When avionics manufacturers develop a piece of equipment that requires an airborne navigation database, they typically form an agreement with a database provider to supply the database for that new avionics platform. It is up to the manufacturer to determine what information to include in the database for their system. In some cases, the navigation data provider has to significantly reduce the number of records in the database to accommodate the storage capacity of the manufacturer’s new product, which means that the database may not contain all procedures.

Another important fact to remember is that although there are standard naming conventions included in the ARINC 424 specification, each manufacturer determines how the names of fixes and procedures are displayed to the the approach identifier field for the VOR/DME Runway 34 approach at Eugene Mahlon Sweet Airport (KEUG) in Eugene, Oregon, as “V34,” different avionics platforms may display the identifier in any way the manufacturer deems appropriate. For example, a GPS produced by one manufacturer might display the approach as “VOR 34,” whereas another might refer to the approach as “VOR/DME 34,” and an FMS produced by another manufacturer may refer to it as “VOR34.” [Figure 6-29]

These differences can cause visual inconsistencies between chart and GPS displays, as well as confusion with approach clearances and other ATC instructions for pilots unfamiliar with specific manufacturer’s naming conventions. The manufacturer determines the capabilities and limitations of an RNAV system based on the decisions that it makes regarding that system’s processing of the airborne navigation database.

Like paper charts, airborne navigation databases are subject to revision. According to 14 CFR Part 91, § 91.503, the end user (operator) is ultimately responsible for ensuring that data meets the quality requirements for its intended application. Updating data in an aeronautical database is considered to be maintenance and all Part 91 operators may update databases in accordance with 14 CFR Part 91, § 43.3(g). Parts 121, 125, and 135 operators must update databases in accordance with their approved maintenance program. For Part 135 helicopter operators, this includes maintenance by the pilot in accordance with 14 CFR Part 43, § 43.3(h).

Pilots using the databases are ultimately responsible for ensuring that the database they are operating with is current. This includes checking Notices to Airmen (NOTAM)-type information concerning errors that may be supplied by the avionics manufacturer or the database supplier. The database user is responsible for learning how the specific navigation equipment handles the navigation database. The manufacturer’s documentation is the pilot’s best source of information regarding the capabilities and limitations of a specific database. [Figure 6-30]

Understanding the capabilities and limitations of the navigation systems installed in an aircraft is one of the pilot’s biggest concerns for IFR flight. Considering the vast number of RNAV systems and pilot interfaces available today, it is critical that pilots and flight crews be familiar with the manufacturer’s operating manual for each RNAV system they operate and achieve and retain proficiency operating those systems in the IFR environment.

Most professional and general aviation pilots are familiar with the possible human factors issues related to flightdeck automation. It is particularly important to consider those issues when using airborne navigation databases. Although modern avionics can provide precise guidance throughout all phases of flight, including complex departures and arrivals, not all systems have the same capabilities.

RNAV equipment installed in some aircraft is limited to direct route point-to-point navigation. Therefore, it is very important for pilots to familiarize themselves with the capabilities of their systems through review of the manufacturer documentation. Most modern RNAV systems are contained within an integrated avionics system that receives input from several different navigation and aircraft system sensors. These integrated systems provide so much information that pilots may sometimes fail to recognize errors in navigation caused by database discrepancies or misuse. Pilots must constantly ensure that the data they enter into their avionics is accurate and current. Once the transition to RNAV is made during a flight, pilots and flight crews must always be capable and ready to revert to conventional means of navigation if problems arise.

Some U.S. airports have been closed for up to several years, with little or no chance that they will ever reopen; yet their “indefinite” closure status – as opposed to permanent or UFN closure, or abandonment – causes them to continue to appear on both VFR and IFR charts and in airborne navigation databases; and their instrument approach procedures, if any, continue to be included – and still appear to be valid – in the paper and electronic versions of the United States Terminal Procedures Publication (TPP) charts. Airpark South, 2K2, at Ozark, Missouri, is a case in point.

Even though this airport has been closed going on two years and, due to industrial and residential development surrounding it, likely will never be reopened, the airport is nonetheless still charted in a way that could easily lead a pilot to believe that it is still open and operating. Even the current U.S. Low Altitude En route chart displays a blue symbol for this airport, indicating that it still has a Department of Defense (DOD) approved instrument approach procedure available for use.

Aircrews need to use caution when selecting an airport in a cautionary or emergency situation, especially if the airport was not previously analyzed suitable for diversion during preflight. Aircrews could assume, based on charts and their FMS database, the airport is suitable and perhaps the only available diversionary or emergency option. The airport however, could be closed and hazardous even for emergency use. In these situations, Air Traffic Control may be queried for the airport’s status.

As the data in a worldwide database grows, the required data storage space increases. Over the years that panel-mounted GPS and FMSs have developed, the size of the commercially available airborne navigation databases has grown exponentially.

Some manufacturer’s systems have kept up with this growth and some have not. Many of the limitations of older RNAV systems are a direct result of limited data storage capacity. For this reason, avionics manufacturers must make decisions regarding which types of procedures will be included with their system. For instance, older GPS units rarely include all of the waypoints that are coded into master databases. Even some modern FMS equipment, which typically have much larger storage capacity, do not include all of the data that is available from the database producers. The manufacturers often choose not to include certain types of data that they think is of low importance to the usability of the unit. For example, manufacturers of FMS used in large airplanes may elect not to include airports where the longest runway is less than 3,000 feet or to include all the procedures for an airport.

Manufacturers of RNAV equipment can reduce the size of the data storage required in their avionics by limiting the geographic area the database covers. Like paper charts, the amount of data that needs to be carried with the aircraft is directly related to the size of the coverage area. Depending on the data storage that is available, this means that the larger the required coverage area, the less detailed the database can be.