Scots RAF gunner Corrie McKeague, who vanished after a night out in 2016, developed a "significant binge-drinking problem" after he found his friend dead on a trainline when he was a teenager, his father has said.
McKeague, from Dunfermline, was 23 when he went missing in the early hours of September 24, 2016, after a night out in Bury St Edmunds, Suffolk.
Police believe the airman, who was stationed at RAF Honington, climbed into a bin which was then tipped into a waste lorry.
An inquest into his disappearance which is due to last for up to four weeks, has begun at Suffolk Coroner's Court in Ipswich.
His father father Martin McKeague said in a statement read by lawyer Peter Taheri, counsel to the inquest: "Corrie was a happy child, however there were major events that shaped Corrie's life.
"When Corrie was 10 years old Nicola (Urquhart, Corrie McKeague's mother) and I had separated.
"At the age of 15, when he was first to find the body of his friend who had just been killed on a train line, I believe Corrie developed a significant binge-drinking problem.
"In his teenage years that impacted his emotional wellbeing and mired many of his relationships.
"Following a visit to my home town in Cupar in 2016 shortly before his disappearance I once again had to have words with him about it.
"We had a falling out over it."
He said that his last contact with his son was on his birthday, September 16, "when I sent him a message to wish him a happy birthday and I sent him money".
He said the death of his son's friend "was a terrible shock for a 15-year-old boy to suffer, and one I don't think he ever truly got over".
Mr McKeague continued: "I don't believe Corrie was ever suicidal.
"This has been a heart-breaking tragedy."
Mr McKeague's mother Nicola Urquhart, in a statement read to the inquest in Ipswich by lawyer Adam Walker, said one of her son's "very close female friends was hit by a train and killed instantly".
"This event had a huge impact on Corrie," she said.
She said Mr McKeague had started to train as a hairdresser, then as a PE teacher, before joining the RAF.
While he was prescribed antidepressants in the past, she said he was "back to his usual happy self" by 2015.
Ms Urquhart said her son "regularly lost his phone or wallet on nights out" but "was never aggressive with or without alcohol".
"There was nothing to suggest Corrie had any problems or concerns around the time of his disappearance," she said.
She said he had told her that he had "bumped a taxi on one occasion, meaning he had run off without paying".
She said that "if a stranger asked him to get into his boot to go to a party" she believed that he would go.
"Despite what's in the press, as far as I'm aware Corrie had never slept in a bin nor had he ever climbed into a bin to sleep," Ms Urquhart said.
Mr McKeague's brother Darroch McKeague said in a statement that Corrie planned to come back to Scotland for Halloween.
He said that when he spoke to his brother on September 23 he was "happy" and "looking forward to his night out".
Suffolk's senior coroner Nigel Parsley said Mr McKeague, who had served in the RAF for three years, drank a "significant amount of alcohol during the evening" of September 23.
He said Mr McKeague was asked to leave Flex nightclub and "was seen on a number of occasions on CCTV".
"He's seen to sometimes be alone, sometimes in conversation with others and seen to obtain food," Mr Parsley said.
He said that at 3.25am on September 24 CCTV captured Mr McKeague entering a horseshoe-shaped area in Brentgovel Street.
"You might find based on evidence that 3.25am is the last time Corrie was seen and known to be alive," Mr Parsley told jurors.
He said police investigations and searches failed to locate Mr McKeague, there has been no contact with family and no financial transactions that can be linked to him.
He said jurors will hear evidence about Mr McKeague's movements on September 23 and 24, his contact with any witnesses and "hypotheses and possible scenarios relating to Corrie's disappearance".
