Incident Report - Auckland, New Zealand
In May 2018, Auckland Cranes experienced a near miss when the wheel nuts of two tyres on a trailer became loose while on route to site. This caused the two front left wheels to become displaced from the trailer, rolling into an embankment on the highway shoulder. The trailer’s axle consequently dragged along the motorway for an unknown duration. This caused damage to both the trailer hub and brakes but thankfully did not result in an injury or fatality.
The driver reported that while travelling to site he initially noticed a vibration in the truck, then later noticed sparks coming from the trailer. His initial suspicion was the sparks were being caused by a tie-down chain dragging on the road. As he was travelling on a motorway, he could not identify a safe position to pull over. When he was able to exit the motorway, upon inspection, he identified two wheels had been lost from the trailer and that the sparks were actually being caused by the trailer dragging along the motorway. He was unable to identify at what point the wheels had dislodged from the trailer during the journey.
After an incident investigation, it was identified the trailer had been recently refurbished including being fully stripped and repainted in the company's Auckland workshop. The trailer brakes and bearings were changed and the rims sanded and repainted. It was reassembled in Auckland and awaiting guards for installation when it was relocated to their Hamilton workshop to have this work completed.
It was on route to the first job following the refurbishment that the incident occurred. The trailer had travelled no more than 300km since the wheels were fitted. The wheels had been torqued up following reassembly, but the trailer had failed to be retorqued since then. Due to the newly painted rims, it is possible the paint had compressed allowing the rims to become slightly loose and the vibration caused the wheel nuts to come off completely.
The root cause of the incident was found to be the lack of a documented process relating to torqueing of wheel nuts and retorquing of wheel nuts post-100km. Auckland Cranes has a tyre contractor visit site almost daily to carry out retorquing on the entire fleet, but this particular trailer missed retorquing as it arrived and left the Auckland yard again before the contractor arrived on site.
Several lessons learned were identified and remedial actions put in place to ensure the prevention of any future incidents of this nature:
A mobile tyre fitter was immediately engaged to re-torque all trucks, trailers and cranes in the fleet.
Documents and processes for torquing of wheel nuts and retorqueing post-100km have been developed and implemented.
A line has been added to all service records to carry out the wheel nut
The branch manager has contacted all other branches to remind them to be vigilant about identifying this issue and encourage the improvement of documentation processes.
In addition, wheel nut plastic indicators were installed on all the Auckland Cranes fleet. Wheel nut plastic indicators can be placed on the wheel nut, with the arrowhead indicators pointing toward each other providing a visual indicator of any movement in the wheel nut. Some trailer owners opt to place wheel nut plastic indicators on all wheel nuts, but it was identified the more efficient option of placing the indicator on just four wheel nuts per wheel would achieve the same safety outcome. Checking of the wheel nut plastic indicator has been integrated into the operator’s daily prestart.
There has been an ongoing conversation in the industry around the merit of the wheel nut plastic indicators, with some viewing them as unnecessary due to the unlikeliness of an incident such as this occurring, where the wheels have become completely displaced from the trailer. This is a stern reminder that just because an incident ‘has never occurred before’ or ‘very rarely occurs’, does not mean we should not take the risks seriously and treat them accordingly.