On Wednesday, David Goodall boarded a plane in Perth bound for Europe. He’s flying there to end his life.

The Western Australian scientist doesn’t have a terminal illness, but last month he celebrated his 104th birthday. He says his health has deteriorated recently – and he wants to die before it gets any worse.

“I no longer find much joy in life. Up to, even up to, say, the age of 90 I was enjoying life. But not now,” Professor Goodall told the ABC.

On Wednesday night, the academic said his final goodbyes to much of his friends and family at Perth Airport. He then boarded the flight to France, where he will visit family before travelling to Switzerland. There, euthanasia - or voluntary assisted dying - is legal, and on May 10 he will be helped to end his life at Life Circle in the city of Basel.

Before he departed, Professor Goodall told Nine News his three grandsons and daughter Karen were among those seeing him off.

"I should be glad when I get on the plane - so far, so good."

While sitting in his wheelchair, he then hugged each of the people gathered to see him off and wished them a wonderful life before boarding the plane assisted by a nurse.

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Professor Goodall, who was born in London on April 4, 1914 and moved to Australia in 1948, is Australia's oldest scientist. Up until recently, he'd been working as an Emeritus Professor in ecology at Edith Cowan University. In fact, in 2016 he made global headlines when the university tried to fire him over his age, but reinstated his position following backlash.

However, after losing his driver's licence due to failing eyesight, the academic has recently been recommended not to take public transport, leaving him mostly confined to his home.

He has previously said that he would have avoided going to Switzerland if he could, but he saw it as the only way he could be in control of the end of his life.

"I don't want to go to Switzerland, though it's a nice country," he told ABC. "But I have to do that in order to get the opportunity of suicide which the Australian system does not permit. I feel very resentful."

In November last year, Victoria became the first state to legalise voluntary assisted dying, but the option will only become available to people in mid-2019 - and then only patients with a terminal illness will be able to proceed.

Professor Goodall told Nine News that he didn't want to leave Australia. Post continues. 

Professor Goodall is being assisted by Australian euthanasia campaigner Philip Nitschke.

Dr Nitschke, who was waiting for the centenarian in France, told AAP he had attempted suicide about two months ago after suffering a fall. He said that his daughter could only get him out of hospital after arranging an independent psychiatric review.

Then, Dr Nitschke said, doctors attempted to prevent him from leaving Australia, arguing he was not fit to travel. However, none were able to stop him from leaving this week.

Professor Goodall told the ABC that he hoped the Australian public understood his decision.

"I am 104 years old so I haven't got much time left anyway."

"I might as well not have (my health) getting worse and worse, making me unhappy as it goes."

-With AAP

If you are experiencing crisis or suicidal thoughts, you can always phone Lifeline on 13 11 14 or the Suicide Call Back Service 1300 659 467.