N8878SAir Tractor AT-301 · 1979

On October 27, 2014, about 0945 Pacific daylight time, an Air Tractor AT-301, N8878S, collided into a center pivot irrigation system, following a total loss of engine power in Basin City, Washington. B and R Aerial Crop Care, Inc., was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 137. The commercial pilot, the sole occupant, was not injured; the airplane sustained substantial damage. The local aerial application flight departed from the Connell City Airport, Connell, Washington, about 0925. Visual meteorological conditions prevailed and the pilot did not file a visual flight rules (VFR) flight plan.

The pilot stated that the purpose of the flight was to apply triticale seed to a field about 15 miles from the departure airport. The pilot made a reconnaissance pass over the field, and after determining no obstacles would be in his flight path, he circled back to the field. When the airplane was about 30-50 feet above ground level (agl), the engine experienced a total loss of power. He maneuvered the airplane to an adjacent field, and while in the landing flare (about 5 feet agl), the engine momentarily restarted for a brief 2- 3 seconds. This temporary thrust propelled the airplane into a center pivot irrigation system located in the field.

An external post accident examination of the engine revealed that one of the cylinder heads contained a crack located in the dome between the forward and aft spark plug holes. The cylinder was removed and sent for further examination.

The airplane, an Air Tractor AT-301, serial number 301-0225, was equipped with a Pratt and Whitney R-1340-S3H1-G engine, serial number 32847.

In July 1999 the Federal Aviation Administration (FAA) issued an Airworthiness Directive (AD) 99-11-02 applicable to Pratt & Whitney R-1340 series engines. The AD required periodic visual inspections for cracks in the cylinder heads at specified intervals of time in service and fluorescent penetration (FP) inspections at cylinder overhaul. Instructions detailing how the inspections for cracks were to be performed was contained within Pratt & Whitney Service Bulletin (SB) 1787 dated September 1983. It stated that maintenance personnel should inspect the cylinder head focusing on the cooling fin roots at the dome area between cooling fins 7 and 8 and fins 8 and 9 (fins counted from the intake port).

According to the AD, visual inspections of the cylinder heads on Pratt & Whitney R-1340 engines that are not cowled and baffled, such as on the Air Tractor AT-301, are required at intervals of 100 hours of time in service. According to a page from the engine log book for the accident airplane, the engine was inspected on April 22, 2014, in accordance with AD 99-11-02 at an engine tachometer time of 1,179.7 hours and a time since major overhaul of 692.7 hours. The first entry on the same engine log page dated April 19, 2013, listed a tachometer time of 999 hours and a total time since overhaul of 512 hours. No other indications of inspections in accordance with AD 99-11-02 were noted on the log page in the 180.7 hours between the log entry on April 19, 2013 and the log entry on April 22, 2014.

The tachometer time at the time of the accident was 1,404.1 hours, a difference of 224.4 hour from the time of the inspection on April 22, 2014. The April 22, 2014, cylinder head inspection was also noted in the airframe log inspection record, and that log entry indicated the next inspection was due in 100 hours. According to SB 1787, after completion of an FP inspection at overhaul, the cylinder head is to be stamped "FP" over the intake port and at least the last 2 digits of the year inspected. Stamps "FP02 R" and "FP06 R" were observed above the intake port of the examined cylinder, consistent with the fluorescent penetration inspections having occurred in 2002 and 2006.

The airplane, an Air Tractor AT-301, serial number 301-0225, was equipped with a Pratt and Whitney R-1340-S3H1-G engine, serial number 32847.

In July 1999 the Federal Aviation Administration (FAA) issued an Airworthiness Directive (AD) 99-11-02 applicable to Pratt & Whitney R-1340 series engines. The AD required periodic visual inspections for cracks in the cylinder heads at specified intervals of time in service and fluorescent penetration (FP) inspections at cylinder overhaul. Instructions detailing how the inspections for cracks were to be performed was contained within Pratt & Whitney Service Bulletin (SB) 1787 dated September 1983. It stated that maintenance personnel should inspect the cylinder head focusing on the cooling fin roots at the dome area between cooling fins 7 and 8 and fins 8 and 9 (fins counted from the intake port).

According to the AD, visual inspections of the cylinder heads on Pratt & Whitney R-1340 engines that are not cowled and baffled, such as on the Air Tractor AT-301, are required at intervals of 100 hours of time in service. According to a page from the engine log book for the accident airplane, the engine was inspected on April 22, 2014, in accordance with AD 99-11-02 at an engine tachometer time of 1,179.7 hours and a time since major overhaul of 692.7 hours. The first entry on the same engine log page dated April 19, 2013, listed a tachometer time of 999 hours and a total time since overhaul of 512 hours. No other indications of inspections in accordance with AD 99-11-02 were noted on the log page in the 180.7 hours between the log entry on April 19, 2013 and the log entry on April 22, 2014.

The tachometer time at the time of the accident was 1,404.1 hours, a difference of 224.4 hour from the time of the inspection on April 22, 2014. The April 22, 2014, cylinder head inspection was also noted in the airframe log inspection record, and that log entry indicated the next inspection was due in 100 hours. According to SB 1787, after completion of an FP inspection at overhaul, the cylinder head is to be stamped "FP" over the intake port and at least the last 2 digits of the year inspected. Stamps "FP02 R" and "FP06 R" were observed above the intake port of the examined cylinder, consistent with the fluorescent penetration inspections having occurred in 2002 and 2006.

According to the NTSB aviation accident database, after AD 99-11-02 became effective in July 1999 there were a total of 23 accidents involving Pratt and Whitney R-1340 engines that had a cylinder failure. There were 9 accidents that involved engine cylinders that cracked circumferentially (head to barrel separation), 4 that involved cylinders that cracked over the dome from spark plug hole to spark plug hole (similar to the accident cylinder), 3 that occurred in the rocker boss area, and 7 noted a cylinder cracked in an unspecified location. None of the accidents resulted in a fatal injury.

Among the four accidents where cracks were located over the dome, the following inspections were noted. The first accident (FTW02LA030) indicated that the last visual inspection per AD 99-11-02 occurred 257.0 hours prior to the accident; another cylinder from the same airplane was found cracked during a visual inspection completed after the accident. A second accident (LAX05LA152) indicated that the last inspection occurred at 60 hours prior to the accident, but the type of inspection was not noted. The last inspection that was documented as completed per AD 99-11-02 occurred 1,050.1 hours prior to the accident. The third accident (CEN10LA420) indicated the cylinders were visually inspected per AD 99-11-02 about 18 hours prior to the accident. In the fourth accident (DFW05CA094), no inspection details were documented.

A similar query was conducted of the FAA's Service Difficulty Report (SDR) database. Among the results, 22 of the reports documented a cylinder crack as the cause of the service difficulty (one report documented 3 cases of cracks). Reports documented 7 findings of circumferential cracks (head to barrel separation), 6 findings of cracks between the spark plug holes (similar to the accident cylinder), and the remaining reports noted cracks that were either in a different location of the head (7 findings) such as the exhaust rocker arm mount or were not specific regarding the crack location (4 findings).

In February 2009, the FAA issued Special Airworthiness Information Bulletin (SAIB) NE-09-09 to alert owners, operators, repair facilities, and FAA inspectors of the potential for cylinder head cracks to develop at the exhaust port on Pratt and Whitney R-1340-series reciprocating engines. The bulletin noted that 6 documented incidents had occurred since 2000. The SAIB recommended that persons conducting visual inspections for cracks per AD 99-11-02 should also include the area around the exhaust port and valve housing in the inspection, and FP inspections at overhaul should include the entire cylinder.

In summary, the NTSB aviation accident and the FAA's SDR databases, revealed that a total of 10 cases were found where the cylinder was cracked between the spark plug holes. Adding the current accident to the list, the total number of documented cases of dome cracks totals 11 over a 15-year span, and at least 2 of those 10 cases involved likely non-compliance with the existing AD. The data also showed that at least 16 occurrences of cracks at the head to barrel joint also occurred over the 15-year span; a rate of occurrence that is greater than the rate of occurrence that prompted issuance of the SAIB.

The cracked cylinder was sent to the National Transportation Safety Board (NTSB) Materials Laboratory for examination. The complete examination report is contained in the public docket for this accident.

The cylinder head contained a crack located in the dome between the forward and aft spark plug holes, substantial enough to prohibit combustion. The crack's origin areas were located between fins 8 and 9 (middle of the dome), within fin 9, and between fins 11 and 12 (aft portion of the dome). The crack extended through the thickness of the cylinder head to the interior surface of the head. The fracture surfaces and adjacent areas on the fins in the dome area were covered with black and gray exhaust deposits. The fracture surface across most of the dome showed relatively smooth features with curving crack arrest lines, features consistent with fatigue. Ratchet lines, radial marks, and arrest line curvature were consistent with cracks originating from multiple origins at the exterior of the cylinder head.

The pilot reported to the Federal Aviation Administration that he ran out of fuel while spraying crops and initiated a forced landing into a field. The pilot stated that he landed hard and the engine was separated from the airframe and subsequently broke in half. The airplane’s fuselage and wing were substantially damaged. Despite numerous attempts to contact the pilot, at the time this report was written, the pilot has not responded to the NTSB investigator-in-charge or submitted a completed NTSB pilot/operator 6120.1 form.