Fresnel Lens Optical Landing System (FLOLS)
The Fresnel lens consists of a lens assembly, cut lights, waveoff lights, and datum lights.
The lens assembly is a box one ft wide by four ft high containing five vertical light cells. Depending on
your position on the glidepath, one of the four upper amber cells or the bottom red cell is visible. The
visible lens indicates your position relative to the glideslope, i.e., above, on, or below the optimum
Mounted horizontally and centered above the lens box are four green cut lights that initially indicate a
Roger ball call to aircraft that are operating under ziplip, EMCON, or NORDO at the ship. Additional
illumination of the cut lights is a call for power. Ziplip is normally used during day Case I fleet operations to
minimize radio transmissions. EMCON is a condition where all electronic emissions are minimized.
Waveoff lights are mounted vertically on each side of the lens box. These red lights are controlled by the
Landing Signal Officer (LSO) and used to indicate that either the deck is foul or the approach is not set up
properly or is unsafe. Bingo is signaled by alternating waveoff and cut lights.
NOTE: On the shipboard model, there are 3 auxiliary waveoff lights on each side and adjacent to the
primary waveoff lights.
Green datum lights are mounted horizontally to the lens assembly with six lights on each side. The
position of the ball in reference to the datum lights provides you glideslope information.
All source lights in the lens box are illuminated during operation (Figure 3). Each of the five cells is angled
slightly from the adjacent cell for a total vertical coverage of 1.5 degrees. The lenses are manufactured in
such a way that only one cell, or part thereof, can be seen from a particular angle. Each cell projects a bar
of horizontal light that appears to be a ball until very close range; therefore, the term meatball or ball is
used to describe the light. As stated previously, the red bottom cell indicates an excessively low condition.
Never accept or finesse a low ball.
Rolling the lens relative to the ships roll axis compensates for the hook-to-eye distance of different type
The ball is visible on the lens at plus or minus 3/4 of a degree vertically from optimum glideslope and
about 20 degrees either side of centerline. These conditions create a wedge-shaped area in which the ball
can be seen on the lens (Figure 4).
Because the lens assembly projects a wedge of light, the closer the aircraft comes to the lens, the nar-
rower the wedge becomes; therefore, smaller glideslope corrections are required the closer the aircraft is
to touchdown. If your aircraft is not in the 1.5-degree wedge, the ball will not be visible. If you understand
glideslope geometry, you will realize the importance of flying to a good start.
(7-01) Change 2