How do pilots find their way?

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I asked my wife if she had any ideas for an article. She said, “You know, I really don’t know how you find your way from one city to another.”  “Great,” I thought, “an article about how airliners navigate!” Or perhaps it was a sly insult; I can never really tell.

Navigation is a really broad subject. Different aircraft have different types of equipment to help pilots find their way. I’ll stick with a generic airliner setup. And don’t worry… I’ll make this really simple and easy to understand!

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Point-A to Point-B starts with a map (or an iPad)

I'm pretty sure Albuquerque is in here somewhere.
Enroute Charts – Maps of the sky

Enroute charts are the road maps of the sky. They display airways that connect any two places you need to go. Airways are designed to keep air traffic organized and separated.

An airline dispatcher uses a computer to help analyze the weather and winds between the origin and destination. He or she then determines the most economic route using the airway system. For U.S. flights, this requested route is electronically sent to an FAA Air Route Traffic Control Center (ARTCC) that analyzes the proposed route and compares it to thousands of other requests as well as traffic currently in the air. The local Air Traffic Control (ATC) facility at the departure airport will tell the pilots just prior to takeoff if the requested route is okay (it usually is) or if any changes need to be made due to traffic congestion or weather.

Time to navigate!
Time to navigate!

Here’s a really simple route. We’re flying from Memphis, Tennessee (KMEM) to Knoxville (KTYS). The symbols MEM, BNA, and VXV are navigation radio aids (NavAids) at Memphis, Nashville and Knoxville. The lines connecting the NavAids are the airways we will be using: J42 and J46. The “J” in J42 stands for “Jet.” Jet airways are high altitude routes for, umm, jets. Our requested route in fancy ATC notation is MEM-J42-BNA-J46-VXV. Simple!

Route from Memphis to Knoxville
Route from Memphis (KMEM) to Knoxville (KTYS):  MEM – J42 – BNA – J46 – VXV

Now that we have our route, we need the convince the airplane to follow it!

The Flight Management System or “The Box”

FMC
Honeywell Pegasus FMS

Onboard just about every airliner built since the early 1980’s is a box called the “Flight Management System” or FMS. Pilots call it simply “The Box.” The FMS is the ship’s navigation brain. When your captain comes over the PA in his captainly swagger and states “The computer shows us landing in Dallas in 43 minutes,” he’s not pulling that number out of his… head. He’s getting that time from “the box”.

The box uses several sensors to keep track of the aircraft’s position. Inertial reference system data, radio navigation signals, and on newer boxes, GPS position are all fed into the FMS to increase accuracy.  The most important part of the box is it’s large database of the airports, navigation aids, and airways necessary for the route. Most everything that’s displayed on the enroute chart above is in the box’s database.

The Boeing 767 that I fly uses an FMS like the one pictured above. Take a look at the flight plan that’s been loaded into the box, it’s the same flight that I highlighted on the map; MEM-J42-BNA-J46-VXV. During our preflight prep, we type the route of flight into the box. In many cases, routes are preprogrammed (or “canned”) and we can type a short route code to retrieve them; this saves us a bunch of typing on long routes.

ehsi
Electronic Horizontal Situation Indicator-EHSI

Enough preflight, it’s time to fly!

Now that our route to Knoxville is in the box, it will be displayed on our Horizontal Situation Indicator screen. This screen shows the route as a solid magenta line (J42 and J46). The big triangle at the bottom is our airplane. Sure enough, you can see the navigation aids we loaded earlier; MEM, BNA, and VXV just offscreen at the top.

After takeoff from Memphis, air traffic control might direct us to “intercept J42.” This means “hop on the magenta line and head toward BNA.”  Our autopilot will follow the magenta line with pinpoint accuracy. The FMS can do lots of other cool stuff that isn’t within the scope of this article. If you want to learn more, check out the FMS Wikipedia page or the FMS SkyBrary Entry.

Other ways we stumble around the skies

During most of a flight, it’s up to the pilots and our FMS to guide the aircraft along the assigned route. But what if another airplane comes cruising along in our direction? What if his magenta line happens to cross our magenta line at the same time and same altitude?

AeroSavvy’s First Law of Aviation: No two aircraft shall occupy the same space at the same time. 

ATC Workstation
Air Traffic Control workstation

This is where Air Traffic Control (ATC) helps us out. The primary job of ATC is “aircraft separation”. Using radar displays and sophisticated computers, controllers have the big picture of all the airplanes in their assigned sector. They can spot a potential conflict while aircraft are still hundreds of miles apart. When they see a problem, they will contact one or both aircraft and instruct the pilots to change course or altitude to avoid the conflict. This usually happens a few times every flight; it’s very routine. As a passenger, there’s no need to worry – relax and enjoy your peanuts and coffee; you paid good money for them!

Tower
Inside Heathrow ATC Tower

Another job of ATC is to help airplanes transition from the cruise phase of flight to landing. Pilots have everything they need on charts and the FMC to do this on their own; but around big cities, there are too many airplanes speeding toward the airport at the same time. To safely separate and space the airplanes to land on the runway, controllers will watch all the planes on their radar display and instruct pilots to change their speed and direction, guiding them with voice instructions onto final approach. This process is called “vectoring”. Once we land, a similar process happens on the ground while taxiing to the gate. A ground controller in the tower watches the busy taxiways and acts as a traffic cop to keep things moving in an orderly fashion.

Of course, there’s more involved in flying a jet from New York to Los Angeles than discussed here. However, you now know more about airplane navigation than most of the folks at your next cocktail party.  (Unless you invite a bunch of pilots; which is a bad idea because they’ll yap on-and-on all night about airplanes!)

Coming up…

Have you ever heard aircraft radio communication? A few airlines let you listen to the pilots and controllers over the aircraft’s entertainment system. In Stuff Pilots Say!  I decipher aircraft communication so you’ll know what to listen for. I’ve even include samples of authentic pilot radio gibberish!

11 Comments

  1. I love it but sir I love to fly one,one day and I did business in high school and I heard you need to have knowledge in maths and physics which I dont so how can I must I out a stop to my dreams

  2. Ken,

    Just discovered this site. Nice work.

    As a navigator from 50+ years ago, I used to do everything your computer does manually, with the aid of nothing more than a blank chart, protractor, dividers, and whizzwheel, (circular slide rule). And a good memory. Was quite a job, and when you missed your clearance, you had to refigure a new plan on the fly. (When that happened, you were worth your weight in gold.)

    I frequently wished for a computer to make all the work easier, and more accurate. Of course when those machines finally arrived, I was out of a job. Still, it was quite a challenge. Best done when you’re young, though.

    • Hi Fred,

      Thanks for the great comments. It’s sad that the skills of the professional navigator have become nearly obsolete. My dad was a navigator in the 50’s on a SAC KC-97. What aircraft did you navigate on?

      Thanks for reading!
      Ken

      • Just returned from a holiday in Scotland. George did the work this time.

        I flew KC-135’s. Sextant and DR [dead reckoning]. Actually, everything was an aid to DR. Everything!

        A real navigation experience was flying solely across the Pacific using pressure patterns and a weather chart. No other aids. Helped doing it at low latitudes, as the drift changes were small there. Final CE near Hawaii was 15 NM. No fixes for seven hours.

        Also had the “pleasure” transiting near the north pole. Used Grid techniques the first time, as the mag compasses were nearly useless. PIA, but quickly discovered that using True North as a reference was just as good, especially for the pilots as the heading numbers they saw on their instruments more closely matched what they were used to seeing using magnetic headings. Strictly a comfort thing. Had to have a steady compass, though. Low precessions, and stable needles. We had the N-1 Compass. A really good reliable instrument. Especially in the round dial era.

        I liked using DR. Always knew where you were. Never got confused by malfunctioning fancy equipment. In fact, I found having more equipment to baby sit increased the uncertainty factor. To me uncomplicated boring was good. Meant everything was going well.

        As you can see, when I started navigating, we had very little equipment for help. You really had to use your head, and as a result, we all developed judgment. (I’ll bet your dad had good judgment.) Overwater navigation in that era was a challenging and very rewarding experience. However, at the end of my 20 years in the cockpit, we had all kinds of electronic equipment to use. By then we had become just equipment operators, computers flew the airplane, and the flying experience was no longer as adventurous. It was time to move on. Glad I did it, though. It was the start of a long life of adventure. That’s what flying, (and life?) is really about, isn’t it? Adventure?

        Fred

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