Friday, August 20, 2010

Update: Cathay Pacific Airbus A330 loss of thrust control during flight

by B. N. Sullivan

The Hong Kong Civil Aviation Department (CAD), Accident Investigation Division, has released preliminary factual information regarding its inquiry into the loss of engine thrust control during flight on a Cathay Pacific Airways Airbus A330-342 aircraft (registration B-HLL).  The crew experienced control problems with both of the aircraft's Rolls-Royce Trent 700 turbofan engines during the scheduled passenger flight from Surabaya, Indonesia to Hong Kong on April 13, 2010, resulting in a high-speed emergency landing at Hong Kong. During the high-energy braking, five tires on the aircraft's main landing gear burst, and fire broke out on the wheels.  Emergency evacuation of the aircraft on the runway caused injuries to 57 passengers, 10 of whom had to be hospitalized.

Engine Thrust Control Problems During Flight

In its first report on this accident [see link below], issued in May of 2010, the CAD revealed that the crew first noticed Engine Pressure Ratio (EPR) fluctuations during climb-out from Surabaya.  Twice during the cruise phase of the flight an ECAM (Electronic Centralized Aircraft Monitoring) message, ENG 2 CTL SYS FAULT was annunciated, and the crew dealt with the situation, following ECAM procedures, in consultation with Cathay Maintenance control.  All engine parameters remained normal, except for some EPR fluctuations.

During descent to FL230, at about 100 nm southeast of Hong Kong, the CAD report says "the ECAM messages ENG 1 CTL SYS FAULT and ENG 2 STALL annunciated within a short period of time. The flight crew completed the necessary ECAM actions with No. 2 thrust lever at idle position. No. 1 thrust lever was advanced to Maximum Continuous Thrust (MCT) position."  At this point, the crew declared PAN PAN, advised Hong Kong ATC that they had No. 2 engine at idle thrust, and requested track shortening and priority landing.

When the aircraft was about 45 nm from the airport and was about to level off at 8,000 ft AMSL, the ECAM message ENG 1 STALL was annunciated.  The crew carried out the ECAM procedures, and declared a MAYDAY.  According to the CAD report, "The commander then tested the engines by moving the thrust levers.  During these movements, the No. 1 engine speed increased to about 74% N1 while the No. 2 engine speed remained at about 17% N1."

"The commander flew the aircraft manually for a visual approach for runway 07L... During the final approach with both thrust levers at the idle position, No. 1 engine was stuck at about 74% N1, and decreased to about 70% N1 during touchdown, and No. 2 engine was stuck at about 17% N1 throughout the approach and landing."

The aircraft touched down at a ground speed of 230 knots.
On landing, the lower cowling of No. 1 engine contacted the runway surface briefly.  Spoilers were deployed automatically.  Only No. 1 engine thrust reverser deployed.  The commander applied maximum manual braking and the aircraft came to a complete stop on the runway.  The No. 1 engine was still running at 76–79% N1 with the No. 1 thrust lever at idle.  The flight crew shut down both engines."
Fuel Problems Discovered

In its second bulletin, issued last week [see link below], the CAD reported preliminary findings related to the accident aircraft's fuel, noting that the aircraft had been refueled at Surabaya prior to its departure for Hong Kong.  The report describes these anomalies:
The examination of engine fuel components revealed that the Main Metering Valves (MMV) of the Fuel Metering Units (FMU) of both engines were seized at positions consistent with the corresponding final engine power.  The Variable Stator Vane Controller (VSVC) of the No. 2 engine was also found seized. Fine spherical particles (spheres) were present in the FMU, the VSVC and the Variable Stator Vane Actuator (VSVA) of both engines.  No faults or failures have so far been observed with any of the removed components, other than those associated with the contamination by the spheres.  Examination and analysis indicated that those spheres could not have been generated from within the aircraft airframe or engine systems under normal operating conditions and environment.

The examination of fuel samples collected showed that there were also spheres in the fuel samples from the engine fuel system and the aircraft fuel tanks.  Traces of such spheres were also present in the monitor filters layers and the fuel samples collected downstream of those monitor filters in the dispenser used to uplift fuel to the aircraft.  These spheres appeared to be similar to those found in various aircraft engine fuel components examined.
The report also states that analysis of data from the Flight Data Recorder (FDR) and the Quick Access Recorder (QAR) revealed "no evidence of unusual command signal from the Electronic Engine Controls (EEC), the manual thrust and the auto thrust systems.  The abnormal engines performance during the flight was believed to have been caused by stiction and eventual seizure of the MMV."

The report goes on to say that work had been performed on the hydrant refueling circuit at Surabaya not long before the Cathay A330 had been refueled there.  The investigation "noted that some of the re-commissioning procedures of that hydrant extension work were not in line with the guidelines and practices commonly used by aviation fuel industry, and that the hydrant refuel system for Stands No. 5 to 10 was used for refuelling, including the subject aircraft, before the completion of the re-commissioning procedures."

The CAD has not yet determined the exact source and nature of the spheres found in the fuel samples and filters.  The investigation is continuing.


RELATED: Dramatic emergency landing by Cathay Pacific A330 at Hong Kong - Apr 14, 2010