Outside the Box

By Gerard Holzmann

When EgyptAir Flight 990 plunged into the Atlantic Ocean on October 31, 1999, the National Transportation Safety Board (NTSB) quickly sent the Navy salvage ship USS Grapple to the scene to recover the plane's two cockpit recorders from the icy depths. Standard equipment on every aircraft, such "black boxes" (they're actually bright orange) serve a dual function: one records the pilots' comments, and the other stores data about the plane's engines, control surfaces, and position. Together they can provide precise information--to the thousandth of second--on the fate of a plane that's disappeared from the radar screens of air-traffic controllers.

You might think that devices for such a purpose are uniquely modern. But the history books tell us otherwise.

About 4,350 years ago, when King Sargon of Akkad unified lower Mesopotamia under his rule, there definitely were no airplanes to worry about. That doesn't mean, however, that people didn't travel. They sailed over large expanses of water in ships, and could conquer almost any distance on land on horseback. The rulers of those days used messengers, whom they dispatched via both modes of transportation, to stay in touch with their peers in other countries. Now what, you might ask, do the royal messengers of ancient kingdoms have to do with the pilots of contemporary air travel? Well, like today's pilots, they traveled very far in short amounts of time (relatively speaking), and they often transported costly goods. After all, for royal couriers to be taken seriously by foreign monarchs, they had carry expensive gifts.

Unfortunately, not only the foreign monarchs knew about the messengers' bounty; robbers, too, knew of its presence. Which meant that the messengers had yet another thing in common with modern pilots: they would occasionally disappear from sight and leave few clues about the cause of their disappearance.

King Sargon is credited with inventing a clever solution to the problem. In addition to the precious gifts, he gave every messenger a sort of black box to carry. The device contained not an electronic recorder but a living one: a homing pigeon. If a messenger was attacked en route, or in any other way saw his mission imperiled, he simply released the pigeon. (It was quite well known at the time that homing pigeons can flawlessly return to their nests, regardless of where they were set free.) The arrival of the pigeon at the palace indicated that the messenger was in trouble. That would prompt the king both to send help and to dispatch a new messenger on the same mission via another route.

We can speculate that the "lost" messenger might have given detailed clues about the nature of his troubles in a note that he'd attach to the pigeon's leg. Early forms of cuneiform writing (an alphabet comprising wedge-shaped characters) were already in use, and happily for the pigeons, papyrus as an alternative to clay tablets had come into vogue. Still, deciphering the hastily written notes back at the palace would have been a laborious task that could be performed only by literary experts.

Sound familiar? Consider the sight of the NTSB experts, huddled last November around EgyptAir Flight 990's dented black box after it was fished from the sea, as they struggled to interpret the crews' cyptic last words.

Gerard J. Holzmann ([email protected]) does research in computer science at Bell Laboratories in Murray Hill, New Jersey.