The aircraft I was assigned had been phased in February 1995. In April of 1995, the 6th Cavalry Brigade had an unfortunate accident with a CH-47D that had recently come out of phase and was in track-and-balance status. A faulty lower drive arm bolt on the forward rotor assembly had sheared in flight, causing the blades to de-phase. As a result, Safety of Flight message CH-47-95-02, Drive Link Hardware Check, was issued.

This message required a visual inspection of the drive arm assemblies on both the forward and aft swash plates. The inspection was to verify a minimum 0.005-inch clearance existed between the threaded end of the bolt and the inside of the lug/swash plate ring, and a minimum 0.001-inch clearance between the bolt head and the lug face of the swash plate.

My company complied with the requirements and we started the inspections immediately. We had six airframes that failed, mine being one. The plan was to come in the next day (Saturday) with a maintenance team and further inspect and correct the deficiencies. Once we had the forward head locked out, we discovered why my aircraft had failed the forward drive arm check. It was because someone failed to install the lower slip bushing.

When starting the corrective procedure of disassembling the drive arm, I removed the cotter pin from the castellated nut on the middle bolt and was surprised to see the bolt had not been torqued. The hardware, per the technical manual, required a minimum of a 400 inch-pounds of torque. It was not present. In addition to this fault, a sleeve bushing had been installed instead of the required hat bushing.

The lack of the proper bushing caused the hardware to loosen over the 40 hours since its assembly in phase. The middle drive-arm bolt was put together with an improper bushing installed and washer stack up (e.g., a thick washer with several thin washers). This gave the appearance of a proper gap and the technical inspectors (TI) signed off during the scheduled maintenance months before. We made all corrections on the airframes and returned them to service.

To this day, I have that cotter pin on a key chain to remind me that no matter how many mechanics, crewmembers, TIs and pilots look at an airframe, there can still be concealed faults or deficiencies with it. No one person or maintenance system is perfect. If something doesn’t look right or if you’re unsure about a maintenance issue, it’s better to ask questions and get a second set of eyes on something before it’s too late.