Something in the Air

By Gordon Walker — December 04, 2013

It’s fair to say that after fire, the wheel, birth control pills, and Starbuck’s coffee, the Internet ranks as one of the most significant inventions of all time (thanks Al Gore). That which we take for granted now, was inconceivable just a generation ago. I’m not THAT long in the tooth, but I do remember having to go to a bank teller to get cash, send mail using envelopes and stamps, and get my supply of “special interest” photographic magazines from the local variety store.  Now, thanks to electronic networking, all of those things can be done quickly, conveniently, and with much less embarrassment, in the case of the last item.

NextGen avionics are reducing the traditional chatter between pilot and controller,
and are ultimately making for safer, more efficient approaches, departures and ground movements, even though the “tower” might be hundreds of miles away.

As we move ahead with the “NextGen” avionics implementation, networking and data transfer begin to play a far more significant role than most of us could have imagined. The movement away from ground based surveillance radar in favour of satellite based Automatic Dependent Surveillance Broadcast (ADS-B) means that, in addition to providing a more accurate position fix, the actual three-dimensional (latitude, longitude, altitude from the GPS) location of the aircraft is being broadcast in a digital data format.  This data is received by other aircraft in the vicinity, and by ADS-B ground stations, which in turn network the information to air traffic control facilities. (ADS-B also transmits information such as heading, and airspeed, and more parameters are planned for the future.) Since the information is placed on the electronic network (think internet) it is instantly available to all users connected to that network. The ramifications of this are huge. Air traffic controllers no longer need to be in the vicinity of the airport they are controlling. It is conceivable that air traffic data from, say, the San Francisco Bay area could be accessed by a controller sitting in an office in North Tonawanda, New York.

Of course, there’s more to air traffic control than just having the controller know the position of the aircraft in the control zone. Clearances have to be issued; confirmations and read-backs have to be broadcast, and so on. We all know that VHF communications are limited to “line-of-sight” range, so even the most powerful of VHF COM transmitters won’t allow for communications between New York and California. Not a problem!  Once again, by networking the voice communications, we are able to communicate instantly between all points on the network, allowing the controller and the pilot to conduct any required verbal exchanges.

The elimination of the requirement for controllers to be on-site at airports will allow controllers from less busy control zones to assist at airports with heavy traffic loads, during peak times. It will also allow ATC operations to be conducted from remote, less expensive sites such as suburban offices or industrial estates, rather than on-site at an airport.

Digitizing voice communications for network distribution and transmission may, however, become a moot point, as NextGen technology strives to eliminate the problem of narrow VHF-com bandwidth. Even with 8.3 Khz channel spacing, VHF voice communication is becoming overloaded. Since increasing the bandwidth is not an option, the best alternative solution is to reduce the amount of spoken word communication, and replace it with digitized data communications.

“DataCom” is the NextGen component making this concept a reality. The traditional air traffic control process follows a sequence in which a controller transmits a clearance, which the pilot writes down, then verbally transmits an acceptance reply. The controller then confirms the pilot’s reply, and the pilot manually enters the clearance instructions into the flight management computer. This process is cumbersome, time consuming, and prone to errors in communication. By employing data clearances, rather than verbal instructions, controllers can now transmit a digitized data clearance to the aircraft. This data burst, which takes only microseconds of airtime, will appear on a cockpit screen to be either accepted or rejected by the pilot.  Should the pilot accept the clearance, acknowledgement will be sent to the control centre, and the actual clearance instructions loaded into the navigation portion of the aircraft’s flight management computer automatically. From the flight management computer, the ATC instructions can then be coupled to the autoflight system. The clearance can be simultaneously transmitted to the airline’s operations centre, allowing dispatchers to calculate fuel loads etc.

In addition to reducing the amount of verbal “chatter” on the VHF-com frequencies, the DataCom system will eliminate the spectre of misunderstood communications between controllers and pilots, and will ensure the aircraft is flown on the flight path the ATC facility intended.
Pilots are typically horrified to hear that the controller handling their flight may actually be located hundreds or thousands of miles away from their location, and totally unfamiliar with the airport and surrounding terrain which they are controlling. This fear is unfounded, as all clearances will be issued in a standard format, which is applicable to the control zone in which they are operating. It would be impossible for a controller to issue a clearance that would take the aircraft outside of the safe operational parameters of the airspace in question.  The ATC software would not transmit inappropriate data, and the aircraft software would not accept it.

Not only will ATC instructions be safe and appropriate for the airport or control zone, but the use of GPS as a primary navigation aid, and ADS-B as a primary ATC protocol enables much more efficient approaches, departures and ground movements. Rather than stacking aircraft in a holding pattern, and forcing all aircraft to use the same ILS approach path, GPS approaches allow multiple approach paths, and facilitate constant vertical descent/near idle approaches. This results in shorter flight times, fewer delays, less fuel consumption, less noise and less pollution. Satellite receivers, designed to receive ADS-B broadcasts and relay them to ADS-B ground stations makes possible full global coverage, providing accurate ATC control of aircraft in remote and trans-oceanic locations.

In addition to these benefits, the digitizing and networking of avionics systems reduces the risk of miscommunication between controllers and pilots, and makes better use of air traffic control resources, both material and human. Sounds like a good plan to me.

Q: How is an air traffic controller using NextGen technology able to verbally communicate with an aircraft hundreds or even thousands of miles away?

Answer to previous question:

Q: What are some of the advantages of ADS-B over ground based air traffic control systems?

A: ADS-B uses GPS to provide a very accurate position fix, which can be seen by other aircraft, as well as air traffic control. It also transmits information such as aircraft heading and airspeed.

About The Author

Gordon Walker

GORDON WALKER entered the avionics industry after graduation from Centennial College in 1980. His career with Nordair, Air Canada, CP Air, PWA, and ultimately Canadian Airlines took him to many remote corners of Canada. Since leaving the flight line to pursue a career as a college professor, Walker has continued to involve himself in the aviation/avionics industry, by serving on several CARAC Committees concerning the training and licensing of AMEs, being nominated to the CAMC Board of Directors, and being elected President of the National Training Association. (NTA).

View all articles by Gordon Walker.