Which of the following is not a mode of wheel brake operation?

• A. Anti-skid
• B. Normal
• C. Parking
• D. Emergency

Answer: (A)

Braking systems operate in distinct modes that define how hydraulic pressure is applied for deceleration. Normal braking uses standard pressure to slow the aircraft in a controlled way. Parking brake is a separate function that locks the wheels to hold the aircraft in place on the ground. Emergency braking provides maximum or rapid deceleration when needed, often with different control behavior to stop quickly.

Anti-skid, on the other hand, is a safety system that actively modulates brake pressure to prevent wheel lock and skidding. It works within the braking process to maintain traction rather than being a separate mode of operation itself. That’s why it’s not considered a mode of wheel brake operation—the other options are modes, while anti-skid is a control system applied during braking.