An ageing workforce alongside claims of a toxic work culture has seen the Transport Accident Investigation Commission (TAIC) lose 13 investigative staff in the last five years - almost a complete overhaul of the investigations team.
Since 2016, nine accident investigators and four investigations managers have left out of a total team of 17. Six of the resignations were retirements.
TAIC chief executive Lois Hutchinson said the agency expected staff turnover to continue at around this level because it had a larger than normal proportion of investigation staff who were close to the age of retirement.
But current and former TAIC staff RNZ has spoken to said there was more to it than that.
Staff described a toxic work culture with one manager "constantly losing [their] temper, shouting and harassing".
TAIC said it had received no formal complaints, but did acknowledge one episode of bullying behaviour which it said was resolved.
However staff said at least four people had complained of bullying and two staff had left because of workplace culture concerns and had signed non-disclosure agreements.
Staff said they were worried the loss of so many experienced investigators would have public safety repercussions.
"The worry is that the rapid erosion of highly trained, experienced and motivated staff and leaders will leave TAIC unable to protect the public from latent or hidden safety issues going forward."
COVID-19 travel restrictions had also made it impossible for new hires to attend accredited training courses held in the UK.
"It is no surprise that COVID-19 has interrupted a high proportion of formal tertiary training - especially overseas. TAIC is managing this with alternative training either sourced elsewhere or on-the-job," Hutchinson said.
Staff also described the top brass at TAIC - the four commissioners and the chief executive officer - as "extremely risk averse" and would "water down" the investigators' reports and recommendations before publishing the final version of the report.
"The commissioners have no or little background in transport and zero in accident investigation, and all they ever say is 'my name is going out on this' before changing the report, often against the expert investigators' advice or wishes," one investigator said.
"A bland, boring report was ideal... because the government and minister is happy, the media are not all over it, they're not upsetting the operators, the regulators, the families... there's no fallout."
TAIC said in response it was "all about safety" and it "recognises that its reports can impact on individuals and organisations".
TAIC is an independent crown entity, the primary purpose of which is to "determine the circumstances and causes of [selected aviation, marine, and rail] accidents and incidents with a view to avoiding similar occurrences in the future, rather than to ascribe blame to any person", according to the Transport Accident Investigation Commission Act 1990.
In other words, it is responsible for investigating accidents with the aim of producing a report that prevents an accident being repeated.
But New Zealander and former Chief Air Accident Investigator for the UAE and former Chief Inspector of Accidents for the Hong Kong Air Accident Investigation Authority Darren Straker said New Zealand risked turning out reports that were substandard.
"The experienced staffing, high turn over of staff and the number of CIA [chief investigators] they've had in the past four years is indicative of systemic organisational disfunction."
TAIC said its reports were of the highest quality and able to withstand international scrutiny from its global counterparts.
The organisation received $7.3 million in funding in the previous financial year.