A safety alert has gone out requiring urgent checks on the towing connections of almost 500 heavy vehicles, including truck-trailers.
A Transport Agency investigation into a Wellington certifier Dick Joyce has identified "a number" of connections not adequately designed for the loads they were certified for, or recertified beyond their viable design life.
The alert covers heavy trucks, logging trailers, buses and motorhomes.
These "further potential safety issues ... must be addressed", the agency's Operational Standards Manager Craig Basher said in a statement this afternoon.
"The safety alert we have issued today requires the operators of all vehicles with potentially affected towbars, drawbeams, or drawbars to urgently have them cleaned and inspected for signs of cracks or other failures, carry out daily inspections before use, and discontinue using the vehicles if any cracks or failures are found," he said.
Mr Joyce has been suspended as a specialist certifier since June, though the agency now said it became aware of problems in a May 2017 audit, but an action plan put in place provided an "unsatisfactory outcome".
Agency records showed 483 vehicles affected, with half of those in Wellington and Wairarapa regions.
He did alot of certifying of trucks in the lower North Island.
The agency has stopped short of revoking any of his certifications, but is not ruling that out.
Earlier Mr Joyce told RNZ he had not taken any shortcuts, and would look at taking legal action against the agency.
An independent engineering analysis of his certification documents and engineering assessments is underway.
Today's alert comes at the same time as the agency is trying to get hundreds of heavy vehicles at the top of the South Island back on the road, which has been a huge extra load on overworked certifiers.
This followed an investigation into Nelson certifier Peter Wastney that led to more than 1500 of his certifications being revoked.
About a thousand of those 1500 vehicles have been checked and 654 recertified, but more than half have now been off the road for 15 weeks.
Those recertifications are being paid for by the agency, costing millions of dollars.
In Mr Joyce's case, the agency said it was still considering its payment responsibilities, but added it was not legally liable and under consumer law, an operator's first recourse was with the supplier.
The agency "will not be paying for loss of income", its safety alert said.
Mr Joyce has previously been investigated over the failure of the bucket of a big cherrypicker 10m above the ground, in Patea in 2002.
Investigating officers in a Labour Department report raised concerns about the effectiveness of an inspection Mr Joyce made of the machine before it failed.
However, while the draft investigation report was released to RNZ, Worksafe said it had no record of there being a final report.
Mr Joyce told RNZ the report's suggestion that corrosion was not spotted was a "red herring".
He said the picker's boom failed due to how it was being used by the operator.