From the removal of steel cutlery on aircraft to increased check-in times, most airlines - and airport authorities - around the world have found themselves grappling with new ways to combat terrorism.
Here is a sample of international reactions to the heightened alert:
Australia: a senior Australian airline safety executive believes that there is a fundamental weakness in the training and motivation of security staff provided by airline contractors - especially those from military or police backgrounds. Their objective, he says, is to apprehend security transgressors rather than providing total security for passengers. Such an approach "is more likely to promote a reactive than an active security environment". He also warns against slavish adherence to rules on minority rights when carrying out passenger profiling to select those who should be subject to additional checks. France: all hold baggage is subject to examination for explosive devices using the explosive detector system (EDS), and freight, post and parcels are also subject to extra scrutiny. The automatic baggage/passenger reconciliation system (SRB) in place at Charles de Gaulle Airport will be extended to Bordeaux, Lyon, Marseille, Nice, Orly and Toulouse. Air France is to place martial arts-trained agents on board flights identified by the intelligence services as being high-risk. They will ensure cockpit access is strictly supervised and intruders "neutralised". Meanwhile the airline itself has acquired 11 extra EDS machines, and a further eight have come from France's civil aviation authority (DGAC). Hong Kong: Hong Kong's International Airport Authority has redoubled efforts to weed out unsuitable applicants for airside passes by carrying out rigorous checks. Japan: Japan Airlines (JAL) says it introduced "a number of specific measures right after the attack", but most of these were to meet the US authorities' requirements for flights to the USA. The measures include thorough inspections of aircraft prior to boarding. Visits to the flight deckwere banned 18 months ago after a passenger entered the cockpit of an All Nippon Airways (ANA) Boeing747-400 and fatally stabbed the captain. Since then, JAL has required cockpit doors to be locked during flight. The ANA attacker exploited a security loophole at Tokyo's Haneda domestic airport by collecting checked baggage containing a knife at the arrivals hall, and then boarding another flight carrying the same bag as hand luggage without having to pass through additional security checks. This loophole, which is unique to Haneda, has subsequently been closed. Singapore: Singapore Airlines has banned occupancy of cockpit jump seats by anyone other than operating flight crew, and has increased its check-in time from two to three hours before the scheduled departure time.Source: Flight International