What It Looks Like

You're doing a careful preflight inspection, including getting down on your hands and knees to closely examine the wheels and brakes. That's when you discover that the brake disc on each main wheel looks like Swiss cheese. The braking surface of the disc is pockmarked with tiny pits. Is this something you should point out to a mechanic before flying the airplane?

Probably. Pitted brake discs can reduce the effectiveness of the brake pads, and cause the pads to wear prematurely. The pitting that you see is the result of corrosion that forms when the airplane sits for an extended length of time, especially when the air is damp or it has been raining. Extreme industrial pollution also can lead to corrosion. At the very least, pitted brake discs should prompt you to make a detailed inspection of the discs and pads to see if they are serviceable.

If the disc is very thin, has multiple grooves or deep scratches, or is noticeably coned (unevenly worn on the braking surface), have a mechanic examine it before taxiing the airplane. Don't be alarmed if you see a thin, powdery coating of rust on the braking surface. Light rust can appear on brake discs within a day after the brakes were last used. You can usually remove the rust from the surface of the disc just by braking once or twice during taxi. A heavier coating of rust probably should be referred to a mechanic because it may be hiding a bad case of the pits.