Aviation Speak

If it hasn't happened yet, sooner or later you're sure to hear your instructor ask a tower controller for "the option." When the tower clears you and your instructor for the option, he or she is giving your aircraft permission to perform a touch and go, low approach, missed approach, stop and go, or full-stop landing. It's up to you - and more often your instructor - what sort of procedure you'll perform when you get your clearance. Chances are you'll find out what procedure that will be at the last possible minute. Most instructors use the option clearance to evaluate student performance under changing circumstances, so don't expect much warning before you hear the instruction that changes your plans.

Visibility

How the term visibility is applied and exactly what it means depends on the circumstances. In the most general sense, visibility is the ability to see and identify prominent unlighted objects by day and prominent lighted objects by night. Visibility is determined by atmospheric conditions such as fog, clouds, and haze rather than by the eyesight of the observer and it is expressed as a distance such as statute miles or hundreds of feet.

Flight visibility is one of several specific types of visibility. It refers to the average forward horizontal distance at which objects can be seen from the cockpit of an aircraft in flight. As a pilot, you will have to make your own determination about flight visibility since there is no trained weather observer in the cockpit with you.

Ground visibility also refers to prevailing horizontal visibility. Unlike flight visibility, ground visibility refers to how far you can see near the Earth's surface - a determination that is made and reported by the National Weather Service or by an accredited observer.

Prevailing visibility refers to the greatest horizontal visibility that exists throughout at least half the horizon circle. In other words, if you can see at least five miles at least halfway around as you turn in a circle and look at the horizon, the prevailing visibility is five miles, even though you may be able to see farther in some directions and not as far in others.

A couple of other types of visibility deal primarily with flights conducted under instrument flight rules. A runway visibility value (RVV) is the visibility determined for a particular runway by an electronic measuring device. A meter provides a continuous indication of visibility reported in fractions of miles. This value is used instead of prevailing visibility to determine takeoff and landing minimums for a particular runway.

A runway visual range (RVR) is also derived from instruments. The range tells pilots how far they can see down the runway from the approach end based on the ability to see either high intensity runway lights or other targets - whichever is farther away. Unlike RVV, RVR tells the pilot what he or she can expect to see from the cockpit of a moving aircraft. Distances are reported in hundreds of feet.