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Safe Use of GPS

Flying Safely with GPS

by Ross Bowie, SatNav Program Manager, NAV CANADA

Most pilots who have used global positioning systems (GPS) agree that it makes flying more efficient and in some ways safer. Previous Aviation Safety Letter articles highlighted some potential hazards of misusing GPS. Many more pilots have started using GPS since the last article, so we thought it timely to review some of the safety issues.

Our experience with various types of GPS avionics suggests good training is essential. A couple of decades ago when the flight management system (FMS) appeared in new airliners, many pilots found that mastering the FMS was more difficult than flying the aircraft. Thanks to modern computers, today’s small GPS receivers have more features than FMSs, and the GPS manual can be thicker than the aircraft's.

Safety depends on using avionics properly. The easy way to learn is to focus on necessary functions: entering and activating a flight plan; making changes to the flight plan in the air, including adding arrival and approach procedures; and navigating en route, in the terminal area and on approach. Find out the best ways to do these things then practice. Many GPS avionics can be used at home or in the classroom. Take advantage of this to learn the basics without wasting fuel, and without having to watch for traffic and fly the aircraft.

Many pilots use GPS as an aid to visual flight rules (VFR) navigation. The key word is "aid," because VFR means seeing the terrain well enough to confirm your position on a map. Avionics used for VFR do not check for errors in satellite signals, so your GPS position could be bad. Finger trouble (entering the wrong waypoint co-ordinates) could have you flying very accurately to the wrong place. A "simple" panel mount or hand held unit depends on hundreds of thousands of lines of software code. When was the last time you made it through a week without your personal computer doing something that made no sense? None of these problems occurs very often, but neither does fuel contamination, and we check for that every day.

GPS accuracy and reliability have led some pilots to depart VFR on days when the visibility is too low for VFR navigation. This could lead to loss of control owing to disorientation or collision with unseen obstacles. When the weather is marginal, a VFR-rated pilot should assume GPS is not available then decide whether to depart. On days when the weather deteriorates en route, it is critical to use your map and fly at a safe altitude.

In instrument flight rules (IFR) flight a key to safety is situational awareness - knowing where you are, where you are headed next and how you are going get there without tangling with obstacles, weather or any other hazard. Keep up with the aircraft and the environment. Know your route, particularly in the terminal area, by preparing before departure and arrival. Time spent studying charts can make all the difference if air traffic control (ATC) changes your clearance; familiarity with terrain and obstacles can ensure awareness of hazards. Verify waypoint co-ordinates, or check that bearings and distances make sense; data bases are far from perfect. Know what the vionics should be doing next and ensure it does what you intended. If it does not, take control immediately, ensure the aircraft follows a safe path, then sort out the problem. Do not become engrossed with the avionics at the expense of flying the aircraft.

The complexity of GPS avionics can increase workload at critical times. With very high frequency omnidirectional range (VOR) stations, all we do is change a frequency and set a course. Time spent programming GPS avionics takes away from managing the flight, but there are ways to reduce the hazard. Complete familiarity with the avionics helps. The key, however, is to minimize programming during departure and arrival, when workload is already high and when the terrain is nearby. At the pre-flight stage, load the flight plan to destination and perhaps from destination to alternate to minimize head-down time and workload during flight. Most airlines discourage any programming of the FMS below 10 000 ft. on arrival. This would obviously not be practical in a Cessna 172, but the message is: get the programming done early and do not try to make major changes near the ground. Your number one job is to fly the aircraft.

One challenge we face with GPS is that the first generation of avionics does not have a common pilot interface. Transport Canada and NAV CANADA strongly support the use of moving map displays to enhance situational awareness. The good news is that the next generation of receivers all seem to have moving maps. Some units are simpler to use than others. It makes sense to evaluate a unit’s user-friendliness before buying.

Next, a controversial issue: if two aircraft on opposite courses are using GPS, does the risk of collision increase? The International Civil Aviation Organization (ICAO), Transport Canada and NAV CANADA, among others, have been studying this for several years and have not come to a conclusion. We rely on various procedures and services to avoid collisions: flying at an altitude appropriate to direction of flight; ATC, using radar and position reports; communications (on the proper frequency or frequencies) with other pilots in uncontrolled airspace and near airports without control or advisory service; and watching for other traffic. Some have suggested flying offset tracks. For IFR operations, ATC separation provides the necessary margin of safety. For VFR, the question is: offset from what? All we can suggest at this point is that pilots using GPS on regular VFR routes could stay to the right of centre. This is already recommended when flying along rivers or valleys. This does not replace communicating, watching for other traffic and minimizing head-down time.

Finally, ensure you are familiar with Canadian regulations. Much of the information on GPS comes from the United States, where pilots can use GPS in lieu of distance measuring equipment (DME) and automatic direction finders (ADF), and can fly overlay approaches without monitoring underlying aids. This is not currently the case in Canada for several reasons: we depend much more on non-directional beacons (NDB) and we do not have the density of VORs, airports or radar coverage. If your aircraft is not equipped for Canadian operations, you will encounter flight restrictions that may cause safety problems.

Transport Canada and NAV CANADA have set up a joint team to review GPS operational, technical and safety issues. If you have any comments on any aspect of GPS operations, please e-mail them to This email address is being protected from spambots. You need JavaScript enabled to view it., or send a fax to NAV CANADA’s SatNav Program Office at (613) 563-5602.