Life Limited to Life Unlimited – Cold Working: Part 2 [Op-Ed]

Back in January, we introduced you to a Beechcraft King Air Spar Inspection Program that could save you considerable time and money. In part two of this series, we’d like to walk you through cold working, a process needed due to wing spar fatigue.

What is Cold Working?

King Air Cold Working - Power Pack and Puller Head — Figure 1. Power Pack and Puller Head

Years ago, upon inspecting their aging King Air fleet, Beechcraft discovered cracks near the spar cap rivet holes. With thorough research and testing, Beechcraft began recommending “cold working” to remedy the issue.

In layman’s terms, cold working strengthens the metallic area surrounding a hole by actually expanding the hole itself. Using a specialized toolkit, an oversized, tapered mandrel is pulled through the hole, creating a compressive “stress zone” that can extend up to one diameter beyond the edge of the original hole. This stress zone provides structural integrity and helps to prevent the initiation and growth of future fatigue cracks.

What are the benefits of performing cold working on King Airs?

Figure 2. Mandrel, puller head, reamer and go-no-go gauges. These come in various sizes depending on the hole size to be Cold Worked.

Reduced Maintenance Time and Cost:
Once the spar fatigue and cold working kit has been installed, your recurring inspection on the center section aft spar is 6000 hours on certain “A” and “B” King Air 200 series aircraft, with no component replacement schedule if the inspection interval is complied with. You greatly reduce the time and money spent on unscheduled fatigue-related maintenance.

Increased Safety:
With the extended life of these components, it is less likely that cracks will occur. If they do occur, you will have an increased chance of identifying the cracks in a repairable condition.

Figure 3. In this view we can see locations on the left-hand lower aft inboard bathtub fitting being prepped for NDI and Cold Working.

No Increase in Weight:
The cold working process was designed around using existing material on the aircraft. Therefore you won’t be adding any weight to your aircraft.

Hampton Aviation has been regularly installing these kits for customers around the world. In fact, there is rarely a time that we do not have an aircraft in our shop for this specific purpose. Give us a call if we can answer any questions about the cold working process.

Don’t miss Part Three of this series coming up next where we’ll discuss outboard spar cap replacement.

Figure 4. In this view you can see the completed product. The affected areas have been re-sized, NDI’d, Cold Worked and new fasteners have been installed.

Figure 5. Here the left-hand wing aft spar at the jack attach point is being prepped for new fasteners.

Figure 6. Here you see a completed product just aft of the right-hand wing jack pad.

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About the Author:

Michael Montgomery: Sales Manager
Aviation Professional since 1992
Certifications: Airframe & Powerplant

In his 21 years of aviation industry experience, Michael has spent 15 years supporting the US Air Force and US Army Fixed Wing programs in various roles such as Lead Mechanic, Director of Maintenance, Project Manager, and Quality Assurance Representative. Additionally, he spent six years in Corporate Aviation in the following roles: Program Manager, Sales and Marketing Manager, and Director of Maintenance. Michael joined Hampton aviation in 2013 to spearhead sales efforts.