What should you do if you detect fire during takeoff above 80 knots?

When fire is detected during takeoff above 80 knots, the proper response is to immediately reject the takeoff. This is crucial because at this speed, the aircraft is close to the point where it can no longer safely stop on the runway. Rejecting the takeoff allows the pilot to apply maximum braking to stop the aircraft on the runway while it is still controllable, thereby maximizing safety for those onboard and allowing for emergency procedures to be initiated as soon as possible.

The decision to reject the takeoff is further supported by the understanding that the aircraft's systems and protocols are designed to handle emergencies early in the takeoff phase. Once above 80 knots, options for stopping or avoiding a fire become significantly limited, making immediate action necessary. Notifying air traffic control is an important step but comes after ensuring the aircraft is stopped and the fire can be attended to. Continuing the takeoff or diverting to another airport would not address the critical situation of an active fire that requires immediate attention.