Magnetic Engines has converted a CFM International CFM56-5B engine from a double annular combustor configuration to the original single annular combustor version as one of several special projects conducted this year. The conversion is aimed at reducing maintenance costs.
The double annular combustor (DAC) was first applied to the CFM56-5B in the 1990s to reduce nitrogen oxides emissions. Filip Stanisic, head of Magnetic Engines, says the DAC variant has a different configuration of main hot-section modules—combustion chamber, combustion case, supports and others—and various fuel components such as fuel nozzles and manifolds. “However, time has shown that the ordinary version of the [CFM56]-5B engine single annular combustor (SAC) has better maintainability and lower maintenance costs,” he says. “Currently, most engines with [a DAC] configuration are either torn down into piece parts or converted to the SAC versions.”
The project included replacing the fan and low-pressure turbine (LPT) major modules due to the expiration of life-limited parts (LLPs) in those modules. Magnetic modified the customer's engine to bring it to regular SAC configuration by replacing around 110 line items. According to Stanisic, the turbine rear frame (TRF) usually requires replacement, too; however, in this case, the workshop replaced the whole LPT major module due to time expiration. “Thus, there was no need to replace the TRF and the fan modules were also replaced due to the LLPs' life expiration,” he says.
The higher maintenance costs associated with the DAC version are linked to its scarcity. “Searching for a vendor capable of repairing DAC components is a significant challenge,” says Stanisic. For example, several months ago, Magnetic Engines began searching for a vendor to repair the combustion chamber of a DAC engine, but despite best efforts, they found the turnaround time for this repair would be over six months with an unpredictable cost.
“Repairing DAC fuel nozzles also proved to be a daunting task,” Stanisic adds. “It is not so much about the price but more about the physical capability of repairing DAC parts.”
Magnetic reports that post-repair engine testing has proven the quality of the work and even shown that the engine's exhaust gas temperature margin improved slightly after the repair.
Looking ahead, Stanisic sees no significant DAC to SAC conversions market, citing only a handful of CFM56-5B DACs still operating in Europe. “From the databases, we can see that only four active airplanes with DAC engines are still in operation, but several of those engines are in storage,” he says.
Magnetic will not make predictions based on such quantities, and globally, it sees around two or three dozen DAC engines still in operation—a figure supposedly too low to suggest a potential future market for that work.
Stanisic authenticated the interchangeability of the engines but said, “it might require certain cockpit adjustments, but the DAC and SAC engines can be operated on the same A320 aircraft in most cases.”
