Can My Expired Airframe Control Bearing Inventory Be Saved?

Imagine you are tracking right ahead of a tight deadline for production. Your machined components stock-in, the bearings are pulled from stock for assembly, and a technician on the line discovers some of the bearings have exceeded recommended lube life. Now what? With new bearings at 20-30 week lead times, buying replacements is a problem. Fortunately, NPB can re-lubricate many types of bearings with a very short turn-around time. Read more about airframe control bearings, their shelf life, and common considerations for relubrication.

Airframe control bearings are a category of bearings generally designed for use in heavy load, oscillatory applications on aircraft flight control systems. These bearings are often full complement, meaning they have no separators between the balls, so they are generally not designed for high speed rotation. The industry specification covering the largest number of airframe control bearings is SAE-AS7949. Some of the most common airframe control bearing part number specifications are MS27641 and MS27646.

Shelf life for airframe control bearings is often limited by the lubricant, which is most commonly grease. Lubricant shelf life in a bearing is commonly defined by a manufacturer's guideline, a government specification, or industry standards. Shelf life for the most common AS7949 standard is 36months. If a bearing exceeds the 36month shelf life, it often cannot be used or installed into an aircraft. However, a bearing exceeding its recommended lube life does not mean it must be thrown away. Many manufacturers, distributors, and repair stations are forced to hold inventory for more than three years. Writing down or throwing away this expired inventory can result in significant losses of value. A good and viable solution is to have these bearings re-lubricated by an AS9100 re-lubrication facility that maintains factory authorization.

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Many common airframe control, needle, metal-on-metal spherical, and rod-end bearings can be re-lubricated or refreshed. Some cannot, like self-aligning stake shielded, or ball bearing rod-ends, due to their design features. Those, if they can be re-lubed at all, should be done by the manufacturer. The most common types that can be re-lubed are listed in a table below this article.

Some bearings for aircraft applications allow for lubricant to be refreshed or additional lubricant to be added through a lube hole or grease fitting. In some cases, aircraft bearings cannot be washed or old lubricant cannot be purged. In this case, the relubrication can be provided as a "refresh" depending on customer requirements.

If you have an expired part and would like to know if it can be re-lubricated, please contact your NPB Sales & Marketing Rep or Regional Sales Manager with the bearing specification, drawing, or a picture of the part. For more information contact your local sales representative.