How are engines numbered? On a commercial aircraft, the number of engine is usually 2, 4 or 6. When the technician or LAE was given task to inspect an aircraft engine no 2 on a 4 engine aircraft. Which engine would they go to?

2 different lecturers of mine had 2 different answer for this and both have experience in working with aircraft engine.

Lecturer A said:

Lecturer B said:


Which one is right? Requesting help from Technician or LAE. A brief explanation would be really helpful too.
The Wikipedia article is clear: engines are numbered sequentially, left to right, as seen by the pilot facing forward. That corresponds to the second of your diagrams.

Twin engined aircraft have just engines 1 and 2 on the port and starboard wings respectively.

Three engined aircraft follow the same convention with the number 2 engine in the fuselage centre line.

Since this appears to be an arbitrary convention I'm not sure what more explanation you're expecting.