Incident Overview
On September 14, 2021, at approximately 1230 eastern daylight time, a Hawker Beechcraft Corp 400A airplane, registration N100FN, sustained substantial damage during a repositioning flight to Charleston Executive Airport (JZI), Charleston, South Carolina. The two flight crewmembers were not injured. The airplane was operated by Aircraft Management Group under 14 CFR Part 91.
Preflight and Maintenance Background
The flight crew performed a standard preflight inspection after the airplane had been released from scheduled maintenance by Winner Aviation, a Part 145 repair station at Youngstown Regional Airport (YNG), Youngstown, Ohio. The only discrepancy noted was a loose screw on the nose cone, which was tightened by a mechanic before departure.
According to Winner Aviation representatives and work orders, on September 13, 2021, the airplane had undergone an A and B inspection requiring removal and re-installation of the engine cowlings. Mechanics involved reported that several fasteners on the left cowling had to be loosened and tightened a second time due to an alignment issue. The mechanic who resolved the issue stated he re-tightened the fasteners and that “everything was secure and double checked.” He also replaced some fasteners because some were missing and others warranted replacement. The following day, another mechanic inspected the airplane before the accident flight and noted no abnormalities. No mechanics observed any dents on either cowling.
Inflight Event
The flight was uneventful until about 15 minutes from JZI. While descending at about 1,500 feet per minute through approximately 21,000 ft, the flight crew heard a loud bang and felt a shudder and yaw. They disconnected the autopilot and noted a noticeable yaw, but no anomalies on flight or engine instruments. The crew continued and landed without further incident.
Post-Flight Findings
During post-flight inspection, the crew discovered that the left engine cowling had entirely separated. Photographs provided by the Federal Aviation Administration (FAA) showed that the fuselage and horizontal stabilator sustained substantial damage. An examination of the left engine found several fasteners missing from the forward and aft attachment areas. No abnormalities were discovered with the cowling fastener receptacle areas or nut plates that remained in place. The aft top attachment area exhibited evidence of rearward pulling of the metal.
The right cowling remained attached. About one month later, a large dent and rippling were discovered in the middle and top inboard cowling areas, and a stripped fastener was observed, but no fasteners were missing.
Investigators contacted local authorities near the presumed area of the cowling separation, but the cowling sections were never located.
Maintenance Manual and Service Information
According to the Hawker Beechcraft 400/400A Maintenance Manual, the cowling consisted of four removable sections secured by several quarter-turn fasteners around the forward and aft engine areas. In December 2006, Raytheon Aircraft Company issued Service Bulletin Nacelles – Engine Cowling Fastener Modification, requiring modification to the attachment hardware to provide threaded fasteners at specific locations. The bulletin stated that three reports of cowling panel separations had been received and that aerodynamic forces could cause panel separation or damage. In October 2007, the FAA issued an Airworthiness Directive making the service bulletin mandatory. The accident airplane was manufactured after the original bulletin and had cowlings modified per the bulletin.
On April 29, 2022, the FAA published Special Airworthiness Information Bulletin (SAIB-AIR-22-10) highlighting incidents and accidents involving cowling separations and providing best practices for proper installation. This accident was one of several events highlighted in the SAIB.