1. From wingtip to wingtip: In this convention, the engines are numbered from the left wingtip to the right wingtip, with the number increasing from left to right. For example, in a four-engine aircraft, the left outboard engine would be numbered 1, the left inboard engine would be numbered 2, the right inboard engine would be numbered 3, and the right outboard engine would be numbered 4.
2. From the front to the back: In this convention, the engines are numbered from the front of the aircraft to the back, with the number increasing from front to back. For example, in a four-engine aircraft, the engine closest to the nose of the aircraft would be numbered 1, the engine behind it would be numbered 2, the engine behind that would be numbered 3, and the engine furthest to the back would be numbered 4.
3. By side and position: In this convention, the engines are numbered by their side (left or right) and their position (inboard or outboard). For example, in a four-engine aircraft, the left inboard engine would be numbered 1L, the left outboard engine would be numbered 2L, the right inboard engine would be numbered 1R, and the right outboard engine would be numbered 2R.
The specific numbering convention used for a particular multiengine aircraft may vary depending on the aircraft manufacturer and model. It is important to refer to the relevant aircraft documentation for the correct engine numbering.
