The FAA's AFH states that "most midair collision accidents occur in good weather", in daylight, and nearby airports/navigation aids. What does this imply?

(One obvious explanation to this fact could be that there is simply much more traffic in this conditions, and despite a much lower accident rate per flight hour there are more overall accidents.)

  • $\begingroup$ Your obvious explanation sounds very reasonable to me, even if correlation isn't an explanation as such. I'm not sure what your actual question is here, are you looking for sources or studies that analyze this topic? $\endgroup$
    – Pondlife
    Commented Dec 2, 2017 at 22:57
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    $\begingroup$ I would say it is because in bad weather everyone is in ifr. Mid-airs are more a vfr phenomenon $\endgroup$
    – TomMcW
    Commented Dec 3, 2017 at 0:41
  • $\begingroup$ Near airports/navaids makes sense because those are destinations (either initial/final or intermediate as a waypoint). It mostly implies that airplanes are hard to see, something ADS-B and Nexgen are helping to avoid. My aircraft makes audible call-outs if I get too near an ADS-B or other interrogation target, as a feature of our Garmin GTX-345 which is integrated into our comms panel. $\endgroup$
    – Ron Beyer
    Commented Dec 3, 2017 at 1:42
  • $\begingroup$ @Pondlife I'm trying to understand if there is a causal connection, e.g. complacency in good conditions leading to more accidents, or merely correlation that has no practical implications. $\endgroup$
    – GJ.
    Commented Dec 3, 2017 at 3:09
  • $\begingroup$ Is it possible/reasonable/common to be flying in IMC without being under ATC? Is it legal to run canyons (say the Coalville-Heber-Sandy route) in the soup, entirely with GPS and good maps, like Ramius did in "Hunt for Red October" ( but with a sub)? $\endgroup$ Commented Dec 3, 2017 at 15:05

1 Answer 1


In poor weather there are apt to be less VFR aircraft and more IFR. IFR are required to participate with ATC and automatically receive separation by time, altitude, and radar (when available). VFR do not require any separation and are not required to participate with ATC. There are also more flights in VFR weather than there are with IFR.

I might get flamed for this, but in general a IFR pilot is more proficient than a VFR pilot. The medical (commercial opps), testing, and currency requirements for a IFR license are usually considerably more complex than VFR - meaning (admittedly there are exceptions i.e. aerobatic pilots) IFR pilots are generally more proficient.

The following added in response to comments below

According to the FAA, "... the majority happen within five miles of an airport" https://www.faasafety.gov/gslac/alc/libview_normal.aspx?id=6851. So, cruise environment is not a factor, and IFR have ATC separation at all times, making this predominantly a VFR landing/takeoff problem. Most IFR flights are commercial requiring a 6mo medical where as private VFR pilots require 2yrs or LSA and Ultralight do not require a aviation medical. (The private medical requirements just changed, but this discussion is based on prior years data.)

In addition to excersize IFR privileges, a pilot must remain current every 6mo where as a VFR pilot does not (except for night landings).

IFR flights will have a higher percentage of two man crews compared to most VFR flights with a single pilot. The extra set of eyes is extremely significant particularly during the landing/takeoff phase of flight.

  • $\begingroup$ That's plausible, but would not be valid if collisions occur at FL300. It would be good to eliminate other possibilities with more details about the circumstances of the collisions. $\endgroup$
    – mins
    Commented Dec 11, 2017 at 14:02
  • $\begingroup$ I'm not sure what you mean by the "medical (commercial opps) ... for an IFR license"? At least in the US, there are no extra medical requirements for an instrument rating, and you don't need to have a commercial certificate either. $\endgroup$
    – Pondlife
    Commented Dec 11, 2017 at 14:09
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    $\begingroup$ And of course, nothing (assuming that the pilot has an instrument rating) prevents a pilot from electing to fly IFR in VMC. It is only the combination VFR in IMC that is prohibited. (The other two possibilities, VFR in VMC and IFR in IMC, are obviously allowed.) If a VFR flight transitions from VMC to IMC, then the pilot must either transition to IFR or get back into VMC. $\endgroup$
    – user
    Commented Dec 11, 2017 at 16:06
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    $\begingroup$ @jwzumwalt: the traffic density is probably much higher near airports, more planes, more accidents. $\endgroup$
    – user7241
    Commented Dec 11, 2017 at 18:47

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