A Cessna 528B, N22AU, was substantially damaged when it was involved in a runway excursion accident at Baltimore-Martin State Airport, MD (MTN). The flight crew reported they flew a normal flight and a stabilized approach in gusty wind conditions. Performance data indicated they would require about 3,000 ft of runway for landing on the 6,995 ft long runway, and they added 5 knots (kts) to the approach speed due to the gusts. Data indicated that the airplane landed in the touchdown zone and at an appropriate airspeed of 110 kts (104 kts groundspeed); however, the pilot’s and co-pilot’s application of brakes was unsuccessful in achieving sufficient braking action. The airplane departed the runway at a groundspeed of 58 kts and came to rest against a perimeter fence 450 ft past the runway. A witness stated the airplane landed long; however, his distance from the runway and his angle of view of the airplane may have prevented an accurate assessment. Although the airplane flight manual states that if the brake system or antiskid fails, the pilot(s) are to attempt to pull the emergency brake, the pilots were unable to locate the emergency brake and instead pulled the parking brake. Although an examination of the braking system failed to find an anomaly, a performance study revealed that during the ground rollout the deceleration was primarily due to aerodynamic drag and free rolling ‘unbraked’ wheel friction for about 5,000 ft and that there was virtually no evidence of deceleration due to hydraulic or pneumatic wheel braking during the rollout. However, the pilots’ inability to locate and use the emergency brake contributed to the insufficient braking. The crew failed to immediately recognize the issue and locate and utilize the emergency brake for supplemental braking authority. Probable Cause: And undetermined failure of the brake system. Contributing to the accident was the failure of the pilots to locate and operate the emergency brake control, which resulted in a runway excursion and collision with terrain and an object.