KC135 Window Installation: A costly lesson on the importance of proper torque values

Sept. 1, 2002
KC135 Window Installation A costly lesson on the importance of proper torque values

I was a young staff sergeant assigned to the Aircraft Rigging (A/R) shop, Dyess AFB, Texas. To this day I remember this lesson on the value of proper torque values, and I still share it during training sessions.

A co-pilot's no. 1 window for a KC135 had been on back order for several days. The aircraft was carried as NMCS; the equivalent to a commercial AOG.

Upon recipt, a new window was issued, and installation proceeded. All hardware was installed except one strip of retaining screws which was accessed through the adjacent frame where the co-pilot's sliding window was stowed while closed and locked. We could not get the retaining strip lined up enough to start any of the screws in this area, so we tightened all hardware that was accessible from outside the airframe.

Our first mistake was tightening hardware before everything was installed. The second mistake? Torque values are fairly low on windscreens, and by tightening without the benefit of a torque wrench, we overtightened the hardware. As we tried to start some of the hardware on the sliding window side, the nutplate receptacles and screw hole were still misaligned, however, not by what would appear to be much.

We decided to try and start a screw. That was our last and most costly mistake. The windscreen was already stressed by not being evenly torqued. By trying to start a screw that was misaligned, we stressed the window to the breaking point.

The resulting "explosion" as the windscreen shattered reverberated throughout the hangar and brought the type of attention we had not wanted. We went from hero's to zero's in the span of microseconds, not to mention having to explain to our maintenance super the events that led up to our incident.

Needless to say, our actions not only caused financial damage, but kept a KC135 from being used for missions. For a couple of young technicians who thought they knew everything, this was an eye-opening lesson to say the least.

Editors Note: This story was submitted by one of our readers and kicks off our new column in AMT — Lessons Learned.
As I mentioned in my August 2002 editorial column, one of the ways that many of us learn safe maintenance practices is through the lessons learned from someone's mistakes or oversights. If we can learn from others mistakes or share our own with others, everyone is more knowledgeable, and safety is enhanced.

So send us your story of an incident that happened to you or someone you know. Tell us the specifics of the incident such as the type of aircraft being worked on and the mistake(s) made. If possible, include any contributing factors that led to the incident like stress, distraction, or lack of resources. Then share what lesson was learned from this event.

I want to stress that company names will not be printed nor will personal names. We don't want to point any fingers, only provide the opportunity to learn from mistakes. Send your story to:

"Lessons Learned"
1233 Janesville Avenue
Fort Atkinson, WI 53538
or e-mail to [email protected]

Thanks to those of you that have already sent in your stories. To those who haven't, why don't you share your story so that others may learn.