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The 3 bar VASI has 3 ranks of lights, The two center show “on glide path” indications. The leftmost
is a low path, and the rightmost is a high path. The all red is too low. The all white indication is too
high.
Another approach slope indicator is the Precision Approach Path Indicator (PAPI). The system provides
a more precise glideslope indication than does VASI. When all 4 lights are white, you are too high.
When all are red, you are too low. When 2 are red and 2 are white you are on a 3° path. Three white on
the left indicate a path of 3.2°. Three red on right indicate a 2.8° path. The open clear circles indicate
white. The darkened circles indicate red.
The Tri-Color system is a single light that projects 3 colors. The above glide path indication is amber.
On glide slope is Green. Below glide slope is red. When the aircraft descends from green to red, the pilot
may see amber during the transition.
There is a similar system called the Pulsating Visual Approach Slope Indicator.(Not shown). It is
somewhat similar to the Tri-color except a solid white indicates on glide path; steady red on a slightly
low path. Pulsating white indicates too high. Pulsating red means too low.
See AIM 2-2. VISUAL GLIDESLOPE INDICATORS for additional information from the Aeronautical
Information Manual.
Airport Beacons
Rotating beacons which operate at night and during times of poor weather assist the pilot to locate the
airport from the air.
Airport Info
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See AIM 2-8. AIRPORT (ROTATING) BEACONS for information on rotating beacon operation.
Wake Turbulence
All aircraft generate some turbulence, called Wake Turbulence. The turbulence from small aircraft is of
little consequence. When the size and weight of the aircraft are great, the turbulence can be severe to
other aircraft.
Cause
A number of factors contribute to wake turbulence. These are slipstream turbulence, jet blast, propeller
wash, and wingtip vortices. The most severe of these disturbances is Wingtip Vortices. To over simplify,
they are small tight horizontal tornadoes of air leaving the wing tips. The turbulence is a byproduct of the
wing creating lift.
A pressure differential is created between the upper and lower surface of the wing. The low pressure is
on the upper surface. This pressure differential creates a rolling airflow at the wing tip inward toward the
fuselage. The ritating air mass trailis rearward. he right vortex rolls counterclockwise; the left vortex is
clockwise.
Vortex Avoidance
Wingtip vortices have certain predictable characteristics. A large aircraft generates vortices from the
moment of takeoff rotation. Takeoff rotation causes significant vortex.
In flight, the sink rate of the vortices is 400 to 500 feet per minute, and levels out 900 to 1000 feet below
the aircraft. Near the runway surface, a tailwind can cause the vortex to persist near the ground for
several minutes if the wind is light.
Large heavy aircraft generates significant vortex on landing. It has a high angle of attack of attack, and is
slow and heavy. The point of greatest wing loading and vortex is the flare to touchdown. This is due to
additional wing load caused by centrifugal force generated in the flare.
When operating on and near large airports with large aircraft operations, caution concerning wake
turbulence must be observed. The strength of the wingtip vortices is greatest then the aircraft is HEAVY,
CLEAN and SLOW. The greatest hazard to small aircraft is coming across a vortex while operating near
the ground.
Each vortex is about 2 wingspans in width and one wingspan in depth. They remain spaced about one
wingspan apart, drifting with the wind. In a no-wind situation, the vortices will persist on the runway.
They move laterally outward about 2 to 3 knots on each side when striking the ground.
Airport Info
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A cross wind will add or subtract from the natural 2 - 3 knot lateral movement of each vortex. With a
light crosswind component of about 3 knots, the upwind vortex can persist for a considerable time. The
vortex movement and the opposing crosswind oduce a stationary vortex.
STAY ABOVE AND UPWIND FROM THE VORTEX.
. Plan your strategy accordingly.
1. When landing on the same runway behind a large aircraft, stay at or above the larger aircraft’s
approach path. Note the touchdown point, and plan to land beyond that point. 2. If landing on a runway
parallel to and within 2500 feet of one being used by a large aircraft, use the same procedure as in 1
above. 3. If landing on a runway crossing the larger aircraft’s runway, cross the other runway above the
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