# NTSB NYC99IA056: Piper PA42-1000, N37KW, Lexington, KY, February 5, 1999 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: February 5, 1999, 10:00 local (14:00 UTC) - Place: Lexington, KY - Location: 37.9887° N, 84.4777° W: Placed by OpenAirDocs: center of Lexington, KY, within about 6 miles (OpenAirDocs) - Nearby events: https://openairdocs.org/map.md?lat=37.9887&lon=-84.4777&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed, report November 22, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 45789 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=NYC99IA056 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/45789/pdf - Page: https://openairdocs.org/ntsb/NYC99IA056 ## Probable cause Improper assembly of the engine gearcase by the manufacturer, which resulted in an uncontained failure of the 1st bull gear. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Miscellaneous/other, descent - normal - reduction gear assy - failure - maintenance - improper, manufacturer (cause) ## Analysis The during descent for landing, the airplane's right engine, a TPE331-14B, experienced an uncontained gearcase failure. Disassembly of the engine revealed that the gearcase was ruptured in the 1st bull gear's plane of rotation and that the 1st bull gear had a 90 degree arc of the rim and gear teeth separated. Metallurgical examination of the 1st bull gear revealed a fatigue fracture that had originated in the gear's bore splines. The fatigue originated in area where the spline thickness was significantly reduced by indentations on the pressure surface of the splines. Review of the engine's overhaul manual revealed a tie-rod was used to provide a clamping force between the spur gear and 1st bull gear. The assembly procedures required that the tie-rod be stretched with a load of 22,000 pounds, and then secured with a nut that was hand-tightened. During disassembly of the gearcase, it was not possible to determine the amount of stretch on the tie-rod, or the breakaway torque on the retaining nut. Maintenance records revealed that the gearcase was disassembled, and reassembled during repairs, which were performed by engine manufacturer. ## Factual narrative On February 5, 1999, about 1000 eastern standard time, a Piper, PA42-1000, N37KW, experienced an uncontained failure of the right engine during a descent for landing at the Blue Grass Airport (LEX), Lexington, Kentucky. The certificated airline transport pilot and passenger were not injured. Visual meteorological conditions prevailed and an instrument flight rules flight plan had been filed for the flight that departed the New Castle County Airport, Wilmington, Delaware, about 0800, destined for LEX. The personal flight was conducted under 14 CFR Part 91. In a telephone interview, the pilot stated the airplane was descending through 19,000 feet, when he experienced a momentary fluctuation in engine torque for the right engine. Shortly thereafter, he heard a "loud explosion," and observed flames emanating from the airplane's right engine cowling. He then secured the engine which extinguished the fire, and declared an emergency. The airplane landed at LEX without further incident. Examination of the airplane by a Federal Aviation Administration Inspector, revealed extensive fire damage forward of the right engine firewall. A 12 inch, by 24 inch hole was found burned through the upper engine cowling. A 5 inch, by 10 inch hole was found in the upper engine case near the combustion section, and a 1 inch, by 3 inch hole was found in the engine inlet gear case housing. Additionally, damage was observed at the first stage compressor blades. The engine, an AlliedSignal, TPE331-14B, was retained for further examination. The engine was disassembled at AlliedSignal, Phoenix, Arizona, under the supervision of a Safety Board Investigator. The disassembly revealed that the gearcase was ruptured in the 1st bull gear's plane of rotation. Additionally, the 1st bull gear had a 90 degree arc of the rim, and gear teeth separated. The combustor plenum was also ruptured; however, the turbine disks, which were located underneath the combustor, were all intact. According to the Safety Board's Metallurgist factual report, the examination of the 1st bull gear revealed a fatigue fracture that originated in the gear's bore splines. The fatigue originated in an area where the spline thickness was significantly reduced by indentations on the pressure surface of the splines. Review of the engine maintenance records revealed that at the time of the incident, the engine had 3,535.1 hours time since new, and 768.1 hours since the last overhaul, which was performed by AlliedSignal. Additionally, the gearcase was disassembled, and reassembled during repairs, which were performed by AlliedSignal on November 19,1996. Review of the engine's overhaul manual revealed a tie-rod was used to provide a clamping force between the spur gear and 1st bull gear. The assembly procedures required that the tie-rod be stretched with a load of 22,000 pounds, and then secured with a nut that was hand-tightened. During disassembly of the gearcase, it was not possible to determine the amount of stretch on the tie-rod, or the breakaway torque on the retaining nut. As a result of the investigation, AlliedSignal advised that it would be revising the TPE331 engine manuals and assembly procedures to require a measurement of stretch on the tie-rod before and after the nut is installed and require that the retaining nut be torqued to some value greater than hand-tight. ## Aircraft - Registration: [N37KW](https://openairdocs.org/aircraft/N37KW), registered now, S/N 425527039, built 1989 (OpenAirDocs) - Reported make and model: Piper PA42-1000 - Registry model: [Piper PA-42-1000](https://openairdocs.org/model/piper-pa-42-1000) (registry code 7104225) (OpenAirDocs) - Registry engine: [AiResearch TPE331 series](https://openairdocs.org/engine/airesearch-tpe331-series) (registry code 01514, turbo-prop) (OpenAirDocs) - Category: Airplane - Serial number: 425527039 - Airframe hours: 3694 - Engines: Garrett TPE-331-14 1000 horsepower turbo prop - Damage: Minor damage - Fire: In-Flight - Flight: Personal, Part 91 - Registered owner: Cumberland Mangmnt & Holdings - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, November 18, 1998, 90 hours before - Departed: ILG, WILMINGTON, DE - Destination: LEX - Flight plan: IFR - Airport: LEX, Blue Grass, runway 22, 7,003 × 153 ft, asphalt ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 40; airline transport; airplane ratings: single-engine sea, multi-engine land, single-engine land; instrument ratings: airplane; medical: class 2, valid medical--no waivers/lim.; seat: left; flight hours: 5,900 total, 750 in this make and model, 4,500 as pilot in command, 95 in the last 90 days, 57 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 150° at 9 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 36 °F, dew point 25 °F - Altimeter: 30.00 inHg - Observed at: LEX ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19990205010899A](https://openairdocs.org/incident/19990205010899A), Feb 5, 1999: Piper PA421000, Lexington, KY, Minor damage. While at 19,000 ft AGL in cruise flight the pilot noticed a small "blip" in the right engine torque gauge. A few moments later he noticed another torque gauge… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.