America’s push to get rid of illegal immigrants with criminal records has generated a boom in deportation flights

It's 4.30am and huge spotlights illuminate the runway. A Boeing 737 – 22 years old, paint peeling, no identification – is ready for loading at the cargo area of Houston's George Bush Intercontinental Airport. A group of US federal agents with shotguns stands before a chain-link fence topped with razor wire. These are the visible defences. ''You don't see all the security; that's the point,'' explains Greg Palmore, a veteran agent with America's leading immigration police force, Immigration and Customs Enforcement.

Three sleek white buses roll to a stop, the words homeland security written along each side. Steel grates cover the windows, armoured doors and thick glass separate the driver from the 42 prisoner passengers. As I step inside, a roar of thick Spanish accents builds from the back of the bus. ''Yo! I am going to kill yooouuuu!''

"I would rather die of hunger than come back here," says Carlos Rojas, a 25-year-old prisoner, as he is shuffled from the bus on to the plane. He shakes the chains hanging from his waist and legs. ''They have us like dogs. The only thing they didn't do is put a chain around our neck. I know we broke the law, but this is too much.''

For decades local US police did not check on the immigration status of those they arrested. There was no collaboration with immigration police. Now immigration law clause 287(g) allows the deputisation of local police as immigration officers, in effect giving them the power to begin deportation proceedings. The Obama Administration initially suspended the law for 60 days for review, but in June the plan not only resumed but was expanded.

Rojas, from El Salvador, complains of the huge number of raids organised by Immigration and Customs Enforcement. ''There are many more raids now. Roadblocks, on the highway, at work – everyone is getting caught.'' This is the result of a strategy to arrest and deport an estimated 11 million illegal immigrants.

Last year 110,000 foreigners were deported after being arrested for crimes. That is expected to increase sharply. Up to 2 million immigrants with criminal records are expected to be deported over the next few years, making a booming business of this reality version of the Hollywood film ConAir.

Many Americans are heartened by what they see as long overdue enforcement of neglected immigration enforcement. But a Human Rights Watch report last year concluded "many of these non-citizens are a far cry from the worst and most violent offenders. Of those who were legally in the country before their criminal conduct, 77 per cent were ultimately deported for non-violent crimes". In a decade-long study of 897,000 deportees, Human Rights Watch found 27,000 deported for assault and nearly 100,000 for drug law violations. The organisation is lobbying to halt deportations to countries of persecution unless the deportee is guilty of particularly serious crime and is dangerous to Americans.

Here at the real ConAir, burly security guards form two rows and search each convict for hidden weapons, including in their mouths. Next to the prisoners are their possessions, reduced to the size of a supermarket carry-bag. One carries a Bible, a toothbrush, letters and a red belt buckle with cow horns raised – testament to a macho swagger reduced to the clank of chains and the shuffle of laceless sneakers. Without belts and shoelaces – removed to avoid suicides – the prisoners' baggy trousers flop like limp sails.

Despite the restraints, one prisoner months earlier broke free and made it across the runway and over the concertina wire. ''We caught him in the woods,'' an agent says.

The plane's itinerary reads like a milk run – hopping around the American south-west, often until there are no seats left. Today's flight starts in Houston, stops in southern Texas, then on to the east coast, where Salvadorean prisoners are loaded aboard like unwanted cargo and shipped home.

On board, prisoners are ordered to stay seated, silent and obedient. The passenger manifest lists each man's most recent crime – drug trafficking, indecency with a child, assault, drunk driving, theft, aggravated assault, sexual assault.

Each prisoner is handcuffed. Chains bind their ankles so tightly they must take baby steps to avoid falling. Another chain hangs around their waist, pulling their hands down so hard they cannot scratch their faces. As the plane thunders down the runway the prisoners scream like children on a rollercoaster – for many, it is their first flight. Some squeeze their eyes shut. Some pray. ''Look how little the cars are,'' says a man charged with armed assault. He is fascinated by the bird's eye view of Houston. ''This is much better than the bus.''

As the flight levels, closely escorted prisoners use the toilet. It is early in the flight and we are full with 124 prisoners – half of them Mexican, half Salvadorean; rival gangs within rival nationalities. The 15 guards are on high alert, though none is allowed to carry a gun. ''It's illegal for us to arrive in a foreign nation with firearms,'' an agent says. Tear gas is impractical. Between the cockpit and the cons is a row of Akal Security guards, seemingly powerful enough to keep the convicts quiet. ''They are very protective of the cockpit,'' the co-pilot assures me.

But the borders are less secure. One prisoner says: ''I will be back here in less than a month. They say that if they catch me again I will get 20 years, but I am still going home.'' ''Home'' is south Texas, which houses a huge Hispanic population, endless rows of taqueria shacks and the poverty-induced chaos that leads to assault and murder.

As the aircraft approaches El Salvador, the men cheer, hoot and celebrate. ''They talk back [to us] and say, 'I'm going home, nothing you can do to me now,''' says Brett Bradford, the Immigration and Customs Enforcement agent in charge of the flight.

At the airport the criminals are handed to Salvadorean officials. They march down the gangway. The thick, tropical heat is not fresh, but it is welcome. Hands above their heads, the men form a line and walk towards a grove of palm trees. Their slow shuffle and slumped postures belie their determination to promptly remobilise and head back towards the US.