The noise is unmistakable and strikes fear into those on the ground: then it appears, the sinister silhouette of an Mi-24 gunship, scanning for targets so it can unleash its terrible firepower.
The helicopters circle out of range of the rebels' inferior weapons, before swooping to bombard the northwest Syrian town of Taftanaz, whose only inhabitants now are fighters after an army assault in April killed dozens of civilians.
Rebels have attacked several air bases with varying degrees of success in the past week in an effort to curb the regime's control of the skies which remains its key advantage in the conflict.
Aerial bombardments kill dozens of people every day across the country.
Taftanaz military airbase, two kilometres (just over a mile) from the town, is the key to Idlib city, which despite large swathes of countryside being in rebel hands, is still controlled by government forces.
The helicopters take off from the airfield round the clock to pound rebel positions.
Taftanaz, situated among olive groves is a ghost town in which the threat of helicopter bombardment is ever present. Rebels, mostly from the town, run alone or in twos in the dusty streets, often without guns for fear of being targeted.
Without anti-aircraft guns the insurgents cannot hope to counter the fearsome air power.
"Sometimes we mount heavy machine guns among the olive trees to set up a field of fire, but this is very dangerous," says one member of the Free Syrian Army.
The gunships mostly fly at medium altitude, out of the range of rebel machineguns.
In addition to rockets, the gunships also drop bombs that are capable of destroying entire buildings, according to FSA fighter Raghib Ghazal.
Among buildings reduced to rubble, the rebels take cover in the more sheltered basements of deserted family homes, whose other floors are completely wrecked.
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Artillery shells explode intermittently around the town. The helicopters above take their time as they pick their next target.
From a rebel position near the airport 15 helicopters -- Mi-17s and Mi-24s -- can be seen waiting on the ground at the Taftanaz base that rebels attacked on Wednesday but failed to seize.
"The attack on the airport was a failure, it wasn't well prepared," admitted Abu Omar, who said one helicopter was destroyed and others damaged.
"The operation was carried out by the Ahrar al-Sham Brigade who arrived here at dawn," the rebel commander told AFP. "There was no real preparation. I refused to take part."
Rebels did manage on Saturday to capture the main air defence building in Albu Kamal on the Iraqi border, the Syrian Observatory for Human Rights said, adding that reports suggested they had seized ground-to-air missiles.
That assault followed a rebel attack on the Abu Zohur airbase in Idlib province in the northwest, where the FSA said on Thursday it downed a MiG warplane shortly after it took off.
"We have not seen a single weapon arrive" from abroad, Abu Omar said of ground-to-air missiles, unable to hide his disappointment at the international community which he considers "complicit" with President Bashar al-Assad.
On the ground, the rebels say they have the upper hand.
"Regime troops cannot take one step outside their bases," he said, pistol and walkie-talkie in hand. "We're on a plain, they would be immediately picked out."
But the same is also true for the FSA, making any attack on the airport difficult. They can be seen.
"God is with us," says Abu Omar. "They have weapons, we have faith."
Attacks from the skies continue in the capital Damascus and in the key northern city of Aleppo, and August was the bloodiest month of the conflict now in its 18th month.
At least 168 people -- 110 civilians among them -- were killed countrywide on Saturday, said the Britain-based Observatory, which puts the death toll so far at more than 26,000.