What’s in a load factor? Yes, planes really are full these days.

Despite the recession and tough times for airlines in general, many of my clients complain that the planes seem a lot fuller. And as U.S. airlines begin to release results for July, load factors really stands out … it’s not their imagination. There may be fewer flights, but they are packed to the gills.

Continental Airlines and United Airlines, in fact, reported domestic load factors of over 90 percent. US Airways was over 86 percent, and AirTran was at 88 percent.

And while these numbers sound high, 90 percent still means maybe a dozen seats left on each plane. In theory. But load factors refer to paying passengers, and passengers on frequent flier awards. It does not refer to airline employees commuting to work, or traveling standby on free tickets.

And yes, many airline employees do actually commute to their jobs on their own airlines. It’s called “deadheading.” And while they, unlike paying passengers, can sometimes sit in a “jump-seat” in the plane’s galleys or cockpit, they will fill a regular seat if it’s available.

Plus, while some employees have told me they are giving up and buying seats on flights when it is critical they get somewhere, many still try to stand-by, especially on casual visit to friends or relatives.

In fact, on a recent trip when I was trying to standby on an earlier flight home on a paid ticket, I talked to a nice United employee who was also on the wait-list. He had a couple days off. and said was hanging out at the airport, in hopes of visiting his daughter and grandson for an evening. And he said, sometimes it worked, sometimes it didn’t, but he didn’t live far from the airport anyway.

The point of all this is that even when an airline shows “only” about a 90 percent load factor, those empty seats are often going to be full. Coupled with the new charges for checked luggage, that also means every overhead bin and underseat storage area in sight.

And of course, the rare flight that isn’t completely jammed is likely to be one of those 6 a.m. options on a Tuesday. Maybe.