Saturday, May 13, 2017

Beechcraft 400A Beechjet, N193BJ: Incident occurred March 13, 2014 near Greater Rochester International Airport (KROC), Monroe County, New York

Aviation Incident Final Report - National Transportation Safety Board: https://app.ntsb.gov/pdf

Investigation Docket -  National Transportation Safety Board: https://dms.ntsb.gov/pubdms

Aviation Incident Data Summary -  National Transportation Safety Board:   https://app.ntsb.gov/pdf

http://registry.faa.gov/N193BJ 

NTSB Identification: ENG14IA011
14 CFR Part 91: General Aviation
Incident occurred Thursday, March 13, 2014 in Rochester, NY
Probable Cause Approval Date: 03/27/2017
Aircraft: RAYTHEON AIRCRAFT COMPANY 400A, registration: N193BJ
Injuries: 7 Uninjured.

NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft incident report.

The No. 2 engine sustained a herring gull bird strike during takeoff climb from Rochester International Airport- Rochester, NY. The impact from the birdstrike resulted in contact between the fan and inlet case that separated eleven (11) of the nineteen (19) fan blades and subsequently led to the failure of the No. 1 bearing housing, and a midshaft fracture of the low pressure turbine shaft. Materials analysis on recovered fan blade fragments determined that all separated blades failed due to overload and no evidence of fatigue was identified. A series of modal tests including: tap hammer, high energy shaker, and computer model simulation were conducted at the system and component level. The tests identified a four nodal diameter coincidence at about 72% N1 speed. When sufficient energy is imparted to the engine fan during a foreign object ingestion event like a birdstrike, it may result in a rub induced excitation and subsequent fan blade separation and catastrophic engine failure.

The National Transportation Safety Board determines the probable cause(s) of this incident as follows:
The probable cause of the uncontained No. 2 engine failure on the Raytheon Beechjet 400A was a herring gull birdstrike that resulted in fan blade contact with the inlet case and rub induced excitation of a previously unidentified natural frequency (resonance) within the engine operating range.

On March 13, 2014, at about 1020 eastern daylight time, a Raytheon Beechjet 400A, N193BJ, equipped with two Pratt & Whitney Canada (PWC) JT15D-5 engines, experienced a No. 2 (right) engine bird strike shortly after takeoff from Greater Rochester International Airport (ROC), Rochester, New York. The crew declared an emergency, returned to the airport, and made an uneventful landing at ROC. During an inspection of the airplane, extensive damage to the No. 2 engine fan and inlet cowl were observed. The compressor cowl had multiple holes and the right wing had an impact mark forward of the engine inlet case. Several weeks after the event, a blade fragment was found lodged in the roof of a building below the flight path. The airplane was registered to Guardian Pharmacy LLC and was being operated as a 14 Code of Federal Regulations Part 91 flight.

INJURIES

No injuries were reported to passengers or crew.

DAMAGE TO AIRPLANE

An on scene examination of the airplane and No. 2 engine cowling were conducted after the incident by the Federal Aviation Administration (FAA) Rochester Flight Standards District Office (FSDO). Minor impact damage was observed on the right wing, forward of the engine inlet. The impacts did not penetrate the outer panel or affect the underlying structure. The No. 2 engine core cowl upper inboard and outboard halves were separated along the forward flange and partially separated along the aft flange. The core cowl flange separations allowed the cowl to bend aft and in the outboard direction. The cowling was pulled away from the engine strut but the engine to strut attachment remained intact. Several cowl breaches were observed around the engine, concentrated along the upper half. The inner barrel of the inlet cowl had 360 degree circumferential tearing around the engine, in line with the fan plane of rotation that was completely detached from the inlet case. The external inlet cowl attachment flange was intact. The fuselage had organic debris splatter forward of the No. 2 engine inlet that was consistent with bird remains.

TEST AND RESEARCH

Engine Disassembly

The engine was shipped to the PWC facility in Bridgeport, WV for examination and disassembly. Eleven (11) of the 19 fan blades were found fractured near the blade root. The engine inlet case was separated from the intermediate case where the attachment flange studs were sheared and/or ripped out. A single flange stud and attaching nut was holding the two cases together at the 5 o'clock position. A chunk of the intermediate case was fractured and missing from the 11 to 2 o'clock positions along the inlet case mating flange. Impact damage was observed throughout the low pressure compressor and booster sections of the engine including a fragmented No. 1 bearing housing. The low pressure turbine (LPT) shaft was fractured aft of the high pressure turbine coupling and the LPT fuel shutoff valve was tripped, indicating the LPT was axially displaced in the aft direction.

Metallurgy

All nineteen (19) fan blades were shipped to the PWC Materials Lab in Longueuil, Quebec, Canada for examination. Eleven (11) of the 19 blades had transverse fractures near the blade platform. The fracture surfaces of all eleven blades exhibited features consistent with ductile overload with no evidence of fatigue. It could not be determined which blade fractured first.

The eight (8) blade airfoils that remained intact all exhibited substantial impact deformation. A band of localized plastic deformation along the same spanwise position, located at approximately the mid-chord and extending over one-third of the chord length on both the suction and pressure sides was also present on all blades. Within the deformation band, surfaces cracks were observed on several blades and it was determined that the damage was consistent with overload.

Microstructure examination verified that the material met drawing requirements. Scanning electron microscope (SEM)/energy dispersive x-ray spectroscopy (EDS) analysis of the fan blade material revealed that the major alloying elements were in the correct proportion according to drawing specification.

Bird Species Identification

Multiple samples of bird feathers and remains (snarge) were sent to the Smithsonian Institute in Washington, DC by the FAA Rochester Flight Standards Division Office, the pilot of the airplane, and the NTSB for species identification. The remains were positively identified to be a herring gull. The average mass of this species is 1085g (2.39lbs). The analysis could not determine if more than one bird was ingested.

Modal Testing

PWC completed a series of tests to determine the root cause of the dynamic response between the fan and inlet case following the birdstrike event. Modal testing was done at both the component and engine level with tap hammers and high energy shakers. Tests were also conducted to measure the sensitivity of the engine to varying levels of stiffness at the engine to inlet case attachment. Finally, tap hammer testing was performed on a JT15D-5 engine installed on a Beechjet 400A representative of the incident airplane. The testing identified a four nodal diameter coincidence between the fan and inlet case at an N1 speed of about 72%. When energy is imparted to the fan by an event like a birdstrike, it can result in a rub induced excitation and catastrophic engine failure. 

ADDITIONAL INFORMATION

Corrective Actions

In response to these findings, PWC is evaluating inlet case damping options to attenuate the identified natural frequency and plans to complete the design change and introduce the modification to the fleet in 2017.

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