James Allison, the outstanding British engineer who has helped transform Ferrari’s fortunes so quickly this season, has been spending the morning flying his plane in the skies above his Oxfordshire home.

In the short gap between Ferrari’s sublime triumph in Malaysia and Sunday’s race in Shanghai he has returned home, to the small hinterland where he can engage in his private passion, squeezed between his hectic working schedule in Italy as Ferrari’s technical director and his severely abridged family life in England.

In the monomaniacal world of Formula One even finding time for a hobby is extraordinary, particularly when tasked with a role that has involved him changing the culture at Maranello. But flying matters to Allison. Formula One may even be described as his second choice because first and foremost he wanted to be an RAF pilot, like his father.

“I’m just about managing to cling on by my fingernails to the one enduring hobby I’ve had from the whole of my childhood and adult life, and that is aeroplanes,” he says. “I’ve had a private pilot’s licence since I was 17. Before that I was a glider pilot and before that an aeroplane modeller. I like mucking around with planes, and mucking around with wood. I would like to make an airplane out of wood. That would be my Nirvana.”

Allison, 47, who returns from Italy to be with his wife and three children every second weekend, just manages to fly enough hours to keep his licence but he no longer takes part in the UK acrobatic events that so excited him. “I was brought up on air bases and been surrounded by planes all my life. But when I was nine or 10 I learned I was colour-blind, and they don’t let you become a pilot in the RAF if you’re colour-blind.

“So I had a focused ambition of cheating my way into the RAF by doing the Ishihara test, the one with coloured dots. They’re designed in a specific way and if you understand how they’re designed, even if you can’t see them, you can figure out what they say. So I studied Ishihara books enough to understand how they were made and could see the pattern, even though I couldn’t really see it.

“I went to Biggin Hill to do the test and was doing marvellously well but the doctor could see the half-second of pause that I took to work it out. So then he gave me another uncheatable test, and I was out.”

Allison flies an Auster Mark Five, which he describes as “a particularly terrible 1930s high wing monoplane that is a ridiculous plane to own”. It’s the same plane his father used to fly him around in as a boy. “We had adventures and it was great fun. But then I went to boarding school and he had to sell it and he was heartbroken.”

Two years ago his father tracked down the plane and bought it back. “He said it was a brilliant bargain at £4,000. And I told him it was only £4,000 because it was a complete bag of bolts.

“I went to see him to pour scorn on the whole idea, to tell him he was a fool and that he should sell it. But instead of feeling the contempt for his purchase I got attacked by a fit of nostalgia as I remembered all the fun we’d had in it. So we agreed to restore it together and we spent the next couple of years making it beautiful.”

During that period, in September 2013, Allison rejoined Ferrari from Lotus, having had a five–year stint with the Italian team in their championship-hogging epoch at the start of the century.

Yet Ferrari endured a difficult season last year in which they did not win a single race. A number of key personnel changed with the departure of the chairman Luca di Montezemolo and two team principal changes in 12 months culminated in the arrival of Maurizio Arrivabene. After five seasons Fernando Alonso left to rejoin McLaren, with Sebastian Vettel replacing him for 2015.

“Ferrari hold a special place in my heart because they picked me up at a low ebb in my career in 1999 [when he lost his job as head of aerodynamics at Benetton],” says Allison.

Sebastian Vettel celebrates his Sepang triumph. ‘Every now and then you get a race that is completely delicious,’ says James Allison. Photograph: Mohd Rasfan/AFP/Getty Images

So his joy after Vettel’s win at the Sepang Circuit last month was unconfined. “It’s been lovely. All over. I’ve been extremely lucky because I’ve been in lots of teams that have won races and won championships by me being in the right place at the right time. Some people never get a race win in a whole career.

“But every now and again you get a race that is completely delicious. It makes you feel like everything is worthwhile. Becca [his wife Rebecca] is the person who I pour out all my worries to. And her normal reaction is ‘why don’t you stop and do something less stressful?’

“I always feel the same thing when she says that, which is that she’s never had the good fortune to feel what it feels like when things go right. It’s tremendously affirming because there’s no hiding when things are bad.

“If you haven’t done a good job it’s paraded in front of the world every two weeks. Your worth is measured so precisely by the progress of your car. And that can be brutal. But when the car goes well it’s a tremendous feeling and it makes all the bits that are tough dissolve away. And all the time that things are tough you think it doesn’t matter, because you’re going to get back to that feeling.”

The old Volkswagen camper van outside Allison’s home is a clue to his modesty. When asked to explain his strengths he says: “I don’t lose my temper, ever, and I work quite hard, so people know I’m putting the effort in.”

When pushed, he expands a little. “I know enough, technically, across the car to know what is important and what’s not as important and I try not to squander effort. And I hope I’m a reasonable judge of character, and that the key appointments I’ve made, previously at Lotus and subsequently at Ferrari, have been ones where my judgment has been rewarded and those people have paid me back a hundred fold.”

But Allison’s most profound impact at Ferrari, he thinks, has been to pay more attention to the subsequent year’s car.

“If I had to be immodest, the main contribution I’ve made has been to break out of the vicious circus Ferrari were in, which was to start the year with not the best car and then throw all efforts behind that car at the track, having a quixotic assault on a championship that was already lost. And pressure to keep pushing with that car, throwing good money after bad, was at the expense of the subsequent year’s car, which meant that car would also come out of the blocks slower.

“If I’ve had any effect it has been to help the team break away from that pattern, to stop robbing the future Peter to pay the present Paul. You pay enormously if you ignore the future. We’re not good enough yet but Ferrari were able to put more into the current car.”

There is a pellucid quality to the way he speaks and he says he learned much from his old Ferrari boss Ross Brawn. “Ross’s skill was in choosing good people and leading with a light touch, but with a strong sense of purpose. I’ve tried to replicate what Ross did, in a very limited way.”

Allison admits Ferrari are still slower than Mercedes, who are strong favourites to win in Shanghai. But he has overhauled the team as fundamentally as he reconstructed the old Auster he now flies.