The sit in TLV, and theoretically in PHL, is why it requires two. Each A330 can serve one city in Europe by itself, since it can theoretically stay on the same round-trip forever because it all takes place in a 24-hour clock. Hence, one airplane. The TLV trip requires a 48-hour clock (which allows for the stay at the gate in TLV) for one airplane to make TLV a second time. Hence, two airplanes to serve a 48-hour cycle. For example, Monday night at 21:15, a/c A leaves for TLV arriving on Tuesday 09:15 (EDT) in TLV. A/c A sits a bit longer than 7 hours and leaves Tuesday afternoon at 16:30 (EDT) and is back on the ramp in PHL at 05:30 on Wednesday, making it available again (after a 9 hour plus sit) to leave WEDNESDAY night for TLV. Meantime, a/b B starts it's cycle on Tuesday night, and is back in PHL Thursday morning. Two aircraft, not three. What is actually does during the theoretical 9 hour sit in PHL is irrelevant to the discussion of what it takes to serve TLV. It can, and does, often do a round-trip to the islands or Mexico rather than sit for 9 hours, but that has no effect on it heading back to TLV that night.