Corrosion and corrosion protection on aircraft
From pit corrosion to Corrosion Prevention and Control Program
An aeroplane is built of metal that is constantly exposed to moisture, temperature fluctuations, de-icing fluids and salt-laden air — a demanding cocktail for corrosion. Corrosion is therefore not a cosmetic beauty spot in aircraft engineering: it is a structural threat that can weaken the aircraft's load-bearing capacity if not detected in time. As an aircraft technician you must be able to recognise corrosion, understand why it occurs precisely there, and know when a finding requires repair according to the aircraft's structural repair manual (SRM) rather than just a cleaning.
§Why corrosion is a big deal in aviation
Aluminum alloys, which make up the majority of many aircraft fuselages, are light and strong, but also susceptible to corrosion if the protective surface is damaged. In 1988, an older passenger aircraft lost a large portion of its cabin roof during flight, and the investigation pointed to widespread corrosion and material fatigue that had not been caught in time. The accident was the starting gun for aviation authorities to introduce requirements for systematic Corrosion Prevention and Control Programs (CPCP) for older aircraft – fixed programs for where, how often, and how to inspect for corrosion.
§The most important types of corrosion you must be able to recognize
| Type | Characteristic |
|---|---|
| Surface corrosion | Evenly gray or white, powdery layer – typically least serious but a warning sign |
| Pitting corrosion (pitting) | Small, deep holes that can cause strength problems even though the surface looks fine |
| Galvanic corrosion | Occurs where two different metals are in contact with moisture between them, e.g. steel against aluminum |
| Fretting | Occurs by friction between two surfaces under vibration, typically at joints and bolts |
| Stress corrosion | Combination of mechanical stress and a corrosive environment — can cause sudden cracking |
| Intergranular corrosion | Corrosion along metal grain structure — can spread below the surface without being visible from outside |
§Where on the aircraft corrosion typically occurs
- 01Bottom zones (bilge areas) where condensation and spills collect
- 02Battery compartment where acid fumes attack metal and wiring
- 03Toilets and pantry where liquid spills penetrate structure
- 04Control cables, hinges and fasteners with limited access for inspection
- 05Areas where de-icing fluid runs down and collects
§How you upgrade from self-employed to business owner
The protection is layered: an anodized or chemically converted surface first then primer and paint and often an extra layer of corrosion inhibitor in hidden cavities where traditional paint is difficult to maintain. Where different metals meet isolation layers or gaskets are used so the galvanic cell cannot form. Bonding — electrical connections between parts — simultaneously ensures that static electricity and lightning are safely conducted away instead of concentrating in one place and creating sparking.
§Corrosion levels — and what they mean for you
Corrosion findings are typically classified into levels based on how serious and widespread it is. Level 1 is light and within the limits in the maintenance manual — here you simply clean and protect the area again. Level 2 requires faster action and often shorter inspection intervals in the future. Level 3 means the damage exceeds the permitted limits and requires repair or replacement before the aircraft can fly again. It is your responsibility to measure against the limit values in the SRM — never to assess by eye.
§Your role in the daily
- 01Keep drain holes and drains free so moisture does not accumulate
- 02Wash the aircraft according to the recommendations, especially after de-icing or flying near the sea
- 03Report visible corrosion, even when it seems trivial — early detection is cheapest
- 04Always follow the SRM's limit values to determine if a finding can be repaired locally or needs to be escalated
§Age, flight hours, and enhanced supervision
The older an aircraft becomes, and the more flight cycles it has behind it, the more important systematic monitoring becomes. The maintenance program for an older aircraft therefore typically contains more and more frequent corrosion inspections than for a new aircraft, because statistics show that the probability of corrosion increases with age and operating hours. This is especially true for aircraft that have flown extensively in humid or coastal climates where salty air accelerates attack on unprotected metal parts. As an aircraft technician you will experience that an aircraft approaching the end of its originally certified service life requires a significantly more detailed inspection program and that corrosion findings here often require extra documentation and follow-up from the quality department.
An important element in daily practice is also understanding the interplay between corrosion and other damage mechanisms. A corroded surface is often more susceptible to fatigue cracks because pit corrosion creates local stress concentrations where a crack can more easily initiate. Therefore, a corrosion finding is never evaluated in isolation—it is always considered in the context of where on the structure it is located and what loads the area typically experiences during flight.