Which of the following can block GPS signal?

• A. Heavy rain
• B. Magnetic dip
• C. Banking the aircraft
• D. Cloud cover

Answer: (C)

GPS needs a clear line of sight to satellites. When the aircraft banks, the fuselage and wings can physically block or shadow the signals from some satellites from reaching the antenna, especially if the antenna is mounted on top and the bank angle is deep. If enough satellites are blocked or the geometry becomes poor, the receiver can lose its reliable fix or degrade to a less accurate one.

Heavy rain and cloud cover don’t block GPS signals in the same way. At the L-band frequencies used by civil GPS, rain and clouds may cause only minor attenuation, not a complete blockage. Magnetic dip affects the aircraft’s magnetic compass, not the GPS receiver, so it won’t prevent GPS reception.