LAST YEAR’S SWEET SPOT: 21 TO 22 WEEKS IN ADVANCE You may already be too late to score a cheap flight to Europe this summer. The booking window for the cheapest tickets has moved further out, from 11 or 12 weeks in advance in 2009 to 21 or 22 weeks in 2011. (Average round-trip fares rose to about $1,500 last year from $1,100 in 2009; this year’s outlook is no better.) - Alex Moskalyuk