Editing Instrument meteorological conditions (section)

==Inadvertent entry into Instrument Meteorological Conditions==

{{main|Continued VFR into IMC}}

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 ''inadvertent entry into instrument meteorological conditions'' (IIMC), or more briefly ''VFR into IMC''. IIMC is a potentially dangerous situation that has resulted in many accidents,<ref>{{Cite web|last=|first=|date=|title=Training Fact Sheet – Inadvertent Entry Into Instrument Meteorological Conditions (IIMC)|url=http://jayc3.sg-host.com/Flysafe/BULLETIN%20IIMC.pdf|archive-url=https://web.archive.org/web/20210207105938/http://jayc3.sg-host.com/Flysafe/BULLETIN%20IIMC.pdf|archive-date=2021-02-07|access-date=|website=|quote=Inadvertent entry into IMC is a situation where deteriorating weather prevents you from flying under visual meteorological conditions when you were planning to fly under VFR.|url-status=dead}}</ref> as pilots may succumb to [[spatial disorientation]], leading to loss of control or [[controlled flight into terrain]].<ref name=Rowland-2017/> 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.<ref>{{cite magazine |url=https://www.airspacemag.com/military-aviation/the-disorient-express-474780/ |title=The Disorient Express |author=LeCompte, Tom |date=September 2008 |magazine=Air & Space |access-date=26 February 2021}}</ref> 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.<ref>{{cite web |url=https://www.planeandpilotmag.com/article/understanding-vfr-into-imc-accidents/ |title=Understanding VFR Into IMC Accidents |author=Ison, David |date=February 6, 2016 |website=Plane & Pilot |access-date=26 February 2021}}</ref>

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{{efn|The authors defined the dangerous flight condition or attitude as one of the following four situations:<ref name=180d/>{{rp|8}}
# A [[Stall (fluid dynamics)|stall]], either normal or accelerated
# A [[Banked turn|bank]] exceeding 45°
# An excessive speed (more than normal fast cruise)
# Obvious or prolonged loss of altitude or directional orientation}} over a period ranging from 20 to 480 seconds.<ref name=180d>{{cite book| publisher=University of Illinois |first1=Leslie |last1=Aulls Bryan |last2=Stonecipher |first2=Jesse W. |last3=Aron |first3=Karl |year=1954 |asin=B0007EXGMI |title=180-degree turn experiment |url=https://archive.org/details/180degreeturnexp11brya/mode/2up|ol=207786M |lccn=a54009717 |oclc=4736008}}</ref>{{rp|16}} The average time to reach a dangerous condition was 178 seconds, echoed in the title of the "178 Seconds to Live" article distributed by the [[Federal Aviation Administration]] in 1993;<ref>{{cite web |url=https://www.faa.gov/about/office_org/field_offices/fsdo/fai/local_more/alaskan_articles/media/178-Seconds_to_Live.pdf |title=178 Seconds to Live |publisher=Federal Aviation Administration |access-date=26 February 2021}}</ref> 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.<ref name=Rowland-2017>{{cite web |url=https://www.avweb.com/flight-safety/technique/surviving-vfr-into-imc/ |title=Surviving VFR into IMC |author=Rowland, David |date=February 5, 2017 |website=AV Web |access-date=26 February 2021}}</ref> In addition, the "178 seconds" average time was extracted from the preliminary evaluation; after training for a standardized procedure to exit IMC, each student pilot was tested three times, and 59 of the 60 resulting simulated flights successfully resulted in a controlled descent out of the cloud deck without reaching a dangerous condition.<ref>{{cite web |url=https://www.aopa.org/news-and-media/all-news/2016/march/pilot/pe_proficiency |title=The lost lessons of '178 seconds to live' |author=Dubois, William E. |date=February 4, 2016 |website=P&E: Proficiency [blog] |publisher=Aircraft Owners & Pilots Association |access-date=26 February 2021}}</ref>