One degree separates the destination’s temperature and dewpoint. The newly issued surface observation paints a picture of early morning weather well below minimums, not to mention the pilot’s personal minimums: 021053Z 20004KT 1/4SM R15/1600V1800FT FG VV002 18/17 A2992 RMK AO2.
And it’s not a localized condition. A stationary front dangles from a low pressure area to the northwest; the surface analysis also indicates widespread mist. A cold front extends from the low, but its sweeping-out effect is probably a day away.
Slight improvement of local conditions is forecast later, to 500 broken and four miles in mist. At that time, the most logical alternate airport is forecast to be 800 overcast, three miles in mist—but as any pilot who has ever waited out lingering fog knows, it can be one of the diciest elements of aviation weather forecasting.
Suppose a pilot forges ahead with this risky trip. He or she might quickly come to confront a major difference between the training environment and for-real cross-country IFR, in which a failure to complete the approach carries a level of urgency quite unlike the casual, time-saving missed approaches you flew on almost every instrument lesson.
When it’s real, decisions demanding the pilot’s divided attention require acquiring, comprehending, and weighing rapidly changing weather data—against the ticking of the fuel clock. Divert? Hold? (Maybe conditions will improve.) Commence a second approach? (Maybe a window of opportunity will open in the fog.)
Fatiguing scenarios. Don’t underestimate the toll they can exact on decision making. When a Piper PA-28R-200 exhausted its fuel on Jan. 13, 2013, while attempting multiple approaches and then, several diversions, the National Transportation Safety Board’s summary of the resulting accident noted the failure of the 598-hour pilot with 77 hours of IMC "to land the airplane at multiple airports that were equipped with adequate instrument approach procedures while operating in low instrument meteorological conditions."
In an accident fatal to a Cirrus SR22 pilot and four others, the NTSB cited spatial disorientation as the probable cause; the crash was also preceded by two attempted approaches and navigational errors captured on radar.
Spatial disorientation? Isn’t that only a hazard for VFR pilots?
No indeed. The report of the Sept. 15, 2012, accident included an instructor’s estimate that the instrument-rated pilot had 1,000 hours total flight time, 75 hours actual IMC, and 650 hours flying Cirrus aircraft.
What’s your margin?