When ARPA data is questionable, what is the recommended approach?

• A. Rely solely on ARPA data.
• B. Discard all other navigational aids.
• C. Only use AIS for confirmation.
• D. Cross-check with AIS and perform independent range/bearing measurements manually.

Answer: (D)

When ARPA data looks questionable, use ARPA as one source among several and actively verify it with independent information. Start by cross-checking with AIS: compare the target’s AIS-reported position, course, and speed with what ARPA shows. If AIS and ARPA agree, confidence grows; if they disagree, investigate the discrepancy rather than trusting ARPA alone. In addition, perform independent range and bearing measurements yourself, using the radar to measure range and bearing to the target and plotting it separately. This independent check helps catch errors from radar miscalibration, clutter, ERBL/locking glitches, or processing faults. By combining AIS validation with manual range/bearing measurements, you maintain a reliable situational picture even when ARPA data is suspect.