CPAER Canada Commercial Pilot Practice Exam 2025 – Complete Prep Guide

Twilight Error in Non-Directional Beacon (NDB) navigation primarily occurs due to the effects of the ionosphere during twilight hours. At dawn and dusk, the ionosphere can refract radio waves differently than during the day or night, leading to inaccuracies in navigation. This phenomenon is particularly significant with medium to low-frequency signals used by NDBs, which can be affected by changes in the ionospheric conditions during these transitional periods.

As the sun sets or rises, the ionosphere undergoes distinct changes that alter the propagation of radio signals. This can cause the received bearing to be inaccurate, resulting in a misjudgment of the aircraft's position in relation to the NDB. The twilight effect is essentially a temporary distortion that can make it challenging for pilots to trust their navigation inputs during these specific times.

While high terrain and electrical interference can affect radio signal reception and navigation accuracy, they are not specifically responsible for the changes observed during twilight hours. Low-frequency radio waves are utilized by NDBs, but the specific phenomenon causing the Twilight Error is accomplished through the interactions with the ionosphere at twilight, rather than the characteristics of the radio waves themselves.