We have all heard the story of how a horseshoe nail was lost, leading to the loss of the horse and its rider, and the message he carried into battle. Because the message was never received, the battle and the war was lost. Its as apocryphal today as when it was written. Examples include the shuttle Challenger tragedy-caused by a defective O-ring-and the Eastern Airlines Lockheed L-1011 that crashed in the Florida Everglades because someone nudged the autopilot switch off while working on a simple landing-gear problem but didnt notice it.
The point is that accident chains usually start from very simple events, pick up steam from other links in the chain and then snowball out of control. I recently had reason to spend a lot of time thinking about the accident chain and how to break its links.
I was flying a 160-nm VFR trip in my Piper Cherokee 140. The weather was typical summer haze, with four to five miles of visibility. I was using ATCs flight-following services at 4500 feet msl over 500-foot terrain. During one of my panel scans, I looked over at the airplanes King KMA-24 audio panel and noticed that the transmitter select knob had fallen to the floor. This is more of an inconvenience than any kind of a big deal.
I reached down, picked it up and placed it back on the shaft where it belonged. Of course, it fell off again-duh, the set-screw had worked loose-and this time I couldnt locate it.
While fishing around on the floor, my heading wandered about 30 degrees. I gave up looking for the knob and got back on the correct heading. I thought, Okay, Ill just turn the selector switch with my fingers. But because the shaft is small, this was not as easy as I thought it would be.
Then I thought, no big deal, Ill just use the selected radio. Then I remembered that radio had a senior moment at the last airport but was working fine now. While this little problem interrupted my normal cockpit procedures, it clearly presented no major problem for the flight. And, I had backup if needed: My handheld nav-comm was in the back seat. And, of course, I was VFR and the weather was good enough to just land at a non-towered airport.
What bothered me, though, was how much this little problem distracted me from my duties as PIC. After letting my heading wander off, I had to consciously remind myself about my priorities: 1) aviate, 2) navigate and 3) communicate.
If I had been in IMC, I think this little problem would have been more mentally distracting, even though it was definitely not significant. When I was safely on the ground and parked, I searched and found the knob under the right seat. Unfortunately, the set-screw was lost and it took a couple of weeks to find a replacement (its not a standard size). So, I have added checking the security of the set-screw to my annual inspection list.
I have trained for many emergencies over the years, but this little problem caught me off-guard, because I never thought about it happening. Fortunately, my training kicked in and I quickly got back to the business of flying the airplane, but this event made me realize how even little problems can create danger, due to the distraction factor.