ATSB: Fatigue crack behind Qantas B737 CFM engine failure
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By Andrew Curran.
A high-pressure turbine blade on a CFM International engine fitted to a Qantas Boeing 737-800 failed due to a fatigue crack, according to a final report released by the Australian Transport Safety Bureau (ATSB) yesterday, April 29.
The report concludes an 18-month investigation into the incident, which occurred at Sydney Airport (SYD) on November 8, 2024.
On that day, VH-VYH (msn 34180) was operating a scheduled flight (QF520) to Brisbane (BNE) when the right engine failed as the aircraft reached V1, the point at which a take-off must continue rather than be rejected, while accelerating on runway 34R.
The failed blade exited the high-pressure turbine disc, damaging other engine components and resulting in a contained engine failure. Parts of the engine landed on grass adjacent to the runway, igniting a fire.
The CFM56-7B24E high-bypass turbofan had been scheduled for removal on 21 November 2024, as it was approaching the manufacturer’s recommended life limit.
The flight crew continued the take-off relying on a single engine, declared an emergency, and prepared to return to Sydney. After holding for approximately 30 minutes, the aircraft landed safely. Fire crews inspected the engine before the aircraft returned to the terminal, where all 181 passengers disembarked without injury.
Investigation findings reveal fatigue cracking
A subsequent examination by Qantas engineers found that two high-pressure turbine blades had separated below the platform from the turbine disc. A borescope inspection conducted on 25 September 2024 had not identified any defects.
The engine was removed and sent to CFM International for teardown inspection at its facility in Malaysia.
The investigation confirmed that two of the 76 high-pressure turbine blades had separated due to fractures in the dovetail region. The remaining blades fractured at the base of the aerofoil due to overstress.
Damage to other engine components was largely attributed to the turbine blade failures. Evidence of birdstrike was found on the fan and low-pressure compressor, but investigators determined this was unrelated to the incident.
Metallurgical analysis identified fatigue cracking in 28 blades, originating at the thinnest section of the dovetail, known as the “min-neck,” on the convex side of the blade.
Blade number 50, one of the two that separated below the platform, showed the most extensive fatigue cracking and was identified as the primary failure. The second blade, number 51, showed no fatigue damage and failed due to tensile overstress.
Investigators concluded that as cracking progressed in blade 50, load transfer through the dovetail was compromised, ultimately leading to separation.
At the time of the incident, there had been 86 similar occurrences of min-neck fatigue cracking leading to blade separation on CFM56-7 engines globally, most involving earlier blade configurations.
In March 2025, CFM revised the recommended removal threshold for affected blade types, reducing it to 17,200 cycles. A newer blade design incorporates modified dovetail geometry to reduce the risk of such failures.
Blade number 50, one of the two that separated below the platform, showed the most extensive fatigue cracking and was identified as the primary failure. The second blade, number 51, showed no fatigue damage and failed due to tensile overstress.
Investigators concluded that as cracking progressed in blade 50, load transfer through the dovetail was compromised, ultimately leading to separation.
At the time of the incident, there had been 86 similar occurrences of min-neck fatigue cracking leading to blade separation on CFM56-7 engines globally, most involving earlier blade configurations.
In March 2025, CFM revised the recommended removal threshold for affected blade types, reducing it to 17,200 cycles. A newer blade design incorporates modified dovetail geometry to reduce the risk of such failures.
Pilots' response praised
The ATSB commended the actions of the flight crew.
“This engine failure occurred at the worst possible moment during a critical phase of flight,” said ATSB Chief Commissioner Angus Mitchell.
“The flight crew responded quickly and decisively, continuing the take-off, declaring an emergency, and conducting the required checklists while planning a return to Sydney.”
“This incident provides a positive example of effective training and procedures, highlighting their importance within the aviation safety framework,” he added.
The ATSB noted that its findings focus on safety factors and are not intended to apportion blame or liability to any organisation or individual.
You can read the final ATSB report here.
Photo: Qantas.
Contact the writer: andrew@aerosouthpacific.com