Can a modern aircraft with a plethora of advanced features just vanish into thin air?
Hard to believe but the disappearance of Malaysia Airlines Flight 370 is a puzzle that is growing even more complex.
"This is a very unusual event," Sid McGuirk, an associate professor of air traffic management at Embry-Riddle Aeronautical University in Florida was quoted as saying.
"It is highly unusual for an aircraft at an altitude - which, at least according to the press, this aircraft was - to drop off the radar," McGuirk added.
Radar facilities are based on land and each one has a range of about 300 km.
So passenger jets on transoceanic flights do go off the radar map for a period of time but that does not mean nobody is keeping tabs on them.
"The flight crews use combinations of high-frequency (HF) radio, satellite-based voice communication and text-data networks to report to Air Traffic Controller (ATC) the exact time, position and flight level when the crossing begins," explained Emily McGee of the Flight Safety Foundation.
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, said a report in LiveScience.