RNAV approach with a database anomaly
An aircraft with a GPS-based RNAV system is cleared for an LNAV approach. On selecting the approach from the navigation database, the crew notices that the final approach waypoint coordinates differ slightly from those on the current paper chart, and that the database cycle is one cycle out of date. The aircraft is in IMC, 15 nm from the initial approach fix, with 25 minutes of fuel above reserve. The airport has an ILS on the same runway, and the crew is radar-identified. The operator's SOP requires the current database cycle for RNAV approaches.
1. Assess whether the crew may continue with the RNAV LNAV approach and what alternatives exist.
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The out-of-date database is the controlling factor: the operator's SOP requires the current cycle, and the coordinate mismatch with the chart indicates the procedure may have changed. Continuing the RNAV approach would breach SOP and rely on unverified data. The correct decision is not to fly the RNAV approach as coded.
Alternatives: request the ILS to the same runway, for which the crew is already radar-identified and which does not depend on the RNAV database; or request radar vectors to a visual approach if conditions permit. With 25 minutes above reserve, there is time to reconfigure and brief the ILS. The judgement tested is resisting the temptation to continue because the aircraft is already established and the discrepancy is 'slight' - in IMC, unverified final approach data is not acceptable.
2. Explain the significance of the coordinate difference and how the crew should handle the database discrepancy after landing.
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Final approach waypoint coordinates define the path the aircraft will fly; a small coordinate difference can shift the final approach course and the missed approach point, potentially placing the aircraft outside the protected area or below the correct descent profile. The difference must therefore be treated as a data-integrity issue, not a rounding error.
After landing, the crew should report the discrepancy through the operator's navigation database reporting process, noting the procedure, cycle, and the chart comparison, so the database provider can investigate. The event should also be recorded in the technical log if the database is found to be incorrect. The exam point is that database anomalies are safety reports, not personal notes, and that the crew's in-flight decision must protect the approach before the administrative follow-up.