No, their airlines are not an ancillary product. They are their main product. According to Boeing's earnings reports, the commercial aircraft segment of the company made up 56% of total revenue in 2018, 42% in 2019, 27% in 2020, 30% in 2021, 38% in 2022, and 43% in 2023. The rest of their revenue is split between the Defense, Space and Security segment, and the Global Services segment.

Prior to 2017, the vast majority of the earnings for the whole company came from the Commercial Airplanes segment. Since then, that segment has been operating at a loss. Since 2022, both Defense and Commercial Airplanes have been operating at a loss.

If you're curious you can look up Boeing's 10-k form. Page 56 has the revenue breakdowns.