Final answer:
An IRS align is not performed during engine start or while the engines are running. It is done on the ground before engine start to align the IRS system with the aircraft's position and heading.
Step-by-step explanation:
An IRS (Internal Reference System) align is not performed during engine start or while the engines are running. It is typically done on the ground before engine start to align the IRS system with the aircraft's position and heading. The IRS system uses various sensors, such as accelerometers and gyroscopes, to determine the aircraft's position and heading relative to the earth.
Performing an IRS align while the engines are running can be dangerous because the aircraft may be moving and the IRS system relies on the aircraft being stationary to obtain accurate readings. Additionally, aligning the IRS system requires inputting the aircraft's current position and heading, which cannot be accurately determined while the engines are running.