On March 31, 2007, about 0927 Pacific daylight time, a Bombardier Learjet 60, N244FX, operated by Jet Solutions LLC, experienced a loss of power in the left engine, a Pratt & Whitney Canada (PWC) PW305A turbofan, while in cruise flight near Palm Springs, California. The pilots reported that while in cruise flight at flight level 410 (41,000 feet mean sea level) about 50 miles east of Thermal, California, they heard a loud bang and the airplane began to vibrate. The pilots shutdown the left engine and declared an emergency. The airplane diverted to Palm Springs where it made an overweight, single-engine landing without further incident. The airplane was operating on an instrument flight rules flight plan under the provisions of 14 CFR Part 135 from Santa Ana, California to Bedford, Massachusetts. The two pilots and one passenger on board were not injured. Use your browsers 'back' function to return to synopsisReturn to Query Page
The on-scene examination of the left engine revealed that one fan blade was fractured transversely across the airfoil adjacent to the blade root platform. All of other fan blades were in place in the fan hub, but all were damaged with nicks and gouges on the leading edges and tips. In addition, the engine's upper and lower cowlings were missing. The FAA notified the Thermal-area law enforcement agencies of the missing cowlings; however, they were never located. The airplane had several scratches and gouges on the left side of the vertical stabilizer. The high frequency radio antenna was separated from the leading edge of the vertical stabilizer and was hanging down on the left side of the airplane.
The left engine was removed from the airplane and shipped to PWC's Bridgeport, West Virginia maintenance facility for disassembly and examination. The fractured fan blade was removed from the engine and submitted to the Safety Board's Materials Laboratory for examination. During the disassembly and examination of the engine, the 23 remaining fan blades underwent a fluorescent penetrant inspection (FPI) and 16 were found to have crack indications on the convex side of the airfoil adjacent to the blade root platform. Because of the number of fan blades from the left engine that were found to have crack indications, the fan assembly of the airplane's right engine was removed and returned to PWC's Bridgeport facility for examination. The FPI of the right engine's fan blades revealed that 5 of those 24 blades had FPI crack indications on the convex side of the airfoil adjacent to the blade root platform in the same area as those noted on the left engine's fan blades.
The metallurgical examination of the left engine's fractured fan blade at the Safety Board's Materials Laboratory revealed a fatigue fracture that had originated from multiple origins on the convex side of the airfoil adjacent to the blade root platform, about 1.5 inches forward of the trailing edge. The metallurgical examination revealed the fatigue crack had progressed through almost the full thickness of the airfoil and was about 0.9-inches long. The origin of the fracture was in the same area on the fan blade as the location of the FPI crack indications that were noted on the other fan blades from the left and right engines. Several of the left and right engines' fan blades that had the FPI crack indications were broken open that revealed fatigue fractures that were of the same orientation and morphology as that noted on the left engine's fractured fan blade. The metallurgical examination of the fractured fan blade and those that had the fatigue cracks indicated the material conformed to the requirements and that there were no indications of any preexisting metallurgical defects.
PWC, using a coordinate measuring machine (CMM), accomplished a dimensional inspection of the intact fan blades from the left and right engines. In addition, the intact fan blades from a second PW305A engine that had experienced an in-flight fan blade separation as well as the fan blades from the other engine on the airplane were dimensionally inspected with the CMM (Refer to ENG07IA034) The dimensional inspection revealed that a number of blades that were all associated with a particular batch lot, heat code (H/C) MCBWF, were on average 0.091-inches below the nominal dimension of 0.273 inches in the area where the fatigue fracture and cracks occurred. According to PWC, that area of the fan blade was the highest stressed area of the PW305 fan blade's and the under minimum-thickness condition would result in stresses that would exceed the material properties.
THe PW305 fan blades are produced for PWC by Blades Technology Limited (BTL) of Israel. According to BTL, at the time the fan blades, which fractured or were found cracked, were manufactured, the forging dies had to be aligned manually. BTL stated that its records for the H/C MCBWF batch indicated that the forging dies had been shimmed during the setup and that it believed the thin airfoil condition was the result of the improperly aligned forging die. At the time the H/C MCBWF fan blades were produced, PWC did not have a dimensional inspection requirement for the fan blades' airfoils. PWC stated that shortly after the H/C MCBWF fan blades were produced and well before the fan blade fracture incident occurred at Palm Springs, it had added a dimensional inspection requirement for the PW305 fan blade airfoils.
According to PWC and BTL records, there were 624 H/C MCBWF PW305 fan blades produced. PWC developed an inspection gage to measure the airfoil thickness with the fan blade still installed in the fan hub although the hub had to be removed from the engine. PWC issued Alert Service Bulletin (ASB) 24588 that required all H/C MCBWF fan blades in service be inspected. Transport Canada and the FAA each issued airworthiness directives to mandate the ASB 24588 PW305 fan blade airfoil thickness inspection. According to PWC, of the 529 H/C MCBWF fan blades that were still in service (the others having previously been removed from service due to damage from FOD, bird strike, etc.), 519 were found to under the minimum thickness and were removed from service. PWC stated that it subsequently made a corporate decision to also remove from service the 10 H/C MCBWF PW305 fan blades that passed the airfoil thickness inspection.