Which fuel pump is used after engine start in the collector tank?

The primary jet pump is the correct choice because it is responsible for transferring fuel from the collector tank to the engine after the engine has been started. This pump operates by creating a low-pressure area that draws fuel into the jet pump from the collector tank, ensuring a steady supply to the engine for optimal performance.

The primary jet pump is designed to function primarily during normal operations, utilizing the engine's operational parameters to maintain fuel flow efficiently. In contrast, other types of pumps like the transfer jet pump and the backup fuel pump serve different roles under specific conditions, such as transferring fuel between tanks or providing redundancy in case of primary pump failure. The emergency fuel pump is typically reserved for emergency scenarios and is not the primary means of fueling the engine during standard operations.

Thus, the primary jet pump’s role is central to the engine’s fuel system following start-up, making it the correct answer.