FCC Acknowledges Errors with TowAir Software

August 11, 1999 – On February 26, 1999 we wrote to the FCC identifying, in our opinion, problems with the Commission’s TowAir software program. Letter to FCC

In January 24, 2001 the FCC responded to our complaint ( FCC letter 1-24-2001 ). The FCC has acknowledged their ‘TowAir’ software program can produce errors when determining notice to the FAA under FAR Part 77.13 for a proposed structure. The FCC has agreed to perform manual calculations to determine if notice to the FAA is required should you disagree with the results of TowAir. While the FCC will not endorse commercial software Airspace & Terps accurately determine notice to the FAA.

To further complicate the issue the FCC issued a letter to individuals or companies that have licensed radio transmitters. The letter was sent because according to the FCC, “..there is reason to believe that you may be in violation of the Commission’s rules.” The FCC’s TowAir program was used to determine if Notice to the FAA was required. It was sent, because the FCC had no record the antenna structure was registered with the Commission.

The letter contained an attachment where the licensee could make a response.

Conversations with an attorney of the Commission (Jamison Prime) concerned this letter, impact on the public and an appropriate response to the letter when, in the opinion of the licensee, the antenna structure does NOT or did NOT require notice to the FAA using a FAA Form 7460-1, “Notice of Proposed Construction or Alteration”. Item number 6 of the FCC attachment.

Here are two scenarios where explaining the reason registration of antenna structure is not required.

Analysis of the structure using the software program Airspace indicated that notice to the FAA was not required under FAR Part 77.13:

The Licensee should respond to the FCC by stating the actual distance to the nearest point of the nearest runway as specified in the Airport Report of the analysis. Also state the amount below the notice surface as indicated in the Airport Report for the structure analyzed by Airspace. This guidance is contained in the FCC’s April 24, 2001 letter. Use FCC Form 601 to make your submission

In many cases the FCC TowAir Software, in our opinion, does not perform calculations on FAA notice criteria as specified by law. The FCC TowAir Program will calculate the distance to the nearest point of the nearest runway correctly when the runway data is available to the FCC program. If the runway data is not available the program incorrectly calculates the distance from the runway to a proposed structure. We believe the calculation are based upon the Airport Reference Point (ARP) data and the length of the longest runway. The program uses the length of the longest runway and constructs a circular runway around the ARP. This method greatly reduces the distance to the proposed structure and then applies the notice slope criteria. When this occurs structures that do not require notice now appear to require notice to the FCC. This clearly explains the “Notice Not Required” response from the FAA when the FCC TowAir software states that notice to the FAA is required. The database of airport/runways used by the FCC contains only about 4,000 of the nearly 8,000 public use runways in the United States. The data used by Airspace and Terps contain nearly 100% of all public use runways in the United States as of September 1, 2001. Our data is under quality control and refined continuously.

An previous analysis of a proposed structure by Airspace® indicated ” Notice Not Required”. This analysis was based upon the official NFDC (National Flight Data Center) Airport Data available at the time of the analysis. NFDC data is the baseline data used by Airspace®. Now, several year later, the airport changed and the length of the runway is longer than before or a new runway was built. Analysis of the antenna structure by TowAir now determines notice is required. In cases such as this, please respond to the FCC as indicated below.

“Analysis of this proposed antenna structure on MM/DD/YYYY specified notice to the FAA was NOT required. Application of the notice criteria, as specified in FAR Part 77.13, on the runways of record, on this date indicated NO penetration of the notice slope criteria occurred. Therefore, registration of this antenna structure was not required.”