14 CFR Part 91 · Subpart E · Maintenance, Preventive Maintenance, and Alterations
14 CFR 91.421: Records for a rebuilt engine
An engine rebuilt by its manufacturer, or by an agency the manufacturer approves, may start a new maintenance record with no previous history. That is what zero time means; an overhauled engine does not qualify.
Section last amended December 30, 2016 · Text current as of October 15, 2026 · Also cited as FAR 91.421 · Read it on eCFR
14 CFR 91.421 in plain English
- A manufacturer-rebuilt engine may use a new record without previous operating history. (a)
- The rebuilder enters the rebuild date, each change made for ADs, and service bulletin changes where the bulletin asks for an entry. (b)
- Rebuilt means disassembled, inspected, repaired, reassembled and tested to the same tolerances as a new engine, with every part meeting new-part limits or approved oversize or undersize. (c)
Common questions
- Is an overhauled engine zero time?
- No. Only a rebuilt engine, as defined in paragraph (c) and done by the manufacturer or its approved agency, gets a new record. An overhauled engine keeps its history and is described by time since overhaul.
Official text of 14 CFR 91.421
§ 91.421 Rebuilt engine maintenance records. Verbatim from the eCFR, current as of October 15, 2026.
(a)The owner or operator may use a new maintenance record, without previous operating history, for an aircraft engine rebuilt by the manufacturer or by an agency approved by the manufacturer.
(b)Each manufacturer or agency that grants zero time to an engine rebuilt by it shall enter in the new record:
(1)A signed statement of the date the engine was rebuilt;
(2)Each change made as required by airworthiness directives; and
(3)Each change made in compliance with manufacturer's service bulletins, if the entry is specifically requested in that bulletin.
(c)For the purposes of this section, a rebuilt engine is a used engine that has been completely disassembled, inspected, repaired as necessary, reassembled, tested, and approved in the same manner and to the same tolerances and limits as a new engine with either new or used parts. However, all parts used in it must conform to the production drawing tolerances and limits for new parts or be of approved oversized or undersized dimensions for a new engine.
Related
AerScheduler keeps inspections, squawks and work orders on each aircraft. It tracks the status; the signed logbook stays the record. See how