Accident Overview
During the landing roll, the aircraft's normal braking system failed due to one or more hydraulic fluid leaks. At the pilot's request, the first officer deployed the drag chute and applied the emergency braking system. The first officer reported that applying the emergency brakes caused the airplane to yaw. In response, the first officer pulled up on the emergency brake handle and then re-applied braking pressure, repeating this action several times during the landing roll.
Emergency Braking Procedure
The Gates' Learjet Flight Training Manual (Page 105) provides specific instructions for using the emergency brake lever: "In using the emergency brake lever, slow steady downward pressure is required. Each time the lever is allowed to return upward to the normal position, nitrogen is evacuated overboard. Brace your hand so you will not allow the lever to move up and down inadvertently on a bumpy runway." The first officer's actions deviated from this procedure.
Outcome
The airplane overran the end of the runway and collided with the Instrument Landing System back course antennae.
Probable Cause
The official probable cause is the first officer's failure to perform proper emergency braking procedures.