Even the most impenetrable bureaucracies have human chinks, and when they are discovered -- even when the breach is discovered purely by accident -- it seems only fair to pass the word.

I found one such chink on a Sunday night early this summer in New York's LaGuardia Airport. The impenetrable wall presented itself in classic form: the evening's final Eastern Air Shuttle to D.C., scheduled to leave at 9 p.m., would not be able to accommodate any of those who had bought tickets for it because a Continental flight had been re-routed and had filled up the plane. Eastern is the shuttle that "guarantees" you a seat on the shuttle at the hour you sign up for, promising that if the plane is full, the airline will put on another one. An irate ticket holder reminded the Eastern representative of this. The Eastern representative said, yes, the company did guarantee that, but tonight there wasn't a backup plane available, so they wouldn't be doing it. The next flight, he said, was at 7 a.m.

Half of the 100-odd people in the line, muttering curses, started looking around for transportation back to the city. The other half, including me, mobbed the Eastern representative, screaming rather than muttering. I was traveling with my brother, who was starting a new job in Washington at crack of dawn the next morning but is essentially a calm person. Ignoring the screeches of "Guarantee, guarantee, what's a guarantee?" he found his way up to the representative and said to him, "I hear that sometimes when the plane seems to be full, it actually isn't. Last month they mislaid about 40 seats one time. Maybe you could ring the check-in desk and ask?"

The Eastern representative must have gone a long time without hearing a quiet voice. Nothing else explains why he focused briefly on my brother, nodded at him and punched some buttons on his phone. I was so surprised that I stopped screaming. The man, apparently on hold, gritted his teeth through a few more waves of complaints while we waited. Then he said to my brother, "Thirteen more seats left. Run."

We ran madly, shoving people aside, and felt like fools when we burst onto the plane. Fully a third of the seats were empty; there were no signs of imminent departure. More people must have figured out our trick, because they continued to trickle on through the next half-hour. At that point the plane finally flew out -- still with two or three empty seats.

To my amazed inquiries, my brother admitted that the same thing had happened to him the previous month on the Boston shuttle. I felt as if I'd discovered non-Euclidean geometry, something quite outside the previously accepted rules. Airline officials I later asked about the phenomenon seemed to feel the same way. Joe Scott of the Eastern Airlines corporate communications department said he'd "never heard of it -- I couldn't imagine that happening." Occasionally, he said, passengers run up to the gate just before takeoff and beg check-in officials to squeeze them on: "I've seen it happen, and it does work, but I don't know how." But on planes that have already turned away passengers? "I have no idea."

A spokesman for Pan Am, Eastern's competition on the shuttle run, which offers a similar guarantee to put on extra planes, suggested one possible explanation. James Arey of Pan Am's public affairs office says that sometimes, at peak hours when the decision has already been made to add a backup shuttle, Pan Am may fly the first plane out on time with empty seats rather than lose its takeoff and landing slots. But he says that's "rare" and would eventually backfire if it made waiting passengers more frustrated.

My guess is he's right. On the other hand, while discovering an irrational, unexplainable loophole in the tyranny of the air scheduling counter may not do much for your faith in the airlines, it can't help restoring a little of your faith in people as opposed to bureaucracy.

Amy E. Schwartz

is a member of the editorial page staff.