There was a transatlantic flight between the New York (JFK) and London (Heathrow) with BA. Before the take off in JFK our B777 had a brakedown. Then all people in the plane sat in the plane without air conditioning for 3 hours (temperature in the plane was about 35 degrees of celcius). About 2 hour BA's mechanics searched for the detail, which is out of service and then replaced it. We will take off with 3 hours delay.