What is one correct procedure for stating the magnetic heading of aircraft flying 90 degrees?

The correct procedure for stating the magnetic heading of an aircraft flying 90 degrees is to express it as "heading zero niner zero." This phraseology adheres to the standardized communication protocols used in aviation to ensure clarity and precision in navigation and air traffic control. By using "zero" before the number, it helps to avoid confusion, particularly when communications are transmitted over radio, where clarity can be critical.

The use of "niner" for the number nine is a specific phonetic choice to reduce the risk of mishearing or misunderstanding, especially in environments with potential interference or background noise. Thus, the complete phrase "heading zero niner zero" ensures that the heading is clearly articulated as magnetic east, ensuring all parties are aligned in understanding the aircraft's directional orientation.