Last week, I told you about the latest attempted airfare hike on the part of U.S. airlines; this was a hike initiated by United/Continental.

And for those keeping score, it was the 12^th airfare hike attempt of the year; for comparison purposes, in all of 2010, there were just three hikes total (and see my chart below for the 2011 data).

This latest attempt didn’t last long. On Friday, there was some matching activity with American, Delta and US Airways joining in on this $6 to $10 roundtrip hike, but things quickly went south – and by Sunday evening, all these legacy carriers rolled back. No hike.

What happened? Well, for one thing, none of the low cost carriers jumped in (though they have, from time to time, initiated some hikes).

Bottom line:  For 2011 hike attempts, the airlines’ batting average is .583.

We’re keeping a close eye out for any future attempts, and I know we’ll see more. In the meantime, here’s my chart on all the attempts so far this year,  and the respecitive success/failure rates.

UPDATE (4-20): The hike sticks; chalk up another airfare hike in the “success” category.

UPDATE (4-19-11): Late last night, American Airlines and JetBlue matched the $10 roundtrip hike, and today they were joined by United/Continental. Alaska Airlines has matched on part of its route system. Still on the sidelines: Southwest, AirTran and US Airways.

EARLIER:

This morning (4-18-11), Delta Air Lines launched a new $10 roundtrip domestic airfare hike across the bulk of its U.S. route system.

This is the 11th attempted domestic hike this year; the first six “stuck” meaning they were successful, but the most recent four collapsed after initial matching by legacy airlines (please see my “hike timeline” below).

That’s not all: last week, legacy airlines modified a slew of summer departures on domestic routes with a $20 roundtrip hike for travel between June 9 and August 21. Moreover, some legacy airlines are tinkering with their peak summer travel surcharges to maintain competitive equilibrium.

What this means is that the airline that first raises prices must get competitors to match (and relatively quickly) or that first airline risks winding up on page five of results on airline ticket price comparison sites – as Delta did after it raised prices earlier today – which effectively puts it “out of sight, out of mind” for many online shoppers. And this adds up, since ticket search sites garner millions of searches a day.

When airlines on are the wrong side of this competitive equilibrium, it is akin to being temporarily pulled from comparison sites (or pulling out of them by choice) – not unlike what we’ve seen with that ongoing situation between American Airlines and Orbitz