What 393.71(a) means in plain language
FMSCR 393.71(a) addresses the fifth wheel assembly—the critical coupling mechanism that connects a tractor to a trailer. This regulation requires that the fifth wheel be free from defects, show no excessive wear, and be properly secured to the vehicle frame.
A defective fifth wheel can include cracks in the casting, worn kingpin pockets, loose bolts or fasteners, metal fatigue, or improper installation. The regulation is straightforward: the assembly must be in good working order and firmly attached. If an inspector finds the fifth wheel compromised in any of these ways during a roadside inspection, they can issue a citation.
This is a safety issue because a failed fifth wheel can cause trailer separation or jackknifing, putting your life, other road users, and your cargo at risk. Even though the regulation sounds narrow, it's one of the foundational requirements of vehicle maintenance that affects every tractor-trailer operation.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.71(a) citations are extremely rare. Our database shows only 1 citation for this code in all time—and zero citations in the last 12 months and last 90 days. This violation ranks #2796 out of 3,036 FMCSR codes by citation volume.
Despite its rarity in enforcement, the severity weight assigned to this code is 8, which reflects the potential safety consequence. When citations do occur, our data shows a 0.0% out-of-service rate—meaning that of the 1 citation on record, the vehicle was not placed out of service. For context, the all-FMCSR average out-of-service rate is 31.4%, so 393.71(a) sits well below that benchmark.
The near-zero enforcement volume suggests one of two things: either drivers and fleets are maintaining fifth wheels extremely well, or inspectors are not targeting this code with high frequency in roadside operations. Either way, if you've been cited for it, you're in a rare category.
Who gets cited most
Our inspection database does not show state-level breakdowns with multiple citations for this code. The single all-time citation in our records was issued to AUTO TRUCK TRANSPORT USA LLC (USDOT 317106). No pattern of state-level concentration or carrier-specific vulnerability emerges from the data.
This absence of a clear pattern reflects the overall scarcity of enforcement. If you operate a Freightliner (the top vehicle make in our cited set, with 2 citations), that does not suggest elevated risk—the sample size is too small to draw meaningful conclusions.
How severe is this compared to similar codes
Within the Vehicle Maintenance category, 393.71(a) is far less cited than related codes. For example:
- 393.9(a) (Inoperable required lamps): 660,737 citations with a 15.4% out-of-service rate—a code cited over 660,000 times in comparison.
- 396.3(a)(1) (Inspection/repair/maintenance - general): 236,919 citations with a 45.3% out-of-service rate—indicating more aggressive enforcement and higher severity outcomes.
- 393.47E (Slack adjuster defective): 180,363 citations with a 0.0% out-of-service rate—another brake-related code that sees far more roadside attention.
The enforcement disparity is striking. Fifth wheel defects are cited once; defective slack adjusters are cited 180,363 times. This suggests either that fifth wheels are more durable, inspectors prioritize other defects, or the technical definition of "defective" is harder to meet in roadside enforcement than the regulatory language implies.
How to avoid it
Prevention is straightforward and should be part of every pre-trip and periodic maintenance routine:
- Visual and tactile inspection before every trip: Walk around the fifth wheel assembly. Look for visible cracks in the casting, rust pitting, or corrosion that has compromised structural integrity. Feel for play or movement in the assembly when you apply pressure—it should be solid.
- Check all fasteners and bolts: Use a wrench or socket to verify that all bolts securing the fifth wheel to the frame are tight. Vibration and road stress can loosen fasteners over time. Tighten any that have come loose.
- Inspect the kingpin pocket and locking mechanism: Ensure the locking jaws are not worn, cracked, or misaligned. The kingpin should seat smoothly and lock securely without resistance.
- Monitor for excessive wear patterns: If you pull the same trailer regularly, watch for uneven wear in the fifth wheel pocket or any signs that the kingpin is not seating correctly (which can indicate a worn pocket).
- Address rust and corrosion early: Fifth wheels are steel and will rust in damp conditions. Minor surface rust is normal, but deep pitting or flaking can signal structural weakness. Use rust-preventive spray or paint on exposed surfaces, especially in winter or near coasts.
- Document maintenance: Keep records of fifth wheel inspections and repairs. This protects you in enforcement interactions and helps you spot recurring issues.
- Use a pre-trip inspection app or checklist: Record the condition of the fifth wheel at the start of each shift. Consistency in inspection habits reduces the chance of missing a developing problem.
The fifth wheel is not a complex system, but it is a critical one. Regular attention to its condition will keep you compliant and safe.