# NTSB FTW98FA239: Bell 206L-3, N27AE, Springdale, AR, May 24, 1998 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Field investigation · Final report - Date: May 24, 1998, 12:35 local (17:35 UTC) - Place: Springdale, AR - Coordinates: 36.179897, -94.14019 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=36.1799&lon=-94.1402&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 3 serious - Status: Completed, report July 2, 1999 - Report: Approved by Office Director - NTSB case key (mKey): 43726 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW98FA239 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/43726/pdf - Page: https://openairdocs.org/ntsb/FTW98FA239 ## Probable cause The failure of maintenance personnel to properly assemble the engine's accessory gearbox, which resulted in a total loss of engine power due to partial blockage of the main oil passage by an o-ring. The blockage reduced oil flow to the turbine shafting, which led to the total failure of the gas producer turbine shaft and the power (free) turbine shaft. A factor was the lack of suitable terrain for the forced landing. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - mech failure/malf, takeoff - initial climb - lubricating system,oil port/passage,internal - blocked(partial) (cause) - maintenance,rebuild/remanufacture - improper, other maintenance personnel (cause) - fluid,oil - flow restricted (cause) - turboshaft engine,gas generator turbine shaft - failure,total (cause) - turboshaft engine,free turbine shaft - failure,total (cause) - Forced landing, emergency descent/landing - autorotation - performed, pilot in command - Hard landing, emergency landing after takeoff - terrain condition - none suitable (contributing factor) - Roll over, emergency landing after takeoff ## Analysis Shortly after the helicopter lifted off from a hospital helipad en route to pick up a patient, the engine lost power. The helicopter descended into a parking lot, landed hard, and rolled over coming to rest on its right side. Disassembly of the engine revealed that both the N1 (gas producer turbine) and the N2 (power turbine) shafts had separated. Coke deposits and rub marks were noted on the outside diameter of the N1 shaft. Coke deposits were also present on the inside diameter of the N2 shaft. Metallurgical examination of the shafts determined that coke build up consistent with reduced oil flow led to rubbing between the shafts. The rubbing produced frictional heat that resulted in softening and subsequent failure of the shafts. An o-ring was found lodged in the main oil passage of the accessory gearbox housing. Oil flow testing and calculations showed that this o-ring reduced the oil flow to the turbine shafting from .82 to between .00 and .10 lbs/min. Maintenance records indicated that the engine had accumulated 531 hours since a 3,500 hour gear train inspection, which included disassembly, cleaning, and reassembly of all accessory gearbox components. ## Factual narrative HISTORY OF FLIGHT On May 24, 1998, approximately 1235 central daylight time, a Bell 206L-3 helicopter, N27AE, operated by Air Evac EMS, Inc., of West Plains, Missouri, sustained substantial damage during a hard landing following a loss of engine power on takeoff from the Northwest Medical Center in Springdale, Arkansas. The commercial pilot and the two medical crewmembers received serious injuries. The positioning flight was operating under Title 14 CFR Part 91 and was en route to Bella Vista, Arkansas, to pick up a patient for transport back to Northwest Medical Center. Visual meteorological conditions prevailed and a company flight plan was filed. The pilot reported that following a "normal start and run-up," the takeoff was made into an 8-knot southwest wind. A "good rate of climb" was established, and the helicopter "cleared the highest and immediate obstacles." The pilot's next recollection was of events after the accident. One of the medical crewmembers stated that after takeoff, the pilot initiated a "normal" left turn "to circle around to the north." The helicopter was facing south when there was a "loud explosion/backfire type of noise from above" which was "followed by complete silence." The helicopter then "rotated around to the left while falling." Witnesses reported that they heard a loud noise and saw black smoke coming from the helicopter shortly after it lifted off from the hospital helipad. According to local authorities, the helicopter descended into a parking lot, one of the main rotor blades struck a light pole, and the helicopter rolled over coming to rest on its right side. AIRCRAFT INFORMATION The helicopter, a Bell 206L-3, serial number 51141, was manufactured on May 15, 1985. Review of the helicopter's maintenance records by the NTSB investigator-in-charge (IIC) revealed that it had accumulated 3,247 hours at the time of the accident. The records indicated that the engine, an Allison 250-C30P, serial number CAE-895188, was installed new when the helicopter was manufactured and had accumulated 3,151 hours and 7,312 cycles at the time of the accident. According to entries in the engine logbook, on December 14, 1995, the turbine assembly was removed at an engine total time of 2,527 hours and 5,990 cycles. On January 10, 1996, the turbine assembly was reinstalled after repair by Dallas Airmotive, Inc., of Dallas, Texas. The repair, as detailed in Dallas Airmotive's Work Order No. EM0016, entailed replacing the 3rd and 4th stage turbine wheels due to cycle limitations (6,000 cycle life limit) and performing a 1,750 hour inspection of the N1 (gas producer turbine) shafting. During the N1 shafting inspection, the N1 turbine-to-compressor coupling shaft or "pea shooter" was found to be "stepped" and a new shaft, part number 23032345, serial number AE68962, was installed. On May 23, 1996, the engine was removed "because of vibration" at an engine total time of 2,620 hours and 6,218 cycles. On August 14, 1996, the engine was reinstalled in the helicopter after repair by Dallas Airmotive. According to Dallas Airmotive's Work Order No. TR0078, the repair included overhauling the turbine assembly, performing a 3,500 hour gear train inspection on the accessory gearbox and a 3,500 hour magnetic particle inspection on the compressor impeller, and test running the engine. At the time of the accident, the engine had accumulated 531 hours and 1,094 cycles since this repair. Review of Dallas Airmotive's complete file on Work Order No. TR0078 indicated that the N1 coupling shaft, part number 23032345, serial number AE68962, was inspected, found to be serviceable, and reinstalled. At the time of the accident, this shaft had accumulated 607 total operating hours. The inner power turbine shaft, part number 23038137, serial number 64110, and the outer power turbine shaft, part number 23038136, serial number 66364, were inspected, found to be serviceable, "alseal" coated, and reinstalled. The main oil delivery tube or "piccolo tube," part number 23033876, serial number 30641, was flow tested, found to be serviceable, and reinstalled. The file for Work Order No. TR0078 contained a completed Dallas Airmotive Form No. A250-504-2, entitled "A250 Assembly C-28/C-30 Gearbox." Item number 17 of this form stated: Place an "O" ring AS3085-010 on each end of the 6896458 oil delivery tube and one "O" ring AS3085-010 on the oil screen. Install the oil screen and delivery tube in housing. Install the shouldered attaching screw and torque to 22-26 inch lbs. Secure with lock wire. This item of the form included boxes for both a mechanic's stamp and an inspector's stamp, and both boxes were stamped. The file for Work Order No. TR0078 also contained a completed Dallas Airmotive Form No. A250-505-3, entitled "C30 Final Build." Item number 2 of this form detailed the turbine to gearbox installation, and step A of this item stated, in part: "insure 'O' rings on spur adapter gearshaft are in good condition. Replace with new if necessary." The mechanic's stamp box and the inspector's stamp box for step A of item 2 were both stamped. WRECKAGE AND IMPACT INFORMATION The helicopter was examined at the accident site by an FAA operations inspector on the afternoon of May 24, 1998. It was then moved to a hangar at the Springdale Municipal Airport where it was examined on May 26 and 27, 1998, under the supervision of an FAA airworthiness inspector by representatives from the engine and airframe manufacturers. On May 27, 1998, the engine was removed from the helicopter and crated for shipment to the engine manufacturer's facility. Examination of photos and reports provided by the FAA, the Springdale Police Department, and the engine manufacturer revealed the following information. The accident site was located in the parking lot behind a restaurant at 813 West Maple Street in Springdale, Arkansas. The helicopter came to a stop heading south-southwest, lying on its right side, in the southwest corner of the parking lot. A metal utility pole located to the right of the helicopter's nose was damaged about 9 feet above ground level. Additionally, a stock trailer parked facing south to the left of the helicopter's nose sustained damage to the upper rear corner of its right side. The left skid separated from both crosstubes, and the aft crosstube separated from the fuselage. Both steps on the left side of the fuselage were broken off, while both steps on the right side remained attached but were bent upward. The fuselage was buckled and vertically crushed with the most severe damage to the bottom aft section. The tailboom was displaced downward, and the bottom of the vertical fin was crushed upward. Both main rotor blades remained attached to the main rotor head. The blue blade was nearly separated approximately 3 feet outboard of the rotor head by a tear running diagonally inward from the leading edge to within about 2 inches of the trailing edge. The white blade was torn chordwise from the trailing edge to the spar approximately 3 feet inboard of the tip. The inboard bottom surfaces of both blades were coated with black soot. Initially, the main rotor head/main transmission could not be rotated by hand. After the engine-to-transmission drive shaft was disconnected, the main rotor head/main transmission turned freely. Tail rotor drive continuity was established from the tail rotor to a torsional fracture in the tail rotor drive shaft between the aft bulkhead coupling and the #1 hanger bearing. Following removal of the engine, binding of the N2 (power turbine) was confirmed by unsuccessful attempts to hand rotate the 4th stage turbine wheel. The N1 (gas producer turbine) was also found bound in place. After several attempts to turn the N1 by hand rotating the compressor impeller, a slight rotation of about 10 degrees could be accomplished, then binding would occur. ## Aircraft - Registration: [N27AE](https://openairdocs.org/deregistered/N27AE-1998-09-28), registration cancelled 1998-09-28, S/N 51141 (OpenAirDocs) - Reported make and model: Bell 206L-3 - Registry model: [Bell 206L-3](https://openairdocs.org/model/bell-206l-3) (registry code 1182108) (OpenAirDocs) - Category: Helicopter - Serial number: 51141 - Airframe hours: 3247 - Engines: Allison 250-C30P 650 horsepower turbo shaft - Damage: Substantial damage - Flight: Positioning, Part 91 - Operator: Air Evac Ems, Inc., doing business as Air Evac Lifeteam - Registered owner: Air Evac Leasing Corp. - Airworthiness certificate: Standard, Normal - Last inspection: AAIP, May 11, 1998, 38 hours before - Destination: BELLA VISTA, AR - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 49; commercial; airplane ratings: single-engine land; instrument ratings: helicopter; medical: class 2, valid medical--w/ waivers/lim; flight hours: 5,163 total, 2,519 in this make and model, 5,073 as pilot in command, 57 in the last 90 days, 18 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 90° at 7 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 88 °F, dew point 63 °F - Altimeter: 29.00 inHg - Observed at: FYV, 10 nm away ## 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 19980524047139A](https://openairdocs.org/incident/19980524047139A), May 24, 1998: Bell 206L3, Springdale, AR, No damage. (-23) According to witnesses the helicopter made a normal liftoff and began to climb to the southwest. Witnesses reported hearing a loud whine followed by… 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.