Prince William speaks of air ambulance work: 'There are dark moments'

It involves teamwork - it's about saving lives - and it helps Britain's future king to feel that he's "making a contribution".

In an interview with the BBC Future website about his experiences piloting an air ambulance, he has spoken about his "dark" moments in the job.

It was William himself who insisted on finding a civilian job after he completed his tour of duty as an RAF Search and Rescue pilot in 2013.

Piloting an air ambulance was his way of finding a new role for himself.

It was a departure from tradition. No royal in direct line to the throne had done such a thing before.

Normally, the progression to the throne for a future king is pretty rigid: a period in the armed services, followed by years of royal duty in support of the monarch until, finally, upon the death of that monarch the crown becomes his.

That's the path being followed by William's father, Prince Charles, but it's been clear for some time that that's not how William sees his future.

As he explained in a BBC interview earlier this year, while his grandmother remains, as he put it, "extremely active at the helm of the royal family" and with his father "incredibly busy" with his charities and other activities, William feels that there is "the time and the space to explore other means of doing a worthwhile job".

And for him that means serving the community at the controls of an air ambulance in East Anglia.

And it is absolutely apparent from the unusually relaxed interview, which he has given to mark Air Ambulance Week, that he relishes his role.

"I really look forward to coming here every day," he says.

"And I love working as a team: that's something that my other job doesn't necessarily do: you are more out there on your own a little bit."

William has perhaps come to realise, more than some earlier generations of royals, that simply being born to a position of immense privilege does not automatically confer a genuine sense of worth and validity. Those are things that even a thoughtful future king has to earn so that he can feel comfortable with himself.

Piloting the air ambulance appears to be William's way of giving his life a sense of broader purpose, alongside the royal duties which take up a good many of the days when he's not heading to Cambridge Airport, where the air ambulance is based.

That's the broader framework of William's life, a framework which leads him to say in this interview: "I want to be a valuable member of the team… at the end of the day (I want to) feel like I have made a difference and a contribution to whatever it is I've done that day."

'Very dark moments'

Inevitably, many of the things witnessed by air ambulance crew members are distressing: this future king is seeing, and helping to alleviate, situations which none of his relatives will have encountered on a regular basis.

"There are some very dark moments," William says.

"You try not to take it away, but sometimes… it can be quite difficult."

And it is perhaps the demanding nature of this job that he chose, one in which he's judged by his team-mates purely on the basis of his own abilities and commitment, that explains why it matters so much to him.