Latest Specifications for Lycoming SI-1009BF Time Between Overhaul (TBO)
Interpretation of Official FAA AMOC Approval (Latest 2026 Version)
Subject: Time Between Overhaul (TBO) Specifications
Applicable Models:All Lycoming engine models defined herein; excluding engines subject to Airworthiness Directive (AD) 2012-19-01 for which the required corrective actions have not yet been completed.
Reasons for this revision
1. Deleted references in the original text regarding Lycoming-recognized FAA-PMA (Federal Aviation Administration Parts Manufacturer Approval) parts;
2. Removed provisions concerning engine overhaul intervals for agricultural spraying operations;
3. Added an Instructions for Continued Airworthiness (ICA) statement and an introductory paragraph to the first page;
4. Added explanatory text to subsection b on the first page;
5. Added a warning statement on page 2 and supplemented the text of existing warnings;
6. Added content to the warning paragraph on page 3;
7. Added dedicated columns for factory-new and factory-overhauled engines to Tables 1 and 2;
8. Adjusted the overhaul hour limits and remarks for several engine models in Tables 1 and 2;
9. Added footnotes for the TEO-540-A1A and TEO-540-C1A engine models in Table 1;
10. Revised the content of Note 6, Note 11, and Note 15.
Failure to read this document in its entirety may easily lead to operational or maintenance errors. Please read the complete service manual to fully understand all airworthiness requirements.
This Service Instruction constitutes Instructions for Continued Airworthiness (ICA).
For engines and crankshafts subject to Airworthiness Directive (AD) 2012-19-01, the crankshaft must be replaced and the crankcase disassembled at the next overhaul, or no later than 12 years from the date the affected crankshaft was placed in service, whichever occurs first, in accordance with the current AD. For any engine subject to AD 2012-19-01 that remains in service but has not yet complied with the AD requirements, the Time Between Overhaul (TBO) shall be maintained in accordance with the latest revision of Service Instruction No. 1596 until the crankshaft is replaced. Until compliance with the AD is achieved, the TBO for these engines will not be extended and will not meet the TBOs listed in this publication.
For Lycoming-series certified engines that have obtained a Type Certificate, and provided that operation and maintenance are conducted in full compliance with all Lycoming technical publications and FAA Airworthiness Directives, this document specifies two categories of overhaul intervals:Time periods calculated based on calendar years, and usage cycles calculated based on operating hours.
The overhaul intervals (TBO) and overhaul extension provisions stated in this document do not apply to engines under the following conditions:
a. The engine configuration differs from that approved in the original Type Certificate;
b. Genuine Lycoming parts, or parts explicitly authorized for use in the Type Certificate Data Sheet or relevant Lycoming service documents, were not used during assembly, repair, or overhaul;
c. Maintenance or overhaul was not performed in accordance with Lycoming-approved procedures;
d. Operating parameters exceed the technical specifications officially published by Lycoming.
Performing engine maintenance or modifications using parts or procedures not approved by Lycoming compromises the engine's durability, operational safety, and reliability; the service life of engines subjected to such non-compliant maintenance or modifications cannot be predicted.
The operator assumes all risks associated with the use of parts, assemblies, fuels, and lubricants not approved by Lycoming; such use will also directly void the engine warranty. FAA-PMA parts and fuels or lubricants approved via FAA-STC are recognized only by the FAA and have not been approved by Lycoming Engines.
The overhaul intervals for engine accessories and propellers typically precede that of the engine itself; the overhaul extension authority approved in this document does not alter the original manufacturer-recommended overhaul limits for accessories and propellers, which must undergo periodic overhaul in strict accordance with the respective manufacturer's requirements.
The content of this revision (Service Bulletin No. 1009) has been approved by the FAA and serves as an Alternative Method of Compliance (AMOC) for paragraphs (f)(1)(i) and (f)(2)(i) of Airworthiness Directive (AD) 2012-19-01.
The overhaul intervals specified in this document are based on the engine being in a state of regular operation (with operational records within any 30-day period); if the engine is scheduled to be inactive for 30 days or longer, please refer to the latest version of Service Letter L180.
Calendar-based Time Between Overhaul (Calendar TBO)
For all engine models, a complete overhaul must be performed within 12 calendar years, calculated from the date of initial entry into service or the completion date of the last overhaul. The establishment of a calendar-based overhaul interval is intended to mitigate engine degradation caused by the passage of time—specifically, the corrosion of metal components and the aging or failure of non-metallic parts such as gaskets, seals, flexible hoses, and fuel pump diaphragms.
Calendar-based overhaul intervals are established using data from accelerated durability tests and actual service statistics from the entire fleet; however, factors such as regional climatic conditions, storage environments, prolonged or frequent preservation periods, preservation maintenance procedures during downtime, and oil change frequencies can accelerate metal corrosion and the aging of non-metallic components, potentially further shortening the actual usable overhaul cycle.
For operations governed by US Federal Aviation Regulations (FAR) Part 91, EASA Part-NCO (Non-Commercial Operations), or equivalent regulations: Only appropriately qualified maintenance personnel (holding equivalent civil aviation maintenance certification from any jurisdiction) may apply to extend the engine beyond the 12-year calendar overhaul limit, provided all the following conditions are met:
1. Written approval is obtained from the competent civil aviation authority;
2. A comprehensive inspection for engine corrosion and aging is performed in accordance with 14 CFR Part 43, Appendix D (or equivalent airworthiness standards from any jurisdiction);
3. The engine is determined to be in a continued airworthy condition. This inspection must be conducted annually (or more frequently if necessary) to continuously verify airworthiness.
If the engine is subject to AD 2012-19-01 and the required corrective actions have not been completed, exceeding the 12-year calendar overhaul limit is strictly prohibited.
Using an engine in an unairworthy condition may cause aircraft crash, serious personal injury and property damage. Unless a certified maintenance personnel issues an airworthiness certification, the engine operation time shall not exceed the 12-year calendar period; if the engine operating parameters deviate from Lycoming specifications, or if there is rust, wear, damage or other potential faults that affect airworthiness, the engine must be shut down immediately and overhauled in accordance with Lycoming technical publications.
Time Between Overhaul (TBO) in Operating Hours
TBOs (in hours) for fixed-wing aircraft engines are detailed in Table 1; those for rotorcraft (helicopters) are detailed in Table 2. TBOs are used to manage wear and tear resulting from routine operations, such as the wear of metal components and high-cycle fatigue damage.
The overhaul interval based on operating hours is established using a combination of accelerated testing and fleet-wide service data. However, due to variations in operational usage and maintenance standards—as well as the complex conditions associated with specialized operations such as aerobatics, agricultural spraying, and aerial dispersal—Lycoming cannot guarantee that every engine will achieve the overhaul interval specified in the documentation. Operators are required to conduct condition monitoring inspections and continuously assess the engine's health and airworthiness.
All parameters in Tables 1 and 2 are subject to the notes at the end of the document, which detail the specific criteria for overhaul intervals across various engine categories. The method for tracking engine operating hours must adhere to the service-time recording protocols established by the airframe manufacturer or operator, and must comply with 14 CFR § 1.1 and equivalent civil aviation regulations in other jurisdictions.
New Factory Engines / Factory-Overhauled Engines: Applicable to the initial overhaul cycle for brand-new Lycoming engines and engines delivered after a factory overhaul.
Overhauled Engines: Applicable to all engines that have undergone overhaul by Lycoming or a third-party maintenance facility.
Table 1 Fixed-wing aircraft — Standards for overhaul intervals (operating hours)
Table 2 Rotorcraft — Standards for overhaul intervals (operating hours)
1. This provision applies only to engines equipped with 12.7 mm (1/2-inch) diameter exhaust valve stems. For engines in this series equipped with 11.1 mm (7/16-inch) diameter exhaust valves, the maximum TBO (Time Between Overhaul) is 1,200 flight hours, regardless of operating conditions. New and overhauled engines equipped with 12.7 mm exhaust valve stems can be identified by checking their serial numbers and manufacture dates against the latest revision of Service Instruction No. 1136.
2. Engines in this category are designed at the factory to accommodate a turbocharging system.
3. The turbocharger may require removal for carbon deposit cleaning and specialized maintenance prior to the engine's major overhaul.
4. The TBO for counter-rotating engine configurations is identical to that of the corresponding standard (clockwise-rotating) engine models.
5.1,200-Hour Standard:For engines not equipped with large main bearing dowel pins, the TBO shall not exceed 1,200 hours.1,400-Hour Standard:For engines equipped with large main bearing dowel pins, the TBO may extend to 1,400 hours. Applicability: Models with serial numbers L-7100-51A and above, or L-101-67A and above; models compliant with the latest revision of Service Bulletin No. 326; and remanufactured engines produced after January 26, 1970.2,000-Hour Standard: For engines equipped with both large main bearing dowel pins and an improved camshaft, the TBO may extend to 2,000 hours. Applicability: Models with serial numbers L-9762-51A and above; IO-360-C1E6 engines with serial numbers L-9723-51A and above; LIO-360-C1E6 engines with serial numbers L-524-67A and above; and models compliant with all requirements of the latest revisions of Service Bulletin No. 326 and Service Instruction No. 1263. Overhauled engines manufactured after October 1, 1972, may follow the 2,000-hour overhaul standard,with the exception of models with serial numbers L-2349-51A and L-7852-51A (these two models are not equipped with improved camshafts and have a maximum overhaul interval of 1,400 hours).
6.Prolonged engine operation involving alternating high and low power settings causes drastic fluctuations in cylinder temperatures, severely compromising engine reliability and service life; furthermore, flight maneuvers that trigger engine overspeeding or significant fluctuations in oil pressure exacerbate abnormal wear and shorten the engine's overall lifespan. For engines used in aerobatic flight, operators should independently determine appropriate overhaul intervals based on the actual proportion of time spent performing aerobatics.Engine condition monitoring and inspection is a mandatory requirement.,Used for the continuous assessment of engine operating conditions and airworthiness status; the final overhaul interval must not exceed the maximum time limit specified in this document.
7. TIO-540-C series engines meeting the following conditions may have an overhaul interval of up to 2,000 hours: models with serial number L-1754-61 or higher; models overhauled at the Lycoming Williamsport factory after March 1, 1971; and models modified to include large main bearing dowel pins in accordance with the latest revision of Service Instruction No. 1225. TIO-540-C series engines that have not undergone this modification are subject to a maximum overhaul interval of 1,500 hours.
8. VO, TVO, and TIVO-540 series engines equipped with connecting rods (Part No. 77450) in accordance with the latest revision of Service Bulletin No. 371 may retain an overhaul interval of 1,200 hours. Models not equipped with these new connecting rods are subject to restricted standards: a maximum of 1,000 hours for VO-540 models, and a maximum of 900 hours for TVO and TIVO-540 models. Detailed specifications for the new connecting rod assembly can be found in the latest revision of Service Bulletin No. 371.
9. For TIO-541-E series engines meeting the following criteria, the Time Between Overhaul (TBO) may be extended to 1,600 hours: engines with serial number L-804-59 or higher; engines overhauled after March 1, 1976; and engines upgraded with improved crankcases and cylinder assemblies in accordance with the latest versions of Service Bulletins 334 and 353. For engines that do not meet these requirements, the maximum TBO is 1,200 hours.
10. Some engines in service have been modified with inverted lubrication systems to accommodate aerobatic flight operations. For engines with this modification, the TBO determination standards are identical to those for the AEIO aerobatic engine series; specific rules are as outlined in Note 6.
Engines determined to be subject tohigh-frequency, normalized operationmay be granted an additional 200 hours of TBO:this applies if, at any time after entering service, the engine accumulates 120 hours or more of operation over any consecutive 90-day period, with no less than 20 hours of operation within any 30-day period.
12. To qualify for the 2,400-hour TBO (Time Between Overhaul) standard, high-compression O-235 engines must be equipped with LW-18729 high-strength pistons; for specific requirements, refer to the latest revision of Service Letter L213.
13. The high compression ratio O-235-F, O-235-G, and O-235-J series engines are not equipped with LW-18729 high-strength pistons.The 2,400-hour overhaul interval standard does not apply.
14. TIO-540-A series engines meeting the following criteria may have a Time Between Overhaul (TBO) of up to 1,800 hours: engines with serial number L-1880-61 or higher; engines factory-rebuilt or overhauled by Lycoming after March 1, 1971; and engines modified to incorporate large main bearing dowel pins in accordance with the latest revision of Service Instruction No. 1225. For TIO-540-A series engines that have not undergone this modification, the maximum TBO is 1,500 hours.
15. Lycoming factory-overhauled engines are automatically eligible for a 200-hour extension to the overhaul interval. For third-party maintenance or field overhaul programs not performed at the Lycoming factory in Williamsport, Pennsylvania, approval for the 200-hour extension requires compliance with all of the following conditions: a. exclusive use of Lycoming genuine parts or parts explicitly authorized by the Type Certificate Data Sheet (TCDS) or official service documents throughout the process; b. strict adherence to Lycoming-approved maintenance procedures; and c. clear notation in Block 12 of FAA Form 8130-3 (or an international equivalent airworthiness form) stating that the maintenance or modification was performed using Lycoming-compliant procedures and genuine or officially authorized parts.
Employing FAA general shop maintenance procedures, or using FAA-PMA parts not approved by Lycoming,Major Overhaul / Maintenance Projects Undertaken,Not eligible for the 200-hour overhaul extension.
If the engine meets the requirements of both Note 11 (high-frequency operation extension) and Note 15 (compliant overhaul extension), the extension periods may be combined, up to a maximum cumulative overhaul extension of 400 hours.
Official FAA AMOC Approval Letter
Subject: Application for a Global Alternative Method of Compliance (AMOC) regarding FAA Airworthiness Directive (AD) 2012-19-01 (AMOC File No.: 26-15; Document Log No.: 26-DOC-06422) Reference Documents:
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FAA Airworthiness Directive AD 2012-19-01
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Service Bulletin No. 1009BF: Overhaul Interval Specifications (Issued July 20, 2026)
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Service Bulletin No. 1596 (Revision): Recommended Overhaul Intervals for Engines Subject to AD 2012-19-01 That Have Not Yet Complied (Issued July 20, 2026)
The information in this document is for reference only and cannot serve as a basis for any maintenance work; for details, please refer to the company blog post "SI1009BF_TBO_Schedule" and FAA AD-2012-19-01.
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