Incident Overview
On 20 March 2002, at approximately 07:40 UTC, a Cessna 750 Citation X aircraft, registration N999CX, experienced smoke in the cabin and cockpit shortly after departing from Zurich Airport. The aircraft, operated by Codex Ltd, was on a ferry flight following maintenance work. The flight crew, consisting of a commander and a copilot, both citizens of Serbia and Montenegro with FAA-issued licenses, had taken off from runway 32 en route to Geneva.
History
Two days prior, on 18 March 2002, the same aircraft had flown from Geneva to Zurich for minor technical repairs. During that flight, smoke appeared in the aft cabin, but the flight was completed normally. The crew suspected the smoke originated from a failed display management unit (DMU) installed in the avionic compartment. The next day, the DMU was replaced, and ground static tests were conducted with engines at idle, but no smoke was detected.
On the morning of the incident, the maintenance company released the aircraft as serviceable. The crew took off at 07:34 UTC. A few minutes after takeoff, smoke appeared in the cabin and then in the cockpit. The pilots donned oxygen masks, processed the COCKPIT/CABIN SMOKE OR FIRE checklist, and decided to return to Zurich. They contacted Zurich Sector Radar, requesting vectors back to the airport. The aircraft was guided to an instrument landing system approach for runway 16 and landed at 07:52 UTC without declaring an emergency. The airport fire-fighting service was alerted and stood by during landing. After landing, the aircraft taxied to the maintenance facility under its own power.
Technical Findings
Examination of the aircraft's two air cycle machines (ACMs) revealed heavy contamination with both combusted and non-combusted oil residues. Both ACMs were replaced in the days following the incident. Subsequent ground tests showed that smoke was produced only when bleed air was supplied from the left engine. A boroscope inspection of the left engine (Rolls-Royce AE3007, serial number CAE-330173) found oil spreading throughout the engine due to a faulty fan carbon seal, with oil burning on hot parts and liquid oil present in the bleed air duct. According to the manufacturer, a service bulletin (SB AE3007C-A-72-133) offered an improved seal design, and several similar cases had occurred previously.
Cause
The flight was aborted shortly after takeoff because of smoke in the cabin and cockpit due to a faulty seal on the fan bearing of the left engine.