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VFR-on-top is an IFR clearance in the US that a pilot can request to allow an IFR flight to use VFR altitudes provided that it can remain in VMC. Requesting and receiving a VFR-on-top clearance doesn't cancel the IFR flight plan.

When is this clearance useful? It allows the pilot a greater choice of cruising altitudes, but why would a pilot prefer to use VFR-on-top rather than request a different IFR altitude? VFR-on-top adds at least one task to the pilot's workload - maintaining VFR cloud clearance - without reducing the IFR workload.

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The VFR on top clearance is often given with a block of altitudes. Such as this from the reference document "Maintain VFR-on-top at or between six thousand and one zero thousand.” With this clearance the pilot can fly any altitude they want within this block of altitudes without having to contact ATC for further clearance. This flexibility can be useful with the conditions are such that the clouds come and go as you fly along. So if you are cruising along at 6500 and encounter a cloud and need to climb to 8500 to maintain clearance you just do it. No need to contact ATC and wait for them to ensure they can clear you higher while the clouds keeps getting bigger and bigger in the windshield.

Even if there are not cloud issues, the ability to change altitudes may be useful in seeking an altitude with more favorable winds.

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In a training environment, VFR-on-top is fantastic. You can use your IFR clearance to punch through a cloud layer to clear skies on top, practice maneuvers (or what have you), and then shoot an approach back down. VFR-on-top can turn a bad weather day into a training day, and anytime you can do that (and get real-world actual instrument experience on top of it) is a good day.

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    $\begingroup$ being cleared VFR on top doesn't automatically allow you to deviate from your route $\endgroup$ – fjch1997 Nov 10 '18 at 2:44
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Being in VMC has several benefits over hard IMC, especially if you don't have an autopilot, so being on top has advantages. :

  • Manual flying with visual reference to the horizon is much easier and less strain than manually flying using instruments for attitude control
  • Being out of cloud enables a pilot to see and avoid traffic
  • Flying in cloud can be bumpy, VFR on top is often much smoother
  • Icing is a hazard when flying in cloud, being on top of them means you won't ice up

VFR on top works well when you have a stratus layer that has an even top, not so well when you have clouds at differing levels, so it's not always a viable option.

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    $\begingroup$ Those are benefits of VMC, not VFR. $\endgroup$ – DJClayworth Sep 18 '14 at 17:53

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