For an aircraft to go missing for hours on end, as the Malaysian Airlines flight did yesterday, is rare but not unheard of, even in the age of high-technology aviation.
The most notable recent case - before the mystery of Flight 370 from Kuala Lumpur to Beijing - was that of an Air France plane carrying 228 people from Brazil to France, which vanished after flying into a severe storm over the Atlantic Ocean in 2009.
The Airbus A330 sent an automatic message four hours after it left Rio de Janeiro, reporting a short circuit. It then went missing mid-ocean, beyond the scope of radar coverage. It was thought at the time to have been struck by lightning.
The wreckage was not found until two years later. A report by French authorities in 2012 blamed a lack of pilot training in unexpected situations and faulty equipment for the disaster. The autopilot was turned off and the pilots pulled up on the nose, causing the plane to lose speed, although the engines continued to work.
Other incidents involve smaller planes. Last month, 18 people were killed after a Nepal Airlines plane lost contact with ground control after taking off from the resort town of Pokhara. The wreckage was located on a hill the next day, and authorities said bad weather caused the crash.
In April 2012, a UTair plane lost contact with the control tower shortly after taking off from Tyumen, Russia. It was later found to have crashed 40 kilometres from the airport, killing 33 people on board.
In perhaps the most mysterious case of recent years, a Boeing 727-223 took off from an airport in Angola without clearance and without contacting the tower. The plane headed out over the Atlantic Ocean, never to be seen again. An American engineer and his Congolese assistant who were aboard the plane were never heard of again.
There have been numerous reports of planes and ships vanishing in the area known as the Bermuda Triangle, in the western part of the North Atlantic. While the disappearances have given the area a mysterious reputation, scientists say vessels were lost there mostly due to human error.
Technological advances have greatly reduced airline accidents in recent years. Monitoring group the Aviation Safety Network said there were just 265 fatalities in airline crashes worldwide last year, the lowest since the second world war.