Is air travel any safer from militant attacks, three years after a group of men tried to blow up transatlantic airliners using liquid explosives?
For many analysts the balance of risk looks little changed: While the industry has tightened security, attackers continue to innovate and transport systems remain a target of choice.
Some take a darker view, arguing a post-2006 toughening of security has been clumsy, producing longer waits at checkpoints that offer attackers a bigger on-ground target. Others complain potential security improvements have been stymied by red tape.
"Yes we are safer, because this plot brought liquid explosives to the attention of regulators and led to new regulations," said Omer Laviv of Israel's Athena GS3, which works with European firms on aviation counter-terrorism.
"But how many other plots are there that regulators may not be aware of?"
Three Britons were found guilty on Monday of plotting to kill thousands by blowing up North America-bound airliners in mid-flight suicide attacks with bombs made of liquid explosives.
The suspected al Qaeda plot, just days away from being put into operation according to British detectives, had huge worldwide ramifications leading to tight restrictions on the amount of liquids passengers could take on board aircraft.
It was a reminder that al Qaeda plots attacks not just for shock and fear but to kill large numbers of people, as it did in the September 11, 2001 suicide hijackings in which 2,992 people died.
"We are still at risk," said security and aviation analyst Chris Yates, noting there is still no widely available system installed at international airports to detect explosives in liquid form, although several technologies are in trials.
Nor is there a widely-deployed technology to routinely guard against a bomber with explosives hidden in a body cavity -- a technique al Qaeda used only last month in Saudi Arabia.
In that case, a suicide bomber on August 27 blew himself up in the Jeddah office of the kingdom's security chief, Prince Mohammed bin Nayef, a member of the Saudi royal family.
Prince Mohammed was not seriously hurt. But the attack revealed al Qaeda to be as innovative as ever: official Saudi media said the explosives were implanted in the bomber's body. Alriyadh newspaper said they were hidden in his anal cavity. Scott Stewart of intelligence company Stratfor said such a technique would likely have "a catastrophic result if employed on an aircraft, especially if it were removed from the bomber's body and placed in a strategic location on board the aircraft."
Other novelties since 2006 include so-called swarm attacks by suicide gunmen who have struck hotels and other targets in Asia using automatic rifles and hand grenades in the past 12 months including the Mumbai attacks that killed 166 people.
"Terrorists will innovate to get around airport security," says David Claridge, of Janusian security consultants, who points to a lack of common standards among aviation authorities around the world as a continuing vulnerability.
The International Air Transport Association (IATA), which represents 230 airlines, says aviation security has improved since the September 11 attacks on US targets, but its website notes lack of global standards "has created an uncoordinated mess".
Yates said measures taken since September 11 had left air passengers generally no safer. He added: "We're still vulnerable... whether it be via something taken into the passenger cabin that we can't detect at an airport or something being secreted into the cargo hold."
Security continues to impose large costs on the aviation sector, which depends on a relatively unimpeded flow of passengers and cargo to work commercially. IATA says airlines and passengers pay USD$5.9 billion in a year in security costs.
Yates said that until governments did more to fund security improvements, commercial airport operators would not invest sufficiently in new technology, he said. Getting new security hardware past barriers of red tape and into airports was sometimes an uphill struggle for manufacturers.
Philip Baum, editor of Aviation Security International, says tougher pre-flight security has produced long lines that could present tempting targets for attacks inside terminals.
Like Laviv, Baum is an advocate of profiling, referring to the practice of analysing the behaviour of passengers before flights to watch for signs of malicious intent, and criticises the aviation security community for being overly reactive.
David Learmount, safety and operations editor of British-based aerospace magazine Flight International, said there were limits to what the industry could do.
"We could have perfect, proactive security," he said. "Heathrow for example could be like a military base in wartime."
"But if you bring in procedures without evidence showing it is necessary, it is something society won't take, and we would completely destroy our own freedom. We don't want to live like that, and we would choke global travel almost to death."