When an owner comes in needing to replace a broken windshield, it falls on the shop to protect his investment and make sure the job is done carefully and correctly. With windshields, “close enough” could result in the owner having to repeat the job only a few short months later.
Andre Pridgen is the manager of Aero Air’s Twin Commander Factory Authorized Service Center and he said windshield work requires patience and close attention to detail. “The single biggest factor that impacts the windshield’s longevity is the way it’s installed.” Do it right and it will last for many years. Rush the job or take shortcuts and it might only last a few months.
It all starts with the prep work. Despite being easy to reach and having ready access to the area, removing the old sealant is the first tricky job. Pridgen said the technician must ensure he doesn’t take away any metal or scratch the nearby paint. “A metal scraper is definitely not the right tool for the job,” he said. Once the old windshield is out and the sealant is removed you can work on getting the new one to fit.
Avoiding a preload is critically important, and that’s harder than it sounds. Because Twin Commanders were designed and built by hand, every airplane is just a little bit different. “The same guy doing the same job on six different serials numbers will have six different installations,” he said. That’s why the new windshield comes as an oversized blank. It must be cut exactly to fit the airframe.
Pridgen said that for an experienced technician who has done many windshields, this step alone may take three days. The windshield is held in place by the center and top fasteners, and a bottom strip holds down the lower portion. It’s important to ensure the new glass lays completely flat on the frame. Any variation here will cause the strap to put unequal pressure on a portion of the glass, which leads to cracks. “It’s very important that it drops into the sealant, and that the fasteners hold it in place, rather than pulling it into place,” he said.
Once the window frame is cut to fit, those fasteners are the next tricky part. Because they aren’t pre-drilled, the technician will have to line up the frame and ensure a clean, straight hole. “We don’t like any porcupines.” Pridgen developed a tool many years ago specifically for this purpose, and he recommends other shops do as well. Something he lathes by hand, it’s essentially a custom drill bushing that matches the countersink on the airframe and ensures a straight hole.
After the holes are drilled and the windshield properly cut, it’s a matter of attaching it to the airframe. This is the final tricky part. The windshield is two pieces (pilot and co-pilot side), but once attached on the center and top strips, acts as one load. “It’s possible to create a preload on the opposite windshield,” he said. Avoiding that goes back to ensuring that the fasteners are working only to hold the glass down, and not as an aid to positioning it in the space. Finally, the bottom strap is tightened down, which should be easy if the glass is properly sized.
Pridgen said some of the difficulty comes from the fact that detailed instructions don’t exist for the job. “It’s just one of those tribal knowledge things to get it to fit without preloading it.” An experienced technician should be able to do the job in a week, from airplane acceptance to delivery, including time to cure the sealant and do any paint touch-ups. For those with less experience, he suggests budgeting two weeks for the job.
And as a note to pilots, the Twin Commander comes with a feature Pridgen said he thinks is unique in the turbine world. There’s an approved procedure with a pressurization spec in the pilot’s operating handbook for ferrying the airplane with a broken windshield, and without a ferry permit. Given that it’s such a specialized job, that means you can take it to a Twin Commander Factory Authorized Service Center, where the work will be done right the first time.
