Commercial jets can also fall off the map briefly when they fly at low altitudes because radar relies on line-of-sight contact. Mountains and other landforms can block the signals going to and from the closest radar stations, as can the curvature of the Earth.
As a result, low-flying jets can be tough to track continuously, especially if their transponders are disabled -- a fact that terrorists took advantage of on 9/11. [9/11 Science: 10 Ways Terrorist Attacks Rocked America]
"The first thing that many of the hijackers did [on 9/11] was turn off the transponder," McGuirk said. "Once they turned off the transponders, then they turned the aircraft back toward whatever their target was."
Someone who wanted to steal the Malaysia Airlines jet could theoretically shut off the transponder and dip down to an altitude of 5,000 feet (about 1,520 meters) or so, he added, while cautioning how far-fetched that scenario is.
"Of course, it's kind of hard to hide a 777," McGuirk said. "Wherever it lands, somebody's going to say, 'Hey! There's a Malaysia Air 777. It didn't crash at all -- it was being stolen.'"