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Air Traffic Services Process Brief - Tall Towers: The FAA's Obstruction Evaluation ProcessAir Traffic Services Process Brief - Tall Towers: The FAA's Obstruction Evaluation Process

Air Traffic Services Process Brief

Tall Towers: The FAA's Obstruction Evaluation Process

The Issue

Update: On July 21, 2010, the FAA issued a final rule that amends 14 CFR Part 77, Safe, Efficient Use and Preservation of the Navigable Airspace. The changes include stronger protections for the National Airspace System and private airports. The rule will allow for greater lead time in assessing tall structures and provide for protection of instrument approaches into private-use airports. AOPA worked with the FAA over the past two decades to encourage greater protection of U.S. airports and airspace and supported the changes that have been adopted in the final rule. The amendments to Part 77 go into effect on Jan. 18, 2011.

The explosive growth of cellular communications and other digital technologies has resulted in a proliferation of tall towers. In 2000, the FAA conducted over 43,000 aeronautical studies to determine the impact of proposed structures on the national airspace system (NAS). This represents a growth of over 100% when compared to 1995 totals. The height of these and other structures can make them a hazard to general aviation, especially at locations relative to airports and navigational aids (both electronic and visual). The Federal Aviation Administration (FAA) has an obstruction evaluation (OE) process to evaluate, mitigate, or eliminate the impact of tall towers and other obstructions to airspace.

The Importance to Our Members

It is important for general aviation pilots to understand the OE process and how the FAA evaluates such objects. Armed with this information, airspace users are able to determine the impact of obstructions on their aeronautical activities. Moreover, this impact may then be communicated in an effective manner to the FAA, allowing pilots to participate in the aeronautical study process.


The obstruction evaluation process begins at regional level within the FAA, and involves all lines of business including Airports, Airway Facilities, Flight Standards, Flight Procedures, and of course, Air Traffic. The roles of each group will be discussed later in this document.

The FAA's philosophy in evaluating objects that may impact navigable airspace is that each is presumed to be a hazard until proven otherwise. This posture clearly favors the aeronautical community, and is consistent with the FAA's overall mission of promoting aviation safety.

If a tower or other object is found to have a significant adverse impact, a "hazard" determination will be issued. However, in nearly 80% of all such cases, the FAA negotiates with the proponent until the conditions are met for a "no-hazard" determination. These efforts are a key benefit of the FAA's participation at this level.

AOPA's Position

AOPA recognizes that balancing the needs of all airspace users is a formidable task and the complexity and diversity inherent to all aeronautical activities ensures that the FAA isn't always in the best position to evaluate every factor that needs to be assessed in an airspace study. This is why in so many cases; studies are circularized to the public for comment. Pilots must be willing to take responsibility for providing comments as appropriate to the FAA region in which the study in conducted. Although AOPA can and often does provide comments on behalf of it members, the prestige of a national organization cannot replace the benefit of our members' intimate knowledge of their operational environment.

This document is intended to provide a high-level overview of the OE process used by the FAA in evaluating the impact of objects affecting navigable airspace. In addition, it is intended to answer many of the questions commonly asked by AOPA members. Finally, this brief will provide the aeronautical community with some strategic insight useful in opposing construction activities, should they feel it's necessary to do so.

The FAA's OE Process

We begin with an overview of the intent and limitations of the FAA's OE process. Aeronautical studies are conducted to determine the impact of an object on the safe and efficient use of airspace. By congressional mandate, the FAA cannot prohibit any construction activities. Instead, the FAA evaluates the proposed construction, and as necessary, works with the proponent to mitigate any impact that may result.

Step 1: When does the proponent need to inform the FAA of its intentions?

Title 14 CFR Part 77.13(a)(1-5) outlines the type of construction or alteration requiring notice to the FAA. Except as provided in Part 77.15, each sponsor who proposes any of the following shall notify the FAA in the manner prescribed in Part 77.17.

There are, however, instances when notification may not be required in spite of meeting these conditions. These conditions are outlined in 77.15(a-d).

In many cases, the proponent will submit their information for study to the FAA in spite of the fact their activities do not meet notice criteria. This often occurs for one of two reasons. The first is simply that the proponent did not know or incorrectly applied the notice criteria of Part 77. The second is that the issuance of a no- hazard determination from the FAA will all but insure no federal entanglements will halt construction efforts.

[See FAR Part 77.]

Step 2: Obstruction Criteria

Now we are assuming that the FAA has been notified of the proponent's intentions and a case has been opened. When this occurs, a specialist in the FAA's regional 520 office (Airspace Branch) will undertake the following:

  • Verify the information (tower height, location, topography, etc.) provided by the proponent. This is a very important step when you consider that nearly 30% of the proposals submitted to the FAA contain errors.
  • Determines if notice was required.
  • Applies obstruction standards.
  • Transmit the proposal as required to the "in-house" offices including: Airports, Airway Facilities, Flight Procedures, Flight Standards, and representatives of the military.

If a proposed structure exceeds any Part 77, Subpart C obstruction standard, an aeronautical study shall be conducted to identify the effects of the proposal on the use of navigable airspace. In this case, the different offices within the FAA determine the possible impact as it relates to their area of responsibility. Clicking on the name of each office will provide a brief overview of each office and its assigned task(s). [See FAR Part 77.]

Air Traffic
Airports Office
Flight Procedures and Flight Standards
Airway Facilities
Military Representatives

Step 3: OE Circularization

Not all proposals or studies are circulated to the aeronautical community for comment. In many cases, the obstruction in question is short enough or distant enough from any airport or navigational aid that no useful purpose would be served by opening the issue to the public.

So when does the FAA circularize a study for comment? Guidance for this is provided in FAA Order 7400.2, Procedures For Handling Airspace Matters. Proposals requiring public notice include:

  • Those that would affect an airport (public use).
  • Those requiring a change in aeronautical operations or procedures.
  • When a structure exceeds obstruction standards.
  • When a structure would have a possible impact on VFR operations.

Conversely, circularization to the public is normally not required for the following:

  • Height reduction of an existing structure.
  • A structure is proximate to a previous study.
  • A replacement structure.
  • A temporary structure.
  • When an obvious substantial adverse impact exists.
  • Increase in minimum obstacle clearance altitude (MOCA).
  • Exceeds the obstruction standards outlined in Part 77.23(a)(2) but lies beyond the airport traffic pattern. [See FAR Part 77.]
  • Increase in minimum vectoring altitude.

With a better understanding of the requirements for circularization, a discussion may now begin on the parties to whom the circulars are distributed. As a rule, the following entities will receive notification of an OE case:

  • All public-use airports within 13 miles.
  • All private-use airports and heliports within five miles.
  • Zat list members (e.g. Alphabet groups, military, and state aviation departments).
  • The adjacent region if within 13 nautical miles of the regional boundary.
  • All control facilities and flight service stations as required.
  • Local zoning and political groups.

The methods used in circularizing a proposal or soliciting comments are relatively simple and straightforward. Public notice is generally provided through the issuance of an automated OE circularization letter and related documents. FAA specialists may also contact the necessary parties by telephone. Finally, informal airspace meetings may be convened to discuss a particular proposal.

Step 4: Evaluating Aeronautical Effect and Issuing a Determination

This is the point at which the FAA determines if an object is a hazard to the aeronautical community. By now, the FAA has already determined if an object exceeds the obstruction standards outlined in Part 77. However, keep in mind that the obstruction criteria set forth in Part 77 are just that, a standard to determine if it is necessary to further study the impact of a construction proposal. This criterion is not regulatory in nature, and exceeding the prescribed standards is by no means a disqualifying factor for a proponent. Simply put, an obstruction is not necessarily a hazard. [See FAR Part 77.]

In order for an object to be considered for adverse effect, one or more of the following conditions must be met:

  • An object must exceed the obstruction standards outlined in Part 77 and/or have a physical and/or electromagnetic effect on air navigational facilities. [See FAR Part 77.]
  • Requires a change to an instrument procedure or minimum flight altitude.
  • Restricts control tower line-of-sight.
  • Reduces airport capacity and efficiency.
  • Affects useable runway length.

At this point, the FAA has still not made a hazard/ no-hazard determination. For a hazard determination to be issued, a substantial adverse effect must exist. This requires a combination of two factors. First, an object must create an adverse effect ( see above). Next, a significant volume of aeronautical operations must be affected. FAA Order 7400.2, Procedures for Handling Airspace Matters, provide guidance on what constitutes "significant volume."

When one of the following occurs, significant volume is considered to exist.

  • One or more aeronautical operations per day would be affected (regardless of the type of activity).
  • An average of one aeronautical operation a week for an affected instrument approach procedure or minimum altitude if the procedure serves as the primary procedure under certain conditions, e.g. a crosswind runway with an instrument approach procedure.

If a significant adverse effect is found to exist, a hazard determination will be issued. In the absence of such a finding, a no hazard determination will be issued.

Fighting Proposed Construction

As a pilot or airport owner reading this brief, you are likely concerned with what you can do to participate in an aeronautical study. The options available to you in fighting a construction proposal largely depend on the type of airport from which you operate. There are two basic types to consider, private and public-use airports. Unfortunately, the FAA's Part 77 process does not take into consideration the private-use facility. [See FAR Part 77.] If such an airport stands to be the only facility impacted, a notification may not be circulated. However, if the aeronautical study is circulated for comment, it may still be worth your time to comment. If you do choose to comment in this instance, keep these points in mind. First, the impact to a private-use airport will not be considered in the study, regardless of the severity. So any discussion based on this point will be futile, and should be avoided. Instead, take a critical look at the system-wide implications of the proposed construction. When doing so, regardless of the public versus private status of your airport, ask yourself the following questions:

  • Will the tower or building impact the approach minimums at a public use airport?
  • If the FAA's circular indicates a change in approach minimums, how will this impact the aviation community? Is this the only approach at your airport predicated on a specific type of navigational aid? Does the impacted approach offer the lowest minimums at that facility?
  • Will the structure in question be close to a visual landmark such as a highway, mine, reservoir, or any other point commonly used as a visual reference for VFR pilots?
  • Will the tower underlie terminal airspace, creating traffic compression and with it an increased risk of a midair collision?
  • Will the structure lie in an area in which a high volume of training activities is conducted?
  • Will the proposed structure lie along commonly used VFR egress or ingress tracks to your airport?

How you answer these and other questions related to adverse effect will largely determine the nature of your comments to the FAA. If your comments cannot be tied to similar factors impacting the safe and efficient use of airspace, and the FAA has no cause for concern, a no hazard determination will likely be the outcome.

Frequently Asked Questions

Additional Resources

  1. To report tower light outages, dial 888/CALL-FCC
  2. Airports, A Valuable Community Resource
  3. Answers for Pilots, 10 Questions: Fighting a Tower Threat
  4. Establishing an Instrument Approach
  5. FAA Advisory Circular 70/7460-1, Obstruction Marking and Lighting
  6. FAA Advisory Circular 70/7460-2, Proposed Construction or Alteration of Objects that May Affect Navigable Airspace
  7. FAA Advisory Circular 150/5190-4, A Model Zoning Ordinance to Limit Height of Objects Around Airports (requires Adobe Reader)
  8. FAA's National Flight Procedures Office
  9. FAA Order 7400.2, Procedures for Handling Airspace Matters
  10. It's Your Airport
  11. National Association of State Aviation Officials
  12. Title 14 CFR Part 77, Objects Affecting Navigable Airspace

Updated Friday, December 29, 2006 11:00:14 AM