If you need to find out the list of passengers on the departing plane, it will be very difficult to get your way. The Federal Law "On Personal Data" prohibits access to such information to individuals. Still, there are some possibilities.
If you find out from the media about the crash of the liner and suspect that your friends or relatives may have been on board, contact the airline immediately. In this case, they have no right to refuse you, moreover, hot telephone lines are specially created to which you can call around the clock. Later, when the first excitement calms down, it will be possible to clarify the list of passengers on the Internet. It will be posted on a special site.
If we are not talking about life and death, it will be very difficult to access passenger data. Try to contact the airline employees and honestly tell us why you needed it. If, for example, because of a sudden outbreak of love at first sight you want to know the name of your fellow traveler and will be able to convince the airline representatives of your good intentions, maybe they will help you. But they are not obliged to do this, and if we are talking about some business matters, they have no right to disclose such information at all.
Use your contacts in law enforcement if you have acquaintances there. The airport databases have access to the employees of the FSB, police, tax authorities. Using their powers, they will probably find out what you need.
Don't try to find data on the internet. Although there are dozens of sites that offer such services, you cannot rely on them, and their services are very expensive. A skilled hacker can break into an airline's database, but this is a criminal offense and it is best not to contact them.
Hire a private investigator. If he has a tracing license, he can request information at the airport. In any case, its capabilities will be much greater than yours.