If my mechanic misses an AD, whose problem is it?

Paragraph (a) puts primary responsibility on the owner or operator, so the FAA can hold the owner responsible for an aircraft flown out of compliance. Mechanics have their own duties under Part 43, but they do not replace the owner's.

Does a leaseback change who is responsible?

The rule names the owner or operator. In a leaseback the school operating the aircraft is usually the operator, so both parties should agree in writing who arranges inspections and AD compliance.

What is a permission letter for an STC?

Paragraph (d) requires written permission from the STC holder before you install an STC you did not buy yourself. Kit sellers usually include it; a used STC kit may not come with one.

14 CFR Part 91 · Subpart E · Maintenance, Preventive Maintenance, and Alterations

14 CFR 91.403: The owner is responsible for airworthiness

The owner or operator is primarily responsible for keeping the aircraft airworthy, and that includes complying with every Airworthiness Directive. The mechanic does the work, but the duty to have it done sits with the owner.

Section last amended December 30, 2016 · Text current as of October 15, 2026 · Also cited as FAR 91.403 · Read it on eCFR

14 CFR 91.403 in plain English

The owner or operator carries primary responsibility for airworthiness, including Part 39, the AD rules. (a)
Maintenance, preventive maintenance and alterations must be done the way Part 91 Subpart E and Part 43 prescribe. (b)
If the manufacturer's manual has an airworthiness limitations section, its mandatory replacement times and inspection intervals are law, not advice. (c)
You may only alter an aircraft under a supplemental type certificate (STC) if you hold the STC or have the holder's written permission. (d)

Common questions

If my mechanic misses an AD, whose problem is it?: Paragraph (a) puts primary responsibility on the owner or operator, so the FAA can hold the owner responsible for an aircraft flown out of compliance. Mechanics have their own duties under Part 43, but they do not replace the owner's.
Does a leaseback change who is responsible?: The rule names the owner or operator. In a leaseback the school operating the aircraft is usually the operator, so both parties should agree in writing who arranges inspections and AD compliance.
What is a permission letter for an STC?: Paragraph (d) requires written permission from the STC holder before you install an STC you did not buy yourself. Kit sellers usually include it; a used STC kit may not come with one.

Official text of 14 CFR 91.403

§ 91.403 General. Verbatim from the eCFR, current as of October 15, 2026.

(a)The owner or operator of an aircraft is primarily responsible for maintaining that aircraft in an airworthy condition, including compliance with part 39 of this chapter.

(b)No person may perform maintenance, preventive maintenance, or alterations on an aircraft other than as prescribed in this subpart and other applicable regulations, including part 43 of this chapter.

(c)No person may operate an aircraft for which a manufacturer's maintenance manual or instructions for continued airworthiness has been issued that contains an airworthiness limitations section unless the mandatory replacement times, inspection intervals, and related procedures specified in that section or alternative inspection intervals and related procedures set forth in an operations specification approved by the Administrator under part 121 or 135 of this chapter or in accordance with an inspection program approved under § 91.409(e) have been complied with.

(d)A person must not alter an aircraft based on a supplemental type certificate unless the owner or operator of the aircraft is the holder of the supplemental type certificate, or has written permission from the holder.

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14 CFR 91.403 in plain English

Common questions

Official text of 14 CFR 91.403

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