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AC 90-117: Why Your Input Is Important to Advancing the Efficiency & Safety of U.S. Airspace

May 12, 2017
By: Carey Miller, Director of Corporate Programs & Business Development

The FAA has published a draft of Advisory Circular (AC) 90-117 that provides comprehensive guidance for aircraft eligibility and operational use of data link communications in the U.S. and other countries. The FAA is seeking comments to this draft, which are due May 15, 2017.

Of particular interest to operators may be the requirements outlined in Chapter 3: Aircraft Eligibility. Specifically, paragraph 3.3.1 states: "For en route National Airspace System (NAS) operations, the avionics system must have "push to load" capability into the navigation system whenever a routing change is received for operations supported by B2 and Future Air Navigation System (FANS) 1/A (+) data link communication systems."

After careful consideration amongst our certification and flight department teams, UASC has taken the position that this provision is too onerous for the user-base and should be removed from the Aircraft Eligibility requirements for several reasons: 1) implementation is cost-prohibitive for the user-base, 2) the benefit of receiving a reroute clearance from Controller Pilot Data Link Communication (CPDLC) versus a much less efficient voice clearance from ATC will be lost, 3) the ATC system enabling en route data link services is still evolving and has already required a new software update for FANS capable avionics that were originally thought to comply 4) a large quantity of aircraft without a FANS solution today won't have option for a significantly lower cost solution.

Today, FANS equipped aircraft without push to load capability are able to receive their departure clearance using DCL, and manually load it into the FMS saving time and money. Significant efficiencies could be gained by using this type of service during the en route portion of the flight as well. Most pilots have experienced reroute clearances using voice that can produce multiple back-and-forth communications to get the new clearance correct. Understanding the waypoints/procedures of the new clearance and spelling them correctly can be a challenge, resulting in several minutes on the radio with Air Traffic Control (ATC). After getting the clearance correct, the pilot enters the new route into the Flight Management System (FMS). Most errors are attributed to pilots misunderstanding controllers and copying clearances incorrectly, not the manual entry of the new clearance into the FMS.

Receiving a new clearance while en route via CPDLC, even without push to load, has significant benefits over voice communications. The pilot has everything needed in text format on the Multi-Function Control Display Unit (MCDU) to copy the clearance down and enter it into the FMS. These benefits include:

  • Reduced pilot errors in understanding clearance.
  • Reduced controller/pilot workload.
  • Higher adoption rate of DataComm services, helping justify the DataComm program.
  • Provides operators with additional justification for upgrading their fleet of aircraft, which could include aircraft without a FANS solution today (i.e. B717, A319, A320, CRJ, EMB, etc.).

Consider the Issues with Push to Load For En Route CPDLC Services Today

  • There are still technical issues regarding the integrity of push to load functionality in the marketplace today. There is documentation of existing operators with the technology experiencing problems with its use, (https://asrs.arc.nasa.gov/publications/callback/cb_443.html). We believe more robust solutions should be available to the user-base before the requirements are implemented.
  • A more complete set of interoperability objectives in AC 20-140C needs to be provided to allow avionics manufacturers the guidance needed to produce a system that is fully compliant. While correctly loading a route in a manner that ensures the route on the aircraft continues to match the route the controller is using on the ground.
  • Avionics manufacturers will have additional time to develop solutions, once the system is proven to be functionally sustainable for both forward fit and retrofit aircraft.

The comment grid for this AC is located on the FAA website (you'll need to scroll down about halfway to find the correct AC and comment document). We encourage the aviation community to review the AC, research the issues and provide comment to the FAA.


Universal Avionics believes the U.S. DataComm program will be a step forward by increasing safety and efficiency of aircraft and controller communications but a "Push to Load" mandate will deter operators from making the investment resulting in a slower acceptance rate of the program.

Read our comments regarding AC_90-117.

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