The Accident that Should've Happened
October 1, 2012
The RQ-7B Shadow has, among others, two six-inch center-wing bolts that secure the wing section to the fuselage of the aircraft. By the technical manual, once the bolt heads are flush with the wing surface, they are then torqued to 50 foot/pounds. Prior to this flight, the aircraft in question had been subjected to scheduled maintenance requiring the removal and replacement of these center-wing bolts.
The crewmember was in the process of performing a postflight service on the aircraft when he opened the aft compartment cover and noticed the two center-wing bolts were loose. The bolts were so loose that the heads were about two inches above the wing surface and only finger-tight. When the crewmember showed this to me, my initial thought was that a prank was being played, so I played it off as such. Once he convinced me he had not loosened the bolts himself and the aircraft did indeed fly for five hours in this condition, my first question was: Why didn't this aircraft crash?
With the center-wing bolts as loose as they were, I was able to grab one of the wings and move it about 10 degrees up and down along the lateral axis. However, during the debriefing, nothing out of the ordinary was reported by the flight crew during the mission.
The Shadow normally reaches about 70 knots at full-engine RPM and is launched from a rail using 2,000 pounds of hydraulic pressure to accelerate the aircraft to flying speed. With the excessive G-load on the aircraft at takeoff, I wondered why the wings did not fold completely off the fuselage upon launch. According to the flight crew, the aircraft performed normally with no reported indication in the control station that anything was wrong.
I inspected the logbooks and found where the scheduled maintenance was annotated by the crew chief and then reviewed by the technical inspector. I pressed the TI for some feedback about the scheduled maintenance performed on the aircraft prior to this flight. (A TI is tasked with physically verifying the proper setting on the torque wrench as well as visually inspecting the crew chief's work upon completion before he signs off on the work in the logbooks.) After some tap dancing, the TI admitted he had trusted the crew chief to supervise himself and took his word that the work had been completed to standard before he signed it off. This was where I began to understand the systemic failure and cause of the issue since the center-wing bolts don't back themselves out after they have been properly torqued.
I then engaged the crew chief, who, after some more tap dancing, admitted he had been in the process of torquing the center-wing bolts in place before something distracted him. Whatever the distraction, it caused him to inadvertently skip the entire step before moving on to other maintenance on the aircraft. Simply put, the crew chief forgot a critical step in the maintenance checklist and the TI took his word that it had been completed properly.
After forming a complete picture of where and how the defects occurred, I reported the incident to the platoon sergeant and platoon leader. The crew chief's and TI's defense was that the aircraft operator was just as at fault for not performing a complete preflight according to the checklist. In fact, the preflight checklist, even today, requires the operator to inspect the aft compartment cover, ensuring it is fully latched. At the time, the operator was not required to open the aft compartment cover to inspect anything inside, although nothing prevented the operator from doing so.
Human beings are prone to error. However, in aviation, errors typically result in injury and/or some form of damage to the aircraft. Due to this incident, the crew chief received corrective training and required immediate re-certification. The TI lost his authority and designation orders for the duration of the deployment. In addition, I added a step to our standing operating procedures requiring the aircraft operator to open the aft compartment and visually inspect the center-wing bolts for security.
This incident served as a valuable training tool for my platoon and an eye-opener for all involved in the operation. This was the first opportunity I had to perform any kind of "post-mishap" investigation. My unit never had another incident like this again and maintained a flawless incident record afterward. However, I still cannot explain why the aircraft held together not only during launch, but also for the entire duration of its flight.