Editor's note: Don Phillips has been covering airlines and air safety for more than 25 years. So when we wanted to chronicle the state of coach-class air travel, we sent Don crisscrossing the country on 18 different flights and told him to record his impressions. Today's multi-part package bears the fruit of that labor.

Don squished himself into small seats, withstood the long lines and satisfied his mid-trip hunger with tiny bags of snack mix and cans of soda. But his 18-flight mission cost The Post only $2,185, an average of $121 a flight--not a bad rate for traveling about 12,000 miles.

Before I begin, I have a confession. I love to fly. It's not only part of my job but an avocation. I always try to get a window seat ahead of the wing, so I can help the pilot fly. But that doesn't mean I'll put up with grumpy service, interminable lines or misleading excuses, all of which can stand between me and my coveted uncluttered window seat.

When I got back from my 18-flight odyssey, my editors asked me to rate my experience on each leg of the trip. Judging an airline by one or two flights is misleading, I protested. For instance, I took three Southwest flights, and each was totally different. One would have convinced me that Southwest is a terrible airline, the other would have convinced me that Southwest is the best airline in the country, and the third would have convinced me that Southwest is an airline designed exclusively for business travelers.

Northwest, if we listen to what "people say," might be considered a bad airline. Some people even call it "Northworst." But my two Northwest flights were great--on time, with friendly and informative crews.

Within those bounds, I will say that the trip changed my mind about several airlines. I had long ago started avoiding Continental and Trans World Airlines, based on some bad experiences. But after this trip, I can say they were pleasant surprises. I won't avoid them again.

United, which I fly more than any other airline because of its large hub at Dulles, remains a mixed bag for me. I have a love-hate relationship with United. As on this trip, some United flights can be marvelous, but the jackboot side of United's personality can roar through. It is no accident that United invented the bag-sizing template for the security scanners--the ones through which most garment bags and other irregularly sized carry-ons won't fit. It is a typical United attitude: We have decided, and you will do as we say. No exceptions. A mass of protests has persuaded United to modify its policy somewhat.

But I know a lot about United's pilot training, and I instinctively rest easy when I settle into my United seat.

Southwest, oddly, is United's cousin in the jackboot category. Southwest people are friendly, even bubbly. But they have rules, too, and they also have a no-exceptions attitude. Just try to get both a camera bag and a computer bag aboard if a full Southwest flight limits carry-ons to one piece. The fact that each is valuable and should never be checked makes absolutely no difference to smiling, happy Southwest people. It can be maddening.

American, Delta and US Airways sit on a middle ground, in my estimation. I have no strong feelings one way or the other.

But the real problem with almost all airlines, except Southwest, is that over the past decade they forgot who they were serving. In a rush to cut costs, airline executives convinced themselves that coach passengers really wanted little more than low fares.

These executives talked about "service" as if they thought they were actually giving service. What they are doing is operating crowded subway cars with wings, pushing patrons as far as they can be pushed with small seats, dwindling food, confusing fare rules, and unbelievably crowded and unfriendly terminals.

Some executives, including one chief executive, have told me privately that they are beginning to understand they let the pendulum swing too far. And the "passenger bill of rights" movement was their wake-up call.

What amazed me is the ability of passengers to adapt and cope, sometimes with relative good cheer, as long as nothing goes wrong.

CAPTION: To a sleep- and space-deprived frequent flier, a flight can start to look like a surreal nightmare.