Why you check mag drop at 1800 rpm on aircraft piston engine opposed?

Answer 1

There are two sets of spark plugs for each piston, there are dual magnetos that create spark for each set of plugs this is a redundant system to increase safety. If one of the magneto is not working properly when you do your mag check the plane is not considered safe to fly, performance will be decreased and the redundancy of the system is gone.