“It was the second or third time I’d seen them. They’d already done an initiation flight with me and it had gone very well. I thought it was a father who wanted to treat his son. It was a flying lesson like any other,” he told RTL radio.

Buy said that the men arrived on time for their lesson at 9.30am on Sunday morning at the aerodrome at Lognes, east of Paris. Instead of boarding the helicopter Buy had prepared – an R44 Robinson with four seats – the two men insisted on a lesson in an Alouette II, capable of transporting five people parked in the same hangar.

Buy refused, saying the Allouette was on loan and not suitable for beginners. In any case, it was too low on fuel, he told the men.

“It was at that moment everything changed and they began to threaten me. I said we couldn’t take off with so little fuel, and they said: ‘Then get fuel quickly.’” His voice breaking, Buy added: “They led me to believe my family was in danger.”

He said he was in “such a state” but managed to put fuel in the helicopter and was ordered to calmly let the control tower know they were taking off in a south-easterly direction.

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“Then [the gunmen] told me to land in a field on the pretext of wanting to urinate. They made me get out of the helicopter and aimed their guns at me.

“I was hit a couple of times with the butts and was told they had decided to take a friend from Reau prison, and it was important for me to do my job well – otherwise my family would be at risk and there was someone outside my home.

“I wasn’t resisting; I didn’t have any choice with two Colts held to my head.”

Buy said he was then ordered to take off again, but had no flight plan or any idea of which direction to go.

“Then they told me to land again. I didn’t know where I was. They ordered me to cut off the engine and put my head down so I couldn’t see the commandos arriving. I could hear bags and people being loaded into the back but I had to guess what was happening from the noise behind the cockpit. I was still being held with a Colt against my head.”

Buy said that his nightmare truly began after the Alouette II, a vintage model, refused to restart.

“At this point the men became really angry. Suddenly I was being hit harder and harder with the gun butts. They kept shouting ‘Start it! Start it!’ but each time the red light came on and it wouldn’t start. There was nothing I could do.

“I suggested we get out and try to solve the problem from the electro-mechanical box on the outside. It was then I saw these men completely hooded in outfits like the Raid or GIGN [French rapid intervention forces] in the helicopter.”

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Buy said that the men, wielding Kalashnikov rifles and reportedly wearing police armbands, began to lose patience with him as he repeatedly tried to start the aircraft without success.

“Maybe they thought I was faking a breakdown, but I felt completely helpless in front of that engine that I had tried to restart five, six times,” he said.

“They became more nasty. I took a blow to the head and I fell to the ground unconscious for several moments. They picked me up … I tried another connection … Finally the engine started and we took off in a hurry.”

The gunmen ordered Buy to fly low over fields “clearly to avoid radar” while they looked for the prison, finally spotting its red walls.

“I asked them: ‘What do I do now?’ They made me pass directly over the prison. I was too busy concentrating on what was a tricky manoeuvre to be worried for my safety. I had to follow their orders.

“I landed in a triangular courtyard on a piece of tarmac about 1.5 metres wide lined with flowers. It was a precise move but that is what I am specialised in. It’s what I teach my students.

“The others got out, leaving a commando with me who ordered me to rise to 1.5 metres and do a half turn in the courtyard.

“I was then told to hold the helicopter just about the ground and wait. I don’t know why. It was extremely precise move to hold it at around 3cms for 10 minutes.

“My worry was that the level of fuel was going down. It was very low. And I didn’t know where they would take me.”

While Buy hovered in the prison’s main courtyard, the only one not protected by anti-aircraft netting, the gunmen cut through a prison door using an angle grinder and burst into the visiting room where Faid was talking to his brother, Brahim.

“After … everyone was on board I took off. I didn’t know who was on board; he [Faid] was pretty quiet. They told me to fly towards Roissy [Charles de Gaulle] airport but not the airport itself.

“Then they ordered me to land in an alley near a Total service station next to a fast road … Everyone got out. I heard them talking about petrol and bleach and I knew they were going to try to set the Alouette on fire.”

The helicopter was found partly burned near Gonesse, northeast of Paris. Buy was taken to hospital where he was treated for shock.