The Afghan Air Force’s (AAF) Russian-built helicopters are wearing out flying close air support missions against the Taliban and need to be replaced with new airframes that the U.S. government is allowed to buy and service, the commander of U.S. forces in Afghanistan told Congress Feb. 4.

Army Gen. John Campbell testified before Congress he has called for a plan to “convert” aircraft like the Russian Mi-17 twin-engine utility helicopters in the AAF fleet “to probably a U.S. aircraft.”

“The frames that we bought for them, the Mi-17s, based on operational losses, op tempo over the next couple years, that will continue to go down and we’ll have to figure out the lifecycle maintenance, so probably a different airframe,” Campbell told the Senate Armed Service Committee (SASC) during what is likely his last testimony in his current position. “We’re going to need support from the Congress once we get through that because that is not included in the current financing of the Afghan Security Forces as we go forward.”

Implementation will fall to Campbell’s successor. SASC on Feb. 4 approved the nomination of Army Lt. Gen. John Nicholson to take over the continued U.S. presence in Afghanistan from Campbell.

The U.S. government has spent $2.4 billion since fiscal 2010 to develop the AAF, of which $912 million was set aside for aircraft and other equipment, according to a January report by the Special Inspector General for Afghanistan Reconstruction (SIGAR).

At present the AAF has 11 Mi-35 helicopters, 49 Mi-17s and 16 MD-530 attack helicopters made by American firm MD Helicopters. The AAF also has 24 C-208 and four C-130 airplanes. An additional 12 MD-530s are being purchased and are scheduled for delivery in 2016.

“For the close air support, it’s a long-term effort to make sure that they have the right rotary wing and fixed-wing support, but that’s going to take several years,” he said.

Buying relatively inexpensive Russian aircraft for the AAF was standard practice until recently. Military arms purchases from Russia have become a victim of imploding U.S.-Russia relations over conflicts in Ukraine, Crimea and Syria. The U.S. military’s intention of holding Russia at bay in Europe was underscored recently by the quadrupling of military spending on the continent for deterrence of further westward aggression by Moscow.

Late in 2015, Indian Prime Minister Narendra Modi–a strong U.S. ally–muddied the waters by donating four Russian-made Mi-25 assault helicopters to the AAF during an official visit to Afghanistan, according to SIGAR. The Pentagon informed the Afghan defense ministry that U.S. funds could not be used to sustain those aircraft because of concerns over sanctions placed on Russia, SIGAR said.

The AAF is searching for other regional partners that could assist with maintenance of the Russian helicopters, SIGAR said. The service has several years yet to go before it is manned and equipped to operate independent of outside help, most of which will continue to come from the U.S. military, Campbell said.

“Close air support and the Afghan Air Force in general…is going to take several more years,” Campbell said in response to a question from Sen. Deb Fischer (R-Neb.). “It takes about three years to build a pilot, so if we pick somebody today they won’t see that pilot for another three years. And that’s just the human capital aspect. That doesn’t include acquiring the platforms.”

The AAF recently received its first four Embraer A-29 Super Tucano aircraft, which are specifically designed for counterinsurgency, close-air support and aerial reconnaissance. Another four should arrive sometime in April or May. Eventually, the fleet will number 20 of the single-engine turboprop aircraft built by Embraer and Sierra Nevada Corp