Rolls-Royce. Accident Investigation. & Engine Disassembly Inspection. Rolls-Royce Allison Model T63-A720 Engine CAE

Transcription

1 Rolls-Royce Accident Investigation & Engine Disassembly Inspection Rolls-Royce Allison Model T63-A72 Engine CAE I 1 3 Department of Public Safety, Utab Warren W. Seitzinger Accident Investigator 4 8 Accident date: I1 February 2 Report date: 15 February 2

2 Engine T63-A72, S,S AE Utah Department of Public Safety. LYoods Cross. UT, 11 February 2 1. SYNOPSIS. 2. FACTUAL INFORMATION. TABLE OF CONTEICTS History of Flight Personnel Information Injuries to Persons Aircraft Information Meteorological Conditions Aids to Navigation Communications Accident Site Information Flight Recorder Wreckage and Impact Information Engine Examination Engine Maintenance and Records Additional Information 3. SUMMARY OF FINDINGS. 4. APPENDICES. 4.1 Photographs 4.2 Investigation Participants

3 Engine T63-A72, S/N AE 46157, Utah Department of Public Safety, Woods Cross, UT, 11 February 2 1. SYNOPSIS On 11 February 2, at approximately 1415 (MST), a Bell OH-58A-t Helicopter, registration N7UT, with an Allison T63-A72 engine, operated by Utah Department of Public Safety (DPS), Woods Cross, UT, was involved in an accident. The aircraft was destroyed upon impact with the terrain after experiencing an in-flight tailboom separation due to a blade strike from the main rotor system. The pilot and a maintenance crewmember, only occupants onboard, were fatalities. The National Transportation Safety Board (NTSB) requested airframe and engine manufacturers assistance in the investigation, Rolls Royce Corporation (RRC) and Bell Helicopter (BHI) complied. The investigation was conducted on 12 and 13 February, on-site, and at a DPS hangar where the wreckage was recovered in Woods Cross, UT. The engine \vas removed and shipped to Rolls Royce Corporation (RRC), Indianapolis, for disassembly and examination. 2. FACTUAL INFORMATION 2.1 Historv of Flight. It was reported that at approximately 14 (MST), N7UT, with a pilot and a crewmember aboard, had departed Skypark Airport, Woods Cross, UT, to conduct a maintenance test flight. At approximately 1415, as reported by a pilot awaiting clearance for departure from Skypark, the pilot of N7UT, while in the traffic pattern, transmitted over the CTAF (traffic advisory frequency) that he was entering an autorotation. Shortly thereafter, as reported by ground witnesses, the aircraft appeared to go out of control, abruptly descended, and crashed. Some of the witnesses had stated that it appeared that the rotor blades had stopped rotating. During the descent, the tail boom (TB) was severed by a main rotor (MAX) blade strike prior to impacting the terrain, on it's left side, approximately 5 feet short of the end of the runway and 3 feet left of the centerline. The aft portion of the TB with tail rotor (TR) gearbox assembly was found approximately 5 feet southeast of the hselage. The remainder of the aircraft, less fragmented debris from the T/B strike, was confined to the primary impact point. NOTE: Per maintenance log entries, operational flight checks uere required for replacement of the free-wheeling unit and fuel control rigging. Interviews with employees of DPS and the maintenance contractor revealed that possibly a M/R RF'M check and a governor (PTG) droop check would also have been conducted. Both the M/R RPM check and the free-wheeling unit operational check would have necessitated autorotational flight for completion. 2.2 Personnel Information. The pilot, 58 year old Thomas S. Rettberg, West Jordan, UT, \vas an employee of DPS, State of Utah. He possessed a Commercial Pilot Certificate, , issued , with ratings in airplanes and rotorcraft. He was instrument rated and also a Certified Flight Instructor in airplanes (4-8-94). He had accumulated approximately 9,5 total flight hours; 8,5 in airplanes and 1, hours in rotorcraft; approximately 5 hours flight time in the OH-58A. He had no previous records of accidents or incidents. The maintenance crewmember, 4 year old Thomas Bahoravitch, was an aircraft mechanic employed by Classic Helicopters, a company contracted for providing maintenance for the DPS helicopters.

4 Engme T63-A72, S/?J AE , Utah Department of Public Safety. ivoods Cross, UT, 1 1 February Iniuries. Both occupants sustained fatal injuries. 2.4 Aircraft Information. (Times are approximate). Model Bell OH-58A-t Serial Number Registration N7UT Airframe Hours, Total Time 515. Last 1 Hour Inspection Engine Model Allison T63-A72 Serial Number CAE Rating 42 SHP Engine Hours, Total Time Meteorological Conditions. The weather observations for the accident time period reportcd VFR conditions; ceiling 4, feet, visibility 1 SM, winds degrees at 8-1 Kts. 2.6 Aids to Navigation. N/A 2.7 Communications. N/A 2.8 Accident Site Information. The site appeared to be an abandoned, above ground, petroleum storage site located on the approach end of runu.ay 16 at Skypark Airport, Woods Cross, UT. 2.9 Flight Recorder. A Performance Analyzer Recorder (PAR) was installed. It was removed and retained by the NTSB for analysis. 2.1 Wreckage and Impact Information. (Reference BH report for detailed description of airframe damage). Physical evidence at the accident site indicated that the airframe h$id experienced an in-flight main rotor blade strike resulting in separation of the aft portion of tie tail boom. The aircraft impacted the terrain parallel to the base of an earthen berm, in (in approximate 9 degree left roll, slight nose low attitude, at a high rate of descent. The entire wreckage was confined to the impact point except the severed portion of the tail boom, with tail rotor gearbox attached and associated parts, which were found within an approximate 5 feet arc of the main wreckage. The force of the impact resulted in upward crushing of the entire left si,ile of the airframe inward to the fuselage centerline and ultimate collapse of the structure due to static overloads. All major airframe junctures were separated and the skid gear assembly was broken away. Both M/R blades exhibited damage signatures consistent with low RPM applied. One blade had evidence of impact with the T/B in the form of leading edge scamng a:id honeycomb separation from the spar. The damaged area of the blade, dimensionally, matched impact imprints on the separated TB. The crashworthy fuel system was intact without aiy detectable fuel spillage. The oil tank had ruptured allowing spillage. The N1 gauge indicated 56%, the pilot's throttle control was found near the flight idle detent.

5 Engine T63-A72, S/N AE 46157, Utah Department of Public Safety, Woods Cross, UT, 11 February 2 Recovery site Investigation: Continuity and functional checks of the following systems were completed and documented by the BHI representative; all were intact and functioned as designed disregarding disconnects due to crash forces: Flight controls to include tail rotor. Engine throttle and governor controls. Hydraulic controls. Engine to transmission drive shaft. Tail rotor drive shafting. Transmission. Tail rotor gearbox. Freewheeling unit functioned as designed. retained by FAA and sent to BHI for further examination Engine Examination. The engine had incurred major damage from crash impacts, the following was noted: All engine mounts were either broken, bent, or pulled from base attachments. The compressor was intact but had ingested a considerable amount of dirt and mud; a rock was found in the inlet. The compressor would not rotate. The starter generator was detached from its mounting clamp; the splined shaft was bent. The mounting flanges of the fuel control unit (FCU) were broken; quadrant throttle indicator was approximately lbth inch above 3 (ground idle). The power turbine governor (PTG) housins nas fractured and separated from the accessory gearbox. The bottom left side (L/S) of the fire shield and the L!S air discharge tube along with the L/S rear of the outer combustion case (OCC) were crushed and flattened inward to the turbine. All L/S rigid fluid lines were bent, broken or distorted. The mounting studs for the turbine were pulled from the gearbox allowing separation and displacement of the turbine. It would not rotate. Tachometer generators - N1 and N2, impact damaged.

6 Engine T63-A72. S M AE 46157, Utah Department of Public Safety, Woods Cross. UT, 1 1 February 2 Fuel Svstem. Fuel cell - intact; contained fuel, approximately 4 gallons. Fuel pump (FP) - intact; rigid lines distorted; main fuel line from airframe was fractured at B-Nut flange; filter \vas clean, filter bowl contained fuel. Fuel line to fuel spray nozzle contained fuel (approximately 2Occ s). Main fuel line (flex) - B-Nut fitting adapter was broken away. Lubrication Svstem Oil tank - ruptured, small amount of oil was present, remainder had drained at impact site. Engine oil filter - intact, clean, oily. Engine oil service lines contained oil. Gearbox contained oil; approximately one quart was drained. Chip detectors, upper and lower, clean no particulate present. 7 It was decided to remove the engine and send it to RRC, Indianapolis for an engine disassembly inspection. - Engine disassembly, RRC, Indianapolis, IN, 5 May 2. The turbine modules were removed and disassembled, the following \vas noted: The turbine to searbox attaching stud bolts were pulled out of the gearbox; the turbine wo.ild not rotate (misalignment and impact damage). The outer combustion case (OCC) was cut away to facilitate removal of the turbine. The combustion liner was intact, heavy carbon deposits were present; an approximate one inch weld repair was noted to the exterior of the liner. No. 8 bearing sump nut retaining ring was not fully seated, however it functioned as designed The lst stage nozzle fire shield \vas laden with gritty, sandy debris (photo #7). The 1 stage nozzle was intact, normal, heavily coated lvith sandy, gritty debris (photo # 8). Gas producer support - the 2 d stage wheel blade track had rotational rubbing imprints f?om the 6 to 9 o clock (impact side), viewed from rear 2 d stage wheel - four blade tips had evidence of rubbing.

7 Engine T , SM AE 46157, Utah Department of Public Safety, LVoods Cross. UT, 11 February 2 ( Engine Disassembly and Inspection, continued) Compressor to turbine coupling (peashooter) - exhibited two areas of heavy, 36 degree rotational scoring, from contact with the turbine shaft to pinion gear coupling (photo ft 1). Turbine shaft to pinion gear, coupling - heavy rotational scoring was exhibited on the inner surface matching, which corresponded with the scoring marks on the peashooter; the splines at the PT end (male) were rounded over as were the engagement splines (female) of the power turbine shaft (PTS). This evidence indicated that the PT was rotating when the PT attaching bolts were pulled from the gearbox resulting in misali,ment of the shafting and disengagement of the PTS from the turbine shaft to pinion gear coupling (photo #'s 11 & 12). PT support - the 3'd stage and 4Ih stage wheel blade tracks had rotational scoring imprints, 6 to 9 o'clock positions (impact side), viewed from rear (photo #'s 14 & 15). Sandy was present in the power turbine section (photo # 13). No. 5 bearing - some bearings felt rough during rotation, possibly from impact damage. It was determined that the compressor lock-up ivas due to the displaced shafting and the ingested mud and debris which had caked in the compressor. The engine was prepared for shipment and returned to the owner 2.12 Engine Maintenance and Records. The engine total time (TTE) was It had 19. ETT when it was installed on the aircraft at TTAF A review of the engine records revealed that all entries of the installed controls and engine modules matched. The last 1 hour inspection was completed 76 hours past at TTAF. There were no pre-mishap discrepancies noted, neither from the engine records nor from intervielvs with DPS aviation personnel, which would have been considered causal factors in inhibiting proper engine performance I The most recent significant maintenance performed, associated Lvith the engine, was an inspection of the freewheeling unit. which necessitated replacement of a cap seal. inner shaft. and a bearing. It was accomplished on 2-1 -, the day prior to the accident.

8 Engine T63-A72, SIN AE 46157, Utah Department of Public Safety, Woods Cross, UT, 1 1 February 2 Component 1 Part Number I Serial Number 1 TSO I TotalTime I Engine Gearbox Compressor Turbine NEW NEW Governor Fuel Pump Fuel Nozzle NEW T18712 NEW YF O Additional Information. The aircraft \vas equipped with a Performance Analyzer Recorder (PAR), which was calibrated to the engine. It was removed and sent to the manufacturer., Avionics Specialties, Incorporated, Charlottesville, VA for interrogation. The following recordings were downloaded:! TOT degrees C TQ Yo NI % ( normal engine idle, ) N 'Yo NR- 65.8% AIS - 34Kts OAT - 4 degrees C i

9 Engine T63-A72, S/N AE 46157, Utah Department of Public Safety, Woods Cross, UT, 11 February 2 3. SUMMARY OF FINDINGS. The aircraft was being flown on a maintenance test flight which would have necessitated autorotational flight to complete component functional checks. The aircraft experienced a tailboom separation, in-flight, caused by a main rotor blade strike. The main rotor blades exhibited damage consistent with a low RPM state at impact; one blade had leading edge impact damage that matched the tail boom impact imprint. There were no engine anomalies noted, internally or externally, during the investigation, which were not a result of crash forces. The engine, on-site, exhibited ingestion of dirt and rocks indicating that it was operating at ground impact. The ingestion of debris in the form of dirt and rocks into the compressor and dirt throughout the turbine modules indicated that the engine was operating during and after impact. The rotational rubbing evidence on the blade tracks of the 2"d, 3rd, and 4th stage turbine wheels indicated that the engine had been operating at impact. The heavy rotational scoring marks on the turbine shaft to pinion gear coupling and matching rotational scoring marks on the compressor to turbine coupling indicated that the engine had been operating at impact. The damaged splines of the turbine shaft to pinion gear coupling and the engagement splines of the PTS indicated that the engine was operating at impact. The recorded PAR data indicated that the engine was operating at idle RPM at impact