Perhaps the clue to their actions are defined by two simple statements -a transponder code of 7700 which will immediately give them priority handling by all ATC units as that gave them some time to consider their actions to get the best result and Manchester giving them clearance to land the way they did -points to correct use of the 7700 transponder code to get them straight into the most appropriate airfield to handle their emergency ---system worked as it should ---the why is a different question ---