As backpacks go, you probably wouldn't want to head off into the backcountry of a national park with Tom Bihn's Aeronaut on your back. But it sure is a handy bag to use to get to the park.

That's because the Aeronaut (MSRP $220) is a traveling bag, a piece of soft luggage designed and intended to make getting to your destination a tad easier. It does so both through its size -- measuring 22" x 14" x 9", it's perfectly suited to slip into the overhead compartment of an airliner -- and its functions -- there are three ways to carry this bag, including a strap system that allows you to carry it like a backpack, and has plenty of pockets for divvying up your stuff.

And these days, when it seems airlines are trying to nickle-and-dime their customers as they travel to their destinations, not having to check baggage can save you enough money for a lunch or even dinner, depending on how many bags you carry.

Now, I must admit that when I first looked at the Aeronaut it appeared to be too small and too compartmentalized to suit my needs or tastes. I've long used a voluminous duffel bag for travels, and my backpack is a top-loader. Why would I want a piece of luggage with three well-defined compartments that in turn can swallow a variety of "Packing Cubes," as this Seattle-based manufacturer dubs them?

Obviously, I didn't realize the structure that was lacking from my life.

When I started packing for my recent trip to Saguaro National Park, I quickly came to appreciate this 2,700-cubic-inch bag. For starters, I could slip a pair of size 11 lightweight hiking shoes into one of the end compartments. By putting the shoes into a Packing Cube designed for the pocket, I could contain any dust or dirt inside the washable cube, not inside the end compartment. The other end pocket was big enough for underwear and socks for the five-day trek, while the main compartment gobbled up a pair of hiking pants, seven shirts, and toiletries. And there was some room left over, too, to handle at least another pair of pants or rain gear if need be.

By utilizing the main compartment's 13.5" x 13.5" x 4.25" mesh Packing Cube (cubes also come in a 200-denier ripstop nylon fabric), I was able to keep my clothes neatly folded, and upon taking the cube out of the compartment I could quickly see which shirt I wanted.

Since I've had a habit, from time to time, of over-packing for trips, the Aeronaut's size forced me to be economical from the outset. But not only was I surprised to see that I had plenty of clothes to get me through my trip, but there even was enough space inside the main compartment to put my laptop -- in its own carrying case -- which enabled me to, in effect, take three carry-ons on the plane -- the Aeronaut, my laptop inside it, and a daypack that I slipped beneath the seat.

There are a few other handy features to this bag: On either end of the bag you'll find two more external pockets. One is zippered and handy to hold your airline ticket, trail maps, MP3 player, small camera, or small paperback guidebook, and the other open-ended and which can quickly and easily accommodate a newspaper or magazine or both. These exterior pockets also have a single strap running across them, making it easy to pull the bag out of the overhead compartment.

And thanks to the variety of Packing Cubes you can acquire, there are a variety of ways to pack. You can stack two or more of the large mesh Packing Cubes in the main compartment, or use a series of the 13.5" x 8" x 3.25" or perhaps the 13.5" x 6.75" x 4.25" Packing Cubes to break down your contents even more specifically and stash them in the main compartment. Or use a mix of the large and smaller Packing Cubes.

And while the Aeronaut certainly classifies as "soft" luggage, its 1,050 denier ballistic nylon exterior is said to be more durable than Cordura and will long stand up to any airline's baggage handlers if you for some odd reason decided to check this piece.

If you need more room, you can either add another Aeronaut, as it will slip under the seat in front of you, or consider Tom Bihn's Synapse backpack (MSRP $120), which offers another 1,160 cubic inches of space and can be slipped under the seat in front of you on your flight. This pack, while not designed as beefy as many of the daypacks available today, comes with one large main compartment and five outside pockets that can hold an array of gear, notebooks, sunglasses, water bottles, or whatever. While it's probably more functional on a college campus or going across town, the Synapse could get you by on most day hikes in a park.

Pros: -- You can carry the Aeronaut like a traditional suitcase, with a shoulder strap, or with back straps that conveniently disappear into a compartment when not in use. Inside the lid of the main compartment is a zippered mesh pocket for those odds and ends that have a sneaky way of getting lost. Durable. This bag will give you years of service. American-made. For more than two decades Tom Bihn has been making his name-branded luggage in Seattle.

Cons: I found the pulls on the 10 YKK zippers a bit too small to quickly grab. No doubt with more use I'll adapt, but a longer pull would be handy. The $3 cost for a pack of cord zipper pulls would be well worth it. Accessories such as the shoulder strap (MSRP $30) and the Packing Cubes (MSRP $15-$18 apiece) can quickly add another $100 or more to the cost of this bag. Of course, there's no need to buy the Packing Cubes if you don't want them, and it's quite likely that another shoulder strap from one of your existing bags will fit the Aeronaut,.