Sanctions have forced Russia's biggest private airline to decommission some of its planes, while the country's national carrier has delayed flights because of staffing shortages, it has been reported.

The woes faced by S7 Airlines and Aeroflot are the latest blow to Russian civil aviation since the start of Vladimir Putin's full-scale invasion of Ukraine, as a government official warned that passenger numbers in Russia will slump.

The head of Russia's federal air transport agency, Rosaviatsia, Dmitry Yadrov, said that S7 Airlines will decommission its fleet of Airbus A320neo aircraft because sanctions have made it impossible to repair and maintain their U.S.-made Pratt & Whitney engines.

S7 Airlines has 28 A320neos in its 101-strong fleet, according to SimpleFlying.com.

Yadrov said that passenger traffic in Russia would shrink this year to 98.1 million passengers from last year's 105 million and that much depends on what S7 does with its withdrawn aircraft, state news agency Tass reported.

"These aircraft carry a significant amount of passengers, but the operation of these engines requires increased attention," said Yadrov.

Also known as Siberia Airlines, S7 is headquartered in Novosibirsk. Its membership of the Oneworld alliance of international carriers was suspended due to Putin's invasion and it was among the Russian airlines banned from the airspace of the EU and other countries.

S7 has been beset with problems over the course of the war, which include having to suspend all international flights at one point, and the owner of the aircraft it leases, AerCap, looking to repossess some of its planes.

In October 2023, S7's problems finding spare parts for engines and servicing reduced the number of its operational Airbus aircraft to around 13, or only one-fifth of its Airbus fleet.

Business newspaper Kommersant reported that S7 Airlines will cut its upcoming winter schedule by up to 15 percent due to aircraft maintenance issues.

Meanwhile, the national carrier Aeroflot is having problems of its own due to a shortage of crew that has caused flight delays, according to Telegram channel Baza, which is linked to Russia's authorities.

The channel said 330 flights were delayed last weekend and 20 canceled, with planes forced to fly with reduced crews. Baza said that last-minute changes to staffing have seen, in some instances, flight attendants boarding after the passengers.

More than 1,500 staff called in sick due to unhappiness with the management over scheduling, which called on many to work more than the normal 90 in-flight hours per month and a lack of leave, according to the Telegram channel Aviatorshina (Aviators).

Aeroflot has denied the reports and said that it had enough flight attendants and pilots to carry out its schedule, state news agency RIA Novosti reported.

Newsweek has contacted Aeroflot and S7 for comment.