Saab 340B, Operation Manual, Page: 144 / 670

AUTOFLIGHT, CAT I
Description
Aircraft Operations Manual
3.1
S
PAGE 4
pointer. When in VNAV mode the letters VNV will
be indicated above the deviation scale.
The deviation scale can also display GS (Glide
Slope).
NOTE
− If a failure to the VNAV system occurs the verti-
cal deviation pointer will be replaced by the let-
ters VNV boxed and in red. The indication will
flash for 10 seconds and then become steady.
PTCH, Pitch hold mode
FCC commands holding of the pitch attitude exist-
ing at time of engagement.PTCH is not manually
selectable but a reversionary mode which is en-
gaged when:
a. VERT SYNC button pressed and released while
in GA mode.
b. VS button pressed and released while in VS
mode with invalid data required for VS mode (i.e.
FD flag is present on display).
VERT SYNC, Vertical Synchronization
If for any reason the aircraft is allowed to deviate
from the FCC commands in certain vertical modes,
normally only when flying manually (VS, IAS, ALT,
GA) the respective reference data can be synchro-
nized to the existing flight condition by the VERT
SYNC button on the control wheel. The synchro-
nization occurs at the time of pressing and be-
comes activated when releasing the VERT SYNC
button.
The reference data is changed in the respective
mode as follows:
a. if in VS mode, the FCC reference data changes
to existing vertical speed.
b. if in IAS mode, the FCC reference data changes
to existing IAS.
c. if in ALT mode, the FCC reference data changes
to existing ALT.
d. if in GA mode, the FCC reference data changes
to existing attitude. The vertical mode display on
EADI simultaneously changes from GA to PTCH.
It is only the reference data that is changed. The
respective mode function is retained. Pitch trim is
not affected. AP will remain engaged.
LATERAL MODES
HDG, Heading mode
− The FCC gives commands to turn to and hold the
heading indicated by the heading bug on the
EHSI. Turn is in the direction of shortest arc. The
heading bug can be manually moved either by
the HDG knob on the Course Heading Panel
(CHP) or by the TURN knob on the APP. The
bug will automatically synchronize to existing
heading when the system is powered up.
− Basic mode at power on. Selectable by HDG
mode button.
− Selection of HDG mode clears any previously
selected lateral mode. Heading can be preset
before selecting HDG mode.
NAV, Navigation system mode
− The FCC commands capture and tracking of the
course defined by the active navigational data
displayed on the EFIS (VOR, LOC, BC or RNAV
if installed).
Applicable to FCC 85/86 − 210:
The capture and tracking gain in NAV − mode is
dependant on the distance to the VOR − station.
In the new Flight Control Computer software −
FCC 85/86 − 210 − DME − data is used in the con-
trol law such that the gain will be based on the
distance, leading to improved performance.
However, if no DME − data is available (e.g. when
VOR2 is used as NAV − source) the gain will be
based on a default value equal to a far distance
from the VOR. This will lead to overshoots at
short distances during capture and tracking.
NOTE
The capture point depends on intercept angle and
closure rate.
− GS is inhibited in NAV mode.
− Mode is armed by pushing the NAV mode button.
FCC automatically reverts to HDG and desired
intercept heading can be selected on the heading
bug.
− Mode is engaged at the capture point and NAV
”CAP” is displayed on EADI.
− NAV mode is retained if changing NAV data
source.
Jun 01/20