Engine number 2 start Exhaust Gas Temperatures (EGT) are generally higher. Engine number 2 is started first because it's on the opposite side of the air bridge. When starting with external air or power it is normal to start Engine number 1 because it is further away from the carts.

On many twin-engine commercial aircraft like the Boeing 737 and Airbus A320, pilots typically start Engine 2 (the right-side engine) first for several technical and operational reasons. One historical reason is that passengers traditionally board and deplane from the left side of the aircraft (Door 1L); starting the right engine first keeps the heat, noise, and exhaust away from the active boarding area. Technically, starting Engine 2 is often prioritized because it is the primary power source for the yellow hydraulic system on an Airbus, which pressurizes the parking brake. By starting the right engine, the pilot ensures the brakes are fully functional before the aircraft begins to move or push back. Furthermore, in many cockpit configurations, the right engine powers the "main" electrical bus that supports critical flight instruments and the "Transformer-Rectifier 3," providing a more stable electrical load for the subsequent start of Engine 1. While modern planes are designed to be flexible, following this "Engine 2 first" SOP (Standard Operating Procedure) remains a core part of pilot training for consistency and ground safety.