A piece of wreckage of the Malaysia Airlines flight MH17 is pictured on July 18, 2014 in Shaktarsk, the day after it crashed. Flight MH17 from Amsterdam to Kuala Lumpur, which US officials believe was hit by a surface-to-air missile over Ukraine, killing all 298 people on board. AFP PHOTO / DOMINIQUE FAGET (Photo credit should read DOMINIQUE FAGET/AFP/Getty Images)

A Boeing 777 flying from Amsterdam to Kuala Lumpur was apparently shot down by a surface-to-air missile over eastern Ukraine on Thursday morning.

I'll start with my normal disclaimer: It is a bad idea to speculate too broadly on the how-and-why so soon after a serious air disaster. Almost always the earliest theories turn out to be either totally off-base or at best incomplete. The media would be wise to exercise as much restraint as possible. We live in an age when people want and expect instant answers, but that just isn't possible when it comes to things like this. There are too many variables, too many people and parts involved: airplane, crew, air traffic control, government and military entities. What exactly happened to flight MH17 is liable to be complex, and possibly a combination of errors involving different parties.

It is fairly routine for civilian jetliners to overfly areas of conflict. Dozens of airline flights pass each day over Baghdad, for example (many of them land there). I have personally piloted flights over eastern Ukraine, close to where the Malaysia Airlines 777 met its fate on Thursday.

There are protocols, as you'd think. Flights are sometimes restricted to particular routes, specific altitudes and airspace sectors. Large chunks of airspace are often totally off limits. Over certain countries -- Afghanistan, for instance -- commercial overflights might be prohibited outright. Compliance with these restrictions is important, but they are not difficult to follow. Thousands of flights deal with them every day. Crews don't simply wander unknowingly into dangerous airspace. On the ground, air traffic controllers are fully aware of who will be passing over, and when.

The FAA had already taken the unusual step of prohibiting U.S.-registered jets from the area the Malaysia flight was traversing. Whether this was due to safety concerns or bureaucratic concerns isn't clear. In any case the airspace was open, and was being used routinely by European and Asian airlines.

This is not the first time a civilian jetliner has been shot down -- accidentally or otherwise. There have been several such incidents over the years. Most notoriously, at least until now, was the Soviet destruction of Korean Air Lines flight 007 in 1983 -- a Boeing 747 flying from New York to Seoul that strayed off course -- and the accidental downing of an Iran Air Airbus A300 by the U.S. Navy cruiser Vincennes in 1988.

Ironically and tragically, the 295 reported fatalities from Flight 17 make it the seventh deadliest disaster in aviation history -- the same spot of infamy held previously by the Vincennes incident. The KAL 007 disaster was, until today, the tenth worst, meaning that three of history's eleven worst crashes were planes brought down by missiles.

That doesn't mean we should expect or accept such things, but sadly they are not unheard of.

And what a double-dose of agonizing luck, meanwhile, for Malaysia Airlines. One of the world's most highly regarded carriers has lost two Boeing 777s in less than a year's span, with neither accident likely being its fault.

Patrick Smith is an active airline pilot, air travel blogger and author. His latest book is Cockpit Confidential: Everything You Need to Know About Air Travel: Questions, Answers, and Reflections. This post first appeared on his blog, www.askthepilot.com.