Precursors

Air France A320 Fuel Leak Occurrence

On August 24, 1997, an Air France A320, F-GHQH, was on a passenger flight from Orly, France, to Lorient, France. The aircraft took off from Orly with 8,500 kg of fuel onboard, which was 2,100 kg over the fuel load required for the trip. As the aircraft approached the planned cruising altitude, the crew received a fuel advisory message indicating that there was a 1,500 kg fuel imbalance between the left and right wings distributed as follows:

Outer Tank LeftInner Tank LeftInner Tank RightOuter Tank RightTOTAL
680 kg1420 kg3030 kg690 kg5820 kg

The Quick Reference Handbook (QRH) procedure for fuel imbalance called for opening the fuel crossfeed valve to balance the fuel quantity. Specifically, the crew opened the crossfeed valve and selected the left wing tank fuel boost pumps OFF. The crew also noted that the fuel-on-board was significantly less than expected. The crew considered the following reasons for the lower than expected fuel quantity:

  • An anomaly at the re-fuelling coupling resulting in a fuel loading error;
  • A possible erroneous fuel indication, (the crew was aware of a number of such previous incidents);
  • Incorrect fuel load; or
  • A fuel leak.

The Captain asked a deadheading company pilot, who was previously qualified on the A-320, to examine the wings for signs of a fuel leak. Because it was nighttime, the inspection was done with the cabin lights turned off and with the aid of a flashlight. This pilot saw no signs of a fuel leak.

After fuel balancing, the left wing tank fuel boost pumps were selected ON and the crossfeed valve was selected to OFF. A descent was initiated, and the fuel load was as follows: 

Outer Tank LeftInner Tank LeftInner Tank RightOuter Tank RightTOTAL
0 kg1160 kg1120 kg0 kg2280 kg

There was subsequent fuel warning of L WING TK LO LVL. In accordance with the ECAM procedure, the crew initially opened the crossfeed valve. However, believing this action to be not appropriate for the situation, the crew turned the crossfeed valve OFF after about 90 seconds.

Four minutes later, the fuel load was, as follows:

Outer Tank LeftInner Tank LeftInner Tank RightOuter Tank RightTOTAL
0 kg580 kg1080 kg0 kg1660 kg

At 20:12 hours, the left engine flamed out, and at 20:19 hours the aircraft landed at its destination with approximately 900 kg of fuel on board.

Bureau d’Enquêtes et d’Analyses pour la Sécurité de l’Aviation Civile (BEA), the French accident investigation authority, conducted an investigation into this occurrence.

BEA’s preliminary analysis of this occurrence and two other serious, fuel-leak occurrences determined that the involved crews could not determine that there was a fuel leak in two of the occurrences, and on the third occurrence, the origin of the fuel loss. (The first occurred in 1995 involving an Airbus A310 aircraft.  The other occurred on an A340 aircraft and was reported to the Accidents Investigation Branch of the United Kingdom.)  Also, the existing checklists were inadequate to effectively determine that a leak existed, and without this precise identification, the existing procedures could lead to inappropriate actions.

Consequently, on September 8, 1997, the BEA recommended that:

A study be immediately conducted into procedures to address this type of event, and that, in the interim, all crews should be immediately informed of the circumstances of the three fuel leak incidents.

In the BEA final report issued in August 2002, BEA further recommended that this incident and other similar occurrences revealed the critical nature of fuel leaks and deficiencies related to the identification of such leaks.
Consequently, the BEA recommended that:

  • DGAC ensure that basic training programs and recurrent training conducted on aircraft take into account the identification and interpretation of all indications of fuel-system failures, and the appropriate actions to be taken;
  • Airline operators review their instructions and procedures relating to the fuel systems to ensure that they are adequate for fuel leak situations;
  • Airbus studies a system that would alert crews, at an appropriate level, in terms of displays and warnings, of abnormal reduction in the quantity of fuel on board aircraft, and define appropriate procedures for such situations.

In response to these recommendations, Airbus took the following actions:

  • Airbus fleet abnormal procedures were amended  to include a FUEL IMBALANCE checklist, including a Caution that the procedure should not be done if a fuel leak is suspected.
  • A FUEL LEAK checklist was added to the Flight Crew Operating Manual (FCOM) Abnormal Procedures, including notes on how fuel leaks could be detected.
  • The abnormal procedure for left and right wing tank low fuel level was amended to include a Caution that this procedure should not be used if a fuel leak is suspected.
  • The Airbus fleet FCOM Standard Operating Procedures were amended to include in the FLIGHT PROGRESS CHECK a requirement to check that the sum of the fuel on board and fuel used is consistent with the fuel on board on departure.  Crews were directed to suspect a fuel leak if the sum is unusually smaller than the fuel on board.

Virgin Airways A340 Fuel Leak Occurrence

On 13 June 1997, a Virgin Airways A340 was on a flight from London to Tokyo. After 1 hour and twenty minutes of flight, the crew discovered a large difference in fuel quantity between the right and left wings. Over a 15-minute period, the crew monitored the situation and did a visual inspection. All engine parameters were reported to be normal. The crew concluded that a fuel leak existed based on the difference of fuel quantity between both wings and the fact that there was a disagreement between the fuel remaining on board and the fuel quantity expected based on the fuel used by the engines. The crew could not determine whether the leak was from the tank or an engine. The crew turned back toward London, and in accordance with the QRH procedures descended the aircraft to the gravity-feed altitude of 20 000 feet and all fuel boost pumps were turned off. On landing, a significant amount of fuel was observed on the runway. The total fuel lost during the flight was 20,000 kg. Post occurrence examination of the aircraft found a fuel leak on the fuel filter on one of the left engines. The flight crew performed the fuel leak procedure in accordance with the published QRH.

A United Kingdom Air Accidents Investigation Branch investigation into this occurrence was not conducted and a report was not published on this occurrence. Reportedly, the only safety deficiencies associated with this occurrence were related to a known technical fuel filter installation fault.
  

Other Fuel Leak Events

The Air Transat accident report stated that there had been at least 25 in-flight fuel-leak events since 1994. Although some of these events were minor in nature, a number were significant in that they led to a loss of fuel that resulted in a serious incident, such as an engine fire or a loss of fuel that resulted in a diversion or emergency situation.

Because the fuel leaks were clearly attributable to technical faults, few of the events were investigated and even fewer were analyzed to determine operational factors that may have increased the seriousness of the event.

Prior to the Air Transat A330 occurrence, there had not been another recorded occurrence that involved total fuel exhaustion due to a fuel leak, although there had been a number of cases of significant fuel loss, some of which would have been mitigated by following the manufacturer's recommended procedures.

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