One of the more subjective directives in the federal aviation regulations (FAR) is found in 91.155 where VFR pilots are instructed, in certain airspace, to maintain “clear of clouds.” The definition of “clear of clouds” is both straightforward and ambiguous.

While it logically means that pilots should refrain from entering clouds, the presence of scattered, or even lightly broken, cloud layers allow opportunity for pilots to skirt immersion in a clouded environment. (This might explain why online searches for the phrase will also bring up discussions of scud-running.)

The National Weather Service (NWS) provides a handy chart for every sort of cloud and cloud layer imaginable, as well as this definition for clouds: “They are the visible aggregate of minute particles of water and/or ice which form when water vapor condenses.”

The FAA draws from that definition in its interpretation, explaining that a cloud “...is a visible aggregate of minute water droplets and/or ice particles in the atmosphere above the Earth’s surface.” To make things more interesting, NASA helpfully introduces crystals into the mix with its explanation of clouds as “a mass of water drops or ice crystals suspended in the atmosphere.”

(For the curious, the NWS states that the difference between fog and clouds is only that a fog base ‘is at the Earth’s surface” whereas clouds are “above the surface.” The FAA is more specific, asserting that fog “begins at a height lower than 50 feet.”)

No official agency explains how a pilot can tell at what point these particles or droplets or crystals, progresses from not impacting VFR flight at all to mild annoyance, increasing concern, starkly problematic, and then instrument meteorological conditions (IMC). Absent a certified weather report, pilots must discern the presence and proximity to clouds entirely on their own. Under Part 135 operations, this often leads to the operational temptation to “go take a look” and see if IMC can be judiciously avoided enroute to the destination.

The cockpit perspective intrinsic to maintaining proper cloud clearance carries over to FAR 91.157, where Special VFR operations are outlined. Again, there is a regulatory requirement for “clear of clouds” to be preserved by the pilot. While air traffic control (ATC) approval is required to obtain a Special VFR clearance prior to departure or arrival, it is again the pilot, from his or her own vantage point, who affirms that the clear of clouds minimum is being met. As Special VFR is generally requested only in marginal conditions, it makes the issue of strict cloud clearance that much more significant.

The phrasing “clear of clouds” has a long history, to the early instrument-flying era when aviation was under the direction of the Civil Aeronautics Board. Its first mention in the Federal Register can be found in 1945 where there is a series of amendments to Civil Air Regulations Part 60: Air Traffic Rules. (The Register—the official daily record of the federal government—contains rules, proposed rules, and amendments, among other public documents. It has been digitized by the Government Accountability Office and is available online back to its initial issue in 1936.)

The 1945 listing mandated that within “airport traffic zones,” ATC could issue clearances lower than stated minimums but the flight must remain “clear of clouds.” In uncontrolled airspace, over 1,000 feet, clear of clouds was the basic requirement (with one-mile visibility).

In the decades that followed, the establishment of Part 91 and the evolution of the nation’s air navigation system has left the declaration “clear of clouds” unchanged. As written in FAR 91.155, the phrase applies to operations in both Class B and Class G (or uncontrolled) airspace.

It is still the pilot who determines that cloud clearance is maintained and thus the pilot who is the sole arbiter of the assessment. (In Jeppesen’s “Federal Aviation Regulations Explained,” the editors note that “...whether a pilot’s judgement is accepted or not will be based on a credibility determination by the administrative law judge.”)

The presumption of pilot responsibility is evident in reviewing accident investigations involving VFR into adverse weather or IMC. Other than data drawn from these NTSB reports, there is no statistical analysis of VFR pilot cloud incursion to be found. So, while many pilots have a story about it, no pilot officially does it, except the pilots that crash while in the midst of it. Under Part 135, this reality raises questions about operational control and the decision-making that dispatches VFR pilots into situations where cloud clearance is questionable.

In July 2015, SeaPort Airlines dba Wings of Alaska crashed a Cessna 207 into the trees at about 1,250 feet on a commuter flight to the VFR-only destination of Hoonah, Alaska. The NTSB cited the deceased pilot for her decision to initiate and continue VFR into IMC. In September 2016, Kenmore Air Seaplanes crashed a de Havilland Beaver floatplane into the water near Lopez Island, Washington. The NTSB cited the pilot’s decision to “land in an area of low visibility and ground fog.”

In March 2019, an Air Logistics Bell 407 charter flight enroute to an offshore oil platform crashed into a marsh near Galliano, Louisiana. Investigators cited the deceased pilot’s loss of control due to spatial disorientation while operating in marginal conditions.

A similar finding was assigned following the investigation into the Island Express Helicopters accident in January 2020 which killed Kobe Bryant and eight others. The charter departed Orange County Airport, then obtained a Special VFR clearance from Van Nuys tower for Camarillo. Investigators determined that pilot’s continued VFR into IMC resulted in spatial disorientation and loss of control.

The similarities in these reports and the hundreds of others like them, across commercial and general aviation, echo investigations from decades ago, as when the VFR pilot of the charter flight that killed himself and Buddy Holly, Ritchie Valens, and J.P. Richardson departed into night IMC in 1959 in Iowa. The probable cause for that accident, written by the Civil Aeronautics Board and commonly referred to “as the day the music died,” cited the pilot’s “unwise decision to embark on a flight which would necessitate flying solely by instruments when he was not properly certificated or qualified to do so.” 

While investigators noted the pilot was not given the most up-to-date weather prior to departure as required, which in this case included a crucial “flash advisory,” they also found that the pilot and operator failed to “obtain all of the available information…”

The owner of Dwyer Flying Service, whose company was approved as VFR-only, told investigators he “relied entirely” on the pilot’s judgement for all aspects of the flight. Sixty years later, Island Express Helicopter’s acceptance of its fatal flight, its operational control and management decision-making, were not part of the probable cause. The company was noted only as a contributory factor for its “inadequate review and oversight” of “safety management processes.” It was the pilot who flew into the clouds that day, and ultimately the pilot alone who was responsible for planning and operating the flight that encountered them.