14 CFR §63.33

1. (a)The aircraft class ratings to be placed on flight engineer certificates are—
   1. (1)Reciprocating engine powered;
   2. (2)Turbopropeller powered; and
   3. (3)Turbojet powered.
2. (b)To be eligible for an additional aircraft class rating after his flight engineer certificate with a class rating is issued to him, an applicant must pass the written test that is appropriate to the class of airplane for which an additional rating is sought, and—
   1. (1)Pass the flight test for that class of aircraft; or
   2. (2)Satisfactorily complete an approved flight engineer training program that is appropriate to the additional class rating sought.