Plane & Pilot
Tuesday, January 1, 2008

VMC Vs. VFR


What’s technically legal isn’t necessarily safe


vmc cs vfrIn basic flight training, student pilots memorize the cloud clearance and visibility criteria for operation under visual flight rules and instrument flight rules (VFR and IFR). Flight schools and instructors drill into students the cloud clearance and visibility requirements for VFR operations in various categories of airspace, all the while neglecting to mention that none of this has much to do with the ability to keep an airplane upright during periods of restricted visibility and/or lack of terrain definition." />

Few pilots experience the joys of winter flight in northern Alaska, and those who do quickly learn to either stay on the ground during marginal conditions or to exercise instrument flying skills to get from point A to point B. But PVFR isn’t exclusive to Alaska.

vmc vs vfr
On a clear, dark night over the desert or other unpopulated area, what’s technically VMC can become dangerous to the VFR-only/non-instrument-rated pilot.
Consider the East Coast of the United States on a hot summer afternoon. Humidity rivals that of a steam room, and temperatures soar. Haze builds until three miles seems like pretty good visibility. In contrast to winter in the north, there are plenty of visual references here, so keeping the airplane right-side up isn’t difficult at all. Or is it?

What if your flight follows the Atlantic coast to a coastal village? The last leg of the flight will take you over a portion of the Atlantic Ocean. Visibilities at reporting stations along the coast are all about five miles in haze. Fairly good basic VFR, right?

The flight includes an intermediate stop to pick up a passenger. Delays caused by business and traffic en route to the airport cause you to arrive at your intermediate stop just after sunset. You spend a few minutes loading your passengers, and then you launch toward your weekend destination. This is the leg of the trip that crosses water, but it’s a beautiful evening with calm winds and smooth sea surface.

The route of flight extends a maximum of about seven miles from shore at one point, crossing a large bay. As you proceed toward your destination, you realize that there’s no longer a visual horizon. The ocean surface is impossible to see as well. Lights on shore are seven miles away—in five-mile visibility.

John F. Kennedy Jr. and his passengers lost their lives in similar conditions a few years ago. This scenario may be a little closer to home than the Alaska flight described earlier, but the conditions are very much PVFR.

Finally, consider a flight in low but legal VFR conditions near Oshkosh, Wis. Departing from the big air show in four-mile visibility, you’re homeward bound—to the east. Reporting stations to the east are declaring clear skies and visibility of 10 miles. To the east, however, lies Lake Winnebago. Do you go around the north end of the big lake or go direct? Again, visual references may be totally absent over the lake, even though visibility is above basic VFR.




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