 hp. Recommended TBO for the O-470-50 is 2,000 hours."

The original O-470 engine produced 230 horsepower at 2,600 rpm.

On September 24, 2002, P. PONK AVIATION, issued a Service Information Letter, SIL 002, to its dealers, owners, operators and overhaul facilities of P. Ponk O-470-50 engines. The Service Information Letter stated the following information:

"O-470-K, L, M, R, S, or U, converted to O-470-50 under STC SE4985NM, and assembled with a wide-rod crankshaft (The "wide rod" crankshaft may be identified as one with 530383 rod bearings installed.)

It has come to our attention that some of the models listed above have been assembled with the higher compression (8.5 to 1) pistons, instead of the lower compression 7.5 to 1 pistons called out in our STC instructions.

Use of the "wide-rod" crankshaft with any piston higher than the 7.5 to 1 compression ratio and a maximum rpm above 2700 is not authorized by our STC and could result in engine failure. Our testing did not exceed the above parameters, and we do not condone or support installation of the higher compression pistons.

Please check the engine records to determine if any overhaul, top overhaul or cylinder change has been performed in which higher compression pistons were installed. If higher compression pistons are found, we recommend immediate engine teardown and complete inspection of the crankshaft, including ultrasound and magnaflux inspections, for defects.

Reassemble the engine in accordance with our STC, installing 7.5 to 1 compression pistons."

No records remained concerning the engine conversion on December 23, 1994. There were no logbook entries that indicated any of the pistons had been changed since the engine was converted to an O-470-50. Only the # 3 cylinder was changed on April 15, 2000, due to low compression. The engine build-up records that documented what parts were installed on the engine during the STC conversion no longer existed.

Parties to the investigation included the Federal Aviation Administration and Teledyne Continental Motors, Inc.

NTSB Probable Cause

The engine failure due to the fatigue fracture of the crankshaft which resulted from the installation of improper pistons during an STC'd engine conversion by other maintenance personnel. Additional factors included the unsuitable terrain encountered by the pilot during the forced landing.