What should a pilot check before a GPS approach?

Before a GPS approach, it is essential for a pilot to check the availability of Receiver Autonomous Integrity Monitoring (RAIM). RAIM is a crucial component that ensures the integrity of the GPS signals. It verifies the accuracy of the satellite data received by the GPS receiver, which is vital for safe navigation, especially when conducting approaches that rely solely on GPS. If RAIM is not available, the integrity of the position information being utilized during the approach could be compromised, leading to potential navigation errors.

The other options, while important in their own right, do not directly pertain to the integrity of the GPS signals necessary for a successful GPS approach. Weather conditions are critical for planning a flight, altitude restrictions are key for ensuring compliance with airspace regulations, and communication with ground services is necessary for overall operational safety and efficiency, but none of them address the specific integrity checks required for GPS navigation. Thus, ensuring RAIM availability stands out as the most critical check before performing a GPS approach.