I had a winter problem with trim in my PA28 because the cable tension was too low and the cable was slipping in the winter when the grease would get stiffer. It was evident though because the trim indicator would not move.
Aluminum has a coefficient of linear thermal expansion that is almost exactly twice that of steel. The aluminum aircraft hull will shrink in the cold twice as much as the steel cables shrink, and the cables lose tension. If they need that tension to drive a pulley to adjust a trim screw, they're going to have trouble grabbing the pulley. And since cables can stretch a little over time, they may have been below spec already.
And if the pulley bearing and screw lubricating greases are stiff in the cold, we now have two problems.
Airplanes rot whether they're flown or not. Time and the environment are bigger enemies than the flight time. I find control system pulleys that haven't been regularly lubed and kept free; they develop sludge as their lubricants dry out and combine with water and dust from the air and soon they won't turn. The cable slides over them and besides having stiff controls, the cable is being abraded and is going to start fraying. Some that have very small contact radii (the cable makes a very small change in direction over the pulley) are inclined to stick sooner since there's little pressure on them. The cables will also fray at these pulleys because vibration chatters them agains the pulleys. There are a couple of bad ones in the 172 at the aft end of the baggage compartment.
Oil and fuel hoses rot or dry out and crack. Imagine a scenario where the fuel hose between the gascolator and carb breaks in flight because it's so old. It's a flexible hose in the first place because the engine moves on its rubber mounts and the hose has to follow it around. If it's old it stiffens and cracks when it's flexed. Imagine an oil cooler hose that could split and spray hot oil on a muffler where it catches fire and continues to burn while the engine, whether it's running or windmilling, keeps pumping oil into the fire until the oil is gone. I see really old hoses way too often. Any rubber or plastic parts lose solvents or whatever it is that keeps them flexible; you can smell those solvents when you smell new rubber. Think tire store. They're leaving right from the time the part is new. Five years is a safe bet for replacing engine fluid hoses. There are also short bits of rubber hose connecting metal fuel lines in a lot of airplanes; the Cessnas have them in the cabin at the wing roots. We find those rotted, too, and if they start leaking in flight you can't shut them off.
Imagine a wing strut that's rusting on the inside and most of it is gone already and nobody notices. A common Aeronca Champ problem. Taylorcraft now too, I think. Wooden wing spars dry and shrink across the grain and if they have metal ribs nailed to them, the metal ends up splitting the wood along the grain. Not healthy for safe flight.
Animals think airplanes are great places to raise families because they're undisturbed for so long. A week is enough to get started on the family. We find bird nests inside 172 elevators (look inside at the rudder end) and wings (they get in ahead of the ailerons) and engines. Bird droppings are corrosive and their nests can foul stuff. Mice are everywhere and they pee on everything and corrode it so fast it's not funny. A dead mouse jammed in a cable pulley is no joke. Mice like to eat the linen ribstitching on fabric airplanes. No ribstitching means the fabric balloons and flutters and maybe the airplane crashes.
Dust gets into everything and soaks up oil and makes gucky stuff that seizes everything. Water can mix with oils and greases and form acids and more sludge. The sun cooks the solvents out of oils and greases and rubber and plastics and fabrics. Its UV degrades all sorts of stuff. Ozone attacks rubber, especially tires.
A mechanic who looks at the logs or Hobbs and says "Only 15 hours this last year; this annual we can just giver 'er the quick once-over and she's good to go" is overlooking something: the last mechanic might have said the same thing, and the one before him, too. So not much gets opened up and looked at real good and the sort of rotten/seized/corroded stuff I've described develops. The owner often wants to avoid big shop costs and is happy if the annual is cheap. In the end, though, the airplane loses most of its value and becomes an unsafe airplane. False economy.
Dan
