Follow the magenta line
A primer on all things GPS
Admit it. You’re a slave. You’d like to think you have free will and can do as you please, but the truth is messy. You have been taught to navigate with pilotage, dead reckoning, VOR signals, and maybe even an old-fashioned nondirectional beacon. But as soon as you were introduced to GPS, you became a servant to the magenta line.
This is nothing to be ashamed of. Those who have been around aviation for some time may lament the “new” pilots today who don’t navigate with a stopwatch and a compass. But times have changed. GPS is an incredibly reliable, accurate, inexpensive, and efficient way to get from point A to point B. Not relying on it is like shaving with a straight razor or writing with a fountain pen. There’s a certain nostalgia factor, but most things evolve for a reason.
The Global Positioning System (GPS)was developed in the early 1970s, not as a means to improve civilian and military navigation, as is often assumed. Rather it was the Cold War, and the necessity to have accurate intercontinental ballistic missiles, that pushed the Department of Defense to create the system. It was only after Korean Airlines Flight 007 was shot down in Russian airspace in 1983 that President Ronald Reagan gave the directive to allow the system to be used for civilian applications.
The first satellites were launched in 1989, and the twenty-fourth satellite to officially fill out the system was launched in 1994. Initially the military, as stewards of the system, degraded the civilian signal to an accuracy of around 100 meters. But starting in 2000, when the signal was no longer degraded, and continuing today with more and improved satellites, the GPS system is amazingly accurate.
Stick out your arm. The accuracy of the GPS signal sent to the receiver in your airplane is less than the distance between the tip of your finger and the middle of your chest, depending on your height. And that's from a satellite signal emitted more than 12,550 miles above Earth.
To get such an accurate signal, your GPS receiver of choice must receive position from a minimum of three satellites. Because of the way the orbits of the 27 satellites (31 total with four in reserve status at any one time) are organized, a minimum of four are within range from any point on Earth at all times.
The satellites simply send out information. It’s the receiver’s job to calculate the time difference between when the signal was sent and when it was received in order to come up with a position and altitude. Every GPS receiver has a page that lists satellite integrity and shows exactly which satellites are being received.
Another form of signal monitoring is called RAIM, or Receiver Autonomous Integrity Monitoring (finally a case of a welcome acronym). RAIM is a type of self-test the receiver completes in order to determine it has the proper accuracy at different phases of flight. When instrument pilots fly approaches to the airport with a GPS, certain signal integrity is required, and RAIM keeps the pilot apprised of that integrity. For VFR pilots, exact navigation isn’t as critical, so there are no regulations. But RAIM is still a good indicator of the health of the signal.
Direct to. Perhaps the biggest benefit of GPS is the ability to fly in a straight line without having to rely on only a sectional and some predetermined checkpoints. Radio navigation, such as VOR, always meant having to fly doglegs and to other out-of-the-way places because of the ground-based station and line-of-sight limitations. Almost all pilots flying with a GPS system start with this simple task, called direct to. In most units, you simply push the D with the arrow through it, enter the airport identification, and press enter. But using GPS like this is like using Microsoft Excel to calculate two plus two. It will do it, but there’s so much more.
First and foremost in getting better utilization out of your GPS receiver is to learn how to go beyond direct to. In certain parts of the country terrain, airspace, and other factors allow direct flights, but in most cases you will need to make turns in your flight plans at least every so often. This is where the mechanics of flight planning that we all learn on the sectional and with a navigation log come in handy. The simple skill of being able to study a route and consider issues such as airspace and terrain apply to all forms of navigation. We may not fill out a navigation log, but using a GPS receiver does not preclude one from having to plan before getting into the airplane.
The devices are able to find all the airports, navaids, and intersections because of an on-board database. Verifying the currency of that database is a must-do preflight task. Generally the data is valid for 28 days, at which point you’ll have to pay for a new database. Current data isn’t required for VFR flight, assuming you have charts on board, but to use a GPS for IFR navigation it is.
Most GPS receivers break down the various tasks and functions via a menu system accessed through a knob, soft keys (screen-based menu system that can change depending on what page you’re on), or hard keys, which are the buttons on the display that have dedicated, never-changing functions. Usually pages are divided into categories such as flight plan, airports, weather, and auxiliary. One of the biggest drawbacks to using GPS is that every unit does things a little bit differently, and thus we have to relearn how to do each task when switching units. As a VFR pilot, it’s important to know how to navigate with the Direct-To function, and how to create and change flight plans. If the GPS is an integrated unit such as the Garmin G1000, a lot more work is in order because that’s the brains of the entire airplane, which must be adequately respected.
Besides flight planning, GPS’s biggest benefit is likely the addition of moving map displays and the staggering amount of situational awareness thereby associated. However, even though the displays provide a great level of detail, and the map follows along on your flight in tandem with the countryside below, they are not foolproof. Displays fail; information can be incorrect or incomplete; and interpretation of the data can be flubbed. For these reasons it’s important to always bring sectional charts, and follow along on the sectional as you would if you didn’t have GPS. With this combination the word “lost” should take a hike from your aviation vocabulary.
So many choices. Because GPS chips are so inexpensive, they are being placed in everything from cell phones to jogging trackers. Combine that with inexpensive touch-screen technology, and a huge range of GPS receiver choices is now available to pilots. These generally split into three categories: panel mounted, handheld, and the iPad. Yes, the iPad is handheld, but if you’ve used one you understand why it’s in its own category.
Panel-mounted receivers are the most expensive, but they are also the most reliable and the most diverse in terms of capability. The necessity
of a hard-wired antenna and a dedicated power source means panel-mounted units are the only ones that the FAA will allow for official navigation. An instrument-rated pilot trying to file /G will need to have an appropriate approved panel-mounted unit. Until recently panel-mounted units were the only ones to have approach and other capabilities anyway. But that’s changing.
Today’s handheld units start at around $500, and even at that price point, they provide a full range of flight planning, charts, and weather connectivity options. Although you cannot use a handheld unit for navigating on instrument flights, the information you get will be useful for situational awareness, regardless of the type of flying you do. Each unit functions a bit differently, so it’s best to comparison shop at a place such as Sporty’s, PilotMall, or other store that carries multiple brands. The best way to do it is at a show such as EAA AirVenture or AOPA Summit, where all the units will be on display.
Finally, the iPad really is in a class by itself. It’s not a dedicated GPS unit, although it does GPS-like functions quite well. Reliability reports vary, with many pilots complaining about overheating, apps locking up, and so on. It’s prudent to make sure you have backups.
If you are going to buy an iPad for flying, there are a few things to consider. The non-3G version doesn’t have the GPS hardware you’ll need for aviation, so a supplemental GPS will be required. These cost about $100. If you use the 3G version don’t expect accuracy like that of a dedicated GPS unit, although one meter isn’t much different than 10 meters when you’re flying VFR. Then you have to decide which app to use, as there are many choices. There is no “best” app, only the best one for you. Just as you would try out multiple handhelds before purchasing, you can try many of the apps as well.
Once you settle on an app, a handheld GPS, or rent an airplane with a panel-mounted unit, it’s time to be a good boy or girl and follow the magenta course line. Resistance is futile.
The FAA is so confident in GPS’ ability to accurately provide position information that it now allows pilots to fly approaches in instrument conditions down to fewer than 300 feet above the ground. To make this possible, the agency built out an additional layer of accuracy on top of GPS called WAAS, or the Wide Area Augmentation System.
WAAS ground stations monitor the GPS satellite signals, adjust them to be even more accurate, and then send that data back to the satellite, where it is sent again to the GPS receiver. Although the purpose of the system is to allow for more precise navigation for instrument approaches, even many inexpensive handheld units boast WAAS capability.