We were asked to provide a quote to remove minor imperfections in the left and right windshields on a 1977 Cessna 340. Upon initial inspection we found some cleaning damage from use of the wrong type of cleaning cloth or perhaps paper toweling, a few very minor chips that measured a maximum of .003” and a few dime sized stripper damaged marks along the center post area. We provided an additional quote to clean the cockpit side and cabin window exterior surfaces; they all had cleaning damage.
Our customer elected to have only the windshields cleaned and polished during the Annual Inspection
which was planned in the next 45 days. We had contacted the service center that was planning the inspection work and made arrangements to perform the work needed.
Work began where the cleaning damage was located along the center post area. An acrylic scrapper was used to remove the window sealant for a more open work area for our tools to remove the stripper damage. When the sealant was removed from the center post and windshield surface, we found some new damage under the sealant. The depth of damage was measured at almost .050” deep. This is beyond limits and well beyond the minimum thickness allowed by the manufacturer. The window was red tagged and the operator was required to install a new windshield.
The hidden damage from stripper caused from the re-paint of the aircraft a few years before had leached under the sealant and burned into the windshield surface. The undetected damage measured 1¾” in length. Left undetected a crack could have grown from the area and potentially serious issues resulting.
We suggest that when performing an inspection on older aircraft take a second look at areas that may cause you to be suspicious of hidden damage, especially related to repainted surfaces near any window. Stripper damage on the windshield being so close to the window edge already indicated that chemicals got under the protective taping during the stripping process during the re-paint. Older aircraft require all of us to perform inspections differently than with newer model aircraft.