Instrument Rating Checkride Practice Test

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Question: 1 / 400

What is the minimum number of satellites needed for a GPS receiver to provide a three-dimensional fix?

2 satellites

3 satellites

4 satellites

To achieve a three-dimensional fix, a GPS receiver needs to determine its position in three-dimensional space: latitude, longitude, and altitude. This requires a minimum of four satellites.

Each satellite provides a signal that helps determine the receiver's distance from it. With three satellites, the GPS can calculate a two-dimensional position (latitude and longitude) by intersecting the spheres of the three satellites' signals. However, to add altitude to this position—essentially determining how high the receiver is—the receiver requires a fourth satellite. The fourth satellite allows the system to resolve the ambiguity in altitude that arises when only considering the two-dimensional fix.

In summary, the correct answer is based on the need for a fourth satellite to achieve a full three-dimensional position.

Instrument Rating Checkride Practice Test

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