Updated at 10:27 p.m. ET
Europe's air safety authority has ordered airlines to conduct new tests on the type of Rolls-Royce engine that failed in a Qantas A380 last week.
Qantas says it is extending the grounding of its superjumbo fleet to complete safety checks.
The European Aviation Safety Authority said in an "emergency airworthiness directive" posted on its website Thursday that airlines using the Trent 900 engines should conduct "repetitive inspections" on certain parts to ensure they are safe.
A Trent 900 engine on a Qantas A380 superjumboas the plane took off from Singapore. The plane made an emergency landing without any injuries.
Singapore Airlines grounded three of its A380 superjumbo jets on Wednesday after tests uncovered problems with the planes' Rolls-Royce engines - a move that comes less than a week after an engine on a Qantas A380 exploded shortly after take-off.
Tests revealed oil stains in three engines on three of the airline's A380s, Singapore Airlines said in a statement. The planes, in Melbourne, Sydney and London, will be fitted with new engines, the airline said.
On Monday, Alan Joyce, CEO of Qantas Airlines, Australia's national airline, said tests had uncovered oil leaks in the turbine area of three engines on three different A380s. All six of the Australian airline's A380s remained grounded Wednesday.
London-based Rolls-Royce, which manufactures engines for A380s by Qantas, Singapore Airlines and Germany's Lufthansa, had recommended a series of checks on the Trent 900 engines.