One of the frustrating aspects of aviation faced by airmen is the lack of concrete, objective definitions in the FARs. Rather than giving us a definition we can use and apply, oftentimes the FAA and the NTSB have opted for taking a "case-by-case" approach in determining how to apply certain terms. Unfortunately, this "I'll know it when I see it" approach isn't particularly helpful for airmen out in the real world.
The FAA recently reiterated this position in a Memorandum issued by the Office of Chief Counsel in response to a request for a legal interpretation submitted by Melvin O. Cintron, manager of the FAA's General Aviation and Commercial Division. Specifically, Mr. Cintron was looking for a legal interpretation regarding the definitions of limitations on experimental aircraft, particularly with regards to Living History Flight Experience (LHFE) flights operations. However, the Memorandum addressed the issue of these definitions more broadly.
The Memorandum initially observed that these terms, along with other terms such as "congested areas," "other than congested areas," "sparsely populated," and "open air assembly of persons" appear in a number of the FARs including:
§ 91.119 (Minimum Safe Altitudes: General);
§ 91.303 (Aerobatic Flight);
§ 91.313 (Restricted Category);
§ 91.319 (Aircraft having experimental certificates: Operating limitations);
§ 133.33 (Operating rules);
§ 137.49 (Operation over other than congested areas)
§ 137.51 (Operation over congested areas: General); and
§ 137.53 (Operation over congested areas: Pilots and aircraft.
Unfortunately, it then stated "[w]e are unable to provide you with discrete definitions for these terms." And the FAA is apparently satisfied with this fact because the Memorandum goes on to state "there has been a long history stretching back over 40 years of using a case-by-case approach in determining how to apply those terms and how they relate to one another" and "[t]his approach 'is well documented and supported by many legal opinions issued by the FAA, the National Transportation Board (NTSB) and federal courts.'"
With respect to "densely populated", "congested area" in the context of FAR 91.119 cases the Memorandum observed that "[t]here is no precise density of population, ground traffic or congestion, or description of the proximity of buildings, or number of residences." It went on to note the term "congested airway" has not been specifically referenced or defined by interpretation. Although the Memorandum speculated as to why that was the case, it did not attempt to provide any guidance or interpretation of that term.
Next, the Memorandum rejected Mr. Cintron's suggestion that pilots should be able to easily determine the meaning of any definitions during their preflight planning using existing navigation aids and charts. According to the FAA, aeronautical charts and NOTAMs only provide "general guidance" for use in complying with FAR 91.119 and a pilot should obtain local information from their local Flight Standards District Office for use with the pilot's prior knowledge of the area and information the pilot obtains from other sources. After all, the Memorandum observed, "[u]ltimately, it is the pilot's responsibility to maintain the minimum safe altitudes required by § 91.119."
Finally, the Memorandum concluded that Mr. Cintron should "review of the appropriate FAA guidance material to determine whether further explanation of these definitions through examples may help users and inspectors to better understand what is meant by these terms." From my perspective, and, I suspect, the perspective of most pilots, this isn't very helpful.
What is troubling for me is that the confusion regarding the meaning of these undefined terms isn't limited to pilots. Inspectors don't know what these terms mean or how they are to apply them to pilots' operations. Unfortunately, this Memorandum tells me that the situation won't be changing anytime soon. As a result, airmen should make sure they are familiar with the areas over which they fly and remember that the FAA, NTSB and the Court will judge a flights compliance with FAR 91.119 using 20/20 hindsight.