Saab 340B, Руководство по эксплуатации

Страница: 573 / 670

INSTRUMENTS AND RECORDERS, AIR DATA SYSTEM
Description
Aircraft Operations Manual
12/1.1
PAGE 1
Apr 01/15
1. GENERAL
The air data system uses three Pitot/Static tubes
which senses the pitot and the static pressures and
feeds that information to the pneumatic instruments
and to the Air Data Computer (ADC). The ADC cal-
culates the various data to be displayed on the
electric instruments and EFIS or to be supplied to
other systems as shown in Fig. 2.
2. MAIN COMPONENTS AND SUBSYSTEMS
2.1 Pitot/static systems
The aircraft is equipped with two main and one
standby pitot/static system (Fig. 1). The two main
Pitot/Static tubes have two separate static cham-
bers. Each static chamber is interconnected with
the corresponding chamber in the other tube. The
purpose is to eliminate pressure differences be-
tween the two systems. The interconnections are
provided with shutoff valves to isolate the systems
for example should a static leak appear. The left
main tube supplies pitot pressure to the ADC and
the right main tube supplies pitot pressure to the
pneumatic instruments.
The standby Pitot/Static tube has only one static
chamber and supplies the standby instruments and
the airspeed sensor.
All three Pitot/Static tubes are electrically heated to
prevent icing. A failure of the heating will light a
caution: L, R or STBY PITOT caution light on the
overhead panel. Also see 11.1, ICE AND RAIN
PROTECTION. The tubes are located as follows:
− Left main tube and standby (upper tube) on the
left side of the a/c fwd fuselage.
− Right main tube on the right side of the a/c fwd
fuselage.
2.2 Temperature probe
The Outside Air Temperature probe (OAT), senses
air temperature for the ADC. The probe is provided
with an electrical heater for anti
− icing. Also see
AOM 11.1, ICE AND RAIN PROTECTION. Should
the heater fail, the OAT caution light on the over-
head panel will come on. The OAT probe is located
on the upper part of the fwd fuselage.
2.3 Air Data Computer (ADC)
The ADC senses the air temperature, it also con-
verts the pitot and static pressures into electrical
signals from which the ADC calculates the various
parameters. These parameters are:
− Altitude (ALT).
− Vertical speed (VS).
− Indicated airspeed (IAS).
− True airspeed (TAS).
− Maximum operating speed (V
MO
).
− Static air temperature (SAT).
These parameters are available as digital values
and analogue signals and are supplied to many sys-
tems as shown in Fig. 2.
The ADC calculates the V
MO
and triggers the mas-
ter warning system to give an overspeed warning
when the speed exceeds V
MO
by 2 kt.
2.4 Instruments
These are two different types of indicators:
− Electromechanical (servo) indicators for the left
pilot, supplied with data from ADC.
− Pneumatic indicators for the right pilot and for
standby instruments, supplied directly with pitot
and/or static pressures.
Altimeters
The ADC supplies information of uncorrected alti-
tude to the electromechanical altimeter. The altime-
ter converts this information into a display, cor-
rected for the barometer pressure, set by a
baroknob on the instrument. The display shows
both a five numerical digital readout and an ana-
logue pointer with a smallest scale increment of 20
ft. The corrected altitude is also supplied to the alti-
tude preselector/alerter. The altimeter also contains
an encoder that furnishes the ATC transponders
with aircraft altitude information related to 1013
mb/2991 inHg.
The pneumatic altimeters are equipped with an an-
eroid which converts static pressure into a mechani-
cal movement of the counter and pointer. Correction
for barometer pressure is set with a baro knob on
each instrument. The display is the same as for the
electromechanical altimeter.
(Cont’d page 5)