FAA Aviation Mechanic Airframe (AMA)Airframe InspectionMedium
During a corrosion inspection of an aluminum wing spar cap near a drain hole, a technician notices small, localized craters with a rough, irregular surface texture but no significant material loss elsewhere. What type of corrosion is most likely present?
- AFiliform corrosion
- BIntergranular corrosion
- CPitting corrosion
- DGalvanic corrosion
Show answer & explanationAnswer & explanation
Correct answer: C. Pitting corrosion
Pitting corrosion appears as small, localized craters or pits on the metal surface, often caused by moisture pooling in low areas such as near drain holes. It is one of the most common and initially hard-to-detect forms of corrosion because the surface area affected is small compared to potential depth.
Why the other options are wrong
- A. Filiform corrosion appears as thread-like trails under paint/finish, not discrete pits.
- B. Intergranular corrosion occurs along grain boundaries, often invisible until subsurface separation.
- D. Galvanic corrosion requires dissimilar metals in contact with an electrolyte, not implied here.
Pitting Corrosion
Localized corrosion that forms small pits or craters on a metal surface, often initiated by moisture pooling in low spots such as drain holes or crevices.
- Appears as small, deep, localized craters
- Often found near drain holes, seams, and crevices
- Can lead to stress concentration and fatigue cracking if untreated
Memory trick: Pitting = pothole-like pits from pooled water