Question

FAA Requirement Table 14-1 on page 655 lists process data consisting of the errors (ft) of aircraft altimeters when they are tested for an altitude of 2000 ft, and the Federal Aviation Administration requires that errors must be at most 30 ft. If x and R control charts show that the process of manufacturing altimeters is within statistical control, does that indicate that the altimeters have errors that are at most 30 ft? Why or why not?

Short answer

The process is known to be within statistical control, which implies it does not violate any condition for the stable process. It does not assure that the errors are at most 30 ft.

Step-by-step solution

Given information

Errors in the altimeters of aircrafts are recorded. The errors require to be at most 30 ft.

The two control charts indicate that the process is within statistical control..

Define statistically control process

Control charts like and R chart are used toanalyze whether the mean and the variation of the process are stable or not. Specifically, a process is not statistically stable if one of these conditions are satisfied:

• There are no obvious patterns or cyclic trend visible.
• There existsno point above or below the upper and lower control limit respectively.
• Run of 8 rule: less than eightconsecutive points must fall above or below the centerline of the chart.

Analyze the situation

It is known that the process is statistically stable, which implies none of the criteria are satisfied in the above process. Specifically, no specific trends or extreme values would be observed along with the specified run of 8 rule.

This does not assure that the errors are in the prescribed range.