TECHNICAL
Looking, but H
Everyone checks their aircraft before flight, but just what do you actually see?
ow many times have you checked over the aircraft at the start of the day or flight and thought — did I really check l that? A recent
conversation went like this: “I looked at the exhaust manifold as I always do, but I simply didn’t see the crack.” It’s a common fault summed up well
by human behaviour author Joe Navarro who characterises it like this: ’The problem is that most people spend their lives looking... but not truly seeing…’ According to the dictionary, the difference
between the two is: ‘looking means to direct your eyes in a particular direction, but to see you must notice or become aware of someone or something by using your eyes’. The psychology behind looking but not actually seeing is well-known. As well as the exhaust shown below
centre, the following pictures are just some of the defects found on aircraft, some might have been easy to spot with a quick look, but others really needed the pilot to
be ‘seeing’ what he or she was looking at… Picture 1 shows a failed Rotax 912
carburettor attachment fitting. The metal attaching plate is, or at least should be, bonded onto the formed rubber sleeve that attaches the carburettor; as evidenced from the corrosion on the metal plate, this fitting has been failed for some time. This type of failure has occurred before on 912 engine installations and Rotax have had several goes at improving the component over the years. After checking just about everything
else, a broken exhaust (Picture 2) was found to be the cause of a severe low rpm engine vibration on a Cessna 172. The left can supplies the carburettor heat on this installation and although heat was available its effectiveness could not be determined. Towards the later stages of failure it was evident that carbon monoxide contamination was a potential safety threat. Of course, the complete engine
installation on a 172, as with many aircraft these days, is difficult to inspect fully during a pre-flight inspection, so it’s essential every now and then to take the cowls off so that early signs of this type of failure can be spotted and problems rectified before they become life-threatening. When it’s pointed out, you can see why
the undercarriage bungee failed in Picture 3 – essentially it’s a one-piece bungee with loops at each end to be secured to the lugs. The edge of the ferrule slowly cut its way through the adjacent bungee wrap and you can just see the 3/32in safety cable which, in this bungee failure, failed to keep the aircraft upright. Here’s an unusual picture (4). This tar- like substance was, after rather a lot of persuading, removed from the crankcase breather bottle of a Jabiru SK. It was clear that this bottle hadn’t been cleaned out for quite some time and this lack of maintenance ended up with the pilot force-landing into a field.
Picture 2
Picture 1
30 CLUED UP Summer 2018
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