MH724 - Incident: Malaysia B738 near Jambi on Feb 25th 2019

A Malaysia Airlines Boeing 737-800, registration 9M-MXH performing flight MH-724 from Jakarta (Indonesia) to Kuala Lumpur (Malaysia) with 120 passengers and 7 crew, was enroute at FL380 about 80nm northeast of Jambi (Indonesia) when the crew received a low fuel indication and decided to divert to Jambi advising they had a problem with the low fuel indicator. The aircraft landed safely on Jambi's runway 31 about 30 minutes later.

The aircraft remained on the ground for about 4 hours while repairs were made and continued to Kuala Lumpur landing there with a delay of about 5 hours.

In 2021 Malaysia's AAIB released their final report concluding the probable cause of the incident was:

The main cause of this incident was attributed to a technical fault of the Fuel Quantity Processor Unit (FQPU). The fault from the bad J1 connector and faulty clock signal from OSC1 was the cause for the unreliable fuel tank 1 quantity indication. It resulted in fuel configuration and imbalance on No. 1 tank light to illuminate.

This caused the fuel from left and right tanks to show a gradual increase in imbalance with fuel “IMBAL” and fuel “LOW” alerts triggered. The flight crew initiated a diversion due to suspected fuel leak caused by the misleading fuel indication.

The AAIB reported maintenance found no fuel leak.

The AAIB analysed:

Flight crew initially suspected a fuel leak due to fuel “IMBAL” alert triggered – where the fuel difference between main tank No.1 and main tank No.2 was more than 453 kgs. The flight crew did the “Non-Normal - fuel IMBAL” checklist which directed them to the “Non-Normal - FUEL LEAK ENGINE” checklist.

The “Non-Normal - FUEL LEAK ENGINE” checklist guided the pilot that there was no fuel leak. However, the fuel imbalance kept on increasing. The flight crew went through the “Additional Information” section of the checklist which gave guidance on reasons that an engine fuel leak should be suspected. As the total fuel quantity was decreasing at an abnormal rate and the fuel LOW alert showed, the flight crew suspected there was a fuel leak.

Diversion Decision to DJB

Due to the fuel leak, Captain mentioned that he wanted to land the aircraft down as soon as possible to avoid any controllability issues. Initially, the decision was the divert to SIN. However, Captain decided to divert to a nearer airport which was DJB, as advised by ATC.

The Operator's Operational Manual – A (OMA) indicated that adequate aerodrome shall have the applicable approach charts. The Operator does not have DJB approach charts in the aircraft as DJB is not listed as an adequate aerodrome for the Operator. Aircraft was already heading to DJB when the Copilot asked the Captain if they can divert to DJB without the approach charts. Captain convinced the Co-pilot that it was a safe decision.

Maintenance Action by Engineering & Maintenance

Initial inspection and troubleshooting carried out by GMF AeroAsia personnel at DJB, no evidence of fuel leak was observed at wing and engine area. Fuel quantity system test revealed that 28- 41108 COMPENSATOR unit having a bad data. A second test was performed, test pass. Water draining was carried out from the tanks. Nil sign of water contamination found in the fuel.

In KUL, MAB engineer carried out microbiological growth on the fuel tank as per AMM 28-10-00. Result was negligible, no further action required.

MAB engineer also carried out inspection on the fuel tank electrical bussing plug for any sign of corrosion or damages to the pin. Nil anomalies found. Fuel Tank wiring continuity and resistance check was performed as per FIM 28- 41 task 807. All continuity and resistance values are within limits. The bussing plug was cleaned prior installation.

Fuel Quantity Processor Unit (FQPU) was replaced for evaluation due nil
positive finding.

The tank No. 1 compensator was also replaced due intermittent bad data previously tested at DJB. Post installation test was satisfactory.

Spurious Unreliable Fuel Quantity Indication

The tank No. 1 indicated 630kg on landing, however, the fuel indication returned to normal after engine shut down. The tank No. 1 then indicated 2380kgs, which was the correct quantity in the tank.

Initial inspection carried out by GMF AeroAsia found no evidence of fuel leak around the wing and engine area. Initial test faulted the compensator. However, the second test carried out found nil anomalies.

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