On the subject of external tanks. I was once, in a VC10, refuelling a pair of Jaguars from Goose Bay to Germany. After a couple of brackets we noticed that we were down on the fuel plan. This didnt particularly concern us at the time because we had a bit extra on board. However, after the third bracket (they were close together between Goose and Sondestrom) I challenged the leader to see if everything was all right. Oh, he said, No2 has been venting from an underwing since top of climb (now he tells us)! At this point we assumed the underwing fuel was unusable and re-planned to keep him within internal fuel range of the diversion. This meant almost towing him until just short of Iceland. This made a big hole in our fuel but we did manage to get him to within range of Lossiemouth before we turned back and landed at Keflavik on absolute minimums.
I have put the final episode of Operation HYDRAULIC at:
https://goo.gl/QBZHg9