Continued VFR into IMC is when an aircraft operating under
visual flight rules
In aviation, visual flight rules (VFR) are a set of regulations under which a pilot operates an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better ...
intentionally or unintentionally enters into
instrument meteorological conditions
In aviation, instrument meteorological conditions (IMC) is a flight category that describes weather conditions that require pilots to fly primarily by reference to instruments, and therefore under instrument flight rules (IFR), rather than by ou ...
. Flying an aircraft without visual reference to the ground can lead to a phenomenon known as
spatial disorientation
Spatial disorientation results in a person being unable to determine their position or relative motion, commonly occurring during periods of challenging visibility, since vision is the dominant sense for orientation. The auditory system, vestibul ...
, which can cause the pilot to misperceive the angle, altitude, and speed they are traveling. This is considered a very serious safety hazard in
general aviation
General aviation (GA) is defined by the International Civil Aviation Organization (ICAO) as all civil aviation aircraft operations with the exception of commercial air transport or aerial work, which is defined as specialized aviation service ...
. According to AOPA’s Nall Report, approximately 4% of general aviation accidents are weather related, yet these accidents account for more than 25% of all fatalities.
Inadvertent entry into Instrument Meteorological Conditions
If weather deteriorates during flight or the aircraft flies into clouds, a flight that started out under VFR may turn into a flight under IMC. This is known as VFR into IMC or Inadvertent Entry Into Instrument Meteorological Conditions (IIMC). IIMC is a dangerous situation that has resulted in many accidents, as pilots may become subject to
spatial disorientation
Spatial disorientation results in a person being unable to determine their position or relative motion, commonly occurring during periods of challenging visibility, since vision is the dominant sense for orientation. The auditory system, vestibul ...
without visual cues, leading to loss of control or
controlled flight into terrain
In aviation, a controlled flight into terrain (CFIT; usually ) is an accident in which an airworthy aircraft, under pilot control, is unintentionally flown into the ground, a mountain, a body of water or an obstacle. In a typical CFIT scenari ...
.
[ Statistics from the Federal Aviation Administration indicate that spatial disorientation is a factor in approximately 15% of general aviation accidents; of those, approximately 90% are fatal. Other statistics indicate that 4% of general aviation accidents were attributable to weather; of those weather-related accidents, 50% resulted from VFR into IMC, and 72% of the VFR into IMC accidents were fatal.
In the ''180—Degree Turn Experiment'' conducted in 1954 by the University of Illinois, twenty student pilots flew from VFR into simulated IMC; after entry, all of them eventually reached a dangerous flight condition or attitude over a period ranging from 20 to 480 seconds.]Federal Aviation Administration
The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
in 1993; however, the original 1954 study was noted for simulating an aircraft the subjects had little to no experience with, and only providing a partial instrument panel.
Examples of accidents involving continued VFR into IMC
* The Day the Music Died
On February 3, 1959, American rock and roll musicians Buddy Holly, Ritchie Valens, and "The Big Bopper" J. P. Richardson were all killed in a plane crash near Clear Lake, Iowa, together with pilot Roger Peterson. The event later becam ...
2020 Calabasas helicopter crash
On January 26, 2020, a Sikorsky S-76B helicopter crashed in the city of Calabasas, California, around northwest of Downtown Los Angeles, while en route from John Wayne Airport to Camarillo Airport. All nine people on board were killed: retir ...
See also
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Notes
References
External links
* {{cite web, url=https://www.planeandpilotmag.com/article/understanding-vfr-into-imc-accidents/, title=Understanding VFR Into IMC Accidents, access-date=11 February 2021
Aviation risks