Section 121.400 - Applicability and terms used(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.Doc. No. 9509, 35 FR 90, Jan. 3, 1970; 35 FR 2819, Feb. 11, 1970, as amended by Amdt. 121-104, 38 FR 14915, June 7, 1973; Amdt. 121-259, 61 FR 34560, July 2, 1996; Amdt. 121-366, 78 FR 67836, Nov. 12, 2013; Amdt. 121-382, 85 FR 10921, Feb. 25, 2020