Since the original survey by Powell, the requirement for aircraft over the Atlantic to maintain their flight-planned or recleared track has been established. The following figures covering flights made by Trans-Canada Air Lines between Canada and the U.K. during the period 8 November 1956 to 16 March 1957 are intended to provide evidence as to the accuracy of estimates necessary in recent calculations appearing in the Journal. Indications of the accuracy of navigators' found winds and of mid-Atlantic position lines are included.