NTSB Factual Report

On January 3, 2001, at 0832 Eastern Standard Time, a Bombardier CL600-2B19 Regional Jet (CRJ), N933CA, operating as Comair flight 5360, sustained minor damage when an engine exhaust separated from the airplane, while approaching Cincinnati/Northern Kentucky International Airport (CVG), Covington, Kentucky. The 3-person crew and the 43 passengers were not injured. Visual meteorological conditions prevailed at the time of the incident. The flight was operating on an instrument flight rules flight plan, between Minneapolis-St. Paul International Airport (MSP), Minneapolis, Minnesota, and Covington. The scheduled passenger flight was conducted under 14 CFR Part 121.

According to the captain, when he reported onboard, a mechanic advised him that the number 1, A system jet overheat loop was not operating normally, and that "he would defer it."

Startup, taxi, and takeoff "occurred without incident;" however, during the climb, an airframe vibration developed. All gauges, readouts, synoptic pages, and airplane controls were normal. The crew contacted Comair maintenance, and attempted to troubleshoot the problem, but could not determine its cause.

The flight attendant reported to the captain that the passengers were either not aware of, or not concerned with the vibration.

The flight continued, and the vibration remained unchanged until the airplane leveled off at 7,000 feet during the approach to Covington. At that time, the crew felt a bump, and then the vibration completely ceased. Again, all gauges, readouts, synoptic pages, and airplane controls were normal. The airplane landed, and taxied to the gate without further incident.

Post-flight inspection revealed that the number 1 exhaust fairing was missing, and that the left, aft fuselage had a dent in the vicinity of station 800, 9 inches below the vertical stabilizer.

According to a Federal Aviation Administration (FAA) inspector, the engine was removed after the incident, and taken to the company's maintenance facilities where an inspection was performed. The exhaust nozzle assembly would have normally been attached to the exhaust frame case with 30 bolts. All 30 bolts were missing, "with no trace." No visible damage was noted to the mating flange, other than what was characterized as "normal wear."

The exhaust frame case had marks on both sides, at approximately the 3 o'clock and 9 o'clock positions, about 6 inches forward of the mating flange. The marks appeared to be aluminum deposits. The exhaust nozzle assembly was never located.

Because Comair maintenance personnel had previously found cracked bolts connecting other exhaust flanges, the FAA inspector requested that the Safety Board examine sample bolts with over 6,600 hours of service. The bolts, which were not from the incident airplane, were also compared to new bolts. According to the metallurgist's factual report, there was no evidence of cracking or over-aging in the used bolts. The new bolts were within the tensile strength and hardness specifications required, and the hardness and the tensile strength results increased from the new bolts to the used bolts.

According to Comair maintenance personnel, on September 9, 1999, the engine was installed on the airplane. On October 18, 1999, the C-sump o-rings were replaced, which required the removal of the tailpipe. There was no mention in the maintenance records of changing the bolts. On May 3, 2000, the tailpipe was found to be loose, and 10 bolts were replaced. The remaining bolts were re-used and re-torqued.

The airplane was being inspected under an approved inspection program (AAIP). According to the operator's report, the last inspection was performed December 15, 2000, 105.7 hours prior to the incident.

According to the FAA inspector, subsequent to the incident, Bombardier was considering a bolt change. In addition, there was ongoing discussion about reusing bolts. In the meantime, Comair changed its engine shop buildup and shop exit manuals to make exhaust nozzle bolts a required inspection item.

NTSB Probable Cause

Missing exhaust nozzle bolts for undetermined reasons. A factor was inadequate maintenance inspection of the affected area.