Tube trains to Heathrow were disrupted over the weekend after a tube door slid open between stations.
No-one was hurt in the incident which happened on the Piccadilly Line of the London Underground on Saturday as the train approached Heathrow Terminal 4 station.
Passengers en route to Heathrow were affected all weekend by the incident, with trains being inspected by Transport for London (TfL) and some union members refusing to operate some trains.
On Sunday, TfL said on its live update that there were still delays and advised passengers to start their journey early.
It said it had carried out checks which showed it was an ‘isolated incident’.
Pat Hansberry, London Underground operations director, told the BBC: "Following an isolated problem with one train door we carried out a full inspection to confirm there wasn’t a wider problem, which resulted in some cancellations."
A spokesman for the RMT union said: "There are serious questions over the safety of the ageing fleet on the Piccadilly Line in terms of braking systems, wheel flats and brake operation that RMT has been raising for well over a year now."
