Inspection Found An 'Inappropriate Modification' In One Airplane

The FAA has issued a Special Airworthiness Information Bulletin (SAIB) directed to registered owners/operators of all airplane models of Univair Aircraft Corporation/under Type Certificate Data Sheets TCDS (A-718/Mooney, ERCO/415C, 415CD) and A787 (ERCO, 415-D, E, G, Forney, F-1, F-1A, Alon, A-2, A2-A, Mooney, M10) alerting them to an airworthiness concern. Specifically, this SAIB provides and references procedures to inspect and repair or replace, as necessary, affected airplanes with main wing spars showing evidence of inappropriate modifications and/or holes with or without cracks.

During the course of investigating an accident on an Ercoupe 415-D airplane, an inappropriate modification was identified. The inappropriate modification was an additional hole drilled and tapped in a location that affected the radius of a flanged member on the main wing center section spar. The probable cause leading to the accident was identified as the pilot’s exceedance of the design stress limitations of the airplane.

Although it was not cited as a probable cause of the accident, the specific location where this hole was drilled can lead to a reduction in strength of the affected structure. The focus of this SAIB is to look for these types of modifications and any cracking that may result from these modifications. In addition, as a result of the investigation into this particular accident, the FAA has identified concerns with the airspeed and flight control systems, which were addressed in Airworthiness Directive (AD) 2012-08-06.

The FAA recommends the use of visual inspection methods to detect inappropriate modifications and/or unfilled drill holes. In addition, correct any cracking that may be a result from these modifications and/or unfilled holes.

When inspecting the front and rear wing spars, wing spar caps, and spar web areas in the wing center section for wrinkles and skin cracks, the FAA says to keep in mind that the inappropriate modifications could exist from prior ownership and may have been overlooked. There have been some airframes in the past that were modified by field approval for installation of Cessna 150 airplane seats and seat rails that required attachment holes in the spar caps.

Visual inspection is the primary means of examining the airplane structure for the presence of cracks and other anomalies that can lead to reduced structural strength. Essential aids for visual inspection include a powerful flashlight, mirror with a ball joint, and a magnifying glass. A 10-power magnifying glass is usually sufficient

(ERCO 415 airplane pictured in public domain file photo)

FMI: SAIB