Which indicator can appear on the HSI to show GPS loss of availability?

Which indicator can appear on the HSI to show GPS loss of availability?

• A. GBAS
• B. RAIM
• C. Flags on the HSI
• D. WAAS

Answer: (C)

GPS data are considered usable only when the receiver can provide position and velocity with acceptable integrity. If the GPS signal is lost or its integrity is degraded, the system marks the data as unavailable and the HSI will display a flag to warn you that GPS guidance should not be relied upon. That visual cue—flags on the navigation display—is what you’d see to indicate GPS loss of availability. GBAS and WAAS are augmentation systems that improve accuracy and integrity but don’t by themselves serve as the direct indicator of GPS unavailability on the HSI. RAIM is the integrity-monitoring process that assesses whether GPS data can be trusted, but the explicit loss-of-availability indicator shown to the pilot on the HSI is the flag.

GPS data are considered usable only when the receiver can provide position and velocity with acceptable integrity. If the GPS signal is lost or its integrity is degraded, the system marks the data as unavailable and the HSI will display a flag to warn you that GPS guidance should not be relied upon. That visual cue—flags on the navigation display—is what you’d see to indicate GPS loss of availability. GBAS and WAAS are augmentation systems that improve accuracy and integrity but don’t by themselves serve as the direct indicator of GPS unavailability on the HSI. RAIM is the integrity-monitoring process that assesses whether GPS data can be trusted, but the explicit loss-of-availability indicator shown to the pilot on the HSI is the flag.