LAX99FA128 · Ercoupe (Eng & Research Corp.) 415E

A ground-based witness, located north of the airport, reported observing the accident airplane's wings rolling right and left to nearly a vertical bank. Thereafter, the airplane entered a spin and impacted the ground while in a 30- to 45-degree nose low pitch attitude. The impact site was 0.6 miles from the approach end of the runway. Pilots ahead and behind the airplane reported experiencing moderate to extreme turbulence in the traffic pattern. The surface wind was reported at 14 knots with gusts to 22 knots. At the time of the accident the airplane was calculated to be between 94 and 127 pounds over its maximum certificated 1,400 pounds gross weight. During the on scene wreckage examination, the left wing's rear spar attachment fitting was found severely corroded, with missing rivet heads and was separated. Metallurgical examination of the severely corroded spar attachment fitting revealed the presence of rivet heads that had failed and popped off in flight and an associated corrosion-related crack that had compromised the structural integrity of the fitting assembly. Unable to sustain the imposed wing loading, the fitting failed in flight. The failed rivet heads and evidence of the corrosion was on the backside of the spar in an area not visible during inspections. In 1995, a one-time visual inspection of the wings' internal structure for corrosion was mandated by the Federal Aviation Administration through issuance of Airworthiness Directive 94-18-04. This 'one time' visual inspection requirement was complied with according to a logbook entry dated 1997, and thereafter the wings were recovered with fabric. In May 1998, the pilot purchased the airplane, which had been manufactured in 1948. In September 1998, the airplane received another annual inspection during which no logbook entry was made indicating that the wing's internal structure had been reexamined for evidence of corrosion. The corrosion developed due to the presence of moisture and the dissimilar metals (steel bracket riveted to an aluminum spar) being in contact with each other. The severity of the ongoing corrosion process between the metal components would not have been evident during an external visual inspection, despite the fact that a required access panel had not been installed pursuant to the AD. The AD inadequately addressed the aging aircraft issue by indicating compliance could be achieved through performance of a one-time visual inspection to ferret out nonviewable evidence of internal corrosion.

Verbatim NTSB analysis and probable cause from the NTSB dataset