What stage air is used to feed the 7B bearing in a gas turbine engine?

The correct answer is the 9th stage air for feeding the 7B bearing in a gas turbine engine. In gas turbine design, the engine typically has several stages of compression where air is progressively compressed before it enters the combustion chamber. The 9th stage is selected because it provides the necessary pressure and temperature characteristics suitable for effective lubrication and cooling of the bearings, including the 7B bearing specifically.

Air from the 9th stage is generally at a high enough pressure to ensure that it can adequately deliver the required flow and is less likely to introduce contaminants that could compromise bearing operation. This stage is also part of optimized airflow management in the engine system, ensuring reliability and performance.

Using air from stages that are either too low or too high could result in insufficient pressure or excessive heat, respectively, which could jeopardize the integrity of the bearing and the overall performance of the engine.