# AC 121-16: Maintenance Certification Procedures

- Type: Advisory circular (guidance, not mandatory unless a rule or AD requires it)
- Status: Historical
- Approved: November 9, 1970
- Last reviewed: October 25, 2024
- This change: Canceled by Memo signed by John S. Duncan (AFS-1) and Richard Mathews (AFS-140); dated 12/04/2015.
- Family: AC 121-16
- 14 CFR parts: 121, 127
- Pages: 4
- PDF: https://openairdocs.org/files/sha256/23/7f/237fa3bc6fa2f11cf2629ad6115917fa3a254c17e91ff27fe112d34c0b875c74
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/884916178B3FD74E862569BC0057D28C.0001
- DRS record last changed: November 22, 2025
- Page: https://openairdocs.org/ac/121-16

## Versions

- [AC 121-16](https://openairdocs.org/ac/121-16) (Historical), approved Nov 9, 1970, 4 pages. Canceled by Memo signed by John S. Duncan (AFS-1) and Richard Mathews (AFS-140); dated 12/04/2015.

## Text

Each page's text from the PDF; open the PDF at a page with #page=N.

### Page 1

.

AC NO: AC lzl- 16 DA T E : 11/9m

**ADVISORY**

CIRCULAR DEPARTMENT OF TRANSPORTATION FEDERAL AVlAl’lON ADMINISTRATION 4 SUBJECT: MAINTENANCE CERTIFICATION PROCEDURES

1. PURPOSE. This advisory circular provides guidance for the preparation of an Operations Specifications - Preface Page which will afford nominal and reasonable relief from approved service and overhaul time limits when a part is borrowed from another operator.

2. APPLICABILITY. The type of Operations Specifications i, PrefaFe P-age .

illustrated in Appendix 1, Figure 1, and described in this advisory circular may be approved for use by Federal Aviation Regulations 121 and 127 operators.

3 . BACKGROUND. Instances have occurred where an operator in need of a part, which was not available from his own stock, was unable to borrow one because the time in service of the available unit exceeded his (the borrower's) approved service and overhaul time limit yet did not exceed that approved for the lender.

4 0 SCOPE AND LIMITATIONS. An operator may borrow and use a part provided by another operator for a maximum of 100 hours (or 50 landings if the service or overhaul time limit is controlled by the number of landings) even though the time in service of said unit exceeds his (the borrower's) approved service and overhaul time limit provided:

a. The part in question has a minimum time of 200 hours (or 100 landings if the service or overhaul time limit is controlled by the number of landings) remaining to service or overhaul in relation to the lender% approved service and overhaul time limit.

b. The part is not specifically life limited. In such a case, the part may not be operated beyond its approved life limit.

Initiated by: AFS-230

### Page 2

Page 2 AC 12146 l3/9p ' 5 . GENERAL, The provisions of this particular preface page, when authorized, apply equally to units borrowed from parts pool by parts pool participants.

L<iting Director , Flight Standards Service Flight Standards Service b , . .b

### Page 3

AC 121-16 Appendix 1 . w9 no Page 1 FIGURE 1. OPERATIONS SPECIFICATIONS - AIRCRAFT MAINTENANCE - PREFACE PAGE -

**BORROWING PARTS**

**EXAMPLE**

**UNITED STATES OF AMERICA**

**FEDERAL AVIATION AGENCY**

**WASHINGTON**

**OPERATIONS SPECIFICATIONS**

XYZ AIRLINES Form Approvcii.

Budgcl Rurvau No. O&ROTS.

**AIRCRAFT MAINTENANCE - PREFACE PAGE**

BORROWING PARTS XYZ Airlines, when in need, may borrow a part from another FAR 121 or 127 operator (or from a parts pool if the operator is a participant of a parts pool agreement) and may use such part for a maximum of 100 hours (or 50 landings if the service or overhaul time limit is controlled by the number of landings) even though the time in service of such part exceeds XYZ Airlines' apptoved service and overhaul time limit providing:

a. The part in question has a minimum time of 200 hours (or 100 landings if the service or overhaul time limit is controlled by the number of landings) remaining to service or overhaul in relation to the lender's approved service and overhaul time limit.

b. The part is not specifically life limited. In such a case, the park qy nbt be operated beyond its approved service life.

.

Effective date Form FAA-1014 (5-47, 35285

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