WPR10FA387

Long-term deterioration of multiple engine fuel vaporizers that led to material failure of multiple turbine blades, which resulted in a complete loss of engine power. Contributing to the accident were the exceedance of specified engine inspection intervals and the unsuitable forced landing location.

The turboshaft-powered aerial application airplane had just departed the airstrip when the pilot/owner heard a loud "crack," and the engine stopped developing power. He executed a forced landing in a water-filled rice paddy adjacent to the airstrip. After touchdown, the airplane nosed over onto its back. The non-U.S. designed airplane was originally manufactured and delivered with a reciprocating engine. About 18 years before the accident, that engine was replaced with a U.S. military turboshaft engine via a Federal Aviation Administration (FAA) field approval. About 15 years after the engine change, and 3 years before the accident, the FAA mandated that piston-to-turbine engine conversions required the use of either an amended Type Certificate or a Supplemental Type Certificate, and that field approvals were no longer appropriate. Detailed examination of the engine revealed that most of the power turbine blades were severely damaged or missing. Material analysis of the turbine components revealed that the first stage turbine blades failed due to short-term exposure to excessively high temperatures and that other turbine blades failed due to impact damage from the thermally-failed first stage blades. The combustor was equipped with multiple fuel vaporizers, nearly all of which exhibited significant long-term thermal damage. None of the vaporizers were within the operable damage limits specified by the maintenance guidance. The damaged fuel vaporizers altered the combustor exit temperature profiles, which precipitated the first stage turbine blade failures. Maintenance records indicated that the 600-hour inspection interval of the engine hot section had been exceeded at least twice in the 14 years preceding the accident, and that, at the time of the accident, the engine had exceeded the hot section overhaul interval by about 300 hours. In-service records for the failed components could not be located. Although they did not contribute to the accident, multiple irregularities with the airplane's maintenance documentation were discovered during the investigation.

HISTORY OF FLIGHT On August 6, 2010, about 0900 Pacific daylight time, a PZL M-18, N70461, was substantially damaged during a forced landing following a complete loss of engine power shortly after takeoff from runway 16 at Sanborn Airport (38CN), Meridian, California. The pilot/owner received minor injuries. The flight was operated under the provisions of Title 14 Code of Federal Regulations (CFR) Part 137, doing business as Martin's Dusters. Visual meteorological conditions prevailed, and no flight plan was filed for the agricultural agent application flight. According to the pilot, the flight was not the first flight of the day. The airplane was loaded with 3,600 pounds of fertilizer and about 120 gallons of fuel; the respective maximum capacities were 5,000 pounds and 150 gallons. The pilot stated that he took off to the south, that the airplane got airborne easily, and that he maintained a low altitude for his application work. Just after he began his turn to the east, he heard a loud "crack," and felt the airplane decelerate. He recognized that the engine had stopped developing power. He leveled the wings and attempted to touch down in the water-filled rice paddy adjacent to, and south of, the airstrip. After touchdown, the airplane nosed over onto its back. The pilot was unable to extricate himself, and a nearby witness assisted him in exiting the airplane. The wreckage was recovered to a secure storage facility a few days after the accident. On September 16, 2010, the wreckage was examined by personnel from the NTSB, the Federal Aviation Administration (FAA), and the engine manufacturer. Subsequent to that examination, the engine was removed from the airplane and shipped to the Honeywell Product Integrity Investigation Laboratory, Phoenix, Arizona. In early December 2010, the engine was examined in detail at that facility by representatives of Honeywell and the NTSB. PERSONNEL INFORMATION The pilot reported that he had a total flight experience of about 20,610 hours, including about 205 hours in the accident airplane make and model. He held an FAA commercial pilot certificate, with airplane single-engine land and rotorcraft-helicopter ratings. His most recent FAA second-class medical certificate was issued in January 2010, and his most recent flight review was also completed in January 2010. AIRCRAFT INFORMATION FAA registration documentation indicated that the airplane was imported new into the United States in 1986. In March 1992, the ASZ62IR M-18 radial (reciprocating) engine and PZL-KALISZ propeller were removed, and a Lycoming T53-L-7A turboshaft engine and a Hamilton Standard 53C51 propeller were installed. That same T53-L-7A engine was the one installed on the airplane at the time of the accident. The airplane was first registered to the accident operator in May 2009. However, the FAA documentation current at the time of the accident incorrectly specified that the airplane was equipped with a reciprocating engine, and the airworthiness category of the airplane was missing from the registration documentation. METEOROLOGICAL INFORMATION The recorded weather observation at an airport 15 miles east of the accident location included winds of 4 knots from 180 degrees, clear skies, and a temperature of 18 degrees C about the time of the accident. WRECKAGE AND IMPACT INFORMATION The airstrip was surrounded by agricultural fields interlaced with a series of levees. After the power loss, the pilot deviated slightly to the east to avoid a levee during the forced landing. Ground scars indicated that the airplane touched down about 850 feet south of the south end of the runway, and came to rest within about 150 feet of the initial touchdown point. The fuselage fractured just aft of the firewall, so that the bulk of the airplane came to rest inverted. The engine section was folded back, with the nose facing aft. The fuselage and cockpit section remained relatively intact, but the canopy section was partially embedded in the soft mud and water, which prevented the pilot form readily exiting the airplane without assistance. The fixed, conventional landing gear remained intact. The vertical stabilizer was crushed and canted forward, and the wings and spray rig were damaged. The engine remained attached to the firewall, the propeller remained attached to the engine, and all three propeller blades were bent aft. There was no fire. ADDITIONAL INFORMATION T53 Series Engine Background Information The T53 series engines were originally designed and manufactured by Lycoming in the 1950s. In 1994, AlliedSignal acquired the Lycoming Turbine Engine Division of Textron. In 1999, the resulting company became part of Honeywell Aerospace. Honeywell Aerospace provided technical assistance for the investigation of this accident. According to the Honeywell Aerospace representative, T53 engine models that contained an "L" in the variant designators were military engines. The T53-L-7A engine was a life-extension conversion of the previous T53-L-7 model. The "A" conversion extended the Time Between Inspection (TBI) to 600 hours, and the Time Between Overhaul (TBO) to 1,800 hours. The Honeywell Aerospace engine examination report contained the following statement in its introduction: "The T53-L-7A engine was designed and manufactured to meet the requirements set forth by the United States Military; as such, the U.S. Military was the design holder and had sole responsibility for developing and maintaining the continuing airworthiness requirements for the T53-L-7A series engine. Honeywell had no knowledge of, nor provided input regarding the installation of the T53-L-7A series engine in the accident aircraft." Engine Maintenance Guidance Since the U.S. military was the design holder and had sole responsibility for developing and maintaining the continued airworthiness requirements for the T53-L-7A series engine, maintenance guidance was only available via U.S. military documentation. Department of the Army Technical Bulletin TB 55-2800-200-31/1 (T53 Inspection Guide) presented detailed information for the subject T53-L-7A engine and many of its components. The inspection guide referred to the "hot end," which included the combustion turbine assembly and the gas producer system. Colloquial industry terminology typically referred to this as the "hot section;" for the purposes of this report they are considered synonymous. Since the -7A variant was a "Long-Life" engine, the specified inspection interval for the hot end was 600 service hours, compared to 400 hours for other variants. The inspection guide provided specific textual and diagrammatic information regarding the wear and damage limitations for the fuel vaporizers. The cited limitations included characteristics and allowable dimensions for burn-off, warping, bulging, out-of-round, cracks, and holes. FAA Approval of Aircraft Modifications Modifications to FAA-certificated aircraft must be approved by one of two means; either a "field approval," or a Supplemental Type Certificate (STC). Any STC- or field-approved modification must comply with all applicable regulations. The FAA Flight Standards division was responsible for field approvals, while the FAA Aircraft Certification Office (ACO) branch was responsible for STC approvals. There were no explicit FAA requirements for an applicant to involve either the engine or airframe manufacturer in a field- or STC-approvals; the only requirement was that the application for approval of the modification must contain all the relevant data required for certification. However, approval of a military version of an engine that did not have a civil type certificate (TC) would require a much greater certification effort than the installation of an engine with a civil TC. FAA Order 8900.1, entitled" Flight Standards Information Management System (FSIMS)" provides field approval guidanc