But a New York court case on Wednesday has shown it is easier than you may think.

An American sting operation has highlighted how easily people can obtain cheap, shoulder-mounted missiles and the vulnerability of airliners to attack.

At the same time, British Airways has cancelled flights to Saudi Arabia on grounds of "increased security risks in the region". 

Air attack is a subject no one in the aviation industry wants to talk about because it could scare off passengers and there is little that can be done.

Mombasa attack

"Airliners come into Heathrow (airport) on a leisurely, gentle descent...they cannot fly like a fighter jet and escape the lock-on of a missile"

Andrew Brookes,
Aerospace analyst

The danger was dramatically highlighted last November when two missiles narrowly missed an Israeli charter plane taking off from Kenya's seaside resort of Mombasa.

However, costs and other factors make a quick fix unlikely. 

"This thing is one of the great kept secrets that people don't want to talk about, especially with airlines having the (financial) problems they have," said aerospace analyst Andrew Brookes.

"Once you're in a sedate climb or descent, you're into an extremely vulnerable situation.

"Airliners come into Heathrow (airport) on a leisurely, gentle descent...they cannot fly like a fighter jet and escape the lock-on of a missile.

"Any military man trained in these should have no problem in shooting one down."

Russian missiles

Russian SAM shoulder-mounted missiles can be bought for less than $1000 and their portable size makes them easy to hide.

With a range of 5km, anybody could target planes landing or taking off from well beyond airport perimeters.

But cost remains the biggest impediment to effective preventative action.

Francis Tusa, editor of the London-based Defence Analysis, said: "The cost of making airliners safe is prohibitive and the problem has been thrust into the spotlight at a time when the industry is still struggling to recover from the September 11 attacks.

"It could cost $10 billion for US airlines to equip (with safety measures) the 6000 or so planes they have flying. There is no way they could afford that." 

And analysts say airlines do not feel the risk is great enough to act.

"For airlines there's still a cost-benefit equation and getting shot down by a missile remains improbable," said one industry official.