Commercial and Business Aviation Advisory Circulars

Aircraft Navigation Databases

PURPOSE

The purpose of this Air Carrier Advisory Circular (ACAC) is to make the aviation community aware of anomalies that have been identified in aircraft navigation databases. The following information was originally printed in the Airspace Newsletter.

REFERENCE

TP 10136, Airspace Newsletter, Issue 2/96, "Check Your Database"

BACKGROUND

Use of Airborne Navigation Databases

Efforts to introduce the use of GPS and other RNAV/Flight Manual Supplement (FMS) procedures as quickly and as safely as possible have revealed that idiosyncracies may exist within the databases and could be the source of potential operational and safety problems.

It is extremely important that pilots who are operating database-dependent navigation equipment be vigilant and monitor the information and guidance data being provided by the aircraft's navigation systems. Some detected anomalies have been the result of software problems; others of the way procedures and information are encoded into the database. These anomalies may be transparent to the user until such time as the aircraft may have departed its expected flight path. Therefore, it is essential that the crew confirm the equipment will respond as expected by not only comparing the database information with the hard copy, but also monitoring the performance of their equipment.

Comparing database information with an independent source is a requirement of the Flight Manual Supplement. Prior to using the equipment for IFR navigation, the crew must verify the accuracy of each selected waypoint using current approved data. If there are any discrepancies between the information in the database and the published hard copy, the pilots must follow the hard copy procedure.

Although anomalies have been found in all areas of the databases, the most significant have been identified in the coding of conventional approach procedures. Database suppliers are emulating conventional procedures to make them compatible with RNAV/FMS type. The emulation is not always correct.

ACTION

Transport Canada is working with industry to resolve the problems that have been identified. Any anomalies are being reported to the database suppliers; all other database users are encouraged to do the same.

CONCLUSION

All FMSs are certified for IFR navigation under the condition that any information taken from the database be verified against an independent source prior to use. It is essential that pilots comply with this requirement by using approach, terminal, and enroute charts to check for discrepencies in FMS generated navigation data.

A.J. LaFlamme
Director
Commercial and Business Aviation