From which source is fuel obtained for the APU?

The fuel for the Auxiliary Power Unit (APU) on the CRJ550 is obtained from the left collector tank. This configuration is designed to ensure that the APU has a dedicated source of fuel that is separate from the main fuel tank system, which is crucial for maintaining optimal performance and reliability of the APU during operations.

Using fuel from the left collector tank allows for a more efficient and safe distribution of fuel, as this tank is specifically set up to supply the APU when needed. This arrangement prevents any potential fuel depletion issues from affecting the main engines, ensuring that both the APU and engines have reliable fuel sources without interfering with each other's operations.

In contrast, the right collector tank, main fuel tank, and auxiliary tank are not utilized for APU fuel supply in this design, which can be attributed to the system layout and the need for redundancy and reliability in the aircraft's energy resources.