Lateral Flight Director Modes

Gulfstream GVII

Eddie sez:

Everything here is from the references shown below, with a few comments in an alternate color.

[Symmetry, §2B-21-70] The active and armed lateral flight director modes are displayed to the left of the autothrottle mode annunciator, directly above the autopilot annunciator.

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Photo: Lateral flight director modes, Symmetry, §2B-21-70, Table 2
Click photo for a larger image

  1. Heading Select Mode
  2. Track Select Mode
  3. Lateral Navigation Mode
  4. VOR En Route
  5. VOR Approach Mode
  6. Localizer Approach
  7. Back Course (BC)
  8. Roll Hold: Basic Mode
  9. Roll Hold: Wings Level
  10. Roll Hold: Heading Hold
  11. High/Low Bank Limit
  12. Emergency Descent Mode (EDM)
  13. Autotune Rules

Last revision:

20191101

Heading Select Mode

[Symmetry, §2B-21-70, ¶1] During HDG, all armed lateral flight director modes are permitted, but a transition of a lateral armed mode to active cancels the heading select mode. The flight director generates roll command outputs to align the aircraft with the heading target displayed on the coupled PFD. The FD receives a heading error from the PFD, and uses the information to compute roll commands to turn the aircraft to the selected target. When the pilot preselects a heading target and subsequently pushes the HDG/TRK button on the guidance panel, the flight director generates commands to turn in the direction of the smallest angle between the current aircraft heading and the preselected heading. When the pilot selects a heading target while HDG mode is active, the flight director generates commands to turn in the direction that the heading select knob was turned.

Track Select Mode

[Symmetry, §2B-21-70, ¶2] During TRK, all armed lateral flight director modes are permitted, but a transition of a lateral armed mode to active cancels the track select mode. The flight director generates roll command outputs to align the aircraft with the track target displayed on the coupled PFD. The FD receives a track error from the PFD, and uses the information to compute roll commands to turn the aircraft to the selected target. When the pilot preselects a track target and subsequently pushes the HDG/TRK button on the guidance panel, the flight director generates commands to turn in the direction of the smallest angle between the current aircraft track and the preselected track. When the pilot selects a track target while TRK mode is active, the flight director generates commands to turn in the direction that the heading select knob was turned.

Lateral Navigation Mode

[Symmetry, §2B-21-70, ¶3] The lateral navigation (LNAV) mode is selected using the LNAV button on the guidance panel. The flight director automatically selects the lateral navigation submode based on the PFD source selected. The lateral navigation mode includes the following submodes:

  • LOC (Localizer is source of navigation)
  • LNAV (FMS is source of navigation)
  • VOR (VOR is the source of navigation).

The FD generates flight director lateral guidance commands to intercept, capture, and track the above submodes.

LNAV -- FMS as Source

The flight director receives a lateral steering command from the FMS, when the FMShas been selected as the PFD source. The FMS lateral steering command is a roll command, that aligns the aircraft with the flight plan in the FMS. The flight director limits the bank angle command to the selected bank angle limit.

The flight director can perform an automatic transition from FMS navigation to an approach or back course mode by the approach preview mode. The selected NAV source for display must be FMS, and the NAV radio must be tuned to a localizer frequency. The previewed approach is then armed by pushing the APR button on the guidance panel. The localizer (or back course) becomes active once the capture criteria has been met for the approach.

VOR En Route

[Symmetry, §2B-21-70, ¶4] The VOR mode is selected using the LNAV button on the guidance panel when VOR is the navigation source associated with the selected PFD. When flying a VOR intercept, the intercept angle should be less than 45°. If the intercept angle is greater than 45° then the flight director initiates an initial heading change (course cut limiting) to prevent/minimize overshooting.

While in the VOR capture or track, if the selected NAV source is retuned to another VOR frequency, the VOR mode cancels and rearms automatically. When the aircraft is passing over the VOR transmitter (cone of confusion), the VOR mode flies toward the selected course reference (over station passage).

If the selected course is unchanged from that selected before entry into over station, the previously computed wind correction continues to be applied and the VOR mode does not command a turn toward the selected course pointer. Changes of course pointer setting when over station results in an equivalent change in the course hold reference when exiting over station.

VOR Approach Mode

[Symmetry, §2B-21-70, ¶5] The VOR approach mode is selected using the APR button on the guidance panel with the VOR as the selected navigation source associated with the coupled PFD. VOR approach mode is displayed as VORAP on the PFD.

The flight director generates flight director lateral guidance commands to capture and track the VOR approach path as displayed on the coupled PFD. When VOR approach mode is armed, heading select mode (HDG) is automatically activated until transition to VOR approach occurs. After the VOR approach mode has been armed, the flight director disarms the mode if the pilot pushes the APR button before the mode becomes active.

When the aircraft is passing over the VOR transmitter (cone-of-confusion), the VOR mode flies toward the selected course reference (over station passage). If the selected course is unchanged from that selected before the over station zone is entered, the previously computed wind correction continues to be applied and the VOR mode does not command a turn toward the selected course pointer. Changes of course pointer setting when over station result in an equivalent change in the course hold reference when exiting over station.

The VOR approach mode uses the radio altimeter to calculate over station passage.

Localizer Approach

[Symmetry, §2B-21-70, ¶6] The FD ILS approach mode is selectable using the APR button on the guidance panel. There are two submodes of ILS approaches - ILS/LOC dual coupled and non-dual coupled. The highest available category is armed when an approach is selected by the guidance panel. Localizer mode performance is the same for both submodes of approach.

After the localizer approach mode has been armed, the flight director disarms the mode if the pilot pushes the APR button before the localizer approach mode becomes active.

Back Course (BC)

[Symmetry, §2B-21-70, ¶7] The back course mode is selected by pushing the APR button. The flight director generates roll guidance commands for capture and tracking of the BC localizer indicated on the coupled PFD. Pushing the APR button on the guidance panel arms BC if the beam deviation is outside the capture range. After the BC mode has been armed, the flight director disarms the BC mode if the pilot pushes the APR button before the BC mode becomes active.

NOTE:

If an ILS approach is armed and the aircraft intercepts the localizer capture criteria on a heading greater than 100 degrees away from the entered inbound course, the BC may become armed/engaged. Once it is armed or engaged, it does not revert back to LOC.

Roll Hold: Basic Mode

[Symmetry, §2B-21-70, ¶8] The flight director enters the roll hold mode under the following circumstances provided current bank angle is within roll hold limits and the absolute value of the current bank angle is greater than 6°:

  • Activation of roll hold mode
  • Engagement of the autopilot while in roll hold mode.

Roll Hold: Wings Level

[Symmetry, §2B-21-70, ¶9] The wings level mode is a submode of the roll hold mode and it is activated under the following circumstances:

  • If no lateral flight director guidance mode is active and the AP is engaged while the magnitude of bank angle is less than 6°
  • If a vertical flight director mode is selected without a lateral mode being selected while the magnitude of bank angle is less than 6°
  • The roll hold mode is active and the magnitude of bank angle reference is set less than 6°, by engaging AP with bank less than 6°

The FD wings level submode gives flight director commands to hold a 0° bank.

Roll Hold: Heading Hold

[Symmetry, §2B-21-70, ¶10] Heading hold is the default FD lateral mode.

High/Low Bank Limit

[Symmetry, §2B-21-70, ¶11] The following apply to the bank angle limit selection function used by the heading select mode:

  • Bank angle limit is automatically set to low (17°) once the absolute value of bank angle is less than 6° after ascending through an altitude of 29,500 feet.
  • Bank angle limit is automatically set to high (27°) once the absolute value of bank angle is less than 6° after descending through an altitude of 28,500 feet.
  • The bank limit selection toggles between high and low bank limit at each setting while heading select mode is the active lateral mode.

Emergency Descent Mode (EDM)

[Symmetry, §2B-21-70, ¶11] When EDM is active, the autopilot initiates an emergency descent when certain conditions are met. When active, EDM is annunciated in red as the active lateral mode on the FMA.

EDM is activated automatically under the following conditions:

  • The autopilot is engaged, and
  • The aircraft is at FL 400 or higher
  • The Cabin Pressure Low message is displayed in the CAS message window.

When EDM is activated, the following actions occur automatically:

  • The FD enters FLCH and HDG hold modes
  • The FD commands a 90° turn to the left (the heading bug on the PFD rotates 90° left)
  • The AT engages
  • A manual speed target of 340 knots is set
  • An altitude target of 15,000 feet is set
  • EDM is displayed in the lateral field of the FMA
  • With the exception of the AUTO button, all the buttons and knobs on the guidance panel are disabled
  • When ASEL is captured, the speed target is changed to 250 knots
  • Speedbrakes are automatically deployed on a preset schedule by the flight control system.
NOTE:

The sidestick controller applied force AP disengage logic is bypassed in EDM. Once EDM is entered, it can only be canceled by disengaging the AP. In EDM, no lateral mode is selected (ROL is active) and the active vertical mode is FLCH. When the autopilot is disengaged, the system remains in the FD modes it was in during EDM.

During EDM, the FD modes are as follows:

  • Lateral field: EDM
  • Autothrottle field: FLCH
  • Vertical field: ASEL

Once ASEL is activated, IAS is annunciated in the AT window.

When the aircraft levels off at 15,000 feet, the FD vertical field transitions to ASEL, then to ALT as in a normal altitude capture. Similarly, the autothrottle field transitions from FLCH to IAS when the altitude is captured.

Autotune Rules

[Symmetry, §2B-21-110, ¶17] The FMS has the capability to automatically tune the associated NAV radio. For ILS approaches, the FMS autotunes the appropriate ILS frequency when the following conditions are met:

  • An ILS approach is selected in the active flight plan
  • The aircraft is within 40 NM direct distance to the destination runway
  • The aircraft is within 75 NM flight plan distance to the destination runway
  • The RNP flight phase is not missed approach.

See Also:

Gulfstream Symmetry Flight Deck for the G500 Aircraft, Pilot's Guide, Revision No. 3b. dated April 10/2019