A helicopter pilot nearly collided with an aircraft when she took off from the wrong runway, an inquiry has found.
The AS350 helicopter and C152 plane crossed about 200ft (60m) apart in Wycombe airspace on 19 January.
The helicopter pilot left the wrong runway at Denham, Buckinghamshire, and started flying south of her planned route.
That put her directly in the path of the light aircraft, an Airprox Board said.
The risk was classed as Category A, the most serious, meaning there was a high risk of collision given that the helicopter pilot "had not seen the other aircraft at all".
"Chance had played a major part" in the near-miss, the report said.
The aircraft pilot was told by Wycombe tower that a helicopter was crossing from south to north in front of it, but the plane's instructor did not take evasive action as they only spotted it at the closest point of approach.
The helicopter pilot was "probably rattled by her earlier mistake", one which she apologised for and was told she was not the first to have made that error, the board found.
"She was shaken by the event," the report said, and it "may have been wiser to land again at Denham, compose herself and then start the flight again".
The report concluded the incident "should serve as a reminder to all pilots to ensure that they were in the correct frame of mind to conduct their flight".