Localizer Approach: Maintaining Accuracy in Challenging Conditions

How does the loss of radio deviation signal affect aircraft during a localizer approach?

A. the aircraft flies in a circle

B. aircraft flies off the centerline on pre-set heading

C. aircraft flies heading with increasing drift angle

The correct answer is B. aircraft flies off the centerline on pre-set heading.

If the radio deviation signal is lost in a localizer approach, the aircraft usually flies off the centerline on a pre-set heading. CMEs as well as wind direction and velocity can impact the aircraft's trajectory.

On a localizer approach, an aircraft is guided to a landing strip by a narrow radio beam. If the radio deviation signal is lost, it would generally result in a scenario where the aircraft flies off the centerline on a pre-set heading. This is because the localizer provides lateral guidance by broadcasting a signal that the airplane uses to align itself with the centerline of the runway.

Distortion caused by Coronal Mass Ejections (CMEs) and the effect of wind direction and velocity can influence the accuracy of the aircraft's trajectory. CMEs can distort GPS-derived positions, reducing the accuracy to the point where the limits required for airplane systems (which must know their positions to within 160 feet) can't be met. This may force the Federal Aviation Administration to restrict flights for certain lengths of time.

A pilot must construct a vector equation that includes the velocity of the plane with respect to the ground, the velocity of the plane with respect to the air, and the velocity of the air with respect to the ground to compensate for these factors. By knowing the last two quantities, the velocity of the plane with respect to the ground can be solved.