What is the approved oil grade type for the Auxiliary Power Unit of a CRJ900?

The approved oil grade type for the Auxiliary Power Unit (APU) of the CRJ900 is MIL-L-7808. This specification denotes a certain type of aviation lubricating oil that meets the stringent requirements for performance and reliability in aircraft operations, particularly in the context of turbine engines and auxiliary power units. The use of MIL-L-7808 ensures optimal lubrication, thermal stability, and protection against wear, which is crucial for the safe and efficient operation of the APU.

The other options, while they may be types of oil suitable for different aviation applications, do not specifically meet the criteria outlined for APU use in the CRJ900 aircraft. For instance, MIL-L-23699 (TYPE II) is commonly used in some engine applications but is not the designated oil for the APU. Mobil Jet Oil II and Castrol 4000 are also reputable products but do not align with the approved standard for the APU in this aircraft type. Thus, MIL-L-7808 is the correct and approved oil grade.