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  4. Part 121
  5. § 121.400
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14 CFR · Part 121

14 CFR § 121.400

Applicability and terms used.

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Read in Subpart N
Part 121 Contents
  • Subpart A: General
  • Subpart E: Approval of Routes: Domestic and Flag Operations
  • Subpart F: Approval of Areas and Routes for Supplemental Operations
  • Subpart G: Manual Requirements
  • Subpart H: Aircraft Requirements
  • Subpart I: Airplane Performance Operating Limitations
  • Subpart J: Special Airworthiness Requirements
  • Subpart K: Instrument and Equipment Requirements
  • Subpart L: Maintenance, Preventive Maintenance, and Alterations
  • Subpart M: Airman and Crewmember Requirements
  • Subpart N: Training Program
  • Subpart O: Crewmember Qualifications
  • Subpart P: Aircraft Dispatcher Qualifications and Duty Time
  • Subpart Q: Flight Time Limitations and Rest Requirements: Domestic Operations
  • Subpart R: Flight Time Limitations: Flag Operations
  • Subpart S: Flight Time Limitations: Supplemental Operations
  • Subpart T: Flight Operations
  • Subpart U: Dispatching and Flight Release Rules
  • Subpart V: Records and Reports
  • Subpart W: Crewmember Certificate: International
  • Subpart X: Emergency Medical Equipment and Training
  • Subpart Y: Advanced Qualification Program
  • Subpart Z: Hazardous Materials Training Program
  • Subpart AA: Continued Airworthiness and Safety Improvements
  • Subpart DD: Special Federal Aviation Regulations
  • Appendix A to Part 121: First Aid Kits and Emergency Medical Kits
  • Appendix B to Part 121: Airplane Flight Recorder Specification
  • Appendix C to Part 121: C-46 Nontransport Category Airplanes
  • Appendix D to Part 121: Criteria for Demonstration of Emergency Evacuation Procedures Under § 121.291
  • Appendix E to Part 121: Flight Training Requirements
  • Appendix F to Part 121: Proficiency Check Requirements
  • Appendix G to Part 121: Doppler Radar and Inertial Navigation System (INS): Request for Evaluation; Equipment and Equipment Installation; Training Program; Equipment Accuracy and Reliability; Evaluation Program
  • Appendix H to Part 121: Advanced Simulation
  • Appendix K to Part 121: Performance Requirements for Certain Turbopropeller Powered Airplanes
  • Appendix L to Part 121: Type Certification Regulations Made Previously Effective
  • Appendix M to Part 121: Airplane Flight Recorder Specifications
  • Appendix O to Part 121: Hazardous Materials Training Requirements For Certificate Holders
  • Appendix P to Part 121: Requirements for ETOPS and Polar Operations
(a)

This subpart prescribes the requirements applicable to each certificate holder for establishing and maintaining a training program for crewmembers, aircraft dispatchers, and other operations personnel, and for the approval and use of flight simulation training devices and training equipment in the conduct of the program.

(b)

For the purpose of this subpart, airplane groups are as follows:

(1)

Group I. Propeller driven, including—

(i)

Reciprocating powered; and

(ii)

Turbopropeller powered.

(2)

Group II. Turbojet powered.

(c)

For the purpose of this subpart, the following terms and definitions apply:

(1)

Initial training. The training required for crewmembers and dispatchers who have not qualified and served in the same capacity on another airplane of the same group.

(2)

Transition training. The training required for crewmembers and dispatchers who have qualified and served in the same capacity on another airplane of the same group.

(3)

Upgrade training. The training required for flightcrew members who have qualified and served as second in command on a particular airplane type, before they serve as pilot in command on that airplane.

(4)

Conversion training. The training required for flightcrew members who have qualified and served as flight engineer on a particular airplane type, before they serve as second in command on that airplane.

(5)

Differences training. The training required for crewmembers and dispatchers who have qualified and served on a particular type airplane, when the Administrator finds differences training is necessary before a crewmember serves in the same capacity on a particular variation of that airplane.

(6)

Programmed hours. The hours of training prescribed in this subpart which may be reduced by the Administrator upon a showing by the certificate holder that circumstances justify a lesser amount.

(7)

Inflight. Refers to maneuvers, procedures, or functions that must be conducted in the airplane.

(8)

Training center. An organization governed by the applicable requirements of part 142 of this chapter that provides training, testing, and checking under contract or other arrangement to certificate holders subject to the requirements of this part.

(9)

Requalification training. The training required for crewmembers previously trained and qualified, but who have become unqualified due to not having met within the required period the recurrent training requirements of § 121.427 or the proficiency check requirements of § 121.441.

(10)

Related aircraft. Any two or more aircraft of the same make with either the same or different type certificates that have been demonstrated and determined by the Administrator to have commonality to the extent that credit between those aircraft may be applied for flightcrew member training, checking, recent experience, operating experience, operating cycles, and line operating flight time for consolidation of knowledge and skills.

(11)

Related aircraft differences training. The flightcrew member training required for aircraft with different type certificates that have been designated as related by the Administrator.

(12)

Base aircraft. An aircraft identified by a certificate holder for use as a reference to compare differences with another aircraft.

Referenced By

Interpretations of This Section (3)

  • DeJoseph, 2013
  • Kane (AFS-250), 2011
  • Nauman, 2005

Advisory Circulars (2)

  • AC 120-109A
  • AC 120-51E

Documents that cite this section, found in their catalog metadata or text. Listed by date, not by significance.

Regulations Referenced

14 CFR Part 14214 CFR 121.42714 CFR 121.441

Reflects the eCFR edition current as of September 29, 2026. Retrieved from ecfr.gov on October 16, 2026.

Primary Source

  • Official Source (14 CFR · Part 121)