What is the usual sequence for starting a turbine?

The correct sequence for starting a turbine is typically characterized by beginning with fuel flow, followed by ignition, and then starter engagement. This order is crucial for ensuring safe and effective turbine operation.

When fuel flow is introduced first, it allows the combustion chamber to be properly prepared for the ignition process. Without fuel present during ignition, there could be adverse effects, including potential damage from unburned fuel and inadequate combustion. After the fuel has started flowing, the ignition system can then efficiently ignite the fuel mixture, leading to combustion and the generation of hot gases necessary for turbine operation.

Once ignition is confirmed and the engine is running, starter engagement can occur. This helps to ensure that the turbine can reach the appropriate operational speed and pressure conditions necessary for stable combustion and overall engine performance.

In the other options, the sequence is not optimal as they either introduce starter engagement too early or lack the necessary preparation with fuel flow leading to ignition, both of which could compromise the efficiency and safety of the turbine starting process.