On August 15, 1998, about 0955 eastern daylight time, a Piper PA-18-150, N3981Z, registered to Sky Signs Inc., operating as a 14 CFR Part 91 banner tow flight, crashed while attempting a banner tow pick-up at the Sky Signs private airstrip, Conway, South Carolina. Visual meteorological conditions prevailed and no flight plan was filed. The airplane sustained substantial damage. The commercial pilot reported minor injuries. The flight originated about 5 minutes before the accident. An FAA inspector who observed the accident stated the pilot was picking up a banner on runway 34. The airplane picked up the banner and was in about a 30-degree nose-up attitude when the left wing collapsed. The airplane rolled to the right about 300 degrees, the nose pitched down, and the airplane collided with the ground inverted. Examination of the left wing revealed the left forward lift strut attachment fitting was severely corroded. The separated left wing forward and aft strut attachment fitting, and the right wing forward and aft attachment fitting were sent to the NTSB Materials Laboratory for analysis. Examination revealed the front face of the forward bracket was subjected to severe corrosion damage. The bracket separated approximately 2.8 inches away from its inboard lower end, at a location corresponding to a vertical position on assembly that is in line with or just below the lower spar cap of the forward spar. Evidence of corrosion was also apparent on the upper and lower sides of the bracket. Binocular microscope examination revealed that the most corrosion damage was on the front face of the bracket. Examination of the aft bracket revealed that it separated through the lower of the five holes used to attach the bracket to the front spar. Binocular microscope examination revealed that a portion of the aft bracket fracture was on a flat plane and contained crack arrest positions typical of fatigue cracking. (For additional information see NTSB Materials Laboratory Factual Report No. 99-49.) The components retained for further analysis were released to M. Jenkins, Sky Signs Inc., on February 12, 1999.