Training / Qualification; Situational Awareness; Confusion; Communication Breakdown; Troubleshooting
Aircraft Equipment Problem Critical
General Maintenance Action; General Flight Cancelled / Delayed
Aircraft; Human Factors
On arrival to the jet; it was noted that an open item existed in the Logbook. The inbound flight had a runaway [electrical] overheat on the L2 window. We were unable to placard the window due to enroute icing conditions. The Mechanic did some troubleshooting and found multiple faults in the system. He changed out a computer; resetting the system. The problem was deemed corrected and signed-off. The Captain and I were finalizing the Before Taxi Checklist when the Overheat light associated with the L2 window came back on. We turned the switch 'Off' and called for Maintenance again. When Maintenance arrived 15 minutes later; the L2 window was still extremely hot. They pulled the Cannon plug and the window started cooling down. Was told if that happened airborne; the window could shatter. For unknown reasons the Temperature Controller did not automatically shut down power to the window and placing the switch to 'Off' did not shut down power either.  Multiple mechanics and differences of opinion; an hour later the jet was taken out of service. The debate was whether it was a faulty window or the Window Heat Controller. As we were leaving the jet; the mechanics were replacing the Window Heat Controller in the cockpit. Checking the Aircraft Maintenance History; I noticed the actual fix was replacing the window. I am concerned if this occurred airborne there is a chance for a major incident. I was briefed recently by a Captain that this happened previously to another B737 and to be ready to pull the cannon plug if we had an uncontrollable window overheat. Coincidentally; these issues are now popping up since we started using the RAM mount attached to the window. I did not previously hear of this issue in the twelve years I have been on the jet. Maybe a step should be added to the QRH if there is an uncontrollable window overheat to remove the cannon plug from the window; as that is the only way to ensure power is removed. Maybe we should not attach a RAM mount directly to the window; as this could needlessly damage it. I doubt the engineers planned those stresses to their design. Everyone I fly with thinks the approved RAM mount is problematic at best. Besides potentially damaging the window; there is a chance of the mount falling off during a critical stage in flight. That is unsatisfactory! I have also seen numerous damaged and unusable window shades. I had it happen to myself and heard complaints with the [RAM] mount hindering both yoke and tiller movements. Obviously we all figured out how not to do that again. But one time was one too many. Lastly; I have seen placements of the RAM mount where I did not have much visibility out of the Captain's window. Again; a major safety issue. There are better and safer alternatives to our current RAM mount. Hopefully common sense will prevail. Preflight.
A First Officer reports about a recurring runaway overheat of their L2 window on a B737-800 aircraft that was previously signed-off. Pilot noted the Overhead P5 Window Heat switch would not shut off electrical power to the window. He also questions whether or not the recent use of RAM mounts on the windows are a contributor to the overheat conditions.