Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 1.5
Communication Breakdown; Situational Awareness; Training / Qualification
Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Rejected Takeoff
Human Factors; Procedure
Training in progress on Local; I was the OJTI. Aircraft X landed runway 28R; and my student instructed Aircraft X to exit taxiway Foxtrot hold short of Runway 28L and remain this frequency. Aircraft X gave an incomplete readback of hold short instructions. My student corrected the pilot and then Aircraft X gave a complete and accurate readback of hold short instructions. My student then cleared Aircraft Y for takeoff on runway 28L. As I was watching the situation develop; it appeared that Aircraft X was getting very close to the runway; at which point I jumped in and canceled the takeoff clearance for Aircraft Y twice; to be sure the pilot heard it. As Aircraft Y was decelerating; Aircraft X was about halfway through crossing runway 28L. Aircraft X was then issued the Brasher warning.
MYF Local Controller Instructor reported of a runway incursion and ground conflict because of an aircraft that crossed halfway onto the runway while a departure aircraft was told to stop twice. The crossing aircraft read back hold short instructions.