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

The primary jet pump is utilized after engine start for several important reasons. Once the engine is running, it is crucial to maintain a consistent and adequate fuel supply to the engine for optimal performance and safety. The primary jet pump is designed to efficiently transfer fuel from the collector tank to the fuel system, ensuring that the engine receives fuel at the necessary pressure and flow rates.

In aircraft fuel systems, the primary jet pump usually operates automatically following engine start-up, as it is typically linked to the engine's operation. It plays a vital role in maintaining fuel system pressure and preventing cavitation in the fuels lines, which can lead to engine performance issues.

The other options—transfer jet pumps, backup pumps, and emergency pumps—serve different functions within the fuel system. Transfer jet pumps usually assist in moving fuel between tanks rather than delivering fuel to the engine after start. Backup pumps are there to provide an alternative fuel supply should the primary system fail, while emergency pumps are used only in critical situations where there is an immediate risk to fuel supply or engine operation.