AP, FD, A/THR MODE CHANGES AND REVERSIONS

INTRODUCTION

The flight crew manually engages the modes.

However, they may change automatically, depending on the:

• AP, FD, and A/THR system integration
• Logical sequence of modes
• So-called "mode reversions".

AP, FD, ATHR SYSTEM INTEGRATION

There is a direct relationship between aircraft pitch control, and engine thrust control.
This relationship is designed to manage the aircraft’s energy.

• If the AP/FD pitch mode controls a vertical trajectory (e.g. ALT, V/S, FPA, G/S):

A/THR controls speed

• If the AP/FD pitch mode controls a speed (e.g. OP CLB, OP DES):

A/THR controls thrust (THR CLB, THR IDLE)

• If no AP/FD pitch mode is engaged (i.e. AP is off and FD is off):

A/THR controls speed

Therefore, any change in the AP/FD pitch mode is associated with a change in the A/THR mode.

Note:

For this reason, the FMA displays the A/THR mode and the AP/FD
vertical mode columns next to each other.

THE LOGICAL SEQUENCE OF MODES

In climb, when the flight crew selects a climb mode, they usually define an altitude target,
and expect the aircraft to capture and track this altitude.
Therefore, when the flight crew selects a climb mode,
the next logical mode is automatically armed.
For example:

AP/FD mode capture and tracking (1)

The flight crew may also manually arm a mode in advance,
so that the AP/FD intercepts a defined trajectory.

Typically, the flight crew may arm NAV, LOC-G/S, and APPNAV-FINAL.
When the capture or tracking conditions occur, the mode will change sequentially.

AP/FD mode capture and tracking (2)

These logical mode changes occur, when the modes are armed.
They appear in blue on the FMA.

MODE REVERSIONS

GENERAL

Mode reversions are automatic mode changes that unexpectedly occur, but are designed to
ensure coherent AP, FD, and A/THR operations, in conjunction with flight crew input
(or when entering a F-PLN discontinuity).

For example, a reversion will occur, when the flight crew:

• Changes the FCU ALT target in specific conditions
• Engages a mode on one axis, that will automatically disengage the associated mode
on the other axis
Due to the unexpected nature of their occurrence, the FMA should be closely-monitored for
mode reversions.

FLIGHT CREW CHANGE OF FCU ALT TARGET ▸ ACTIVE VERTICAL MODE NOT POSSIBLE

FCU change resulting reversion to VS mode

This reversion to the V/S (FPA) mode on the current V/S target does not modify the pitch
behaviour of the aircraft.

It is the flight crew's responsibility to change it as required.


FLIGHT CREW HDG OR TRK MODE ENGAGEMENT ▸ DISENGAGEMENT OF ASSOCIATED

MODE ON THE VERTICAL AXIS

This reversion is due to the integration of the AP, FD, and A/THR with the FMS.
When the flight crew defines a F-PLN, the FMS considers this F-PLN
as a whole (lateral + vertical).
Therefore, the AP will guide the aircraft along the entire F-PLN:

• Along the LAT F-PLN (NAV – APP NAV modes)
• Along the VERT F-PLN (CLB – DES – FINAL modes).

Vertical managed modes can only be used, if the lateral managed NAV mode is used.
If the flight crew decides to divert from the lateral F-PLN,
the autopilot will no longer guide the aircraft along the vertical F-PLN.

Therefore, in climb:

Lateral mode change and vertical mode reversion

In descent:

Lateral mode change and vertical mode reversion

This reversion to V/S (FPA) mode on the current V/S target
does not modify the pitch behavior of the aircraft.
It is the flight crew’s responsibility to adapt pitch, if necessary.

THE AIRCRAFT ENTERS A F-PLN DISCONTINUITY

NAV mode is lost, when entering a F-PLN discontinuity.
On the lateral axis, the aircraft reverts to HDG (or TRK) mode.
On the vertical axis, the same reversion (as the one indicated above) occurs.

THE PF MANUALLY FLIES THE AIRCRAFT WITH THE FD ON,

AND DOES NOT FOLLOW THE FD PITCH ORDERS

If the flight crew does not follow the FD pitch orders, an A/THR mode reversion occurs.
This reversion is effective, when the A/THR is in THRUST MODE (THR IDLE, THR CLB),
and the aircraft reaches the limits of the speed envelope (VLS, VMAX):

reversion to speed mode

AP, FD, A/THR MODE CHANGES AND REVERSIONS

Applicable to: MSN 4354, 4405, 4413, 4450, 4490, 4526

INTRODUCTION

The flight crew manually engages the modes.
However, they may change automatically, depending on the:
‐ AP, FD, and A/THR system integration
‐ Logical sequence of modes
‐ So-called "mode reversions".

AP, FD, ATHR SYSTEM INTEGRATION

There is a direct relationship between aircraft pitch control, and engine thrust control.
This relationship is designed to manage the aircraft’s energy.

‐ If the AP/FD pitch mode controls a vertical trajectory (e.g. ALT, V/S, FPA, G/S):

A/THR controls speed

‐ If the AP/FD pitch mode controls a speed (e.g. OP CLB, OP DES):

A/THR controls thrust (THR CLB, THR IDLE)

‐ If no AP/FD pitch mode is engaged (i.e. AP is off and FD is off):

A/THR controls speed

Therefore, any change in the AP/FD pitch mode is associated with a change in the A/THR mode.

Note:

For this reason, the FMA displays the A/THR mode and the AP/FD vertical mode
columns next to each other.

THE LOGICAL SEQUENCE OF MODES

In climb, when the flight crew selects a climb mode, they usually define an altitude target,
and expect the aircraft to capture and track this altitude.
Therefore, when the flight crew selects a climb mode, the next logical mode is automatically armed.

For example:

AP/FD Mode Capture and Tracking (1)

The flight crew may also manually arm a mode in advance,
so that the AP/FD intercepts a defined trajectory.

Typically, the flight crew may arm NAV, LOC-G/S and F-LOC-F-G/S.
When the capture or tracking conditions occur, the mode will change sequentially.

AP/FD Mode Capture and Tracking (2)

These logical mode changes occur, when the modes are armed. They appear in blue on the FMA

MODE REVERSIONS

GENERAL

Mode reversions are automatic mode changes that unexpectedly occur, but are designed to
ensure coherent AP, FD, and A/THR operations, in conjunction with flight crew input
(or when entering a F-PLN discontinuity).

For example, a reversion will occur, when the flight crew:

‐ Changes the FCU ALT target in specific conditions
‐ Engages a mode on 01 axis, that will automatically disengage
the associated mode on the other axis
‐ Manually flies the aircraft with the FD on, but does not follow the FD orders,
which leads to the aircraft to the limits of the flight envelope.

Due to the unexpected nature of their occurrence, the FMA should be closely-monitored for
mode reversions.

FLIGHT CREW CHANGE OF FCU ALT TARGET ▸ ACTIVE VERTICAL MODE NOT POSSIBLE

FCU Change Resulting Reversion to VS Mode

This reversion to the V/S (FPA) mode on the current V/S target does not modify the pitch
behaviour of the aircraft.

It is the flight crew's responsibility to change it as required.

FLIGHT CREW HDG OR TRK MODE ENGAGEMENT ▸
DISENGAGEMENT OF ASSOCIATEDMODE ON THE VERTICAL AXIS

This reversion is due to the integration of the AP, FD, and A/THR with the FMS.
When the flight crew defines a F-PLN, the FMS considers this F-PLN as
a whole (lateral + vertical).

Therefore, the AP will guide the aircraft along the entire F-PLN:

‐ Along the LAT F-PLN (NAV – F-LOC modes)
‐ Along the VERT F-PLN (CLB – DES –F-G/S modes).

Vertical managed modes can only be used, if the lateral managed NAV mode is used.
If the flight crew decides to divert from the lateral F-PLN,
the autopilot will no longer guide the aircraft along the vertical F-PLN.

Therefore, in climb:

Lateral Mode Change and Vertical Mode Reversion

In descent:

Lateral Mode Change and Vertical Mode Reversion

This reversion to V/S (FPA) mode on the current V/S target
does not modify the pitch behaviorof the aircraft.
It is the flight crew’s responsibility to adapt pitch, if necessary.

THE AIRCRAFT ENTERS A F-PLN DISCONTINUITY

NAV mode is lost, when entering a F-PLN discontinuity.
On the lateral axis, the aircraft reverts to HDG (or TRK) mode.
On the vertical axis, the same reversion (as the one indicated above)occurs.

THE PF MANUALLY FLIES THE AIRCRAFT WITH THE FD ON,
AND DOES NOT FOLLOW THE FD PITCH ORDERS

If the flight crew does not follow the FD pitch orders, an A/THR mode reversion occurs.
This reversion is effective, when the A/THR is in THRUST MODE (THR IDLE, THR CLB),
and the aircraft reaches the limits of the speed envelope (VLS, VMAX):

Reversion to Speed Mode

A/THR in SPEED mode automatically readjusts thrust to regain the target speed. The FD bars
will disappear, because they are not being followed by the PF.

TRIPLE CLICK

The "triple click" is an aural alert. It is an attention-getter,
designed to draw the flight crew's attentionto the FMA.

The PFD FMA highlights a mode change or reversion with a white box around the new mode,
and the pulsing of its associated FD bar.

The reversions, described in the previous paragraph, are also emphasized via the triple click aural
alert.

Note:

The triple click also appears in the following, less usual, cases:

• SRS ▸ CLB (OPCLB) reversion: If, the flight crew selects a speed on the FCU
• The V/S selection is "refused" during ALT *:
The flight crew pulls the V/S knob, while in ALT*
• The V/S target is not followed, because the selected target is too high,
and leads to VMIN/VMAX.