Aviation Electronics Technician 1 - Historic Naval Ships Association

CHAPTER 9AUTOMATIC CARRIER LANDING SYSTEMThe most demanding task facing a pilot is thelanding of the aircraft on an aircraft carrier in roughseas. Landing an aircraft on a stationary land airstripis hard enough. Add to that task the motion of thecarrier in the water, the wave action, and the vortex ofair caused by the island, and you can see the problemsfacing the pilot.With the electronic technology of today, thecarrier landing is made easier for the pilot. Theautomatic carrier landing system (ACLS) is a greataid to the pilot. This system, once engaged, providesthe aircraft with the following capabilities:Data link roll commands are used to interceptand lock onto the landing pattern.Data link pitch commands establish the properglide path.The autopilot provides warnings if theautomatic carrier landing mode becomesuncoupled or is degraded.This system does not guarantee a perfect landing,nothing can do that. What this system does do is toensure that the pilot and aircraft have the best andsafest possible approach and descent to the carrierdeck and touchdown.AUTOMATIC CARRIER LANDINGSYSTEM COMPONENTSLearning Objective: Recognize systems,subsystems, and components used in theautomatic carrier landing system.Although this system is used on the aircraft, someof the subsystems are located on the aircraft carrier.There is no ACLS “box” on the aircraft. This systemuses parts of other systems already onboard theaircraft. Figure 9-1 shows how the ACLS componentsinterface and the signal data.AUTOMATIC FLIGHT CONTROLSYSTEM AN/ASW-42The automatic flight control system (AFCS orautopilot) is located on the aircraft. This systemprovides the interface between the data link and theaircraft flight control surfaces. It is the system thepilot uses to select ACLS. The AFCS providesswitching and signal conditioning, engage logic,command signal limiting, and failsafe interlocks. Thefailsafe interlocks are required to couple and processdata link signals to the pitch and bank channels of theAFCS. Automatic synchronization is provided in allthree axes.DIGITAL DATA COMMUNICATION SETAN/ASW-25BThe digital data communication set (DDCS)receives the data link messages and signals, screensout invalid messages, and then sends the signals to theAFCS. The DDCS is located in the aircraft.RECEIVING-DECODING GROUPAN/ARA-63The receiving-decoding group (R-DG)determines the glide-path errors from the carrier’sinstrument landing system radar. It also converts thedata into signals for the pilot’s flight path crosspointers. The R-DG is used for airborne monitoringof Mode I approaches and for Mode II. All threemodes (Mode I, Mode II, and Mode III) will bediscussed later in this chapter.INSTRUMENT LANDING SYSTEMAN/SPN-41The instrument landing system (ILS radar)transmits the glide path pulse-coded Ku-bandinformation from the carrier to the aircraft. Thissystem is located on the carrier and uses two antennas.One antenna is used to transmit azimuth information,and the other transmits elevation information. Bothsignals are processed by the R-DG on the aircraft.9-1