# AC 91-55A Ed Update: Reduction of Electrical System Failures Following Aircraft Engine Starting - Type: Advisory circular (guidance, not mandatory unless a rule or AD requires it) - Status: Current - Approved: September 25, 2026 - Family: AC 91-55 - Pages: 3 - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/DRSDOCID198350608220260928123235.0001 - Page: https://openairdocs.org/ac/91-55 ## Versions - AC 91-55A Ed Update (Current), approved Sep 25, 2026 - AC 91-55A (Historical), approved Oct 11, 2023 - AC 91-55 (Historical), approved Oct 28, 1980 ## Text ### Page 1 U .S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Reduction of Electrical System Failures Following Aircraft Engine Starting Date: 10/11/23 AC No: 91-55A Updated: 9/25/26 Change: (Editorial) Initiated by: AFS-300 1 PURPOSE OF THIS ADVISORY CIRCULAR (AC). This AC is to warn General Aviation (GA) aircraft owners/pilots and maintenance personnel operating under Title 14 of the Code of Federal Regulations (14 CFR) parts 43, 91, and 145 of possible total electrical system failure following aircraft engine starting. The contents of this document do not have the force and effect of law and are not meant to bind the public in any way, and the document is intended only to provide information to the public regarding existing requirements under the law or agency policies. 2 AUDIENCE. This AC applies to operators of reciprocating-engine-powered aircraft and maintenance, repair, and overhaul (MRO) organizations. 3 WHERE YOU CAN FIND THIS AC. You can find this AC on the Federal Aviation Administration’s (FAA) website at https://www.faa.gov/regulations_policies/advisory_cir culars and the Dynamic Regulatory System (DRS) at https://drs.faa.gov. 4 WHAT THIS AC CANCELS. AC 91-55, Reduction of Electrical System Failures Following Aircraft Engine Starting, dated October 28, 1980, is canceled. 5 BACKGROUND. This AC is being issued in response to a safety recommendation made by the National Transportation Safety Board (NTSB) to the FAA. Aircraft accidents and incidents have occurred shortly after takeoff because the starter relay (solenoid) failed mechanically in the “on” position. This condition causes the starter to run, and if allowed to continue, can result in electrical system overload, overheating of components, and in some cases complete failure of the electrical system and/or destruction of the starter motor and drive assembly. Destruction of the starter drive shaft and gear assembly may also damage the aircraft engine. 6 SAFETY SUGGESTIONS. During maintenance activities, inspect the starter motor, electrical cables, and starter relay areas for evidence of overheating and damage. In addition, a good practice for pilots is to be completely familiar with instrument readings, cockpit sounds, and other indicators following normal engine starting periods. Indications that problems are developing in the starter system could be low voltage, high ammeter or loadmeter readings, dimming of lights, or excessive noise in radio receivers. A noted change in such known normal conditions could indicate prolonged starter motor running and the engine should be shut down. No further flight operations should be attempted until the cause is determined and repaired. ### Page 2 2 7 AC FEEDBACK FORM. For your convenience, the AC Feedback Form is the last page of this AC. Note any deficiencies found, clarifications needed, or suggested improvements regarding the contents of this AC on the Feedback Form. Wesl ey L. Mooty Acting Deputy Executive Director, Flight Standards Service ### Page 3 OMB Control Number: 2120-0746 Expiration Date:12/31/2027 Advisory Circular Feedback Form Paperwork Reduction Act Burden Statement: A federal agency may not conduct or sponsor, and a person is not required to respond to, nor shall a person be subject to a penalty for failure to comply with a collection of information subject to the requirements of the Paperwork Reduction Act unless that collection of information displays a currently valid OMB Control Number. The OMB Control Number for this information collection is 2120-0746. Public reporting for this collection of information is estimated to be approximately 20 minutes per response, including the time for reviewing instructions, searching existing data sources, gathering, and maintaining the data needed, completing, and reviewing the collection of information. All responses to this collection of information are voluntary. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to: Information Collection Clearance Officer, Federal Aviation Administration, 10101 Hillwood Parkway, Fort Worth, TX 76177-1524. If you find an error in this Advisory Circular, have recommendations for improving it, or have suggestions for new items/subjects to be added, you may let us know by emailing this form to the Flight Standards Directives Management Officer at 9-AWA-AFB-120-Directives@faa.gov. Subject: AC 91-55A, Reduction of Electrical System Failures Following Aircraft Engine Starting Date: _____________________ Please mark all appropriate line items: ☐ An error (procedural or typographical) has been noted in paragraph ____________ on page _______. ☐ Recommend paragraph _____________ on page __________ be changed as follows: ☐ In a future change to this AC, please cover the following subject: (Briefly describe what you want added.) ☐ Other comments: ☐ I would like to discuss the above. Please contact me using the information below. Submitte d by: Date: ______________________ FAA 1320-73 (01/25) SUPERSEDES PREVIOUS EDITIONS --- From OpenAirDocs.org, an independent open copy of FAA data. Only the Federal Register edition on govinfo.gov is the official legal text of an AD.