The Irish Aviation Authority has begun an investigation into Monday's incident at Dublin Airport involving two aircraft - one from Aer Lingus, the other from Ryanair.
The Aer Lingus flight from Boston was coming in to land when the pilot saw a Ryanair aircraft on the runway and abruptly regained altitude.
The Ryanair pilot had been awaiting clearance for take-off, but had lost contact with the air traffic control tower. Noting the problem, the Aer Lingus pilot made contact with ground control and was instructed to do a "go-around" until he received clearance to land.
Ms Lilian Cassin, the Irish Aviation Authority's corporate communications officer, said initial findings suggested the Aer Lingus aircraft was at 800 feet when it was forced to abort the landing. She said while passengers may have felt they were nearer the runway, it was difficult to judge the distance from an aircraft.
Passengers reported that the aircraft seemed to be on the point of landing before swooping upwards again.
Initial investigations have suggested that the frequency blockage might have been caused by a third aircraft which was preparing to depart.
Ms Cassin said the frequency was blocked for less than five minutes. This forced the Ryanair pilot to remain on the runway until he got clearance for take-off from the control tower.
Frequency blockage could be caused by something as simple as someone pressing, or forgetting to press, a button, according to the IAA. Only one person can transmit on the frequency at one time, so if the microphone is unknowingly left open, another pilot cannot access it. "It is quite unusual to see this happening but it's not unheard of, so that's why we have contingency plans in place," Ms Cassin said. Contingency plans allow pilots to establish contact on another frequency.
The IAA investigation is expected to be completed within three or four weeks.
