Date: 7th June 2022
Location: Sydney, Australia, to Auckland, New Zealand
Aircraft: Boeing 737-400 Freighter, registration ZK-TLL
Operator: Airwork
Flight Number: HT-2
Crew: 2 (pilots)
Summary of Events
On 7th June 2022, Airwork Flight HT-2, a Boeing 737-400 freighter operating from Sydney, Australia, to Auckland, New Zealand, landed safely in Auckland after a seemingly uneventful flight. However, during taxiing, the crew discovered that the centre fuel tank remained full, while the main fuel tanks supplying the engines were nearly depleted.
The flight had been conducted with the centre fuel pumps switched off, meaning the engines exclusively used fuel from the main tanks. This error, unnoticed until landing, posed significant risks, especially if a go-around had been required during the approach into Auckland.
New Zealand’s Transport Accident Investigation Commission (TAIC) investigated the incident and identified several contributing factors, including crew oversight, operational pressures, and deficiencies in the operator’s safety management system (SMS).
Aircraft and Crew Information
Aircraft
The Boeing 737-400 freighter is a reliable, widely used aircraft in the cargo industry, equipped with three fuel tanks: two main tanks and a centre tank. Fuel management involves switching on the centre fuel pumps to ensure optimal usage before transitioning to the main tanks.
Crew
The flight was operated by two experienced pilots. However, the increased workload due to operational changes contributed to procedural oversight.
Sequence of Events
1. Pre-Flight and Departure:
• The crew reprogrammed and replanned the departure due to a runway change and curfew constraints at Sydney Airport.
• During these preparations, the crew omitted to turn on the centre fuel pumps, a step in the Before Start checklist.
2. Enroute to Auckland:
• The flight proceeded normally, with fuel consumption limited to the main tanks.
• The centre fuel pumps remained off throughout the flight, leaving the centre tank unused.
3. Approach and Landing:
• The crew conducted an autoland due to fluctuating visibility at Auckland Airport.
• Upon landing, a main fuel pump low-pressure light illuminated, prompting the crew to check the fuel configuration.
4. Discovery of Fuel Discrepancy:
• The crew found the centre tank full (4,000 kg of fuel) and the main tanks nearly empty (640 kg of fuel combined).
Investigation Findings
The TAIC released its final report, identifying the following contributing factors:
Crew Actions
• Centre Fuel Pumps Left Off:
The crew omitted to activate the centre fuel pumps before engine start, a step mandated in the Before Start checklist.
• Checklist Oversight:
Distractions during pre-flight preparations led to the crew missing the pump activation and failing to detect the error during subsequent checklist reviews.
Operational Pressures
• Runway Change and Curfew Constraints:
A last-minute runway change and the approaching curfew at Sydney Airport added to the crew’s workload, contributing to procedural errors.
Potential Go-Around Risks
• Fuel Depletion in Main Tanks:
If a go-around had been required during the approach into Auckland, the main tanks would likely have been exhausted due to the engines’ high power demands, increasing the risk of engine failure.
• Checklist Logic:
The aircraft’s standard checklist assumed the centre fuel would have been used by this stage of flight, leaving no explicit procedure to activate the centre pumps during a go-around scenario.
Operator and Regulatory Oversight
• Inadequate Flight Planning:
The operator’s flight plans did not meet regulatory or company requirements for Extended Diversion Time Operations (EDTO).
• Deficient Safety Management System (SMS):
The operator’s SMS was found lacking in identifying and mitigating risks, as highlighted by prior audit findings.
Safety Concerns and Potential Outcomes
Had a go-around been necessary:
1. The engines would have rapidly depleted the remaining 640 kg of fuel in the main tanks.
2. Without an explicit checklist or procedure to activate the centre fuel pumps, the crew may have been unable to access the 4,000 kg of fuel in the centre tank.
3. The high workload during a go-around would have further complicated troubleshooting, increasing the likelihood of engine failure.
Recommendations
To Operators
1. Enhanced Checklist Design:
• Revise checklist logic to include procedures for activating unused fuel tanks in non-standard scenarios, such as go-arounds.
2. Crew Training:
• Provide additional training to reinforce the importance of thorough checklist adherence, even under time pressure.
3. Operational Risk Management:
• Address identified deficiencies in SMS to better anticipate and mitigate risks related to fuel management and flight planning.
4. Pre-Flight Briefing Enhancements:
• Ensure flight crews receive updated weather forecasts and compliant flight plans for EDTO operations.
To Regulators
1. Increased Oversight:
• Conduct more rigorous audits of operators’ SMS to ensure compliance with regulatory standards.
2. EDTO Compliance Monitoring:
• Verify that operators adhere to all EDTO requirements, including alternate airport planning and fuel reserves.
Conclusions
The incident highlights the critical importance of adherence to pre-flight checklists, robust safety management systems, and proper operational oversight. While the safe outcome demonstrates the resilience of the crew and aircraft, the potential for a catastrophic event underscores the need for systemic improvements.
The findings serve as a reminder to operators and regulators alike of the importance of addressing human factors, operational pressures, and procedural gaps to enhance aviation safety.
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