searchingheaven BHPian

Join Date: Jan 2011 Location: KDCA-KDFW-VOBL Posts: 323 Thanked: 1,410 Times

Re: Boeing 777 - Pilot's Review



Autopilot Flight Director System



The AFDS consists of three autopilot flight director computers (AFDCs) and the Mode control Panel. The MCP provides control of the autopilot, flight director, altitude alert, and autothrottle systems. The MCP is used to select and activate AFDS modes, and establish altitudes, speeds, and climb/descent profiles.



The MCP looks like this.





Don't get confused by looking at it. Yes, there are a lot of buttons. But I will explain the function of each & every one below.

LNAV

As the name suggests, LNAV provides lateral guidance to the aircraft. It's all transparent to the pilot, as he enters his route as specified in the clearance and flight plan into the FMS (Flight Management System). The route shows up as a magenta line on the lower flight display, and as long as the autopilot is engaged in the LNAV mode, it will follow that line across the ground. LNAV however does not tell the plane what altitude to fly.

As the name suggests, LNAV provides lateral guidance to the aircraft. It's all transparent to the pilot, as he enters his route as specified in the clearance and flight plan into the FMS (Flight Management System). The route shows up as a magenta line on the lower flight display, and as long as the autopilot is engaged in the LNAV mode, it will follow that line across the ground. LNAV however does not tell the plane what altitude to fly. TRK HOLD/SEL & HDG HOLD/SEL

HOLD button will cause the plane to keep its heading (or track). Pressing SEL allows you to select the heading  the plane will turn to the heading dialed on the screen above. The important difference between HOLD and SEL is in how the plane behaves when heading selector knob is being turned. In HOLD mode  it will hold your heading. In SEL mode  it will turn as you turn the knob.

HOLD button will cause the plane to keep its heading (or track). Pressing SEL allows you to select the heading  the plane will turn to the heading dialed on the screen above. The important difference between HOLD and SEL is in how the plane behaves when heading selector knob is being turned. In HOLD mode  it will hold your heading. In SEL mode  it will turn as you turn the knob. LOC

lateral mode used for flying localizer and ILS approaches.



lateral mode used for flying localizer and ILS approaches. VNAV

Vertical navigation. Similar to the LNAV  its fully automated mode that follows altitude profile programmed in FMC. Additionally  it takes over the autothrottle and controls your speed. VNAV is activated at 400 ft over terrain (or more). On the ground, it's only armed. When you are in VNAV  the AP will climb and descent according to altitudes programmed in FMC but you have to allow for the climb or descent by setting the altitude on MCP and pushing the selector button.

Vertical navigation. Similar to the LNAV  its fully automated mode that follows altitude profile programmed in FMC. Additionally  it takes over the autothrottle and controls your speed. VNAV is activated at 400 ft over terrain (or more). On the ground, it's only armed. When you are in VNAV  the AP will climb and descent according to altitudes programmed in FMC but you have to allow for the climb or descent by setting the altitude on MCP and pushing the selector button. FLCH

Flight level change. As the name suggests  vertical mode allowing for changes in altitude while keeping the speed of the aircraft constant at the set value. This is the most used mode while adjusting altitude during cruise.

Flight level change. As the name suggests  vertical mode allowing for changes in altitude while keeping the speed of the aircraft constant at the set value. This is the most used mode while adjusting altitude during cruise. VS/FPA

Vertical speed modes. The plane will keep selected vertical speed or flight path angle.

Vertical speed modes. The plane will keep selected vertical speed or flight path angle. Altitude Hold

Press it and the plane will hold its current altitude. Really simple.

Press it and the plane will hold its current altitude. Really simple. APP

APP  activates LOC as lateral mode and intercepts glide slope (G/S) of ILS approach.

This is a photo of the FMC(Flight Management computer). This is the brain of the aircraft and tells the autopilot where to go, how to go, how fast to go, and what altitude to go at. When LNAV and VNAV are active, the FMC provides the data to the AFDS. Note that the MCP is the higher authority in case of a conflict. For eg. at DTY waypoint, the forecasted altitude is FL195. But let's say that ATC has cleared you only upto 15000 ft. So you will enter 15000 ft into the altitude window on the MCP. The 777 CAN NOT and WILL NOT cross 15000 ft(i.e the altitude dialled in the MCP).







This is the EFIS(electronic flight instrument system) control panel. It is also visible at the extreme left of the MCP photo. In simple terms, the controls on this panel select display range and mode (for example, map or compass rose) and enter data (such as selected heading). It also has 2 additional knobs. The left one sets the minimums altitude(height) callout. This is the height at which the we must have adequate visual reference to the landing environment (i.e. approach or runway lighting) to decide whether to continue landing; or go around. The right one sets the barometric pressure for the baro altimeter. The buttons at the bottom are for displaying/hiding specific details for eg. Airports/Weather/Terrain/Stations/Position etc.







The Autopilot has to control three parameters to fly the plane. Its speed(throttle), its bank angle & its pitch. The roll(bank angle) is controlled by LNAV or HDG/TRK Hold/Select or LOC mode. The pitch is controlled using VNAV, FLCH, V/S, HOLD, or APP mode.



The autothrottle modes can be any of the following



 THR  The autothrottle applies thrust to maintain the vertical speed required by the pitch mode.

 THR REF  Thrust is set to the selected thrust limit displayed on EICAS.

 IDLE  Displayed while the autothrottle moves the thrust levers to idle; IDLE mode is followed by HOLD mode.

 HOLD  The thrust lever autothrottle servos are inhibited. The pilot can set the thrust levers manually.

 SPD  The autothrottle maintains the selected speed displayed on the PFD. Speed can be set by the MCP IAS/MACH selector or by the FMC, as shown on the FMC. The autothrottle will not exceed the operating speed limits or the thrust limits displayed on the EICAS.



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Two important points:



What does armed/active mean?



When the mode is armed  it will activate automatically when certain conditions are met. Usually when the plane is in such position that the armed mode can take over. Armed mode is indicated by white text on primary flight display. Active mode is indicated by green text.



This figure illustrates the difference between armed & active.





Difference between heading and Track



Heading is where the nose of the aircraft points, while track is the ACTUAL path traveled over ground - just like a set of tracks I would leave behind in the snow or sand, relative to North. The Autopilot/AFDS of the 777 is a delight to use and deserves an exclusive post. I will be going into the details here, so please feel free to ask questions.The AFDS consists of three autopilot flight director computers (AFDCs) and the Mode control Panel. The MCP provides control of the autopilot, flight director, altitude alert, and autothrottle systems. The MCP is used to select and activate AFDS modes, and establish altitudes, speeds, and climb/descent profiles.The MCP looks like this.Don't get confused by looking at it. Yes, there are a lot of buttons. But I will explain the function of each & every one below.This is a photo of the FMC(Flight Management computer). This is the brain of the aircraft and tells the autopilot where to go, how to go, how fast to go, and what altitude to go at. When LNAV and VNAV are active, the FMC provides the data to the AFDS. Note that the MCP is the higher authority in case of a conflict. For eg. at DTY waypoint, the forecasted altitude is FL195. But let's say that ATC has cleared you only upto 15000 ft. So you will enter 15000 ft into the altitude window on the MCP. The 777 CAN NOT and WILL NOT cross 15000 ft(i.e the altitude dialled in the MCP).This is the EFIS(electronic flight instrument system) control panel. It is also visible at the extreme left of the MCP photo. In simple terms, the controls on this panel select display range and mode (for example, map or compass rose) and enter data (such as selected heading). It also has 2 additional knobs. The left one sets the minimums altitude(height) callout. This is the height at which the we must have adequate visual reference to the landing environment (i.e. approach or runway lighting) to decide whether to continue landing; or go around. The right one sets the barometric pressure for the baro altimeter. The buttons at the bottom are for displaying/hiding specific details for eg. Airports/Weather/Terrain/Stations/Position etc. The autothrottle applies thrust to maintain the vertical speed required by the pitch mode. Thrust is set to the selected thrust limit displayed on EICAS. Displayed while the autothrottle moves the thrust levers to idle; IDLE mode is followed by HOLD mode. The thrust lever autothrottle servos are inhibited. The pilot can set the thrust levers manually. The autothrottle maintains the selected speed displayed on the PFD. Speed can be set by the MCP IAS/MACH selector or by the FMC, as shown on the FMC. The autothrottle will not exceed the operating speed limits or the thrust limits displayed on the EICAS.----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------When the mode is armed  it will activate automatically when certain conditions are met. Usually when the plane is in such position that the armed mode can take over. Armed mode is indicated by white text on primary flight display. Active mode is indicated by green text.This figure illustrates the difference between armed & active.Heading is where the nose of the aircraft points, while track is the ACTUAL path traveled over ground - just like a set of tracks I would leave behind in the snow or sand, relative to North. Last edited by searchingheaven : 12th May 2016 at 20:38 .