N961JDPiper PA-28R-200 · 1973

On April 3, 2012, about 1400 eastern daylight time, a Piper PA-28R-200, N961JD, was substantially damaged during a forced landing at McEntire Joint National Guard Base (MMT), Eastover, South Carolina. The private pilot and the passenger were not injured. Visual meteorological conditions prevailed. The airplane was not operating on a flight plan, from Barnwell Regional Airport (BNL), Barnwell, South Carolina, to Tappahannock-Essex County Airport (XSA), Tappahannock, Virginia. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91.

According to the pilot, the previous evening, he added one quart of oil to the engine, and in the morning, prior to a first flight from Lakeland Linder Regional Airport (LAL), Lakeland, Florida, to BNL, he conducted a "complete" preflight inspection. After arriving at BNL, and subsequent to refueling, the pilot completed another "walk-around" inspection. The flight departed BNL about 1330, and approximately 25 minutes later, the [Lycoming IO-360-C1C] engine began to run rough. The pilot checked the magnetos, and noted that all four cylinder head temperatures and all four exhaust gas temperatures were normal. The pilot reduced power to 20 inches and 2,000 rpm, but engine roughness increased, and oil pressure dropped to 0 in about 1 minute.

The pilot planned to divert to Columbia Metropolitan Airport (CAE), Columbia, South Carolina; however, the airplane had descended to 1,500 feet when he saw MMT, and he decided to divert to runway 32.

Because of the rapidity at which the forced landing scenario developed, the pilot did not have time to change to the tower frequency, and as he approached the runway, he saw an F-16 take off from runway 14. After another F-16 took off from runway 14, the accident airplane was caught in its wake turbulence and rolled about 45 degrees. As the airplane continued to descend, through about 100 feet agl, the pilot was able to recover it to wings level but did not have sufficient altitude to properly align with the runway. He landed the airplane at a 20- to 30-degree angle to the runway, and it veered off the right side. To avoid a terrain drop-off, the pilot then aligned the airplane parallel to the runway but it struck a "runway remaining" sign about 50 mph before coming to a stop.

After deplaning, the pilot observed engine oil covering the nose landing gear and the landing gear doors.

According to the responding Federal Aviation Administration (FAA) inspector, subsequent examination of the engine revealed that the #1 cylinder, upper aft through bolt was sheared off, that two #1 cylinder upper mounting studs had pulled loose from the crankcase, and that the crankcase at the #1 cylinder aft lower through bolt was cracked, with an oil leak in that vicinity.

The engine halves and through bolts were later examined at Lycoming Engines. Examination of the engine case halves confirmed that the cylinder #1 upper aft through bolt was broken. Internally, the crankcase halves exhibited pitting and a frosty appearance of the metal on the #2 and #3 upper main bearing support webs, consistent with fretting.

According to FAA 8083-30, fretting occurs when "when two mating surfaces, normally at rest with respect to one another, are subject to slight relative motion. It is characterized by pitting of the surfaces and the generation of considerable quantities of finely divided debris. Since the restricted movements of the two surfaces prevent the debris from escaping very easily, an extremely localized abrasion occurs."

According to maintenance records, at airplane tachometer time 2,958, the engine underwent a major overhaul by Zephyr Aircraft Enginesthat was signed off on July 29, 2002. The overhaul included an engine crankcase overhauled by CSI, Incorporated. On January 9, 2007, at tachometer time 3,448, a hairline crack was found in the crankcase. The engine was disassembled by Zephyr and reassembled with a rebuilt crankcase supplied by CSI. On September12, 2010, about tachometer time 3,751, after the airplane arrived at Lubbock Preston Smith International Airport (LBB), Lubbock, Texas, Lubbock Aero found that one intake pipe was loose on cylinder #1, one on cylinder #2, and one exhaust nut was missing from cylinder #1. Five cylinder hold down studs were also found broken on cylinder #2. The missing nut was replaced on cylinder #1, and the intake pipes were resealed. Cylinder #2 was removed, the studs were replaced, and cylinder #2 was reinstalled followed by a successful engine run.

In the June 2014 issue of Sport Aviation, the author of the "Savvy Aviator" column noted that, according to a veteran mechanic/expert witness, "who specializes in research on fastener torque and engine assembly practices,…the root cause of spun bearings, thrown rods, and separated cylinders is simply, 'a failure to achieve sufficient preload in the assembled fasteners.'"

The author further noted that, "preload is the technical term for the clamping force created by tightening a fastener (typically athreaded bolt or stud) that holds assembled parts together. Having sufficient preload is the key to a strong and reliable bolted joint that will not loosen, break, or shift under the load. In order for a bolted joint to be stable under cyclic repetitive stress, the preload on the fasteners must be greater than the maximum stress that is trying to pull the joint apart. If this condition is met, the joint will not separate and the fasteners won't 'feel' the repetitive stress cycles. But if it isn't, the joint will shift under load and the fasteners will ultimately fail from repetitive stress fatigue."

The author also noted that the expert identified five "obstacles to achieving proper fastener preload" during cylinder installation on an engine already mounted on an airplane:

1) The fasteners are not new.

2) The fasteners may not be adequately lubricated.

3) The lubricant is of poor quality.

4) Wrench access is limited.

5) Manufacturer instructions are incomplete.

The complete article can be found in the public docket for this accident.