LATERAL GUIDANCE (LNAV) - GENERAL
Lateral guidance (LNAV) is the function in the FMS that sends commands to
the flight guidance computer to laterally steer the aircraft. LNAV guides the
aircraft along a flight path set by the pilot including flight plans, departures,
holding patterns and approaches.
LNAV maintains the aircraft within an airway or protected airspace. LNAV
general rules are the following:
• the FMS must be selected as the primary navigation source.
• a minimum of one leg must be defined for LNAV calculations.
• LNAV is available for all phases of flight.
• leg sequencing is performed with inside turns between two legs.
• LNAV bank angles are normally as for rate 1. Roll rate is 3° per
second.
• the distance shown for each leg of the flight plan accounts for the
distance travelled due to the change in course from one leg to the next.
• a lateral track alert (waypoint identifier flashing) is given for each
waypoint sequence. The alert is given 30 seconds before starting a
turn.
VERTICAL GUIDANCE (VNAV) - GENERAL
Vertical guidance (VNAV) gives a complete vertical profile for the entire flight
and is integrated with the lateral flight plan. Using FMS VNAV, the operator
can define vertical profile information that may be manually flown by pilot.
VNAV altitude profile must be flown manually.
VNAV computes TOC (Top Of Climb), TOD (Top Of Descent) and BOD
(Bottom Of Descent) points and gives a vertical deviation for path descents.
TOC and TOD defining data are displayed in PROGRESS 2 page on MCDU.
VNAV general rules are the following:
• for VNAV operation, performance initialization and activation of altitude
selector (ALT SEL) is required.
• it is recommended to set the altitude selector at the altitude cleared by
ATC
• for climbs, only TOC information is provided on the MFD. The TOC is
the location at which the aircraft should complete the climb.
• for descents TOD information is provided on the MFD and VPATH
(vertical flight path) on the PFD. On MCDU a BOD (Bottom of descent)
information is also presented. The TOD is the location at which the
aircraft should commence a descent. The BOD is the location at which
the aircraft should complete the descent.
• when the altimeter is adjusted to display height above the ground
(QFE) rather than sea level, VNAV should not be used.
The FMS produces two types of vertical deviations one for VPATH and one
for VGP (Vertical Glide Path).
VPATH (VERTICAL PATH)
The FMS creates a vertical path and shows it when an altitude constraint is
entered to descend to a WPT in the flightplan or an approach is activated;
eg. Descent angle constraint to a custom WPT (defined by the pilot).
The VPATH cannot be flown automatically with the FD.
NOTE
When an ILS approach is entered in the Arrival to the DEST
waypoint, a VPATH is created. The VPATH deviation can be
displayed by previewing the ILS on the HSI (PRV button on Display
Controller).
VGP (VERTICAL GLIDE PATH)
The FMS creates a VGP and shows it when a published non-precision
approach is entered in the Arrival to the DEST waypoint, ie the approach
definition is retrieved from the Jeppesen database and is not modified.
The VGP can be flown automatically with the FD (see chapter 22-00-00).