History of the Flight
The aircraft, an Airbus A340-642 (registration G-VATL), departed Hong Kong at 1621 hrs on 7 February 2005 for a scheduled passenger flight to London Heathrow. Prior to departure, the technical log noted that both Fuel Control Monitoring Computers (FCMCs) had been reset on the previous sector. During pre-flight, FCMC 1 and FCMC 2 each failed once, but successful resets were performed. Shortly after takeoff, an ECAM advisory 'FCMC2 FAULT' appeared with no associated actions; the commander delayed a reset until reaching cruise altitude. At cruise, a reset attempt using the Quick Reference Handbook was unsuccessful. No further fuel system warnings occurred until later.
At 0330 hrs on 8 February, while cruising at Flight Level 380 over Dutch airspace, the No 1 engine lost power. The crew secured the engine and decided not to relight it, continuing on three engines. The fuel contents for the inner 1 tank, which feeds engine 1, read zero. Suspecting a fuel leak, a crew member inspected the engine area from the cabin but saw nothing unusual. Soon after, the No 4 engine power fluctuated and the inner 4 tank also indicated zero fuel. The commander opened all fuel crossfeed valves, and the No 4 engine recovered. A 'MAYDAY' was declared, and the crew initiated a diversion to Amsterdam Schiphol Airport. At that time, total fuel on board exceeded 25,000 kg, but significant fuel was located in the trim, centre, and outer wing tanks. Manual fuel transfer was started, but the expected ECAM indications were not immediately seen, leaving the crew uncertain of the exact fuel status. The aircraft landed at Amsterdam without further technical problems.
Flight Data Recorder Analysis
Flight data recorder information showed takeoff with 135,450 kg of fuel. Normal fuel transfer occurred during climb. At 1928 hrs, at FL 354, transfer from the centre tank stopped with 5,300 kg remaining. At 0328 hrs, the inner 1 tank fuel quantity reached zero; 40 seconds later, the No 1 engine began to run down and was subsequently shut down. At 0340 hrs, the inner 4 tank quantity reached zero, and the No 4 engine began to run down. At 0345 hrs, an attempt to restart the No 1 engine was unsuccessful. At 0347 hrs, manual fuel transfer from trim, centre, and outer tanks to the four inner tanks began. At 0349 hrs, all inner tank quantities increased. Touchdown at 0410 hrs with 22,960 kg of fuel remaining; inner tank quantities were 2,641 kg (inner 1), 5,922 kg (inner 2), 5,370 kg (inner 3), and 2,583 kg (inner 4). Fuel transfer continued until engine shutdown.
Aircraft Examination
After landing, the Central Maintenance Computer generated a Post Flight Report detailing faults recorded during the flight. A physical examination was conducted according to the manufacturer's advice. Fuel quantity indications were verified against magnetic level indicators. Tests of fuel pumps, valves, cockpit lighting, and warning displays revealed no abnormalities. Engine runs, including a start of engine 1, were normal. A manual refuel was performed, and the aircraft flew a non-revenue flight to Heathrow. At Heathrow, low-level fuel warnings for inner 1 and inner 4 tanks were verified as working normally, and valve operation was confirmed. The two FCMCs, two Fuel Data Concentrators (FDCs), two Flight Warning Computers (FWCs), and two System Data Acquisition Concentrators (SDACs) were inspected and removed for further testing. Inspection of the computers, wiring, connectors, and installations did not reveal any defects.
Computer Tests and Findings
Removed computers were sent to manufacturers for bench and full acceptance tests. Prior to testing, data from internal memories of the FCMCs, FWCs, and SDACs were downloaded. The FDCs, which have no internal memory, were also tested. No defects were found; all computers performed as expected.
Downloaded data from the FCMCs indicated that FCMC 2 suffered a loss of ARINC 429 data bus A at 1934 hrs and failures of some discrete output commands from the FCMC in control at that time (which FCMC was in control is unknown). The FWCs reported two occurrences of ARINC 429 data bus A and B output failures from FCMC 2. One instance could be attributed to the in-flight reset of FCMC 2 by the crew; the other could not be correlated to any crew action.
Safety Recommendations
Following the investigation, the AAIB issued two safety recommendations:
- Safety Recommendation 2005-36: Airbus should review the FCMC master/slave determination logic on affected A340 aircraft to prevent an FCMC with a detected discrete output or ARINC 429 data bus output failure from remaining or becoming the master FCMC.
- Safety Recommendation 2005-37: Airbus should review the logic of low fuel level warnings on affected A340 aircraft so that the FDC low fuel level discrete parameter always triggers a low fuel level warning, regardless of the condition of other fuel control systems.
Safety Action by Operator and Manufacturer
On 10 February 2005, the aircraft operator issued a Company Notice requiring crews to monitor inner tank fuel contents and initiate manual transfer if any tank showed less than 1,500 kg. Additionally, any ECAM fuel system warning in flight would require monitoring of fuel transfer for the remainder of the flight. On 15 February 2005, the aircraft manufacturer issued an Operator Information Telex / Flight Operation Telex (OIT/FOT) advising pilots to monitor the ECAM fuel page every 30 minutes and providing a procedure to apply if automatic fuel transfer was lost.