Missiles of the type used in a failed attack on an Israeli plane in Kenya last week would most likely knock out one engine, but airliners would still be able to fly on the others, a military expert who headed a European country's investigation into the threat told AFP.

"The warhead on an SA-7 is around one kilogram (2.2 pounds), which is very small. The missile will always hit an engine, because they are heat-seeking.

"Worldwide regulations insist that even if an airliner's engine blows up all the parts remain within an armoured envelope, so the risk of damage to the wing or fuselage is limited," the expert, who now holds a diplomatic post, said on condition of anonymity.

Extensive tests in his home country some years ago had proved that the current alarm over the threat of a plane being downed by these weapons was exaggerated, he said.

"But at the political level no government can afford to say to its citizens 'Hey, don't worry, it's not dangerous so we're not going to do anything about it'. There would be an uproar from the population.

"I can only say that the risk of losing life seems to me very low and I would be ready to go and test it myself in the aircraft."

A retired airline captain and former air force fighter pilot told AFP he agreed to a certain extent with the military expert, but was not quite as convinced that a direct hit could not result in "catastrophic failure" of the plane's systems.

"Certainly an airliner can lose an engine and still fly. A Boeing 747 has four engines, but even those with two engines such as the smaller 737 or some of the Airbuses, would be okay.

"But there has got to be a chance that an explosion would cut through some of the hydraulic control systems in the wing or cause a fire."

Shoulder-fired missiles such as the Russian-designed SA-7 Strela used in Kenya are widely available on the black market, having spread after the collapse of the Soviet Union, at prices ranging from as little as 10,000 dollars, the European diplomat said.

The al-Qaeda network of terrorist mastermind Osama bin Laden reportedly possesses a number of SA-7s as well as US-built Stingers, which were distributed to Afghan fighters resisting Soviet occupation in the 1980s.

These portable surface-to-air missiles, also known as MANPADs, are typically specified as having a range of around five kilometres (three miles) and are effective up to an altitude of about 12,000 feet (3,500 metres).

Counter-measures vary from protecting airport perimeters to fitting airliners with military-style anti-missile technology.

An airliner, which usually cruises at an altitude of around 30,000 feet, would take about 10 minutes from take-off to climb out of danger, meaning that a terrorist could be positioned as far as 50 kilometres from an airport, the diplomat said.

To fully protect such a radius would be impossible, although flight paths or "footprints" would be smaller and easier to patrol.

Aircraft could also be fitted with missile decoy equipment, but the cost could be prohibitive.

While decoy flares themselves would cost only around 500 dollars each and installation about 100,000 dollars, missile detection equipment could cost up to a million dollars per aircraft, the diplomat said.

Israel's governmental Rafael Armament Development Authority has said that every Israeli civilian aircraft could be equipped with military-type anti-missile radar scrambling technology within months at a cost of around two million dollars per aircraft.

Robert Karniol, Asia-Pacific editor for Jane's Defence Weekly, told AFP that MANPADS have been used with varying degrees of success against civilian aircraft in civil war zones such as Angola and Sri Lanka for years.

The problem now posed by the growth of global terrorism and the increasing preference for "soft" civilian targets is whether the whole world should be considered a civil war zone.

SPACE.WIRE