Optical Landing System

An Optical Landing System (OLS) is used to give glidepath information to pilots in the terminal phase of landing on an aircraft carrier. [Aircraft Launch and Recovery Operations Manual http://www.lsoschool.org/images/stories/files/pubs/Instructions/cnal&p_al&r_ops_man(13800.3f&9d).pdf] From the beginning of aircraft landing on ships in the 1920s to the introduction of OLSs, pilots relied soly on their visual perception of the landing area and the aid of the Landing Signal Officer (LSO in the US Navy, or "batsman" in the Commonwealth navies). LSOs used colored flags, cloth paddles and lighted wands.

Mirror Landing Aid

The first OLS was the Mirror Landing Aid, one of several British inventions made after the Second World War revolutionising the design of aircraft carriers. The others were the steam catapult and the angled flight deck. The Mirror Landing Aid was invented by Nicholas Goodhart [ [http://www.fleetairarmoa.org/pages/fleet_air_arm_history/history.shtml Fleet Air Arm website - Accessed 21 August 2008] ] . It was introduced on British carriers in 1954 and on US carriers in 1955.

The mirror landing aid was a gyroscopically-controlled concave mirror on the port side of the flight deck. On either side of the mirror was a line of green coloured "datum lights". A bright orange "source" light was shone into the mirror creating the "ball" (or "meatball" in later USN parlance) which could be seen by the aviator who was about to land. The position of the ball compared to the datum lights indicated the aircraft's position in relation to the desired glidepath: if the ball was above the datum, the plane was high; below the datum, the plane was low; between the datum, the plane was on glidepath. The gyro stabilisation compensated for much of the movement of the flight deck due to the sea, giving a constant glidepath.

Initially, the device was thought able to allow the pilot to land without direction from the LSO. However, accident rates actually increased upon the system's initial introduction, so the current system of including the LSO was developed. This development, along with the others mentioned, contributed to the US carrier landing accident rate plummeting from 35 per 10,000 landings in 1954 to 7 per 10,000 landings in 1957. [www.robertheffley.com/docs/CV_environ/Basic%20IFLOLS%20Lecture%5B2%5D.ppt.]

The LSO, who is a specially qualified and experienced Navy pilot, provides additional input to the pilot via radios, advising of power requirements, position relative to glide path and centerline. The LSO can also use a combination of lights attached to the the OLS to indicate "go around" using the bright red, flashing wave off lights. Additional signals, such as "cleared to land," "add power," or "divert" can be signaled using with a row of green "cut" lights or a combination thereof.

Fresnel Lens Optical Landing System (FLOS)

Later systems kept the same basic function of the mirror landing aid, but upgraded components and functionality. The concave mirror, source light combination was replaced with a series of fresnel lenses. The Mk 6 Mod 3 FLOLS was tested in 1970 and had not changed much, except for when ship’s heave was taken into account with an Inertial Stabilization system. These systems are still in wide use on runways at US Naval Air Stations. [LSO NATOPS Manual http://www.navyair.com/LSO_NATOPS_Manual.pdf.]

Improved Fresnel Lens Optical System (IFLOS)

The IFOLS keeps the same basic design but improves on the FLOS, giving a more precise indication of aircraft position on the glideslope. A prototype IFLOLS was tested aboard USS George Washington (CVN-73) in 1997 and every deploying aircraft carrier since 1999 has had the system. Although called Improved "Fresnel" Lens Optical Landing System, IFLOLS actually uses fiber optics rather than Fresnel Lenses.

Additionally, IFLOS offers:
*Better illumination
*Sharper ball definition
*Increase viewing distance
*More maintainable / less degradation at high temperaturesWith more cells and sharper ball definition, the ball appears to move more often and more rapidly to glideslope corrections.

Manually Operated Visual Landing Aid System (MOVLAS)

The MOVLAS is a backup visual landing aid system used when the primary optical system (FLOLS) is inoperable, stabilization limits are exceeded or unreliable (primarily due to extreme sea states causing a pitching deck), and for pilot/LSO training. The system is designed to present glideslope information in the same visual form presented by the FLOLS.

There are three installation modes aboard ship: STATION 1 is immediately in front of the FLOLS and utilizes the FLOLS waveoff, datum, and cut light displays. STATION 2 and 3 are independent of the FLOLS and are located on the flight deck port and starboard side respectively. MOVLAS is nothing more than a vertical series of orange lamps manually controlled by the LSO with a hand controller to simulate the ball.

MOVLAS Components

;Lightbox:MOVLAS is nothing more than a vertical series of orange lamps manually controlled by the LSO with a hand controller to simulate the ball. [Carrier Naval Aviation Training and Procedures Standardization (CV NATOPS) Manual http://www.lsoschool.org/images/stories/files/pubs/NATOPS/CV-NATOPS-2004.pdf] ;Hand Controller:The hand controller is located at the LSO workstation. A handle is provided so the LSO may select the position of the meatball. The pickle switch is attached to the end of the controller handle. As the handle on the LSO controller is moved up or down it lights three or four consecutive lamps in the light box thus providing a meatball.;Repeaters:MOVLAS repeaters show where the LSO is displaying the meatball to the pilot. One repeater is displayed on the Integrated Launch And Recovery Television Surveillance System (ILARTS).

Pitching deck

The fresnel lens has two modes of stabilization. The most precise is line stabilization (LS). In LS, the glide path is stabilized to infinity; that is as the deck pitches and rolls, the lens is pitched and rolled to maintain a steady glideslope fixed in space. This mode is only good to about 3° of pitch and about 1-2° of roll. From 3-5° pitch, point stabilization is used, where the glide slope is fixed around a point 2500 feet aft of the lens. That is, while the deck may pitch up and down, the point 2500 feet aft is fixed in space, so that the oscillation is reduced. Above about 5° pitch or when the rate of pitch/roll is excessive, the displayed glideslope becomes unreliable. In these cases, the LSO switches to the MOVLAS. Only the most experienced LSOs will control aircraft with MOVLAS during heavy sea states. [Pitching Deck videos http://www.youtube.com/watch?v=SvPJonTxhjo] [www.youtube.com/results?search_query=pitching+deck&search_type=]

ee also

* Flight deck
* Aircraft Carrier Operations

References

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