Russia’s commercial aircraft fleet could falter within months and risks being largely grounded in a few years as sanctions block essential spare parts from Boeing Co. and Airbus SE, according to Jefferies Group LLC.

“They’ll be able to fly for the next six months to a year fairly well, then parts start breaking and you’ll need replacements,” Jefferies analyst Sheila Kahyaoglu said during a conference call Tuesday on the implications of Russia’s invasion of Ukraine. “Then you’ll start getting into safety issues.”

Commercial jets needing heavy maintenance, typically carried out every six years, will be stricken because required components won’t be available, Kahyaoglu said. “People in Russia are not going to be able to get around.”

Crippling economic sanctions mean the prospects for air travel—domestic and international—for those in Russia look increasingly uncertain. The country’s 789 commercial planes account for about 2.7% of the global fleet, Jefferies said. Flag carrier Aeroflot PJSC has 187 aircraft with an average age of 6.3 years, according to its website.

Most aircraft operated by Russian carriers are rented from foreign leasing firms, including AerCap Holdings NV. Russian authorities are keeping some of them, leaving the fate of jets worth about $10 billion hanging in the balance.

There’s little hope of foreign owners retrieving their planes, which may eventually become worthless, according to Kahyaoglu.

“Good luck getting an aircraft out of Russia,” she said. “Those aircraft are in six years going to be totally dead money, because they’re not going to be able to get the parts at all.”

There were 523 aircraft from foreign lessors in Russia as of March 10, consultant IBA said. Of those, 142 belong to Dublin-based AerCap, the world’s biggest aircraft leasing firm, followed by SMBC Aviation Capital Ltd. with 35.

Under European Union sanctions tied to the invasion of Ukraine, Irish lessors have until March 28 to cancel the contracts.