Aviation regulators—including the FAA—had issued a series of notices to pilots in recent weeks prohibiting air space very close to the crash site.
"This was a very commonly used route and passenger jets fly at high altitudes over many of the world's hotspots all the time," said Norman Shanks, professor of aviation security at Britain's Coventry University. "They chose the most direct and economic flight route possible, which keeps their fuel costs down and is something we expect as customers. They were no different from any other international airline."
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MH17 was flying at 33,000 feet when disaster struck—well above the trajectory of missiles commonly used by militias in ground conflict, and high enough that its routing was approved by the airline's flight planners, air traffic controllers and ultimately the pilots.
However, with pro-Russia separatists apparently in possession of surface-to-air missile, airlines might have to be more vigilant about avoiding trouble spots.
"This incident is unprecedented really," Greg Waldron, Asia managing editor Flight Global told the BBC. "A lot of the weapons used by separatists and other guerrilla groups simply don't have the range to get [to 33,000 feet], they don't have the accuracy to hit something like an airliner."
Why was MH17 over a conflict zone?
Flight plans are drawn up by airlines and pilots and submitted to air traffic controllers for approval. Ultimately, pilots fly the agreed routing—unless they receive or request adjustments from air traffic controllers while en route.
MH17's exact flight plan—a routing defined by a series of waypoints and air corridors—has not been confirmed but appears to have included airway L980, a busy section of air space that acted as an airborne freeway between northern Europe and southern Asia.