The disappearance of Malaysia Airlines Flight MH370 three weeks ago has sparked discussion among aviation and security experts about the gaps that exist in airline security and what needs to be done about them.
On March 8, MH370 was en route from Kuala Lumpur to Beijing with 239 crew members and passengers on board when air traffic controllers lost contact with the Boeing 777-200ER jet about 50 minutes after take-off at 12.41am.
The authorities believe the plane's communication systems were deliberately shut down and the aircraft taken off its intended path. MH370 flew on for more than six hours after contact with air traffic control was broken.
The plane also continued to transmit electronic "pings" that were picked up by satellite provider Inmarsat. The last signal was captured at 8.11am on the same day it went missing.
By then, as we now know, the aircraft was somewhere over the vast Indian Ocean and almost out of fuel.
With no nearby landing site, the plane is presumed to have plunged into the water. A massive multinational hunt is now on for debris of the plane.
Investigations have revealed that at least two passengers on the ill-fated flight had boarded with stolen passports.
There is also speculation as to whether the captain and co-pilot, alone or in collaboration, deliberately diverted the plane with criminal intent.
The incident has prompted tighter security at many airports.
At Changi, there is closer scrutiny of passports. Selected flights - based on risk assessment - are subjected to tighter screening. This includes more thorough checks such as pat-downs for departing passengers.
Such measures will go some way to boost the airport's security, aviation security experts said.
But unless Singapore is prepared to follow the example of Israel, it is not possible to eliminate all risks, said Mr Paul Yap, who headed the aviation security team at Changi Airport before leaving in 2006 to teach at Temasek Polytechnic.
At Israeli airports, travellers turn up four hours before their flights in order to allow time for security and other checks. Families and friends are not allowed to send them off.
For the tiny Jewish state in an Arab world, security comes first. For travellers, however, the price is long queues and inconvenience.
For Changi Airport, which prides itself on its efficient operations, this is not a feasible option. "The key is to strike a balance between the need to ensure secure skies on the one hand and passenger facilitation on the other," Mr Yap said.
Airport Police commander Sam Tee said earlier this week: "Over-security or under-security is equally sinful, and we should not go to the end of each spectrum."
It boils down to risk management, he added.
To stay on top of the game, security agencies must work hand-in-hand with airport operators, airlines and other stakeholders to assess risks.