GPS for VFR Navigation — Databases and Maps

by Andrew Graham, Project Engineer, SatNav Program Office, NAV CANADA

Global positioning system (GPS) can be a tremendous aid to visual flight rules (VFR) flying. No more getting lost and having to ask for VHF direct finding service (VDF) steers. Those time and distance calculations you have to do for your flight test all go away. Newer models with moving map displays make navigation a piece of cake; no more trying to read town names on water towers. Some receivers even tell you when you’re about to fly into controlled or restricted airspace.

This all sounds great, and it usually is. However, there have been cases reported where receivers have not depicted airspace boundaries correctly, and well-intentioned pilots have blundered into areas where they ought not to have gone. Naturally, this upsets air traffic control (ATC), and the pilots shoulder the blame briefly before passing it along to the GPS receiver manufacturer. Who’s at fault in these cases?

Well, unfortunately, it’s the pilots.

CAR 602.60 states that pilots shall not conduct a VFR OTT (over the top) or night VFR flight without carrying

... all of the necessary current aeronautical charts and publications covering the route of the proposed flight and any probable diversionary route.

The CARs don’t say anything about day VFR chart requirements. However, CAR 602.71 states:

The pilot-in-command of an aircraft shall, before commencing a flight, be familiar with the available information that is appropriate to the intended flight.

At present, paper charts (VFR navigational chart [VNC], world aeronautic chart [WAC], and VFR terminal chart [VTA]) are the only authoritative source of VFR navigation information in Canada. Nevertheless, if avionics manufacturers supply aeronautical information, isn’t that information checked to ensure that it’s accurate and complete? Well, yes and no. It’s important to understand the database requirements for instrument flight rules (IFR) versus VFR. Data used for IFR flight (navigation aids, airports, published fixes, and instrument procedures) must meet specific standards. In VFR avionics, while there is nothing to prevent a receiver manufacturer from depicting topographic features or airspace boundaries to assist in situational awareness, there is no standard or verification process to ensure that all information is presented accurately. That may sound odd, but remember what the “V” in “VFR” stands for. VFR ensure that the pilot will be able to navigate with respect to visible landmarks, using a chart, watch and compass. There are no provisions for another means of navigation to replace visual reference to the ground. Pilots may use GPS to supplement visual navigation techniques, but are not to rely on it.

It is worth noting that some receivers present an explicit warning to pilots that the receiver is to be used only as an aid to VFR navigation, and that any data presented is for reference only.

Transport Canada Aircraft Certification and NAV CANADA are currently investigating this issue. The ultimate solution may come with the advent of “paperless” cockpits, but this will depend on the development of detailed standards. Unfortunately, with database accuracy would likely come increased costs, both for the verification of the information, and for regular database updates.

Until this is resolved, by all means, cross-check your position using GPS, but don’t use it as your only means of navigating. Don’t let confidence in your GPS receiver tempt you to fly in marginal weather. And finally, always carry and use up-to-date paper charts (don’t forget the chart updating data in the Canadian Flight Supplement (CFS), and (NOTAMs) and report avionics database anomalies to the manufacturer.

Safe flying.

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