Aerofly FS simulates the autopilots of the Boeing 737-500, 747-400, 777-300ER and 787-10 to a very high level of realism. Pretty much all autopilot modes used every day by airline pilots are simulated and interactions with the mode control panel (MCP) works just like the real thing.
Introduction to advanced autopilots
The autopilot panel in Boeing aircraft is called Mode Control Panel (MCP). It allows pilot to select new autopilot modes and change selected values.
From left to right the knobs in the latest Boeing aircraft are used for
The knobs for speed and altitude can be pushed in and the heading knob has a button on it that can be pushed as well.
The Flight Mode Annunciator (FMA) is the most important instrument when using the autopilot. The FMA is the upper section of the primary flight display (PFD) and it displays to the pilot what the autopilot is currently doing and what modes have been activated.
The FMA is split into three columns:
Below the FMA we find a status indication for the flight director (FLT DIR) and autopilot (AP, LAND 2 and LAND 3).
Superimposed on the attitude indicator of the primary flight display (PFD) we can see the flight director (F/D), visible as a horizontal and vertical magenta line. The flight director can be turned on and off for by setting both F/D switches on either side accordingly. When both flight directors are off and the autopilot is also off the entire system is turned off and is reset.
The horizontal flight director bar moves up and down to indicated the target pitch attitude. When the bar moves up you should pitch up to catch the bar with the current attitude. The bar moves back to the center when you are at the target pitch angle.
The vertical flight director bar moves left and right to show a target bank angle. When you roll to the side of the deflection the flight director bar moves back towards the center to indicate that you are at the target bank angle.
The autopilot a actuates servos that move the control column, control wheel and rudder pedals to steer the plane. This provides direct feedback to the pilots. Pilots can override the servo to take manual control and the autopilot disengages. But this usually requires some force and the disengagement isn’t soft and isn’t the preferred method.
To successfully engage the autopilot a couple of conditions have to be met first:
To engage the autopilot
The Auto-Throttle System (A/T) drives servos on the thrust levers in the cockpit to adjust engine thrust when engaged. Pilots can overpower the servos and manually take control at any time, the Auto-Throttle then disengages but stays armed unless the A/T ARM switches are turned off as well. A/T is usually armed before takeoff and disarmed after landing. During landing the A/T system automatically pulls back the thrust levers to idle during flare and disengages when reversers are selected.
To engage A/T
For route planning and long-term complex navigation functions the aircraft is equipped with a Flight Management System (FMS) that stores the flight plan and pre-programmed performance values and computes the most economical flight profile. Pilots can change the flight plan or enter values through either a Control-Display-Unit (CDU) or a Multi-Function-Display (MFD) in the cockpit.
We perform the preflight items for the FMS in our cold and dark tutorial of the 787:
B787 Cold and Dark TutorialNote - In Aerofly FS you don’t have to program the FMS yourself, you can also use the navigation menu for this.
Over the years several changes have been introduced to real world Boeing autopilots. The core functionality remained but some components of the MCP were moved around or redesigned. The most modern aircraft like the 777 and 787 are near identical but still have a lot in common with the older 747-400 and the even older 737-500 with classic cockpit in Aerofly FS.
Button labels changed:
Per default the flight directors are usually already turned on for your convenience.
The lateral flight director mode switches to HOLD mode and the commands lateral steering inputs to stay on the heading at the time when the wings were leveled after mode engagement.
The flight director vertical mode changes to HOLD and commands vertical steering inputs to stay at the altitude at the time the button was pushed.
To engage the autopilot
To disengage the autopilot
To engage A/T
To disengage the A/T temporarily
To turn off the A/T system
The autopilot turns the aircraft to the new target heading. When you adjust the heading knob the aircraft will turn in the direction that you rotated the heading knob and near 360° turns are possible.
The rotation direction of the knob simulates the desired pitch rotation of the aircraft (nose up/down). To select a higher climb rate the wheel has to be moved down. For a descent the wheel has to be moved up.
During FLC mode the autopilot pitches up or down to acquire the selected airspeed. Meanwhile the auto-throttle commands climb thrust if the target altitude is higher than the current altitude or idle thrust for the descent.
LNAV uses the flight management system (FMS) to follow the entered flight plan laterally (left and right). The LNAV mode can be armed on the ground before takeoff or in the air.
The LNAV mode can engage when the route path is intercepted or when you are close to the route (within about 2NM either side).
VNAV is a combination of vertical steering and automatic airspeed adjustments. It factors in the altitude and speed constraints on the route as well as the aircraft performance and economical factors. VNAV can be armed on the ground before takeoff or in the air.
VNAV engages directly during the climb, it then commands a climb airspeed and levels off at altitude constraints.
When the cruise altitude is reached (VNAV armed) VNAV PATH engages. Before the top of descent (TOD) you can set a lower altitude, then the autopilot will descent automatically at the TOD.
During the descent VNAV PATH engages when you intercept the planned vertical profile of the route.
After takeoff the vertical navigation target airspeed (VNAV SPD) is kept below the maximum allowed flap speed with a 5 knot margin.
During approach phase VNAV tries to slow down to approach airspeed. The airspeed is kept above the minimum speed for the next lower flap setting.
When you capture the glide slope VNAV disengages and you have to manually adjust airspeed again.
The Auto-Throttle (A/T) can be used to set takeoff thrust automatically.
On the FMA we can see the auto-throttle engagement in the mode THR REF. The thrust levers are moved forward to the selected takeoff thrust setting.
When the flight directors are turned on when on the ground the lateral mode TO/GA automatically engages. It also engages when you push the TO/GA switches on the thrust levers.
This lateral TO/GA mode is used after lift off to maintain the runway heading. In case of a go-around the heading at the time of the mode engagement is used.
Similar to the lateral TO/GA mode the vertical TO/GA mode also engages when F/Ds are engaged on the ground or when TO/GA switches are pressed.
The vertical TO/GA mode is used after lift off to pitch for a speed of V2 plus 20 knots or the current speed when go-around is performed.
When the vertical TO/GA disengages the selected airspeed is set to the current airspeed to avoid a sudden thrust decrease.
Once the mode engages (above 50 feet RA) the autopilot follows the route laterally to the destination.
When the aircraft is above acceleration height the VNAV mode can engage right away for the climb and the speed window blanks. VNAV SPD is shown in the FMA.
At cruise altitude or when the vertical descent profile is intercepted VNAV PATH engages and the aircraft descents to the selected altitude on the computed vertical route profile.
When VNAV is engaged the airspeed window blanks and the target airspeed is computed automatically.
After takeoff
During approach
When VNAV is engaged we can take manual control of the airspeed and manually set an airspeed or Mach Number.
When VNAV is engaged the autopilot will still level off at the selected altitude. When the selected altitude is not the cruise altitude then VNAV ALT mode will be shown.
During the climb or descent VNAV will stick to the altitude constraints programmed in the route. In the real world you can intervene and push the altitude knob to delete the next altitude constraint on the route and to continue the climb or descent. Note - The constraint deletion is not yet implemented in Aerofly FS.
When the localizer moves towards the center the autopilot turns to the selected course and captures the localizer.
After localizer capture, when flying an ILS, we can capture the glide-slope (G/S).
When localizer mode is active and when the glide-slope moves towards the center then the autopilot can capture it.
Note - When VNAV was engaged before you now have to manually adjust the selected MCP speed.
Configure the aircraft systems like for a normal landing.
Below about 1200ft RA you should see a white ROLLOUT and FLARE mode being armed in the FMA. If the modes are not showing up you cannot perform an automatic landing and have to land manually. Autoland is not possible with our 737.
When FLARE is armed it automatically engages at about 50ft RA. The autopilot arrests the descent rate and flies the aircraft onto the runway.
At about 20ft RA the A/T reduces thrust to idle and then goes to HOLD mode, releasing the servos for a potential go-around.
When the aircraft has touched town the autopilot uses the rudder to stay on the localizer and maintain the centerline.
Before flying over the top of descent, when cleared lower
Instead of flying an indicated airspeed we can choose to fly a Mach Number, a fraction of the speed of sound.
When you are flying faster than Mach 0.45:
Note - This mode is only available in the newer Boeings like the 777 and 787.
Instead of a magnetic compass heading we can fly a magnetic or true track across the ground. The autopilot compensates for the wind drift in this mode.
To use a true heading or true track
Note - This mode is only available in the newer Boeings like the 777 and 787.
To fly at a fixed climb/descent angle relative to the ground we can use the flight path angle (FPA) mode. The autopilot then compensates for the wind drift.
Interested to learn how to start the Boeing 787 from a cold and dark state with engines and all systems turned off? This tutorial describes the start-up process for the Dreamliner.
787 Cold and Dark TutorialIn the Aerofly Wiki we dive deep into the Boeing 777-300ER flight deck and perform a full flight between Denver and San Francisco. This tutorial also shows the CDU preflight process, which can be applied to the 747 and 787 as well.
777-300ER Wiki Tutorial
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