What is the maximum allowed alteration of an altimeter reading during a case leak test at 18,000 feet?

The maximum allowed alteration of an altimeter reading during a case leak test at 18,000 feet is set to ensure that altimeters maintain precision and accuracy under pressurized conditions. According to FAA regulations, during a leak test, an altimeter must not vary from its indicated pressure by more than ±100 feet. This tolerance recognizes both the tolerance level for accurate instrument performance and the practicalities of real-world testing scenarios.

This value is established to help in distinguishing between acceptable performance for aviation safety and calibration standards. A deviation greater than this threshold could indicate potential issues that may compromise the accuracy of the equipment, which is crucial for flight safety, especially at higher altitudes where aircraft operate closer to performance limits. In comparison, other values provided do not align with the established standards, making them inappropriate for use in this context.