Qantas Airways and several other airlines altered their flight paths some time ago to avoid Ukrainian air space after fighting flared up in the region, raising questions about why others did not do the same.
The issue of whether to avoid flying over conflict zones has come into sharp focus after the downing of Malaysian Airlines Flight MH17 on Thursday, killing all 298 people on board.
International civil aviation regulators had imposed no restrictions on crossing an area where pro-Russian rebels are fighting Ukrainian forces, and the majority of carriers had continued to use a route popular with long-distance flights from Europe to southeast Asia.
But the fact that a handful of companies decided to circumnavigate the disputed territory underlined inconsistencies in airlines' approach to passenger safety.
Aviation experts said piecemeal and potentially conflicting advice from aviation regulators further confused the situation, and called for clearer guidance on which areas to avoid.
In addition to Qantas, Air Berlin, Asiana Airlines, Korean Air Lines and Taiwan's China Airlines decided to avoid Ukrainian airspace several months ago.
Cathay Pacific Airways changed its routes some time ago, but did not specify when, and a source familiar with the situation said British Airways had also been avoiding the area where the flight went down.
"Although the detour adds to flight time and cost, we have been making the detour for safety," said a spokeswoman for Asiana, which has been diverting its once-weekly cargo flight some 150 km (93 miles) below Ukrainian airspace since March 3.
The European Aviation Safety Agency did issue a safety bulletin, accompanied by recommendations from both the U.N.'s International Civil Aviation Organization (ICAO) and Brussels-based Eurocontrol, on April 3, advising that Crimean airspace should be avoided. Russia annexed Crimea from Ukraine in March.
But those directives did not apply to the airspace over Ukraine being traversed by Flight MH17 when it was brought down.
It was not immediately possible to verify which airlines had adopted which routes.
Flight paths and altitude vary according to factors such as weather, the amount of traffic on busy corridors and flight restrictions. Flying higher helps burn less fuel, but pilots do not always get to the altitude requested when airways are busy.
No undue risk
Malaysian Transport Minister Liow Tiong Lai said on Friday the national airline took no undue risk in flying over Ukraine, a route he stressed was approved by the ICAO and widely used by other airlines.
"We've flown this route for many years, it's safe and that's the reason why we are taking this route," Liow told a news conference where reporters repeatedly questioned why the airline chose to fly over a conflict zone.