Description

On 14/15 April 2022, a Rolls Royce 700 engined-Airbus A330-300 (ZS-300) which was to be operated by South African Airways on a scheduled international passenger flight from Accra to Johannesburg as SA053 experienced problems when refuelling at Accra. The significant delay involved could not be accommodated within crew duty time limitations and so departure had to be delayed until the following afternoon. A right wing fuel low pressure message at FL 410 about five hours into the flight led to descent to FL 190 to enable gravity fuel feed but was then followed by a right engine stall annunciation which did not affect manual thrust control. No exceedance was annunciated and the flight was continued to the intended destination without further developments.

Investigation

A Serious Incident Investigation was carried out by Ghana Aircraft Accident and Incident Investigation Bureau (AIB) assisted by the Accident and Incident Investigation Division (AAID) of the South African Civil Aviation Authority who had notified the AIB of the in-flight occurrence which followed the refuelling difficulties at Accra prior to departure for Johannesburg. In respect of the in-flight fuel low pressure indication, the engine manufacturer reviewed the QAR data and made their analysis and findings available to the Investigation. Data from the CVR and FDR were not downloaded and after-flight maintenance action in respect of the in-flight fuel system messages was not available to the Investigation. Flight crew experience information was not recorded but it was noted that the airline travelling engineer who oversaw the refuelling process at Accra had 7½ years experience which included 5 years working on the Airbus A330. The two fuel supplier shift supervisors involved had respectively 8 and 4 years experience of fuelling aircraft.  

What Happened 

The aircraft had arrived in Accra in mid evening on 14 August with 9 tonnes of fuel remaining in tanks. Refuelling for the return flight commenced using a refuelling tanker as the aircraft had been parked in a position where hydrant refuelling was not possible.

After 600 litres of fuel had been loaded, the process abruptly stopped despite no illumination of the Electronic Water Sensor (EWS) on the refuelling tanker which was reported to have been constantly monitored. The refuelling supplier shift supervisor was satisfied that there was no problem with the tanker but as the flight crew present reported that an ECAM ‘AFT TRANSFER FAULT’ had been annunciated and the flight deck fuel quantity indications were indicating that the fuel quantity in tanks could not be computed, fuel from the tanker was checked using a water detector capsule test which was negative. In conjunction with the engineer overseeing the turnround, the flight crew reset both FCMCs (Fuel Control and Monitoring Computers) and refuelling was recommenced but further interruptions to the refuelling process continued and each time it was restarted after a negative water detector capsule test.

Eventually, it was decided to move the aircraft to a position where the refuelling could be completed from a hydrant and this method eventually completed the required fuel loading without similar interruptions. It was considered likely that the higher maximum fuel flow rate (4,140 litres/minute) compared to that from the fuel tanker (2,300 litres/minute) contributed to the lack of any further fuel flow interruptions. By the time the uplift of 43,225L of fuel was finally completed after almost 5 hours, crew duty time limitations meant they needed a full minimum rest period at their hotel before operating so the flight departure had to be delayed until 1500 the following day.

The flight proceeded normally until it was over southern Namibia when an ECAM message ‘FUEL R WING PUMP LO PR’ was annunciated. The required Abnormal Procedure ‘FUEL GRAVITY FEEDING’ requiring a descent to not more than 20,000 feet was followed (descending to FL190). Once there, an ‘ENGINE 2 STALL’ condition was annunciated and when the ECAM action - reducing thrust on the affected engine - was taken, it ceased although when thrust was increased on two subsequent occasions, the same ECAM message appeared and the same response cleared it. The remainder of the flight was completed without further event and the ‘FUEL R WING PUMP LO PR’ message remained on the ECAM after landing.

Why It Happened 

The implied finding from a review of the pre-flight refuelling issues was that water in the fuel was likely to have been there before the refuelling started and at normal concentrations. Water in fuel samples taken after the flight was also within normal concentrations so after ruling out other possibilities, the problems with pre-flight refuelling were tentatively attributed to the relatively low flow rate of fuel from tanker.

In respect of the in-flight ECAM messages indicating low fuel pressure, examination of the QAR data by Rolls Royce indicated the following:

• All engine parameters were within expectations until shortly after gravity feed was initiated.
• From this point, the right engine was trying to achieve thrust but was unable to at higher thrust lever angles i.e. Actual EPR could not achieve Command EPR.
• Fuel Flow was erratic at the point of surge warning, spiking between ̴ 1,500lbs/hour and ̴ 8,000lbs/hour during the first surge warning.
• It is not clear if the engine actually surged or the surge detection logic was triggered due to the abnormal conditions.
• There was no evidence of LP fuel filter blockage, there was no impending filter bypass message in the Post Flight Report and no filter bypass was reported by the aircraft operator.

Their conclusion was that the engine was unable to provide the required thrust due to fuel starvation for an undetermined reason.

The Investigation concluded that the most likely scenarios were either icing in the tank pump output pressure sense line and/or the main fuel pump low-pressure warnings were erroneously generated by freezing of fuel pressure switches. Either way “the result was that normally operating fuel pumps were switched off as per the displayed ECAM procedure”. And based on water in fuel sampling after flight and over the following few days in the ground, water contamination was only found well within normal levels.

Conclusions in Summary 

1. The problems with pre-flight refuelling were tentatively attributed to the relatively low flow rate of fuel from the tanker.
2. The fuel starvation experienced in the later stages of the flight was probably attributable to icing in either the tank pump output pressure sense line or to freezing of the fuel pressure switches. 
3. The two issues were not causally related and excess water in the fuel when loaded or when used in flight was not a factor in either case.

Eight Safety Recommendations were made as a result of the Investigation findings as follows:

• that Airline Operators should report incidents which may affect the safety of aircraft promptly to the appropriate local authorities. [2023/09-1]
• that Technical Crew and Refuellers must ensure that the fuel clear and bright check is conducted together with the water test procedure during refuelling. It should be thorough and must follow the IATA-recommended guidelines. [2023/09-2]
• that Airline Operators should ensure that the regular maintenance water drain checks of aircraft fuel tanks is meticulously adhered to as recommended. Water drain procedures must always follow recommended guidelines. [2023/09-3]
• that Airport Authorities must monitor and ensure that fuel and lubricants drained from aircraft and ground equipment is disposed of at designated safe locations. Airline Operators and Service Providers should drain fuel and lubricants into special containers for disposal at designated safe locations. The Regulator should ensure compliance. [2023/09-4]
• that Airline Operators must conduct due diligence prior to signing on new fuel companies. Quality Audits should be carried out by Airline Compliance departments on fuel companies at all Airports where fuel is uplifted to ensure quality standards are maintained. [2023/09-5]
• that Airline Operators should be familiar with the various special equipment that fuel companies use to ensure the quality of fuel supplied such as the Electronic Water Sensor (EWS) system. Operators should disseminate information on such systems to operating crew and maintenance personnel. [2023/09-6]
• that Airbus and Rolls Royce should conduct further investigations into the cause of engine no.2 ECAM stall indication at FL190 during the gravity feed fuel procedure on the investigated flight. [2023/09-7]
• that Airbus and Rolls Royce should conduct further investigations to establish the cause of the failure of engine no. 2 to respond appropriately at FL190 during (the) gravity feed procedure on the event flight. [2023/09-8]

The Final Report was published on 4 October 2023.

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• Fuel Starvation
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