Isn't the plural of Airbus, Airbuses.

I thought that 's means possessive except in unusal circumstances, such as to delineate. For example:

Ralph's: as in Ralph's shoes
Ralphs: as in several Ralphs in the room

737: one 737
737's: as in 737's engines
737s: as in two 737
737's: as in two 737's landing on the runway. Ok because the ' separates a number and s

SAABs: 2 SAAB cars
SAAB's: acceptable for 2 SAAB cars as the SAAB part is not just a plain word

Does anyone agree?