Turbofan Spool Up | Why so slow?
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413Modern Turbofan engines are an engineering marvel, but they are always slow to spool up from ground idle. They then accelerate quickly once above a certain N1.
The EEC carefully limits fuel flow at lower engine speeds to prevent engine surge/stall and excessive temperatures and the engine components (shaft/compressor blades etc) need to overcome the inertia to accelerate to higher speeds. Once up to speed more fuel can be introduced to allow for faster acceleration.
This is why idle thrust on approach (approach idle) is higher than ground idle as we need to ensure thrust can be added quickly in the event of a go around.