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BREAKING THE CHAIN

November 19, 2018

After reading through the maintenance insert in our last month’s issue, I decided to take a slightly different tack this month, stay in the hangar, and write something a little more prosaic yet hopefully as useful to you as an aviation hangar tale.

 

 

I’m often the ‘willing ear’ to hangar tales of incidents or near-incidents and regularly find myself thinking; “if you had only just done that differently, the whole thing would never have happened.” We all know that incidents, in nearly all cases, are not created by a single event or action, but are the result of a series of apparently innocuous actions, which, when strung together, forge the ultimate and ofttimes disastrous result. This is known as the ‘accident chain’.

After an aviation incident, we, or the investigators, normally review each event in the accident chain, as these comprise the contributing factors leading up to the incident. The theory, with which you’re all familiar, is that breaking any one link in the chain could possibly have avoided the whole damn incident.

In my experience, the actions that make up the links generally stem from ‘human factor related issues’, aka pilot error, rather than pure mechanical failure. That’s not to say that mechanical failure doesn’t happen; it merely means that our decision-making sometimes plays a significant role in the result, and maybe surprisingly, this decision making extends beyond the in-flight activities. I guess that what I’m trying to say is that what you do before and after the flight is as important as what you do while flying. And while we often practise in-flight exercises like stalls, EFATO and the like, aren’t we just a bit fatalistic about in-flight mechanical issues, thinking that there’s little, if anything that we can do about them?

With that said, let’s look at two ways that I think are important to extend our decision making process to break the accident chain and prevent mechanical issues from becoming accidents. 

The first way is the post-flight inspection.

Perhaps counter-intuitively, the post-flight inspection is the most important inspection you can perform. You’ve just had a great flight and your first thought is to hangar the plane, go grab a beer and tell everyone about it, and the end of your flight may appear to be the least likely first link in accident prevention. But it’s actually the best time to be thinking about safety with a clear head.

Pre-flight inspections, while critical, are a not a great time to be making good decisions. You have all sorts of other pressing issues on your mind; weather, fuel, loading, passengers, navigation and the like, and as a result, your ability to laser-focus on the pre-flight is a challenge. And an even greater danger is posed by how you handle your decision-making process if you happen to find an issue.

The pre-flight inspection is the perfect time for rationalisation and what I call ‘magic thinking’ to initiate the error chain. You have a mission, somewhere to go or people waiting for you, and if you discover anything that might delay the trip, your first instinct is to justify continuing. Time isn’t on your side, so you’re likely to make different decisions than you might otherwise make. The oil could be a bit on the low side, a tyre could be just a tad flat, a nick could be found in the prop, the engine idle could be rough, or something simply may not ‘feel right’ during the pre-flight inspection. There’s a strong temptation to think, “It’s only a short flight, it will be OK.” - Haven’t we all heard of ‘get-there-itis’?

If the same situations emerged during a post-flight inspection, the resulting thinking is likely to be very different. Time is not a factor, so you will likely decide to get any issues sorted out. Buy a case of oil, pump the tyres, properly dress-out the nick in the prop, and book the plane in to eliminate the rough idle. You have time to chat to your AMO, get a second opinion, or dig deeper into something that seems a little bit off beam. You won’t fly until the plane is perfect because you’re no longer under pressure to do so.

So, add a thorough post-flight inspection to your routine. Open the cowl after each flight and inspect the engine, check the control surfaces and everything else that you would typically check on a detailed pre-flight – plus a lot more. This is the ideal time to find and fix problems because the pressure is off and you can be focused on preventative maintenance.

The second way is to learn to listen to your plane.

Aircraft don’t magically heal themselves. That may sound obvious, but if you sincerely want to protect yourself, your family and your aircraft, read that sentence again and take it to heart.

As aircraft owners and/or pilots, we develop an acute ability to be ‘in touch’ with the aircraft we fly. Sometimes it’s conscious, like when we hear a new noise or feel a weird vibration. Other times it can be subconscious, such as when we have that nagging feeling that ‘something just isn’t right’. Either way, it’s critical to address the situation head-on and have the issue resolved.

This can be especially challenging with intermittent symptoms. The temptation to dismiss a symptom that hasn’t recurred is part of normal human psyche. However, there are times when we only have one chance to recognise that a serious situation is developing.  The consequences of ‘magic thinking’ at this stage could be disastrous. - Here’s a case of my own as an example.

About six months ago, I was returning after a flight in the Bonanza. Just after touchdown, we noticed a faint burning smell, which had that nose-wrinkling electric taint. It was there for only a few seconds and had vanished by the time I’d vacated the runway. After shutdown, I put my somewhat prominent nose to work to track down the smell. I sniffed above the panel, below the panel, the back seats, and in the engine compartment - no smell. I flipped some switches, tested avionics, etc. – still no luck. No matter what I tried, my nose couldn’t find anything wrong.  Eventually I put it down to something external (maybe a trash fire or tyre smoke from my landing), hangared the Bonnie and went to grab a beer.

A few days later, we were back at the airfield planning to go flying, but I decided to take my own advice and find the source of the burning smell before flying again. The same process as before was equally fruitless, so I decided to get my head down, literally; I grabbed a torch and after performing the vertebra-wrenching contortions that only yoga fanatics and avionics technicians consider normal, got the aforementioned head below the panel. 

So there I was, with my head between the rudder pedals, inspecting behind the panel while Mike simultaneously flipped the switches. Still no smell - but suddenly my fingers touched something hot enough to get my attention (and the attention of most of the people in the clubhouse). The main bus-bar for the lights, pitot heat, etc. was damn near red-hot. After shutting everything down and letting it cool, I found that the nylock nut securing the main power cable to the bus-bar was loose, very loose. The connection had been arcing, widening the hole and working its way loose and the arcing was generating the heat.

It turned out that the smell was caused by the overheating nylon in the nylock-nut which got hot enough to melt and burn its nylon. That moment when the plastic burned out of the nylock nut was the only opportunity to notice a problem from the pilot’s seat. Once the nylon was gone, so was the smell and also the locking capability of the nut.

The consequences of ignoring this one-time, elusive signal could have been a complete electrical failure in-flight or even an onboard fire. The repair was simple, and while we were having the nut replaced, we had our AMO check everything else behind the panel – just for good measure.

Listen closely to what your aircraft is telling you, its trying to save both your lives.

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