A technical fix to ensure other civilian airliners aren't shot down

The awful crash of Malaysian Flight 17 in the Ukraine combat zone seems likely to have been caused by a long-range surface-to-air missile. At this writing, who launched the missile remains undetermined. Regardless of who's guilty - why is a modern software-driven weapon capable of striking a civilian jet in the first place?

All commercial airliners send out transponder signals that identify them as civilian. In most cases, what's employed is a protocol called Mode C, which is not used by military aircraft.

Modern radar-guided long-range anti-aircraft missiles - like the one apparently used to shoot down Malaysian Flight 17, like the one the United States cruiser Vincennes used in 1988 accidentally to shoot down Iran Air Flight 655, killing 290 civilians - don't pay any attention to what mode a target's transponder is in. They lock onto a radar image chosen by the gunner, then once launched relentlessly seek to hit.

That's the old way of designing long-range anti-aircraft missiles. Now that software and improved chips give weapons lots of processing power, there's no reason anti-aircraft missiles could not be programmed never to lock on to, or try to hit, targets broadcasting a civilian identification code. An international agreement could require this of all nations that make or field long-range SAMs.

Of course, verification would be a challenge. But verification of nuclear arms reduction agreements has gone reasonably well, as has verification of multilateral agreements on chemical arms and land mines. There aren't many nations that manufacture or field long-range advanced SAMs. To get all to agree on programming anti-aircraft missiles so they refuse to strike civilian aircraft is a doable objective.

Cheating would be a worry. But the world's militaries have been reasonably good at not shooting at vehicles and ships marked with the red cross or red crescent. And cases of putting those symbols on fighting vehicles or ships have been rare. It would be impossible to guarantee that a military - or a quasi-military such as the Russian separatists in Ukraine - would not try to cheat by broadcasting a civilian code from a military aircraft. But this would only work once.

The weapons officer of the Vincennes saw a radar blip headed straight toward his ship, and made a horrible mistake. Whoever launched the missile that likely destroyed Malaysia Flight 17 would have seen a radar blip headed straight toward him. Today's long-range anti-aircraft missiles are not programmed to know what they are flying toward, only to seek the blip chosen by the gunner.

This needs to change. Improved electronics could make it practical to program long-range anti-aircraft missiles to refuse to attack aircraft broadcasting on a civilian transponder mode. As ever-more civilian aircraft take to the world's skies, the need to protect them increases daily.

Manufacturers boast of making "smart weapons." Someday there might be precision-guided munitions that refuse to lock on to hospitals or refugee centers - GPS locations of such places could be loaded into the bombs' software. A smart tank that refuses to fire toward a school can be imagined technologically.

For today, the first step should be an international agreement to engineer anti-aircraft missiles so they will not track or seek targets broadcasting in civilian mode. Much of the aviation world is moving to a new. data-rich broadcasting standard called ADS-B. Long-range weapons need to be "taught" that standard too.

In the era of beyond-visual-range missiles, numerous civilian jetliners have been shot down by mistake. The United States and Russian Federation should join to forge an international initiative to prevent this from happening again.

© (c) Copyright Thomson Reuters 2014.