One of the biggest dangers in aviation is flying with an airplane that has structural damage to the fuselage or any other part.
For structural damage I mean cracks, corrosion or any signs that indicates some kind of weakening of the structure.
Follow me and do this exercise now.
Imagine an airplane, and visualize which are the main parts that make it up if you look at it from outside.
You’ll see the fuselage, wings, elevators, rudder, engines and landing gear.
It is extremely dangerous when one of these parts has some form of metal weakening. The consequences can be disastrous, as you can imagine.
Let’s clarify a couple of points.
Do you know of what material an airplane is made of?
It is made of aluminum, mainly. Latest generation are also made of carbon fiber which allows to reduce the weight (B787 – A350)..
But most of the airplanes are still made of aluminum. Each one has an internal “skeleton” covered with aluminum panels joined with rivets.
When I talk about cracks or structural damage I refer to these aluminum panels.
Making many cycles (one cycle equals to one takeoff and landing), the airplane fuselage expands and shrinks whenever flying at 30,000 feet.
At higher altitudes the external pressure decreases, while the internal pressure remains approximately equal to 2,000 meters of altitude. It means that the internal pressure is higher than the external one.
This causes the fuselage to expand, it widens and then shrinks again when going up and down.
These cycles of expansion and shrinkage cause a phenomenon called Fatigue and can be very dangerous for metals. For this same reason, airplane windows are oval.
I’ll give you an example you can experiment at home.
Search a wire or one of those aluminum hangers or a paper clip. Start to bend it repeatedly always in the same point and you will start to feel that the wire will begin to heat up and get weak up to the point it breaks.
This phenomenon is called Fatigue.
The same thing happens to the airplane fuselage. Clearly it doesn’t bend, but these cycles of expansion and shrinkage weaken the structure.
The various maintenance checks and aircraft goes threw, make it possible to identify these weak points that can be found either between an aluminum panel and the other or in correspondence with a rivet or other positions.
There are different points of the fuselage where a crack can generate. Some of these cracks are not identifiable by man, but the maintenance cycles also provide a check with a sort of “X-ray” that allow to look inside the metal.
Other times there may be corrosion formations, or the fuel tanks are too old and must be changed completely.
Also the wings and engine pylons should be closely supervised. With time cracks may be present or the metal simply weakens.
Obviously you don’t need to fear. The life of an airplane may exceed twenty years of service, something that a car rarely manages to do.
This is possible because the maintenance is performed regularly and the checks are very accurate and meticulous.