Usually yes, with conditions — but this is set by your installation's flight line instruction, not by a single departmental rule, so the local instruction is the one that binds you. The pattern across them is consistent: headgear worn as protective equipment or required for carrying arms is authorised, and secured cold-weather headgear such as a watch cap or a cinched boonie is authorised, provided none of it interferes with hearing protection. What is consistently prohibited is loose headgear near running engines or in windy conditions, for the obvious reason that anything that blows off becomes foreign object damage.
Readers asked this on CheckMyRegs and CheckMyAFI 3 times — this page answers it from the official catalogs and the publications’ own text.
| Branch | Controlling publication | Dated | Source |
|---|---|---|---|
| Air Force | AVIANOABI 21-102 Current Installation flight line instruction — the pattern, not a departmental rule | 2023-04-11 | Official link |
| Air Force | AFI 13-213 AFRC Sup MARCHARB Sup Current Airfield driving supplement carrying the running-engine prohibition | 2024-05-14 | Official link |
| Army | AR 95-1 Current Army flight regulations, including clothing and equipment | 2018-03-22 | Official link |
| Navy | OPNAVINST 3710.7V Current Naval air training and operating procedures | 2016-11-22 | Official link |
Hats or headgear required as protective equipment during maintenance and servicing, or required for personnel carrying arms, are authorised on the flight line and in industrial aircraft maintenance areas.
“6.1. Hats or headgear required as PPE during maintenance, servicing, or as required for personnel carrying arms are authorized on the flight line or in industrial aircraft maintenance areas (providing wear does not interfere with proper wear of double hearing protection).”
A seasonal watch cap, micro fleece hat or boonie with the strap cinched is authorised on the flight line, and may be worn within twenty-five feet of running engines when secured under ear defenders.
“6.2. Wear of the seasonal OCP watch cap, micro fleece hat or boonie cap (with strap cinched) is authorized on the flightline or in industrial aircraft maintenance areas and can be worn within 25 ft. of running engines if secured under ear de fenders or ground communication headset providing wear does not interfere with proper wear of double hearing protection.”
The rule that appears everywhere is the prohibition — no hats around operating engines or in windy conditions, with hard hats permitted for contractors inside a designated construction zone.
“4.13.6. (Added-MARCH) Do not wear hats around operating engines or during windy conditions. Hard hats may be worn by contractors when inside a designated construction zone.”
Authorisation is conditional on the headgear not interfering with proper wear of double hearing protection, so a hat that lifts a muff off the seal is not authorised whatever else it satisfies.
“6.1. Hats or headgear required as PPE during maintenance, servicing, or as required for personnel carrying arms are authorized on the flight line or in industrial aircraft maintenance areas (providing wear does not interfere with proper wear of double hearing protection).”
These are installation-level flight line instructions rather than a departmental rule, so read your own base's version — the specifics on distance and headgear type do vary.
“6.2. Wear of the seasonal OCP watch cap, micro fleece hat or boonie cap (with strap cinched) is authorized on the flightline or in industrial aircraft maintenance areas and can be worn within 25 ft. of running engines if secured under ear de fenders or ground communication headset providing wear does not interfere with proper wear of double hearing protection.”
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Updated 2026-08-01. CheckMyRegs is an unofficial index — always cite the official publication.