B737-800
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Conflict Ground Conflict; Less Severe; Ground Incursion Runway
Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach
Human Factors; Procedure
On approach to runway 13L at JFK; at approximately 1;000 feet; long after we had been given clearance to land; an A330 aircraft crossed the runway at the approach end necessitating a go-around.  The aircraft was being towed across the runway.  The tower controller directed a go-around just a we had decided to go-around because of the conflicting aircraft.  We asked the controller who authorized the aircraft to cross in front of us; but he didn't know who the aircraft was talking to.  We executed the go-around and landed uneventfully on runway 22L. I believe it is obvious that the tower controller needs to be the person that authorizes aircraft to cross an active landing runway--- not someone that is unaware of the landing traffic.
We were cleared to land Runway 13L referencing an A-320 ahead of us. I had the landing traffic in sight and was concentrating on their clearance of the runway. About 300 feet AGL I told the First Officer (FO); who was flying; to continue; being certain that the previous aircraft would be clear before our touchdown. The FO questioned me and as I was saying 'yes; they are clearing' he initiated a go-around just as Tower called 'Go-around.' I looked at the landing zone to see an A-330 being towed in front of Runway 13L. The tail was dead center on the runway as we went around.Be sure taxiing/towing aircraft talk to tower before transiting the approach end of any runway. They should be on tower's frequency so aircraft can identify them and where they are in relation to the runway.
B737 flight crew executes a go around at low altitude as an A330 under tow crosses the runway in front of them. The Captain does not initially detect the incursion as he is watching to insure that the aircraft landing ahead has cleared the runway.