FLIGHT MANAGEMENT SYSTEMS

In addition to the items that are available on a conventional cockpit aircraft, glass-cockpit aircraft, as well as aircraft with an approved RNAV (GPS) system, usually give the crew the ability to set the final approach course for the approach selected and many other options to increase situational awareness. Crews of FMS equipped aircraft have many options available as far as setting up the flight management computer (FMC), depending on the type of approach and company procedures. The PF usually programs the FMC for the approach and the PM verifies the information. A menu of available approaches is usually available to select from based on the destination airport programmed at the beginning of the flight or a new destination selected while en route.

The amount of information provided for the approach varies from aircraft to aircraft, but the crew can make modifications if something is not pre-programmed into the computer, such as adding a missed approach procedure or even building an entire approach for situational awareness purposes only. The PF can also program a VNAV profile for the descent and LNAV for segments that were not programmed during preflight, such as a standard terminal arrival route (STAR) or expected route to the planned approach. Any crossing restrictions for the STAR might need to be programmed as well. The most common crossing restrictions, whether mandatory or “to be expected,” are usually automatically programmed when the STAR is selected, but can be changed by ATC at any time. Other items that need to be set up are dictated by aircraft-specific procedures, such as autopilot, auto-throttles, auto-brakes, pressurization system, fuel system, seat belt signs, anti-icing/de-icing equipment, igniters, etc.

AUTOPILOT MODES

In general, an autopilot can be used to fly approaches even if the FMC is inoperative (refer to the specific airplane’s minimum equipment list [MEL] to determine authorization for operating with the FMC inoperative). Whether or not the FMC is available, use of the autopilot should be discussed during the approach briefing, especially regarding the use of the altitude pre-selector and auto-throttles, if equipped. The AFM for the specific airplane outlines procedures and limitations required for the use of the autopilot during an instrument approach in that aircraft.

There are just as many different autopilot modes to climb or descend the airplane, as there are terms for these modes (ex. Level Change [LVL CHG], Vertical Speed [V/S], VNAV, Takeoff/Go Around [TO/GA], etc.). The pilot controls the airplane through the autopilot by selecting pitch modes and/or roll modes, as well as the associated auto-throttle modes. This panel, sometimes called a mode control panel, is normally accessible to both pilots. Most aircraft with sophisticated auto-flight systems and autothrottles have the capability to select modes that climb the airplane with maximum climb thrust and descend the airplane with the throttles at idle (LVL CHG, Flight Level Change [FL CHG], Manage Level, etc.). They also have the capability to “capture,” or level off at pre-selected altitudes, as well as track a LOC and glide slope (G/S) or a VOR course. If the airplane is RNAV equipped, the autopilot will also track the RNAV generated course. Most of these modes will be used at some point during an instrument approach using the autopilot. Additionally, these modes can be used to provide flight director (FD) guidance to the pilot while hand-flying the aircraft.

For the purposes of this precision approach example, the auto-throttles are engaged when the autopilot is engaged and specific airspeed and configuration changes will not be discussed. The PF controls airspeed with the speed selector on the mode control panel and calls for flaps and landing gear as needed, which the PM will select. The example in figure 5-20 begins with the airplane 5 NM northwest of BROWN at 4,500 feet with the autopilot engaged, and the flight has been cleared to track the Rwy 12 LOC inbound. The current roll mode is LOC with the PF’s NAV radio tuned to the LOC frequency of 109.3; and the current pitch mode is altitude hold (ALT HOLD). Approach control clears the airplane for the approach. The PF makes no immediate change to the autopilot mode to prevent the aircraft from capturing a false glide slope; but the PM resets the altitude selector to 2,200 feet. The aircraft will remain level because the pitch mode remains in ALT HOLD until another pitch mode is selected. Upon reaching BROWN, the PF selects LVL CHG as the pitch mode. The auto-throttles retard to idle as the

Figure 5-20. Example Approaches Using Autopilot.

airplane begins a descent. Approaching 2,200 feet, the pitch mode automatically changes to altitude acquire (ALT ACQ) then to ALT HOLD as the airplane levels at 2,200 feet. In addition to slowing the airplane and calling for configuration changes, the PF selects approach mode (APP). The roll mode continues to track the LOC and the pitch mode remains in ALT HOLD; however, the G/S mode arms. Selecting APP once the aircraft has leveled at the FAF altitude is a suggested technique to ensure that the airplane captures the glide slope from below, and that a false glide slope is not being tracked.

The PF should have the aircraft fully configured for landing before intercepting the glide slope to ensure a stabilized approach. As the airplane intercepts the glide slope, the pitch mode changes to G/S. Once the glide slope is “captured” by the autopilot, the PM can select the missed approach altitude in the altitude pre-selector, as requested by the PF. The airplane will continue to track the glide slope. The minimum altitude at which the PF is authorized to disconnect the autopilot is airplane specific (Example, 50 feet below DA, DH, or MDA but not less than 50 feet AGL). The PF can disconnect the autopilot at any time prior to reaching this altitude during a CAT I approach. The initial missed approach is normally hand flown with flight director guidance unless both autopilots are engaged for autoland during a CAT II or III approach.

The differences when flying the underlying nonprecision approach begin when the aircraft has leveled off at 2,200 feet. Once ALT HOLD is annunciated the MDA is selected by the PM as requested by the PF. It is extremely important for both pilots to be absolutely sure that the correct altitude is selected for the MDA so that the airplane will not inadvertently descend below the MDA. For aircraft that the altitude pre-selector can only select 100-foot increments, the MDA for this approach must be set at 800 feet instead of 740 feet.

Vertical speed mode is used from the FAF inbound to allow for more precise control of the descent. If the pilots had not selected the MDA in the altitude pre-selector window, the PF would not be able to input a V/S and the airplane would remain level. The autopilot mode will change from ALT ACQ to ALT HOLD as the airplane levels at 800 feet. Once ALT HOLD is annunciated, the PF calls for the missed approach altitude of 4,000 feet to be selected in the altitude pre-selector window. This step is very important because accurate FD guidance will not be available to the PF during a missed approach if the MDA is left in the window.

NOTE: See Maximum Acceptable Descent Rates under the heading Descent Rates and Glidepaths for Nonprecision Approaches.