the next type of model 40 was the model 40c. it had a bigger cabin so that four passengers could be carried. model 40as had their engines changed to even lighter ones. model 40as with this new engine were called the model 40b-2. the model 40b-4 was another model which had the cabin of the model 40c and the engine of the model 40b-2. boeing model 40s were made until february 1932.