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WARNING: Wheels Might Come Off

WARNING: Wheels Might Come Off

WARNING: Wheels Might Come Off


Headquarters and Headquarters Company,
50th Infantry Brigade Combat Team
New Jersey Army National Guard
Lawrenceville, New Jersey

Whether you fly or drive, we’ve all seen those same famous words in our operator’s manuals: NOTES, WARNINGS and CAUTIONS! These simple messages are printed for a reason, and here is an example that highlights their importance.

An Army National Guard unit in my state was conducting a routine convoy movement from their home station to a field training site for the monthly drill weekend. Within 20 minutes of leaving, the lead vehicle experienced an abnormal vibration. The driver and crew both smelled smoke, followed by a loud noise and a sudden drop. The truck’s right-front wheel had just flown off, causing the vehicle to veer off the highway.

How did this happen, you ask? Well, it turns out the M1097 High Mobility Multipurpose Wheeled Vehicle (HMMWV) has a long history of similar problems. But here’s what you need to know. (WARNING: You may just learn something from this article!)

The HMMWV is one of the most widely used ground vehicles in the U.S. Army fleet. As a troop-carrying vehicle and prime mover, the M1097 shares many common components with other vehicles and even uses the same maintenance manual. One unique feature of the HMMWV driveline is the geared hub assembly and spindle bearing. On the M1097, this system includes a lock washer and retaining nut that must be inspected and serviced after each semi-annual inspection.

When properly installed, the lock washer has slotted tabs that are bent into grooves on the retaining nut. This prevents the retaining nut from backing off while the vehicle is in motion. The service manual and repair procedure contain a very clear message: “WARNING, ensure lock tab on lock washer is bent completely into the slot on the retaining nut.” Guess what happens when you skip this step? The entire wheel falls off the vehicle!

Preventive maintenance checks and services, or PMCS as we all know it, is a crucial skill for vehicle operators. It’s a basic task that is routinely practiced at the operator level and reinforced with good leadership. But can you blame a private first class if the wheel falls off their truck? Even if they did their PMCS? In this case, no. You must dig a little deeper.

The higher headquarters unit conducted an on-duty National Guard accident investigation to determine what went wrong. They discovered the accident vehicle recently returned from depot sustainment maintenance. This type of PMCS is 20- and 30-level work that goes well beyond checking your tire pressure and oil level. The operator and crew were not at fault. In this case, the problem was a geared hub assembly that was not assembled correctly and then not checked by a mechanic supervisor. The warning message was not followed, and the vehicle was returned to the fleet. From the outside appearance, there was no indication of fault or failure even though anyone inside the vehicle could be seconds away from a real disaster.

Did the mechanic intentionally ignore the warning message? I don’t think so. Did the mechanic supervisor intentionally fail to check the mechanic’s work? I doubt it. But right or wrong, the maintenance quality assurance process should have caught this problem by adhering to the warning and installation procedures listed in the technical manual. In the safety world, we call this type of mistake “human factors,” and many Army accidents share this problem.

In the case of this HMMWV mishap, no Soldiers were injured. The crew was wearing proper gear and driving the correct speed, and the vehicle was later recovered without incident. The mishap could have been much worse if any of those procedures had not been followed. In the end, the only true cost was some pride and a few dollars’ worth of common repair parts.

The lesson in this incident is simple: Pay attention to your safety messages! It turns out the retaining nut and lock washer on the M1097 is a well-documented problem. The first Safety of Use Message describing the issue was published more than 10 years before this mishap occurred. That was eight and a half years before this young driver even joined the Army. He would have never known about this history. This accident serves as a great reminder for those of us who have been on duty for several years. Take time to read and understand older safety messages on your equipment and comprehend the impact.

Warning messages like the one discussed above are printed in the operator’s and maintenance manuals for a reason. You need to take them seriously and make sure all your subordinates do the same. Injury to personnel and damage to equipment will happen if you don’t pay attention. After a maintenance task is completed, don’t forget about quality assurance. Always have someone inspect your work. As leaders, operators and maintainers, it is our responsibility to do our jobs by the book. That goes for every task, every standard, every time. If not, the wheels might come off when you least expect it!



  • 8 January 2023
  • Author: USACRC Editor
  • Number of views: 385
  • Comments: 0