FIVE Cathay Pacific jets have had to shut engines in flight during the past six weeks, forcing them to return to Hong Kong or divert elsewhere. Four of the shut-downs occurred within the past two weeks, and all five were on Boeing 747 jumbo jets. One was caused by birds getting sucked into the engine. The incidents have caused concern among some pilots who said the number was unusually high. One Cathay 747 pilot said that while the loss of one engine posed few problems, the loss of a second would be considered an ''emergency situation''. Cathay Pacific and engine manufacturer Rolls-Royce initially acknowledged only four of the incidents, on July 3, August 3, August 4 and August 7. Cathay later confirmed the fifth on August 11. The airline's engineering director Roland Fairfield said even the four shut-downs of which he was aware was an unusually high number over the period. Geoff Landamore, regional executive of Rolls-Royce International, initially said he knew of only one shut-down, but later said he knew of four since July 3. When told there were five, he said: ''I'm amazed. The RB211 is one of the most reliable engines in the world.'' Rolls-Royce boast that an RB211, the family of engines on all of Cathay's fleet, would only expect to have to be shut down every 50,000 flying hours - about once every 10 years. ''That means a four-engined 747 would suffer a shut down about once every 21/2 years.'' Mr Landamore said the resident Rolls-Royce engineers were helping engineers at the Hong Kong Aircraft Engineering Company (HAECO) strip down one of the engines concerned to investigate the cause of the problem. He said he believed two other engines were waiting to be examined. One shut-down was caused by a bird strike on takeoff from Kai Tak, but the cause of the others, resulting in either vibrations, overheating or air surges, is being investigated. A spokesman for Boeing said the company in Seattle was aware of the incidents but was not drawing any conclusions. ''[Some of the engines] have been shipped back to HAECO and are being investigated,'' he said. Cathay spokesman Phil Burfurd said all the incidents were minor and there was nothing to suggest a pattern. ''Engine shut-downs happen from time to time and it could be that these have all happened close to each other,'' he said. ''We have got one of the most reliable engine operators in the world and this does not cast any doubts whatsoever on our operation.'' HAECO engineering director Keith Law would not comment on the investigations. ''It is quite normal for engines to get shut down because of a problem,'' he said. Cathay has a total fleet of 55 aircraft, all 747s or Lockheed TriStars. All can fly safely with the loss of one engine. Aircraft fly to the nearest airport where a spare engine can be picked up when a shut-down occurs. All Hong Kong registered airlines are obligated to send a mandatory occurrence report to the Civil Aviation Department (CAD) within 96 hours of a shut-down. A CAD spokesman was unable to say whether it had received all the reports. Other airlines contacted, including Dragonair and Singapore Airlines, said they were unaware of any higher than average incidents of shut-downs. Cathay has lost thousands of dollars due to the incidents caused mainly by having to reschedule flights. The airline's aircraft have also been involved in a number of other incidents recently leading to investigations. In June, a flight to Bangkok turned back after an hour when the aircrew realised it had been under-fuelled.