A British engineer who is thought to have been the last person to speak to the pilot of the doomed Helios aircraft had refused to return to Cyprus for questioning because of fears for his safety, the Cypriot transport minister said yesterday. Haris Thrasou said the engineer was not refusing to testify and that arrangements were being made for members of the Greek investigation team to fly to London to interview him. Shortly after the Helios Airways plane took off on August 14, the captain reported a problem with the equipment cooling system. While discussing ways to resolve it with the engineer in question, all communication was lost and nobody was able to make contact with the Boeing 737-300 again. The engineer may also have been part of a team that serviced the aircraft the night before the flight, after the crew had complained about a noise from the rear door. A theory behind the crash is that after compression tests, the system was left switched to manual and the aircraft was not pressurized when it took off, losing oxygen as it climbed.