scud running in mountains

Note the power lines on the ridge

The US National Transportation Safety Board (NTSB) statistics for any particular year during the past two decades include a list of the most frequent causal factors for general aviation accidents.

The troubling point of these statistics is that the same things are causing the same accidents year after year. This points out the need for continued refresher training to establish a higher level of flight proficiency for all pilots.

Doesn’t this remind you of the saying, “Fool me once, shame on you. Fool me twice, shame on me.” It should bother us that we, as pilots, are unable to learn from the mistakes of others.

The first item on the NTSB’s top ten list is “inadequate pre-flight preparation and/or planning,” that denotes we must spend time thinking about the flight.

Will the flight extend into the night? Do I need a flashlight? Is the destination airport lighted? Are services available at my time of arrival?

What if I run into a venturi effect over the mountains? Will I have enough fuel to continue the flight to the destination?
Suppose un-forecast weather crops up, where will I go? What will I do?

These examples show that pre-flight planning is not just a matter of digging out the plotter and computer.

The next item on the NTSB list is “landing accidents—excessive speed on the landing roll or failure to correct for crosswind conditions.”

The third item is “continued VFR flight into adverse weather conditions.” Each year some 200 accidents are listed under this category. The really sad part about this is about 65 percent of these accidents are fatal.

How do these accidents occur when everyone knows that pushing the weather on a VFR flight is not wise?

Is it that the pilot cannot recognize “adverse weather conditions” from a distance and unintentionally gets in the weather? Most times intentional scud running is the main culprit. Those scattered clouds that are easily flown around in open country can be a menace in a narrow canyon. Yet pilots continue to scud run. And, not all of them are low-time pilots who haven’t learned better. Some are high-time pilots—maybe instrument-rated—and mostly of sound judgment.

Flying above a layer of clouds with the sun at your back will produce a "glory" if the cloud is composed of liquid water. This rainbow circle is caused by a diffraction phenomenon. Beware of icing in these clouds if the outside air temperature is near freezing or below freezing.

Often the aircraft's shadow is visible in the centre of the "glory" rainbow ring.

Some pilots scud run successfully, having found it necessary to do so from time to time because of ice or turbulence aloft, strong headwinds at IFR altitudes, navigation equipment failures, or flying to a destination that does not have an instrument approach facility.

Whatever the reason, they do it. But, they have disciplined themselves and learned how to scud run safely.

Experienced pilots develop rules that they will not deviate from under any circumstances.

Minimum weather: 2,000-foot ceiling and 5 miles visibility. If weather reports of five miles visibility or better do not exist at stations beyond the destination, don’t go.

Do not scud run a route you have not previously flown at 1,500 feet AGL or less. Even so, the terrain looks much different when the weather is bad.

Do not scud run toward worsening weather. The tendency to push on for a few more miles is just too great.

scary practice

One frightening pilot technique unconsciously practiced by many pilots when the weather is marginal is that of flying near the cloud base. This is a natural tendency since it places the airplane farther away from the ground. But, you have to realize the forward visibility will be severely limited near the cloud base, allowing you to fly into trouble before you can see it.

An experienced pilot will fly low. Divide the area from the ground to the cloud base into thirds and fly the middle or lower third. If terrain constraints prohibit this, don’t fly.


Keep navigation simple by following a highway or railroad. Pay attention to your chart to make sure there isn’t a tunnel. Be cautious about following a river. That’s where the poorest visibilities tend to gather.

Turn on all your lights. It’s not likely that anyone else will be out there with you, but if they are, you want them to see and avoid your airplane. When flying through a narrow canyon like The Gorge between Portland and The Dalles, Ore., it is customary to remain to the right side, just as on a highway, to avoid pilots going the other way.

Throttle back to a comfortable slow-speed cruise to keep the terrain features clearly in sight.

life saving manoeuvre

It is with hesitation and trepidation that the following manoeuvre is presented. Not because it is difficult to perform, but because someone is going to use it as a crutch to scud run when he shouldn’t. Remember, this is an “out,” not a manoeuvre that is reserved as a routine part of flight. This is an emergency lifesaving manoeuvre.

Suppose your weather check meets your parameters for safe flight. You take off and fly toward the destination and somehow get lulled into a situation where the visibility makes you a strong candidate for flying into cumulo-granite.

Descend close to the ground and find a prominent landmark that can be circled without worrying about the lateral terrain clearance. Fly around and around until the visibility improves. You might be stuck there for a long time. The object is to remain flying without running into something.

Kelvin-Helmholtz Billow Clouds are similar to whitecaps on a lake and indicate turbulence.

Different form of Kelvin-Helmholtz Billow Clouds.

Scud running is, like Russian roulette, a dangerous game. With reduced visibility only the foolhardy flirt with Mother Nature.

When the visibility is unrestricted beneath the clouds, a look-see may (with a strong emphasis on may) be tried. Be careful.

Even with good forward visibility, the unwary can get trapped in an area with low clouds that does not allow room for an escape manoeuvre.

When the terrain tightens up (narrows), it may be difficult to continue the flight. Some scud-runners have had to land the airplane in trees to avoid a more serious out-of-control crash.

Rotor turbulence may affect the controllability of the airplane when manoeuvring at low altitude and slow airspeed.

Pilots have flown into trouble before they even see it by flying near the base of the clouds. Experienced pilots divide the area between the cloud base and the ground into thirds and fly in the lower third. If the terrain does not allow this, the smart pilot avoids the area.