Corrosion; A major problem in aviation...

Corrosion is one of the greatest enemies of airframes. Somany accidents occured due to corrosion. On April 28, 1988, 18 feet of skin ripped off an Aloha Airlines B737-200 in flight. Corrosion is also believed to have resulted in engines 3 and 4 falling off the wings of two B747-200 freighters; a China Airlines 747 in 1991 and an EL AL 747 in 1992. In both instances, the aircraft crashed. In the EL AL incident, which occurred in Amsterdam, all four crew members were killed along with 50 people on the ground.
Clearly, corrosion is something that demands detection, treatment, and, where possible, prevention.

Forms of corrosion.
There are many forms of aircraft corrosion. The most commonly known occurs when aluminum interacts with water, creating aluminum oxide. It is not just the exterior skin that is vulnerable; as the airframe expands and contracts in response to sunlight, heat, and cold, water can penetrate into rivet holes and thus deeper into the aircraft. As well, water spilled onto galley floors, or leaking around old toilets and sinks, can find its way into the airframe.

A less obvious but equally deadly form of decay is galvanic corrosion. This occurs on the atomic level, when ions flow between two adjacent, chemically different materials. Galvanic corrosion doesn’t just occur between metals; a composite/metal pairing can also result in ions being transferred.

How do we detect corrosion?
Generally, corrosion is detected visually. Technicians go over every accessible inch of an airframe during maintenance, or when the aircraft has been stripped down to the bare metal for repainting.

How do we treat corrosion?
Once corrosion has been detected, treatment is a must. In some cases, the damage is superficial enough to be removed, and then for the repaired area to be protected with anti-corrosion products. In others, corroded components may have to be removed and replaced.

Airframe corrosion doesn’t happen overnight. It can take a year or more for corrosion to seriously weaken an airframe. So the best way is to inspect the airframe regularly using a range of available techniques and tools.

Prevention is better than cure.