An Emirates airline jet flying from Australia turned around and landed safely Thursday after a burning smell was detected on board, prompting a frantic search by air crew and fear among more than 100 passengers, the airline and witnesses said. The cause of the problem on the Airbus A340-500 was not immediately known. Emirates flight EK425 carrying 120 passengers from the western Australia city of Perth to the Middle East city of Dubai returned to Perth and touched down without incident about two hours after takeoff. Aircraft engineers were investigating the cause of the burning smell. “The decision to return to Perth was a precautionary measure one and a half hours into the flight and all passengers disembarked normally after the plane landed,” Emirates said in a statement. “Emergency services were activated as per standard procedure but were not required. Safety was not compromised at any point,” it said. Passengers said the pilot announced that a smell of smoke had been reported and he was returning to Perth as a precaution. They reported the smell getting stronger after the plane landed.