14 CFR §63.31

1. (a)Be at least 21 years of age;
2. (b)Be able to read, speak, and understand the English language, or have an appropriate limitation placed on his flight engineer certificate;
3. (c)Hold at least a second-class medical certificate issued under part 67 of this chapter within the 12 months before the date he applies, or other evidence of medical qualification accepted for the issue of a flight engineer certificate under § 63.42; and
4. (d)Comply with the requirements of this subpart that apply to the rating he seeks.