NextGen Air Traffic Control and You


In this month’s edition of the Radar Contact Show we are going to look at how the FAA’s NextGen version of air traffic control will affect you.

We’ll also look at what it means to be off your assigned altitude and what to do if ATC calls you out for being off altitude.

I’ll tell you the real life story of how two airliners departing from Midway Airport would have collided had ATC not intervened. The cause was not that unusual. In fact, you may be vulnerable to it the next time you fly.

Advise when ready for departure by clicking the play button below.

Show Notes:

  1. Question. ATC tells you to maintain 3,000 but you let your altitude drift upward. At what reading on your altimeter would ATC question you for being off your assigned altitude?
  2. Your altitude is reported to ATC by the Mode C feature of your transponder.
  3. Mode C reporting is calibrated to 29.92 regardless of what you have dialed into your altimeter. ATC adjusts your Mode C information to the barometric setting for the area in which you are flying.
  4. ATC’s radar system rounds the altitude displayed for your flight to the nearest 100-foot increment.
  5. A controller will consider you off altitude when the altitude displayed on his screen is plus or minus 300 feet off your assigned altitude. This occurs when your Mode C reports 250 feet, or greater, above or below your assigned altitude.
  6. Initially, ATC will give you the benefit of the doubt if an off-altitude alert occurs. Your controller will remind you of your assigned altitude, the current altimeter setting, and the altitude he sees on his radar display for your flight.
  7. There should be no consequences for being off an assigned altitude if the error causes no traffic conflict.
  8. As a CYA maneuver, I strongly recommend filing a report with NASA’s Aviation Safety Reporting System (ASRS) if ATC announced you were off your assigned altitude. The link to the ASRS is
  9. File your ASRS report within 10 days of the incident to receive immunity from civil penalties by the FAA. There are specific conditions that must be met to receive immunity. The ASRS website has the details on the FAA’s immunity policy.
  10. The FAA’s NextGen version of air traffic control is in development. You will begin to see the effect on your flying in less than 5 years.
  11. Right now, it looks like the greatest impact to general aviation will be ATC’s transition to aircraft tracking via ADS-B.
  12. ADS-B will not only allow ATC to track your aircraft, using ADS-B will also allow you to track aircraft flying nearby.
  13. With a full complement of ADS-B Out and ADS-B In on board, you will be able to detect aircraft in your area that may not be in sight.
  14. By Jan 1, 2020, all general aviation aircraft that participate in air traffic control will need to have at least ADS-B Out installed.
  15. Even if you are not in contact with ATC, you will still need to have ADS-B installed by 2020 if you fly in or near the following airspace:
    • Class A and B. (Positive control is required when operating inside these airspace classes.)
    • Class C.
    • Class E airspace areas at or above 10,000 ft MSL over the 48 states and District of Columbia, excluding airspace at and below 2,500 ft AGL.
    • Airspace within 30 nautical miles (nm) at certain busy airports from the surface up to 10,000 feet MSL; airports listed in appendix D to part 91.
    • Above the ceiling and within the lateral boundaries of a Class B or Class C airspace area up to 10,000 feet MSL.
    • Class E airspace over the Gulf of Mexico at and above 3,000 feet MSL within 12 nm of the coastline of the United States.
  16. The full details of what is coming under the FAA’s NextGen program are available at (By the way, the FAA owns one of the few websites where you still need to add www. to the address! It figures.)
  17. A few days before the airing of this show, two airliners began takeoff rolls on intersecting runways at Chicago’s Midway Airport. One of the two airliners was not actually cleared for takeoff.
  18. ATC intervened to prevent the airliners from colliding at the intersection.
  19. The two airliners were using similar sounding call signs. It’s unclear at this point if ATC took any steps to alert the flight crews of both aircraft that they had similar sounding call signs.
  20. This incident serves as a cautionary tale. You want to do everything possible to distinguish your call sign from another call sign that sounds similar to yours. Towards this goal, be sure to always include your aircraft’s make or model when stating your call sign. Never use your abbreviated call sign unless ATC uses it first.
  21. Here’s a quote from air traffic controller Heather McNevin on the use of call signs. “Pilot tip – when talking to ATC, remember to use your callsign EVERY time. My perspective is I’m talking to 20 people at any given time.” (From her Twitter feed.)



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2 thoughts on “NextGen Air Traffic Control and You”

  1. 1- Regarding transponder reporting altitude set at 29.92 sounding ridiculous… I don’t know if it’s because I’m a computer software architect but that sounds correct to me. If the transponder were to report using whatever setting was entered on the Kollman’s window, and not everyone is using the same value (either as an input error or various through geographic region being covered by radar) then the altitudes displayed would be all wrong.

    Having everyone’s aircraft report at a default value and then adjusted by the ATC system based on what I’m sure is a digitally acquired local area pressure setting, ensures correct altitudes across the board.

    2- You state that the ATC will have you turn off your transponder if the altitude it reports conflicts with what you report your altimeter is indicator, suggesting that the transponder could be the only thing wrong in the equation. Could there be mechanical errors (assuming round dials) with the altimeter?

    3- I guess NextGen ATC explains how products like Aero Glasses can possibly show traffic on augmented reality devices (HUD headset) and using computer interpreted sectionals and aircraft interpolated position.

    I LOVE the future! 🙂

    1. Eric,

      Good comments and questions. Thank you.

      Let’s think this through a little further. It really doesn’t matter how the transponder’s Mode C reports altitude. If the pilot has the wrong barometric setting in his altimeter, the transponder is going to faithfully report the pilot being off altitude, 29.92 notwithstanding. So altitude reporting is still dependent on a human dialing the correct setting into the altimeter.

      Calibration error in the altimeter, mechanical malfunction, stray electrons, sloppy flying are all reasons ATC allows for an aircraft to be plus or minus 200 of an assigned altitude. At 300 feet or higher, ATC is going to investigate the reason.

      It looks like the future in aviation is going to get here a lot quicker in the hands of private enterprise. By the time NextGen begins to show itself here in the U.S. it will be at least 7 years behind what the most of the developed world is already doing for air traffic control. Europe, Canada, and some Pacific Rim countries have already implemented ADS-B and Controller Pilot Data Link Communications (CPDLC). In fact, transoceanic tracking services (e.g. Gander Radio, Shanwick Radio) have already taken the next step to a more advanced system called ADS-C.

      You’ve heard about Newark Liberty Airport running a test program for communicating departure delays to cockpits via data link? Big deal. Maastrict Center in the Netherlands has been controlling airborne aircraft by text communication and data uplinks for more than a year!

      Thank you for adding to the discussion, Eric. I really appreciate it.


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