Eclipse Aviation Corporation EA500 N875NA incident near Rockford, Illinois

Probable cause

The improper installation of the forward edge of the left-hand wing-to-body panel, causing the fairing to separate from the airplane during an in-flight encounter with light turbulence. Contributing to the event was the use of small-head screws and grommets in securing the fairing.

NTSB analysis

The positioning flight was in cruise flight and had just encountered light turbulence when the left-hand wing-to-body fairing separated from the airplane. The panel had been last removed by company maintenance personnel performing maintenance relating to the autopilot system. The forward flat portion of panel had four screw holes in the underlying structure, but the fairing had only three 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 though four screw holes were available in the underlying structure. An inspection of the airplane revealed that all of the screws were intact except for three screws located at the forward flat edge of the fairing. The respective nuts for these three screws were in place. All but one of the screws and grommets for the curved fairing piece had pulled through the fairing and were attached to the underlying structure. Two and possibly three screw holes at the forward edge of the flat piece of fairing did not have grommets in place and radial cracking of the finished coat was observed at these holes. Also, a delamination ring was observed on the backside of the flat piece of fairing at the screw holes. With the absence of grommets there is a reduced force necessary to pull through the fairing. The outer diameter of the screw head and grommet differ by 0.040 inch. Larger grommets with an integral flange are used in other areas of the airplane, which provide more surface area, distribute contact forces, and improve adhesion to the screw hole. According to the operator, the repetitive removal of screws would result in the countersunk metal grommets loosening from their adhesive bond to the composite fairing.

Text from the NTSB. Open the NTSB docket for CHI08IA200 for the full record.