Home › CFR › Title 14 › Part 3814 CFR Part 38 — Airplane Fuel Efficiency CertificationSubpart A — General§ 38.1— Applicability.§ 38.3— Definitions.§ 38.4— Compatibility with airworthiness requirements.§ 38.5— Exemptions.§ 38.7— Incorporation by reference.§ 38.9— Relationship to other regulations.Subpart B — Determining Fuel Efficiency for Subsonic Airplanes§ 38.11— Fuel efficiency metric.§ 38.13— Specific air range.§ 38.15— Reference geometric factor.§ 38.17— Fuel efficiency limits.§ 38.19— Change criteria.§ 38.21— Approval before compliance testing.§ 38.23— Manual information and limitations.