The polarized windows in a King Air were designed to block sunlight for passengers sitting on the sunny side of the cabin. They are the King Air’s answer to that little sliding shade found on airliners and elsewhere, and they do the trick nicely, but with one major drawback: They are prone to burning out and turning brown.
King Air passenger window assemblies consist of three panes. The exterior pane is not part of the polarization system. The other two panes – a middle, stationary pane and the interior, rotating pane – produce the polarization effect which offers many gradations between clear and maximum darkness. Passengers can choose to control the glare and still see the view if they wish. However, when the inner pane is turned to the darkest position, heat is trapped between it and the stationary pane. This heat buildup burns out the panes.
On the Ramp or In the Hangar
I know it is common practice to turn all the rotating panes to the max dark position if your King Air has to stay parked outside for a few days. The idea is to keep the aircraft interior from becoming lava-hot while the aircraft is sitting outside in the blazing sun. Unfortunately, this is exactly what destroys those polarized panes.
For the last 45 years I have been telling King Air owners and pilots: “Never leave the polarized panes in the dark position, even if parked inside the hangar! Always leave the cabin windows in the non-polarized position whether parked inside or out.” Doing so will prolong the life of the polarized panes immensely.
Really damaged King Air panes not only look burned out but can look bubbled (delaminated) or even cracked! I can’t tell you how many times an anxious owner or pilot has called me about a cracked window, only to find after closer inspection (and me telling them what to look for) that the problem was with the stationary pane of the polarizing set, and not the exterior aircraft window.
Pane Remedies
Back when I had my shop, I always squawked a burned-out pane if I found one, but in my discussion with the customer I would suggest they wait until several windows need replacement before addressing the issue. It’s not an airworthy item.
Most aircraft owners shudder at the prospect of window replacement. It is a labor-intensive project in addition to the cost of parts. In 2011, when I first wrote about King Air cabin windows, a set of polarized panes for a King Air (the fixed, middle pane and the rotating interior pane for one window) ran about $600. Today it’s more than double that. A King Air 200 has 11 windows, including the window over the potty. If you figure in one-to-two hours of labor per window … you get the idea.
One way to save a little bit of money on pane replacement is to change only the middle, stationary pane. Rarely, if ever, have I seen the interior rotating pane go bad. The source of burn out is the middle pane. Your rotating panes can get scratched by exuberant children or wayward ski poles, but if they are not scratched too badly, why not keep them and just have the middle panes changed? The labor is the same, but this way you can reduce the cost of parts by up to half and still fix the unsightly burn out.
I am pleased to report that the company providing PMA polarizing panes for King Air windows is still going strong. I chatted with them recently. In these inflationary times, they are about to review their pricing for 2023, but even so, it’s probably a better deal than ordering from the factory.
Changing Panes – A Painstaking Job
Changing windowpanes on an aircraft requires great attention to detail. If the slightest amount of dust or lint is left on the new stationary pane, it will show up like fluorescent dandruff when the rotating pane is turned to max polarization. If this happens, the new pane must be removed and cleaned carefully, then reinstalled.
Back in the day, I could change out the windowpanes in a King Air in one to 1½ hours per window, providing the King Air had the older style interior configuration. By this I mean that each window is surrounded by a separate reveal that looks like a flat frame around the window. If the interior configuration does not have these reveals, then all bets are off on labor projections.
If money is no object, consider switching from the polarizing windows all together. There are retrofit options out there with pleated shades, and so forth. But they come with a cost, and they have their share of drawbacks as well.
Aesthetics Versus Practicality
Modern aircraft interiors often have one-piece sidewalls. They give a sleek and seamless look which lends a feeling of spaciousness to a relatively small space. Unfortunately, to gain access to the windows for replacement, the one-piece sidewall has to come out, and this is difficult and time consuming. It is best done after all the seats have been removed.
Mechanics need access for inspections, which is something to think about if a new interior is in your future. The Phase 3 inspection checklist mainly consists of cabin items and requires removal of all the seats. Scheduling window replacement or other interior projects concurrent with a Phase 3 helps the shop to be more efficient.
The 2,500-cycle cabin inspection requires removal of the entire interior – headliner, sidewalls, seats, carpet – everything comes out. Here is another opportunity to schedule an interior project. Conversely, if your King Air is going in for an interior refresh or replace, you might consider having that cabin inspection done at the same time, even if you are 500 cycles early. From a maintenance perspective it makes a lot of sense.
For me, the King Air is a magnificent aircraft, both in performance and appearance. Enhance the look of your King Air by protecting your windows from burnout; and consider replacing burned out panes when the budget allows.