What provides the magnetic heading reference in typical aircraft direction-indicating systems?

• A. A single magnetic compass
• B. Two independent compass systems
• C. GPS heading reference
• D. Inertial reference system

Answer: (B)

Two independent magnetic compass systems provide the magnetic heading reference because the heading indicator (the gyro-based direction-indicating system) relies on a magnetic input to stay accurate. Magnetic compasses are vulnerable to errors from the airframe’s metal, nearby electrical systems, and during maneuvers (acceleration and turning errors). Relying on a single compass could leave you with an unreliable heading. With two separate compasses, you get redundancy and a cross-check: if one shows an anomaly, the other can be used or the standby compass can take over, keeping you oriented even when one source is off. The other options don’t fit because GPS heading isn’t magnetic, and inertial systems drift and don’t provide a magnetic reference on their own.