A commercial pilot banned from carrying passengers due to fears he might commit murder suicide with a plane had his medical certificates suspended after just two emails from his ex wife's new husband.

Auckland man Captain Graham Lindsay has been fighting to clear his name in the Wellington District Court since mid-2020, after the passenger ban was put in place in 2018.

The ban, and other conditions imposed on him, came after an "acrimonious divorce" spanning many years, his lawyer Fletcher Pilditch said.

In 2016, his ex wife's partner approached the Civil Aviation Authority (CAA) suggesting it was possible Lindsay might try to commit murder-suicide by deliberately crashing a passenger jet.

Despite having a spotless record relating to aviation safety and his behaviour at work, two emails from the informant was all it took for the CAA's principal medical officer to decide to suspend Lindsay's medical certificates.

When the initial complaint was made, Lindsay was made to undergo medical surveillance for two years, while still being allowed to carry passengers for his airline, Cathay Pacific.

But in 2018 the restrictions were upgraded to include the passenger ban.

While the passenger ban was eventually lifted, Lindsay is appealing against the CAA's decision in court on principle, arguing it should never have been put in place to begin with.

The case resumed in court this week, with the CAA's principal medical officer Dr Dougal Watson giving evidence about the process for initially suspending Lindsay's medical certificates.

Watson made the call for suspension after receiving two emails from the informant, despite having no other evidence of issues with Lindsay's behaviour, and no record of his personal issues interfering with his work.

The emails referenced behaviour from Lindsay towards his ex-wife in previous years, and the fact there had been a protection order granted against him, though the protection order was lifted a year later in 2015 due to there being no incidents between Lindsay and his ex.

Earlier in the divorce process - but still years before the protection order was laid - there was also an incident in which Lindsay allegedly threatened to harm himself in front of the couple's children.

Watson agreed in court there was no evidence that unsafe behaviour at work had ever arisen in Lindsay's career.

Pilditch walked Watson through 12 emails sent from Lindsay following the decision to suspend his certificates, with Watson agreeing they were all polite, co-operative, and appropriate.

Watson could not recall having any other contact with Lindsay outside those 12 emails, yet went on to describe Lindsay as controlling and manipulative in emails to other professionals involved in the suspension and assessment process.

When questioned about his assertion, he said he could not recall why he could not remember why he'd called Lindsay controlling.

"I cannot piece it together comfortably in retrospect looking back six years," Watson said.

Following on from that there was one incident where Lindsay called a CAA staff member and allegedly harassed her over the phone, but that was the only known adverse interaction.

Regardless, Watson later said Lindsay had been "controlling and aggressive" throughout the CAA's dealings with him, and that their "earliest dealings" saw him manifest this behaviour.

Watson could not provide an explanation for why he had said that, when all of the email interactions had been polite and appropriate.

On one occasion Lindsay emailed Watson to let him know his psychological assessment would be delayed because the psychologist the CAA asked him to see was on holiday.

Watson then forwarded the email to the psychologist and noted it was an example of passive aggression, due to Lindsay referring to the psychologist as Mr, rather than Dr.

"Do you not think that's something of an overreaction to what may have been an innocent mistake?" Pilditch asked.

Watson said he felt it was passive aggression and flagged it as such.

Pilditch suggested that whenever Watson had the opportunity with Lindsay, he "leapt to the worst conclusion about him".

Watson will continue giving evidence tomorrow.