So how much do these things weigh?

A 747's maximum certified takeoff weight is in excess of 800,000 pounds, and the new Airbus A380 will break the million mark. A fully packed 757 might be 255,000 pounds, while a 50-passenger regional turboprop will top out around 50,000.

There are weight limits for the different operational regimes, including ones for sitting at the gate, taxiing, taking off and landing. But the constraining factor for a specific takeoff or landing, remember, is not necessarily the structural restriction of the plane. Runway length, temperature, wind, barometric pressure, etc., can all influence payload.

As most people know, smaller airports with smaller runways are generally served by smaller planes. But this is more a function of practicality than size, strictly speaking. While you'll never see a 747 at La Guardia, that's not to imply one couldn't fly there. Rather, its payload would be so restricted by, to put it one way, the proximity of Flushing Bay as to render it economically unfeasible.

Because fuel loads are such a large percentage of overall weight, pilots rarely think of fuel in terms of gallons but almost always as pounds. (Some quick metrics, just so you know: It's about 6.7 pounds to the gallon. One kilo is 2.2 pounds and a gallon equates to 3.78 liters.) Everything from initial fueling to enroute burn is measured by weight, not volume. A fuel load of, say, 200,000 pounds may be a third or more of a wide-body airplane's sum heft.

Before boarding, we were told our flight was weight restricted because of a malfunctioning system. Is it the crew's decision to take off when something important is not working?

Airplanes can depart with various inoperative components -- usually noncritical equipment carried in duplicate or triplicate -- depending on guidelines laid out in something called the MEL (minimum equipment list) or CDL (configuration deviation list). Any component listed in either of those books is "deferrable," as we call it, so long as the outlined conditions are met. These conditions can be quite restrictive and complicated, depending on what's broken. Many things, of course, are not deferrable at all, and any malfunctioning item must be repaired within a set number of days or flight hours. Before any flight is dispatched with a deferral, it must be documented and coordinated between the crew and maintenance personnel.

Above and beyond the deferral process, no respectable airline will pressure a crew to operate any flight. The final call, if you will, is the captain's, regardless of what the MEL or CDL allows.

What are pilots looking for when they walk around the plane prior to departure? Watching this procedure from the terminal, it doesn't seem a very in-depth inspection.

Money, usually. Loose change, jewelry, that kind of thing. Or reading graffiti that the workers sometimes leave on the grimier panels ("Vote No" is a common one around contract time).

Actually, the walk-around inspection is a supplemental, for-the-record sort of thing done in addition to the more serious checks performed at various intervals by the maintenance staff. It's essentially a superficial perusal and not a whole lot different from checking your oil, tires and wipers before a road trip.

Much of the more technical preflight routine takes place out of view in the cockpit, where systems are put through tests before departure. Mechanics and pilots each have their own procedures to run through, before and after every flight.

Do you have questions for Salon's aviation expert? Send them to AskThePilot and look for answers in a future column.

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