Flashcards in Auto Landing System Deck (42):
When being engaged but without selecting a particular mode, autopilot enables?
Aeroplane stabilisation with attitude hold or maintaining vertical speed and possibly automatic trim
The computer of the autopilot system uses, among others, the following parameters:
• Vertical speed
What does the autopilot roll out mode control during an autoland?
Maintains the localiser centreline by controlling rudder/nose wheel steering
A pilot engages the CWS of a conventional autopilot and carries out a manoeuvre in roll. When the control wheel is released the autopilot will?
Maintain the flight attitude obtained at that moment.
With CWS selected it allows the A/C to be flown manually but if the pilot releases the hand controls the autopilot will hold the pitch and roll (attitude) selected at that moment.
If no autopilot modes are selected, most pilots will not engage in CMD, all you get is CWS inner loop stability and auto trim.
An autopilot system must provide at least?
Aircraft stabilisation functions.
In autopilot, what are stabilisation functions?
Pitch and wing levelling are stability functions
In autopilot, what are the (flight path) guidance functions?
• Speed (IAS, Mach)
• Altitude hold
• G/S interception (part of APP mode)
APP - approach mode
The vertical flight path modes of an autopilot system are:
• Altitude hold
• Glide slope intercept and track
Larger high perf aircraft tend to have relatively low natural levels of aerodynamic damping. POF theory: more stably less control therefore less stable more control ability.
Such a system would set up a series of oscillations around the axis it was trying to control. Consequently these airliners will have additional feedback loops within the closed loop which directly sense aerodynamic behaviour as simply control surface deflection feedback system would be insufficient.
A modern airliner autopilot derives its inner control loop from?
IRS rate gyros
The outer loop can provide a number of inputs including:
• Vertical speed
• Radio Nav data
• ILS data
• IRS data
What is AFCS?
Auto flight control system.
When designing an auto pilot system the manufacturer has to reconcile between 2 conflicting requirements, stability and control ability.
(POF theory, the 2 are inversely related to each other).
The AFCS balances between stability and control ability by increasing or decreasing the gain of the amplifiers in the feedback loops.
It adjusts for each flight phase and density altitude.
Before A/P engages, what occurs?
A/P self tests, going through a series of interlocks, to check that set parameters are met before A/P is engaged.
If parameters are not met an interlock will not close and the A/P will disengage accompanied by aural and visual warnings.
Along with interlock checking, A/P will check that the A/C is correctly in ..... Before taking control of the A/C.
A/P will check that the A/C is correctly in trim before taking control of the A/C to ensure smooth A/P engagement known as automatic synchronisation using synchronised circuits. These circuits monitor current position in pitch and roll and align the actuators to a synchronised position before A/P engagement.
Normally only one A/P is used at any one time. What is the exception?
In the case of autoland when "APP" is pressed and both A/P is engaged due to the fail operation/fail passive system.
APP allows both autopilots to auto capture and follow ILS localiser and G/S
To disengage A/P the pilot has to...?
Press the button twice, the second time to cancel the aural and light warning of disengagement.
Button on steering wheel or a disengage bar on MCP.
As part of A/P, auto trim system is carried out to ensure that the A/C remains trimmed to ....
• relieve stress on the control surfaces
• ensure that the A/C can be handed smoothly back to the pilot after autopilot disengagement.
• this is done by keeping A/C in trim in pitch
With the A/P engaged, the following modes can be selected in roll:
• HDG hold
• VOR tracking
• ILS tracking
With the A/P engaged, the following modes can be selected in pitch:
• altitude hold
• Mach hold
• IAS hold
• Vertical speed
• VNAV FMC tracking
For LNAV to engage, the A/C must be within... of the active route?
For LNAV to engage, the a/c must be within 3nm of the active route.
If it is the A/C will automatically turn towards and then fly across the established route.
If the A/C is outside 3nm of the active route the crew must turn the A/C to intercept the route on an intercept track within 90˚ of the active route.
The intercept track must also allow the A/C to intercept the active route before reaching the active waypoint on the route.
When engages the LNAV mode captures and annunciated in green in the roll section of the FMA.
What must a pilot do to capture VOR LOC?
The pilot must set the course on the MCP and arm it by pressing the VOR LOC button. This will be annuciated in white on the FMA beneath the currently active mode.
As the radial approaches the VOR LOC captures it and becomes active, turning green in the FMA and displaying in the roll channel.
Though VOR LOC can simultaneously capture the G/S and localiser as well when in APP mode, what are the dangers?
If APP mode is active before the A/C is stable i.e. A/C not yet established on the localiser, there is a danger that the G/S is captured first and the A/C starts descending before the A/C is ready to.
So in practise pilots will capture the VOR first before enabling APP.
V/S mode is pressed during level flight, what happens?
The A/C remains armed ready for climb or descent at V/S rate.
This is the same if the A/C is in ALT HOLD mode.
• V/S will engage instantly if A/C already in climb or descent.
• To initiate a climb or descent a new altitude must be set in the altitude window.
V/S is set via the vertical speed thumb wheel on the MCP.
What is the primary purpose of LVL CHG?
The name is slightly misleading as the primary control of level change mode (LVL CHG) is to control speed during a level change.
• When LVL CHG is in active mode, pitch and thrust commands are coordinated to climb or descend the A/C to the selected altitude at the selected speed.
Climbing in A/P:
When LVL CHG is engaged, the thrust levers will move to the thrust limit set to the climb, and then...
The A/C will climb at whatever rate of climb which gives the speed selected in the IAS/MACH window.
The ROC is auto varied to maintain this speed throughout the climb.
FMA annunciation MCP SPD to indicate that the A/C is climbing at the set speed on the MCP.
N1 is annunciated to indicate that the N1 limit is the controlling thrust mode.
What happens to thrust during a descent with A/P?
The thrust levers are retarded, that is pulled back into idle thrust and changes to 'arm' in the A/P channel on the PFD annunciator to indicate that thrust levers may be adjusted manually if required.
What happens if LVL CHG is engaged but the MCP speed window is blank?
The speed on the PFD airspeed indicator becomes the target speed and is then display in the IAS/MACH window.
If LVL CHG mode is used to intercept an ILS glide slope, with APP mode armed, it will inhibit after G/S capture.
APP mode then becomes active mode with G/S replacing MCP spd as the active pitch mode.
What happens when the VNAV mode is engaged?
When VNAV is engaged, the IAS/MACH window blanks and the A/C follows the vertical profile programmed into the FMC.
The FMC also drives the A/T to maintain the programmed speed and thrust level.
The A/C will level off at the altitude selected in the MCP ALTITUDE window unless lower constraint has been set in the FMC vertical profile.
With VNAV engaged, the FMA pitch channel annuciator will be VNAV SPD or VNAV PTH.
What happens with auto throttle annunciation when VNAV SPD is engaged?
VNAV SPD means that the A/C is following the vertical profile set up on the FMC. Thus when VNAV is engaged, auto throttle will show:
• In a climb, 'N1'
• In the cruise, 'FMC SPD'
• In the descent, ' RETARD' followed by 'ARM'
How is VNAV mode disengaged?
• selecting another pitch mode e.g. V/S, LVL CHG or ALT HOLD.
• Capturing the glide slope using an armed APP mode.
• Flaps extending beyond 15˚
What happens when ALT HLD is selected?
• it will level the A/C off and maintain the uncorrected barometric altitude being flown when the button was pressed.
• If the A/C is climbing or descending in V/S or LVL CHG mode, the A/C will continue until it reaches the altitude selected in the ALTITUDE WINDOW.
Once the A/C reaches this altitude it will indicate ALT ACQ followed by ALT HOLD on the FMA annunciator.
When is CWS engaged?
CWS is used to steer the A/C whilst it remains in A/P mode.
This can be done by selecting CMD A or CMD B.
The annunciator will announce CWS P (pitch) or/and CWS R (roll).
AFCS system commonly controls the A/C in....
Speed, vertical and horizontal space.
This combination is known as mixed modes.
What are the most significant mixed modes in an AFCS system?
The AFS auto applies the pre-determined max pwr and controls it at this setting. During the go around the AFCS pitches the A/C up to the optimum angle and maintains it.
The AFCS first captures the localiser and maintains it. Subsequently it captures and maintains the glide path while controlling the A/C's speed during the final approach.
Purpose of Auto land?
Enable A/C to continue a LDG with low limits
What must you have to enable A/C to autoland?
2 auto pilots, auto thrust, radio altimeter, ILS receiver
* 3 auto pilots to have fail operation
During auto land, monitoring pilot will call out?
Auto land can only be performed if..?
A/C meets tech specs
Captain received special training
Airfield approved for auto land
The alert height for an auto land is the height at which...?
Must be able to see the appropriate visual cues for LDG.
Below alert height... ?
The radio altimeter fails.