After ignition, the starter must assist the engine until it reaches what type of speed?

The starter's role in a gas turbine engine is to assist the engine in reaching a speed where it can continue to accelerate without any additional external assistance. This speed is known as the self-accelerating speed.

At this point, the combustion process within the engine produces enough thrust to overcome the inertia and drag, allowing the engine to continue to accelerate independently. Once the engine reaches this self-accelerating speed, it can sustain operation through its own power generation, transitioning to a self-sustaining condition.

Reaching idle speed implies that the engine is operating at its minimum stable speed necessary for continuous operation, but it does not fully utilize the engine's capacity for thrust generation. Operational speed generally refers to speeds needed for specific engine performance or flight conditions, which comes after the engine has achieved self-accelerating speed. Maximum speed represents the hypothetical highest speed the engine can achieve but is not what the starter specifically assists in reaching during the ignition phase.