Aviation Electronics Technician 1 - Historic Naval Ships Association

Figure 9-3.-Mode I landing sequence.to fuel or safety status to determine landing priorities.It is here that the aircraft is assigned a data linkchannel for automatic landing. The pilot is clearedfor approach when the LDG CHK indicatorilluminates on the discrete message indicator. Thepilot prepares for landing by ensuring the APC is inautomatic and that all the other subsystems are on andoperating.As the aircraft continues its approach and passesthrough the acquisition radar window, the LCC radaracquires the aircraft, and the ACL RDY lamp lights onthe discrete message indicator. The acquisition radarwindow is located approximately 4 miles astern of theship. When the ACL RDY lamp lights, the CATCCsystem begins sending vertical and lateral errorsignals, which represent the actual displacement ofthe aircraft from the approach path. These signals areconverted to a display on the VGI. At this time, thepilot requests the approach mode desired—Mode I forfully automatic touchdown.The LCC system transmits a COUPLE discretesignal to the aircraft. This signal indicates that pitchand bank commands may be coupled to the autopilot.At this time, the pilot ensures that the APC isengaged; the landing gear, flaps, and speed brakes areextended; and the aircraft is near the approach speedwith wings level. With the autopilot turned ON and inAUTO, the pilot then switches the ACL/OFF/PCDswitch to ACL. This couples the data link to theautopilot. The pilot will then verbally acknowledgeengagement of the autopilot. The ground commandcontroller then sends the CMD CONT discrete signalto the aircraft. At this time, the system begins sendingpitch and bank command signals to the aircraft. Asthe aircraft continues down the approach path, and atapproximately 12.5 seconds from touchdown, the 10SEC discrete message will be sent. This messageinforms the pilot that deck motion compensation isbeing added to the glide-path commands.Compensation is in the form of a slight increase ordecrease in aircraft attitude as needed to adjust for themovement of the touchdown point in response to thecarrier’s movement. At 1.5 seconds from touchdown,the landing system freezes the pitch and bankcommands, and the autopilot holds the aircraftattitude until touchdown.SAFETY PROVISIONSThe automatic carrier landing system has manyprovisions to protect the pilot and the aircraft fromhuman errors or equipment failures. The monitor linkuses the ILS AN/SPN-41 to independently check theLCCS flight path progress. This allows the pilot tomonitor position in relation to the safe glide path.When the aircraft exceeds the Mode I flight path9-5