Flight Crew Air Transport Pilot (ATP)
Situational Awareness
ATC Issue All Types; Conflict Ground Conflict; Critical
Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach; Flight Crew Requested ATC Assistance / Clarification
Human Factors
HPN airport; holding short of Runway 34; awaiting takeoff clearance; the crew observed the following. A Gulfstream was cleared to land runway 34. The Gulfstream was in the landing flare at approximately 40 feet when tower issued 'go around; go around' to the Gulfstream. We were watching it land when the command was issued. The Gulfstream pitched up and executed a go around as a small Cessna landing runway 29 passed directly under the Gulfstream on the landing rollout. I estimate 50 feet separation; at most. We observed this from about 150 yards away. This was about as close as it gets without an explosion. The Gulfstream returned for a landing and ask 'why the go-around'.  Tower replied; Cessna landed without landing clearance. Nothing else was said between Tower and the Gulfstream. I believe Tower/ATC/Approach made a near fatal error in not recognizing the proximity of the Cessna to the cleared to land Gulfstream. After the event; operations resumed normally with business jets/airliners landing 34 and small aircraft landing one after another Runway 29. I believe during these type of operations a high level of vigilance should exist between only highly experienced Tower/ATC Controllers. I have seen similar incidents happen at HPN. Tower controller seemingly [had] 'lack of experience' or [experienced] 'loss of situational awareness.'
Corporate jet Captain reported observing a near-collision between a Gulfstream landing on HPN Runway 34 and a Cessna landing on Runway 29. Reporter was of the opinion it was an ATC error.