What 393.91-BU means in plain language
FMCSR 393.91-BU applies specifically to buses and concerns the condition and installation of passenger seating. This regulation requires that all seats be properly secured to the bus frame and that any aisle seats meet specific equipment standards. Loose seats, seats that move under normal driving conditions, or seats installed with improper hardware or design fall under this violation.
If an inspector finds that a seat rocks, shifts, or isn't bolted down securely, you'll be cited. The same applies if seats along the aisle don't meet the structural or safety specifications that the regulation defines. This is a straightforward mechanical and installation issue—it's about ensuring passengers have a stable, safe seating platform during transport.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.91-BU is a low-volume violation. We've recorded 169 all-time citations for this code, with 98 citations in the last 12 months and 23 in the last 90 days. That ranks it #1264 out of 3,036 FMCSR codes by citation frequency—meaning inspectors cite this far less often than many other vehicle maintenance issues.
The out-of-service (OOS) rate for 393.91-BU is 7.1%, meaning only 12 of the 169 citations resulted in the bus being ordered out of service. This is substantially lower than the all-FMCSR average OOS rate of 31.4%. In practical terms, most 393.91-BU citations don't ground your bus immediately; you typically receive a citation and are given time to repair the seats before your next inspection or compliance deadline.
Monthly trends over the past year show citation counts ranging from 1 to 15, with slight increases during winter months (December 2025 and January 2026 each saw 8 citations with 3 out-of-service placements). This suggests seasonal scrutiny, possibly during periods of higher bus utilization or stricter inspection schedules.
Who gets cited most
Our inspection records show that citations for 393.91-BU are geographically concentrated. In the last 180 days, California led with 9 citations and a 0.0% OOS rate. New Jersey followed with 6 citations, also at 0.0% OOS. Nevada, however, stands apart: it recorded 6 citations in the same period but with a 100.0% OOS rate—meaning all Nevada citations resulted in out-of-service placement.
Arizona (5 citations, 0.0% OOS) and Vermont (3 citations, 0.0% OOS) round out the top enforcing states. The dramatic difference between Nevada's enforcement outcome and other states suggests either stricter compliance standards in Nevada or a pattern of more severe seat defects being identified during inspections there.
By carrier, our data shows fleets such as New Jersey Transit Corporation with 9 all-time citations, Sacramento City Unified School District with 4, and Airport Service Corp with 4. These represent the organizations with the most recorded violations for this code in our database, though the relatively low absolute counts reflect how uncommon the violation is across the industry.
How severe is this compared to similar codes
When compared to other vehicle maintenance codes in the same regulatory category, 393.91-BU is a minor violation. Code 393.9(a)—inoperable required lamps—has been cited 660,737 times with a 15.4% OOS rate, making it far more frequent and more likely to result in immediate out-of-service action. Similarly, code 396.3(a)(1) concerning inspection/repair/maintenance has 236,919 citations with a 45.3% OOS rate, indicating inspectors treat general maintenance defects more seriously.
Code 393.78, which addresses windshield condition defects, has accumulated 157,894 citations but only a 0.3% OOS rate—even lower than 393.91-BU. This suggests that while window defects are cited more frequently, seat security issues, when they do occur, trigger a slightly higher enforcement response. Still, at 7.1%, the OOS rate for 393.91-BU remains well below the all-FMCSR average and below most comparable codes.
How to avoid it
Preventing a 393.91-BU citation requires a methodical pre-trip seat inspection:
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Check every seat mounting bolt and hardware. Before passengers board, physically push and pull on each seat to ensure it doesn't move. Bolts should be tight and hardware should show no corrosion or damage. If you feel any movement, flag it immediately for maintenance.
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Inspect for cracks or breaks in seat frames. Bent or fractured frame members can prevent proper mounting and create looseness. Walk the length of the bus and visually examine the structural integrity of every seat base.
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Verify aisle seat compliance. If your bus has seats positioned in or near the aisle, confirm they meet the structural and equipment standards for aisle-mounted seating. Improper aisle seats are a common citation trigger under this code.
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Document your inspection. Keep a pre-trip checklist that includes seat security verification. This creates a record that you were performing due diligence and can protect you if a defect develops between inspections.
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Schedule preventive maintenance during low-utilization periods. Our data shows citations cluster in winter months, suggesting higher inspection activity. Plan seat repair and tightening before peak travel season to avoid being caught out of compliance during busy periods.
Our inspection records also show that co-occurring violations sometimes include brake and windshield defects cited alongside seat issues. While these are separate problems, they often indicate a bus that hasn't received routine maintenance. A comprehensive monthly maintenance review—not just pre-trip checks—will catch seat problems before an inspector does.