Flight Instructor Ratings
In order to teach others how to fly you will need a flight instructor rating. There are 3 kinds required for teaching different kinds of flying. The first is the Certified Flight Instructor(CFI), second is Certified Instrument Instructor(CFII), and third is Multi-Engine Instructor(MEI). As you earn your pilot certificates you will need a an instructor that holds the appropriate instructor rating for the training. These pilot ratings will come into play for you down the road if you decide you want to become a flight instructor. Flight instructing is a common way for pilots to build their flight time for the Airline Transport Pilot license.
The CFI is used to instruct student pilots for the private pilot license and commercial license. A CFI can also perform bi-annual flight reviews that are required to keep pilot licenses current. This is the most common instructor. The CFI is often considered the most difficult and most failed checkride.
The CFII is required to teach students for the instrument rating. Flying on Instrument Flight Rules(IFR) requires a great attention to detail and thus requires an additional rating to teach others the skill.
Last, but not least, is the MEI. Multi-Engine aircraft are very complex machines so it makes sense that an instructor would also need more training and a certification to prove it. The MEI will teach you the different characteristics of a multi-engine aircraft and help you be successful in these larger birds.