Richardgb,
Yes, whilst direction is unknown, it is suggested that the data does have a time stamp allowing the distance to be calculated from emission to reception. The arcs probably designate quite narrow corridors. Logically, arcs can be drawn for all the pings. A calculation of the probable maximum distance that the plane could have flown from the last point recorded should intersect the arc. Likewise, similar plots for the other pings should indicate if the plane was indeed fling approximately straight. This should be more obvious for the southern arcs but should also be possible for the northen.