What happened
On 7 September 2016, an Emirates Boeing 777-31HER aircraft, registered A6-EGA, was operating a scheduled passenger flight from Dubai, United Arab Emirates, to Brisbane, Queensland. On board were 22 crewmembers and 308 passengers.
At about 1916 Central Standard Time (CST), the left engine oil quantity started to decrease from 16.4 quarts, stabilising at 2 quarts at 1927, when the aircraft was about 650 km north-west of Adelaide, South Australia, and at flight level (FL) 353.[1] The flight crew contacted company engineering and operations staff and advised them of the situation.
The flight crew received a left engine low oil engine-indicating and crew-alerting system (EICAS) message and conducted the associated non-normal checklist. At about 1951, the flight crew shut the left engine down (Figure 1).
Figure 1: Flight data plot including oil pressure and engine shutdown
Source: Aircraft operator analysed by ATSB
The flight crew contacted air traffic control, declared a PAN[2] and conducted a diversion to Adelaide Airport, which was the nearest suitable airport. The flight crew commenced a gradual descent to FL 270, and were subsequently cleared for the area navigation (RNAV) approach to runway 05 at Adelaide. The aircraft landed without incident, and arrived at the parking bay at 2056. There was no damage to the aircraft or injuries to crew or passengers.
A subsequent engineering inspection found the left oil supply line to bearings numbers 4 and 5 had fractured and the associated clamp was broken (Figure 2).
Captain comments
The captain commented that the flight crew managed the situation in accordance with their procedures. The weather in Adelaide was beautiful and the aircraft performed well and handled exactly as it did in the simulator in training.
Engine manufacturer investigation
The manufacturer is investigating the following aspects:
- Turbine centre frame (TCF) Supply Tube 2061M79G02:
- evaluating high cycle fatigue (HCF) capability of the TCF tube when a clamp is separated/broken
- studying tube dynamic behaviour, due to broken clamps and its interaction with external components.
- Numbers 4 and 5 Oil Supply Tube 2034M68G01:
- evaluating effects of missing piston ring and clamp separation on the external hardware
- correlating finite element analysis (FEA) (stress analysis) with event findings
- running analysis to verify integrity of current system.
- Clamp Damage:
- mapping broken clamp findings from operator data and shop inspections
- reviewing installation procedures and design characteristics and their effect.
Figure 2: Fractured oil supply line
Source: Aircraft operator
Safety analysis
The left oil supply line to bearings numbers 4 and 5 fractured, resulting in a loss of oil and oil pressure from the left engine. The flight crew received a left low oil pressure warning and followed the associated checklists, shut down the left engine and diverted the aircraft to Adelaide.
Findings
These findings should not be read as apportioning blame or liability to any particular organisation or individual.
- The oil supply line to bearings 4 and 5 fractured at a welded joint and its support clamp was broken, resulting in an oil leak and therefore low oil pressure and quantity in the left engine.
- Following the receipt of a left low oil pressure warning, the flight crew completed the non-normal checklist, shut down the left engine and conducted a diversion to Adelaide.
Safety action
Whether or not the ATSB identifies safety issues in the course of an investigation, relevant organisations may proactively initiate safety action in order to reduce their safety risk. The ATSB has been advised of the following safety action in response to this occurrence.
Aircraft operator
The operator performed a fleet-wide inspection and found no leaks or cracks on any other engine.
Safety message
This incident provides an excellent example of effective crew resource management techniques when faced with an abnormal situation. Additionally, regular proficiency checks in the simulator including scenarios of a single engine failure allow flight crew to respond appropriately in the event of such an occurrence in flight.
Aviation Short Investigations Bulletin - Issue 56
Purpose of safety investigationsThe objective of a safety investigation is to enhance transport safety. This is done through:
It is not a function of the ATSB to apportion blame or provide a means for determining liability. At the same time, an investigation report must include factual material of sufficient weight to support the analysis and findings. At all times the ATSB endeavours to balance the use of material that could imply adverse comment with the need to properly explain what happened, and why, in a fair and unbiased manner. The ATSB does not investigate for the purpose of taking administrative, regulatory or criminal action. TerminologyAn explanation of terminology used in ATSB investigation reports is available here. This includes terms such as occurrence, contributing factor, other factor that increased risk, and safety issue. Publishing informationReleased in accordance with section 25 of the Transport Safety Investigation Act 2003 Published by: Australian Transport Safety Bureau © Commonwealth of Australia 2017
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- Flight level: at altitudes above 10,000 ft in Australia, an aircraft’s height above mean sea level is referred to as a flight level (FL). FL 353 equates to 35,300 ft.
- PAN PAN: an internationally recognised radio call announcing an urgency condition which concerns the safety of an aircraft or its occupants but where the flight crew does not require immediate assistance.