On October 17, 2005, at 0025 eastern daylight time, a Bombardier CL-600-2B19 regional jet, N244PS, sustained minor damage when the left engine exhaust nozzle and fairing departed the airplane during cruise climb near West Grove, Pennsylvania. Night visual meteorological conditions prevailed at the time of the incident. The flight was being operated by PSA Airlines, Inc., as a scheduled revenue flight under the provisions of 14 Code of Federal Regulations Part 121. The flight crew and 48 passengers on-board were not injured. Flight 2319 departed Philadelphia International Airport (PHL), Philadelphia, Pennsylvania, at 0004 and was en route to Dayton International Airport (DAY), Dayton, Ohio. The flight crew reported hearing a "small thud" while climbing through 15,000 feet msl. The flight crew stated that they monitored the aircraft engines and no anomalies were noted. The flight crew attributed the event to possible wake turbulence and elected to continue on to DAY. The airplane continued without further incident and during a post-flight inspection the flight crew noticed the left engine exhaust nozzle and fairing were missing. The left engine exhaust nozzle was found in West Grove, Pennsylvania, about 26.5 nm west-southwest of the departure airport. The nozzle was examined and its attachment hardware was missing. The bolt holes used to install the exhaust nozzle to the engine were elongated and had evidence of fretting. The exhaust nozzle manufacturer, Bombardier-Shorts, issued Service Bulletin CF34-NAC-78-024 on January 24, 2003, to address "exhaust nozzle bolt attachment failures." The most current service bulletin revision was dated April 1, 2004. The service bulletin called for the removal of the existing hardware and replacement with "new, improved hardware." This maintenance was to be completed at the "operator's earliest convenience or within a maximum of 4,000 hours." The incident airplane, serial number 7912, was issued an airworthiness certificate on April 16, 2004, and at the time of the incident had accumulated 3,440 hours since new. Service Bulletin CF34-NAC-78-024 had not been complied with, according to the maintenance records. Subsequent to the accident, the operator immediately inspected their entire fleet of Bombardier CL-600-2B19 regional jets and found three additional aircraft with either missing or loose attachment exhaust nozzle hardware. The operator ordered replacement kits for the entire fleet and will comply with Service Bulletin CF34-NAC-78-024 upon delivery of the replacement parts.