A second engineer has been suspended amid safety investigations into broken and cracked towing connections on heavy truck-trailers.

Photo: RNZ / Supplied

Before this latest suspension, more than 1400 trailers had already been taken off the road for checks, repairs and replacements.

The New Zealand Transport Agency (NZTA) said it now recognised it had "issues" with its certification system.

The second engineer suspended is Dick Joyce, a double Olympic gold medallist in rowing, who runs the biggest heavy vehicle certifying firm in the Wellington region, at Seaview.

He was suspended indefinitely last Wednesday. The agency confirmed this on Friday when RNZ asked.

The first suspension was of Peter Wastney of Nelson, after a trailer he certified snapped right off a truck on the Hope Saddle last August. The truck operator has described it as a "sickening" close call.

Mr Wastney surrendered his certifying licence before it could be revoked, but recertifying those trailers is causing huge ongoing disruption to truckers at the top of the South Island.

In the latest suspension, of Mr Joyce, it is not clear how many truck trailers might be affected. So far, none have been ordered off the road.

It would be a few days until it knew what other steps might be needed, NZTA said.

Mr Joyce told RNZ yesterday the numbers were "nothing at all" like those in the Wastney case, adding the two situations were "entirely different".

He refused to comment further.

NZTA declined an interview, and noted that Mr Joyce could still challenge his suspension in court.

It had suspended him based on "less than satisfactory outcome" of ongoing audits, the agency said.

Mr Joyce had been audited quite frequently, and given a chance to demonstrate improvement, but his performance "got worse and worse", it said.

He was suspended as a chartered professional engineer in January 2016; though an engineer does not need to be a chartered professional engineer to work as a certifier, this was another factor, the agency said.

The industry body Engineering New Zealand said it suspended Mr Joyce's registration two years ago as he "did not demonstrate proof of current competence in his most recent assessment".

Three or four other engineers who work for Mr Joyce, covering as far afield as Hawke's Bay and Taupō, are not affected by the suspension.

The industry is struggling with a shortage of certifiers - there are only 80 or so nationwide - made worse by the already intense pressure around the mass recertification of the Peter Wastney trailers.

Industry insiders speak of some serious problems confined to a handful of certifiers, exacerbated by a decade or more of hands-off regulation by NZTA.

In the Wastney case, RNZ understands the crucial job files on virtually all the truck-trailers were missing lots of key information.

It is understood the Transport Agency's sole heavy vehicle certification auditor John Long had been warning the agency for years about this, but the agency let Mr Wastney carry on.

The agency declined to comment about this.

It is refusing to release the past audits of Mr Wastney to RNZ under the Official Information Act.

"This is because the legal liability of various parties is currently unclear, and it is necessary for the parties to preserve their positions until liability issues are resolved, either through consent or litigation," it said.

It also refused to release internal emails about the audits.

"We have determined that a substantial amount of work would be required to research and collate the information you have requested. On that basis, I am refusing your request," Brandon Mainwaring, senior manager of Operational Policy, Planning and Performance, said by email.

The wider issues are that trucks have been allowed to get bigger, while at the same time the rules have been getting looser: For instance, truckers no longer need to get semi-trailer kingpins checked at 100,000km like they used to.

In addition, the New Zealand Standard that governs engineering quality is seen by some in the industry as being weak, and some engineers prefer using the Australian Standard.

RNZ previously reported on years of concerns within NZTA about some semi-trailer designs leading to corrosion and cracking, culminating in a safety alert in February covering 1000 semi-trailers, mostly refrigerated units.

To tackle this, the agency is bringing in improved, mandatory inspections of truck skid-plates later this year.

Asked if its certification audit system was badly flawed, the agency told RNZ it wasn't - but added it was recognising that "there's an issue" and was lifting capacity.

RNZ understands this means perhaps tripling the auditing team, from a single auditor nationwide, to three or four.

Any such changes would come just a short time after two big restructures, in 2014 and 2016.

The Road Transport Forum has been scathing of the agency's loss of technical talent in these restructures.

"There's some real concerns about rapid expansion of roading infrastructure over eight or nine years, with our folks reporting some quite persistent jobs not being done to a satisfactory standard," Road Transport Forum chief executive Ken Shirley said.

"Pavements fail within months or less."