On July 17, 2008, at 1655 central daylight time, an Eclipse Aviation Corporation EA500, N875NA, operated by North American Jet Charter group, LLC, sustained minor damage during an in-flight separation of the left hand wing to body fairing near Rockford, Illinois. Visual meteorological conditions prevailed at the time of the incident. The 14 CFR Part 91 positioning flight was operating on an instrument flight rules flight plan. The two pilots were uninjured. The flight last departed from Pinedale, Wyoming, and was en route to Chicago Executive Airport, Chicago/Prospect Heights/Wheeling (PWK), Illinois, where it landed without further incident.
The captain and first officer reported that the airplane was in cruise flight at 5,000 feet mean sea level and at 250 knot equivalent airspeed (KEAS). The first officer reduced engine power so as to enter an approaching cloud deck at 220-230 KEAS. As the airplane entered the clouds, the airplane buffeted "slightly." Immediately thereafter, the flight crew heard a "loud bang and short rumble" originating from the left rear portion of the airplane. The airplane then landed without further incident at PWK.
Inspection of the airplane revealed that the left hand wing to body fairing, part number 12238005, had separated from the airplane, except for a piece of outboard curved fairing. The fairing was a carbon fiber fairing with a foam core. The right hand wing to body fairing was attached with all of its screws in place. The right fairing displayed a gap of about 1/4 inch along its bottom inboard edge with all of the screws secured in place. Later serial number EA500s in the operator's fleet displayed progressively smaller gaps between panels/fairings. Inspection of the left engine revealed no foreign object damage from the fairing separation.
All of the left hand wing to body fairing screws were still attached to the underlying structure except for the forward most three screws, which were missing. The associated nuts to these three missing screws were in place and were later used in the installation of a replacement fairing. There were four screw holes in the underlying structure, but the fairing made use of only three of those screw holes. Inspection of the operator's other EA500 airplanes showed that some fairings made use of four screw holes while others made use of three screw holes even through four screw holes were available in the underlying structure.
The forward outboard piece of curved left hand wing to body fairing was still retained by one screw. All but one of the screws that attached this portion of curved fairing had pulled through the fairing. The remaining attached section of panel along with a portion were recovered near Rockford, Illinois.
The recovered pieces of fairing and exemplar screws were sent to the National Transportation Safety Board Materials Laboratory for examination. The fairing is secured with grommets that are designed to conform to the countersunk recess in the fairing screw holes and to the countersunk screw heads. The grommets are specified to be glued into the screw holes of the fairing during the manufacturing/assembly process. Exemplar screws and grommets for use with the wing to body fairing were 0.273 inch and 0.311 inch, respectively. Some panels on the airplane, such as those surrounding the engine, used a grommet with a large flange.
There were significant differences in damage to the screw holes on each of the fairing pieces. Edge views show typical damage around screw holes on both pieces. The interior surface of the flat fairing piece was not deformed or raised in the vicinity of the screw hole or elsewhere on the interior surface. In contrast, the interior surface of the curved fairing piece was raised in the vicinity of the screw holes compared to the rest of the interior surface, and the screw hole was surrounded by broken fiber bundles. The average inner diameters and standard deviation of the four countersunk holes on the flat fairing piece was measured as: 0.210 +/- 0.004, 0.213 +/- 0.004, 0.224 +/- 0.007, 0.207 +/- 0.002).
The interior surfaces of the fairing pieces have reinforcement layers along the screw hole-containing edges. Delamination of the fiberglass layers from the reinforcement layer was observed in the flat piece. The layers along the edge of the curved fairing piece were still adhered to one another. Delamination of the reinforcing layer from the rest of the fairing induced a color change on the interior surface. This indicator of delamination was also observed around the screw holes on both fairing pieces.
The screw holes on the fairing pieces were inspected from the exterior surface for signs of damage and the presence of glued-in-place grommets. The four screw holes in the flat piece did not contain grommets in any of the screw holes. Radial cracking of the finished coat was observed around two and possibly three of the four holes on the flat fairing piece.
The airplane and left hand wing to body fairing accumulated a total time in service of 261 hours. The fairing had been removed several times in order to perform the manufacturer's recurring maintenance on the airplane fuel system. The fairing was last removed for autopilot maintenance on July 16, 2008, at an airplane total time of 255 hours. The operator reported that the metal grommets begin to loosen when the fairing is repetitively removed to access to the fuel system. The operator stated that they had not submitted Federal Aviation Administration Service Difficulty Reporting System regarding grommet to fairing separation.