(Reuters) - The U.S.-led effort to train the Afghan air force faces big challenges ranging from security threats to possible repercussions from a new review of infrastructure and equipment projects, the U.S. general in charge said.

"This is a hard deal. We're far from 100-percent guaranteed on delivery," said Air Force Brigadier General John Michel, who leads NATO Air Training Command Afghanistan, which is due to complete its training of the Afghan air force by December 31, 2017 - three years after most U.S. forces leave Afghanistan.

The one-star general cited progress in training and planning for Afghanistan to assume control over the air force but said many factors were outside his control.

Michel spoke to Reuters this week during the annual Air Force Association conference here.

He said the NATO-led International Security Assistance Force was re-examining all infrastructure projects after a report that one $37 million aviation facility may have been used to store opium and other concerns raised by Congress.

A group of U.S. lawmakers this week called on U.S. Attorney General Eric Holder to use all available resources to back up the Pentagon's criminal investigation into potentially improper payments made by an Army aviation unit that awarded contracts to Russian and U.S. firms to maintain and overhaul Russian-made Mi-17 helicopters.

Michel said Marine Corps General Joseph Dunford, who heads ISAF, was trying to insulate the training command from any fallout from the procurement problems, which were linked to a different unit. But some consequences were possible, he said.

"If they downscale some of our infrastructure (and cut aircraft), there's a degrading effect on our capacity," he said. "All of these become impediments to our success while we fight the clock."

Michel, who arrived on the job seven weeks ago, said about 70 percent of the hangars, taxiways and other infrastructure needed to support the air force, which is due to expand to around 8,000 people from 7,000, were completed.

But he said he fears the remaining 30 percent might never get built if problems identified in a recent report by the Special Inspector General for Afghanistan Reconstruction (SIGAR) lead to project cancellations.

"You have to have concrete and buildings to operate from," he said.

'SMALL BUT MIGHTY'

The training mission is being led by 649 U.S. military advisers, contractors and advisers from other NATO forces. Their ranks will swell to 1,114 over the next two years after four Lockheed Martin Corp C-130 cargo planes and 20 A29 Super Tucano planes built by Sierra Nevada Corp arrive.

A dozen Mi-17 helicopters are also expected in coming weeks, Michel said.

The NATO advisers are helping Afghans develop the skills to operate, maintain, develop budgets for and manage what Michel calls a self-sustaining, "small but mighty" air force.

Afghani pilots will be trained to carry out missions, respond to natural disasters, and evacuate casualties in a mountainous country that still lacks roads and other forms transportation.

One of the biggest challenges has been ensuring that about half the force learns English, Michel said, noting that recruiting was difficult in a country where literacy in native languages was at just 31 percent.

Michel's unit now runs seven English courses, serving about 420 students at any given time.

Security at six training sites in Afghanistan is another worry, with attacks or threats setting back training efforts and forcing trainers to reinforce security, he said.

"The more we have to do those kind of (security) missions, the more we have to degrade training," he said.

A longer-term concern is whether the Afghan military can afford the estimated $600 million to $620 million a year it will cost to run the air force.

That question, Michel says, could have big implications for the training effort, and is being debated by Dunford, the Marine Corps general, and Afghan leaders.

"We're going to consume 15 to 20 percent of their budget. We need to know today if that's sustainable," Michel said.

Despite the challenges, he said the Afghan air force was flourishing in many respects.

A casualty evacuation that once took three days can now be executed in three to four hours, and Afghan pilots recently evacuated 300 villagers threatened by major flooding, Michel said.

The air force is also laying the groundwork for the emergence of an Afghan aviation sector and the related infrastructure that will help Afghanistan attract foreign investment, he said.

"Aviation opens you to the world," Michel said. "It seeds the investment that Afghanistan is going to need to really flourish going forward."

(Reporting by Andrea Shalal-Esa; Editing by Xavier Briand, Eric Walsh and Eric Beech)

http://www.reuters.com/article/2013/09/21/us-usa-afghan-airforce-idUSBRE98J10G20130921