This is the 9841st most frequent Russian word.
авиакомпанией
"Airline" (a company that provides air transport services for passengers or cargo).
The word 'авиакомпанией' is the instrumental case of 'авиакомпания' (airline), used here to specify the means or mode of transport for the subject.
Я летел авиакомпанией, предоставляющей комфортный сервис.
I flew with the airline that provides comfortable service.
In this sentence, 'авиакомпании' is in the prepositional case, indicating the location where someone works.
Она работает в крупной авиакомпании.
She works at a large airline.
The word 'авиакомпании' here is in the genitive case, showing possession or association with the airline.