DEN07IA055

While climbing through FL 240, the No. 1 engine experienced a fan disk separation, which resulted in the separation of the inlet, fan rotor assembly, the fan containment case, and portions of the thrust reverser. The airplane reversed course and landed without further incident. Postincident examination revealed minor damage to the aft portion of the fuselage and empennage. An examination of the remaining airplane systems revealed no anomalies. Portions of the fan disk were recovered and examination of the fan disk revealed fatigue striations emanating from the aft bore corner of the fan disk. The striations came from an area that exhibited characteristics consistent with arc-out damage, which was the result of improper assembly and marking procedures during the electrochemical etching process. This damage was not detected during the manufacturer's quality assurance process used by the manufacturer. Further, the operator did not detect this damage while conducting the inspections prescribed through required airworthiness directives because the inspection procedures required were not detailed enough to detect the arc-out damage and the maintenance personnel did not receive appropriate training. Following the incident, the manufacturer issued alert service bulletins and the FAA issued an airworthiness directive to resolve these issues.

History of flight

On January 25, 2007, at 1647 mountain standard time, a Bombardier CL-600-2B19, N17337, operated by Mesa Airlines, doing business as U.S Airways Express flight 2985, sustained minor damaged when it experienced a fan disk separation while climbing through approximately 24,000 feet (FL240), 8 miles west, southwest of Cripple Creek, Colorado. Day visual meteorological conditions prevailed at the time of the incident. The regularly scheduled domestic passenger flight was being operated under the provisions of Title 14 Code of Federal Regulations (CFR) Part 121 on an instrument flight rules flight plan. The captain, first officer, flight attendant, Federal Aviation Administration (FAA) inspector, and 50 passengers were not injured. The flight departed Denver International Airport (DEN), Denver, Colorado, at 1629 and was en route to Phoenix, Arizona.

According to an interview, subsequent telephone conversations, and a written statement from the flight crew, they were climbing through approximately FL240 when they heard a loud pop and experienced a vibration or buffet. The airspeed began to slow. The crew reported that they were not able to maintain a climb configuration or a level altitude, and initiated a controlled descent. They observed a "no oil pressure" indication for the number one engine along with a maximum indication on the N1. Thrust was reduced to idle power.

The crew reported that they reversed course for a return to DEN, and were able to maintain an altitude of 12,000 feet mean sea level (msl). The flight crew received vectors for a visual approach and landed uneventfully. The crew did not report any airplane controllability issues after the separation.

Damage to aircraft

The National Transportation Safety Board investigator-in-charge (IIC) arrived at DEN approximately 0800 on January 26, 2007. The Safety Board IIC, a Safety Board powerplant engineer, a Safety Board structural engineer, the FAA Aviation Accident Investigation (AAI-100) IIC, and representatives from Bombardier, General Electric (GE) Aviation, and Mesa Airlines, examined the airplane and number one engine on January 27 and 28, 2007. Examination of the number one engine revealed that the inlet, fan rotor assembly, fan containment case, and portions of the thrust reverser (TR) were all missing. Examination of the airplane revealed damage to the fuselage, in-line with the plane of rotation of the number one engine fan rotor, and marks on the vertical and horizontal stabilizers.

Personnel information

The pilot, age 40, held an airline transport pilot certificate with an airplane multi engine land rating, and a commercial pilot certificate with an airplane single engine land rating. In addition, he held type ratings in the Beech BE-1900 and CL-65. He was issued a first class airman medical certificate on November 2, 2006. The certificate contained no limitations. According to Mesa Airlines, the pilot had logged approximately 11,000 hours total time; 4,000 of which were in the make and model of the incident airplane.

The first officer, age 34, held a commercial pilot certificate with airplane single engine land, multi engine land, and instrument ratings. In addition, he held a type rating in the CL-65, with the limitation of second-in-command privileges only. He was issued a first class airman medical certificate on February 16, 2006. The certificate contained the limitation "must wear corrective lenses." According to Mesa Airlines, the first officer had logged approximately 3,700 hours total time; 2,300 of which were in the make and model of the incident airplane.

Aircraft information

The incident airplane, a Bombardier CL-600-2B19 (serial number 7337), was manufactured in 1999. It was registered with the FAA on a standard airworthiness certificate for transport operations. The airplane was powered by two GE CF34-3B1 (serial number 872749 and 872190, number one and two respectively) turbo fan engines.

The airplane was registered to Wells Fargo Bank, operated by Mesa Airlines, and was maintained under a continuous airworthiness inspection program. At the time of the incident, the airframe had 19,629 hours total time, and 15,438 total cycles. The incident engine (No. 1) had 13,627 hours time since new (TSN), and 10,849 total cycles since new (CSN). According to the Engine Service Record, the incident engine was installed on the event airplane on January 10, 2007. Previously, the No. 1 engine had been installed on a company airplane; serial number (SN) 7410.

Meteorological information

The closest official weather observation station was Colorado Springs Municipal Airport (COS), Colorado Springs, Colorado, located 32 nautical miles (nm) east, northeast of the incident site. The elevation of the weather observation station was 6,187 feet msl. The routine aviation weather report (METAR) for COS, issued at 1654, reported, winds, 140 degrees at 9 knots, visibility, 10 statute miles; sky condition, clear, temperature 05 degrees Celsius (C); dewpoint, minus 04 degrees C; altimeter, 30.18 inches.

Flight recorders

Cockpit Voice Recorder

The airplane was equipped with a Fairchild Model A 100S 30-minute solid-state cockpit voice recorder (CVR). The CVR was secured and sent to the National Transportation Safety Board's (Safety Board) Audio Laboratory for readout. The CVR had not sustained any heat or structural damage and the audio information was extracted normally from the recorder. The recording consisted of four channels of excellent quality audio information. The arrival and landing back into DEN was captured on the recording. The engine separation occurred prior to the start of the recording. A CVR group was not formed and a transcript was not prepared.

Flight Data Recorder

The airplane was equipped with an L-3 Communications Fairchild Model F1000 digital flight data recorder (DFDR), which recorded 412 parameters of airplane flight information using solid state media as a recording medium. The DFDR was secured and sent to the Safety Board Vehicle Recorders Laboratory for readout. The DFDR had not sustained any heat or structural damage and the information was extracted normally from the recorder. A DFDR group was not formed. For this incident, 82 parameters were checked and validated, and a report was prepared.

Review of the DFDR data showed that the takeoff and climb were normal. At a time(T) of T = 546 seconds (9 minutes and 6 seconds after takeoff and 4 minutes and 9 seconds prior to the fan disk separation) the vibration level for the No. 1 engine fan rotor assembly (N1) started to increase from a relatively stable level around 0.7 mils. At T = 635 seconds, the vibration level reached over 1 mil and continued to steadily increase to 1.5 mils and 1.8 mils at T = 746 seconds and T = 789 seconds, respectively. After T = 789 seconds, the vibration quickly increased and reached its maximum value of 2.65 mils at T = 794 seconds, corresponding to the time just before the fan disk separation.

The fan rotor assembly, just prior to the fan disk separation, had been stable at approximately 95 percent N1 and the airplane was steadily climbing at around 290 knots. At the moment identified as the fan disk separation, the fan rotor speed had increased to 99.6 percent N1 and the airspeed started to decrease; however the airplane continued to climb for another twelve seconds before the pilot initiated a descent. The fan rotor assembly speed reached its peak, 133.94 percent N1 one second after the disk separation, and immediately started to decrease. The fan rotor assembly speed continued to decrease and eventually reach zero percent N1 at T = 879 seconds (1 minute 24 seconds after the fan disk separation). The airplane's airspeed and altitude eventually stabilized at 200 knots and 11,000 feet, respectively as the airplane returned to DEN.

Medical and pathological information

FAA toxicological tests were not performe