Russia and Belarus are accused of colluding to help Russia obtain spare parts for military aircraft operating over Ukraine. Belarus is subject to some sanctions because of its support for Russia but not nearly as many sanctions as Russia itself. Belarus can still get spare parts for military and civil aircraft, but transferring any of those to Russia would get Belarus subjected to the same aircraft-related sanctions Russia is suffering from. Ukrainian military intelligence discovered and publicized this deal, which enables Western nations to use their space satellites and embassy personnel to check up on this activity
The Ukrainians probably got the tip from pro-Ukrainian Belarusians. There are a lot of those in Belarus. That’s how the West found out that in late July Belarus agreed to send 200 soldiers to Syria to replace the many more Russian troops brought back to Russia to replace losses in Ukraine. Belarus has refused Russian requests to send its troops into Ukraine. While the Belarus dictator is pro-Russia, most Belarussians are not and some openly support Ukraine.
The Belarussian government cooperated because Russia had been propping up a pro-Russian ruler who recently faced large scale demonstrations protesting his misrule and vote rigging. Russia sent in troops that enabled Belarus to deploy all its more reliable security forces against the demonstrators. Despite that, Belarus would not send its troops into Ukraine but a month after the February invasion began did cooperate in secretly treating Russian casualties. Belarus medical personnel were more willing to talk about what was happening with all those dead and wounded Russian soldiers and it eventually became known that Belarus railroad staff were cooperating with their Ukrainian counterparts to sabotage railroad access to Ukraine for Russian trains crossing the border parts of Ukraine the Russians considered safe.
Many Belarussians continue supporting Ukraine and sabotaging the Russian war effort. Some of the sabotage came in the form of timely reports on what Russian troops were doing in Belarus. After March Russian soldiers were allowed to freely loot and some managed to get back to Russia with a lot of loot. Many of the retreating troops passed through Belarus, where local and international media were free to report on them. Belarussian police also ignored the large amount of loot being sold in hastily organized markets, or shipped via parcel shipping offices that regularly sent packages to Russia. It was obvious that many of the Russian soldiers brought civilian goods looted from Ukrainian homes and businesses as they were being forced out of northern Ukraine
New troops headed for Ukraine early in the war arrived via Belarus. These new arrivals became aware of the truckloads of dead or wounded Russian soldiers returning and Belarus hospitals crowded with Russian wounded. Returning Russian soldiers told the new troops that the Ukrainians were putting up quite a fight and Russian units were taking heavy losses, especially in terms of armored vehicles, including tanks, destroyed by Ukrainians using portable weapons. The Russian military took their wounded, at least the ones the Ukrainians didn’t capture, back to military or militarized civilian hospitals in Russia and neighboring Belarus. Many of the badly wounded arrived dead and their deaths and the condition of the surviving Russian troops, were declared state secrets. There were severe punishments for those who revealed to the public what was going on. It was less obvious what returning Russian commanders were telling officers in the newly arrived units. Most officers are circumspect in their comments but some are clearly fed up with how the Russian efforts are being mismanaged after only six weeks of fighting. Since then, the situation has gotten worse for Russia and that encourages Belarussians because a Russian defeat in Ukraine might mean a new government in Russia that would end Russian support for the corrupt Belarussian ruler.
Because of the 2022 sanctions, China is now Russia’s largest trading partner and, together with Belarus and a few other nations, continues to trade with Russia. The other half is currently halted, or soon will be, by sanctions. Russia has experience in evading economic sanctions and knows that greed in notoriously corrupt countries provides customers willing to switch to heavily discounted Russian oil. Belarusians don’t want their nation to be hit by Russia-level sanctions and that makes it difficult for the Belarussian government to carry out any sanction-violating scheme with Russia.