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A
747-400
MAINTENANCE MANUAL
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34-12-00
ALL ú ú 12 Page 24 ú Feb 18/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
(5)
BARO corrections No. 1 and No. 2 come from the pilot's EFIS control panels. The No. 1 input to the ADCs is supplied by the captain's EFIS control panel and the No. 2 input is supplied by the first officer's EFIS control panel. The captain's PFD displays the No. 1 baro-corrected altitude output. The first officer's PFD displays the No. 2 baro-corrected altitude output. The cabin pressure control system uses the No. 3 baro-corrected altitude output corresponding to input No. 1 for the left ADC and to input No. 2 for the right ADC. Use of different altitude outputs for the two altitude displays permits each pilot independent control of his display setting when both displays are operated from a single ADC.
(6)
The resolver voltage signals from the AOA sensor is converted to digital angular information and computed with respect to AOA rotation angle. The indicated AOA data is then in digital binary form for ADC output and further ADC calculations.
(7)
The variable resistance in the TAT probe provides an analog input to the TAT computation circuit. Here, the signals are converted to digital form and output to the CPU.
(8)
Several discretes are coded to inform the ADC and interfacing systems of sensor heater status.
(9)
The ADC is set for either a right or left system by shorting the SDI (source/destination identifier) pin to common.
(10)
Each ADC has four ARINC 429 digital data buses transmitting identical data. A fault on one bus does not affect data on other buses. The following data is output on each bus.
(a)
Pressure altitude is derived from the static pressure input which is compensated for ambient temperature and corrected for static pressure source errors. The range is from -1000 to +50,000 feet.
(b)
The BARO corrected altitudes are computed from pressure altitudes and the BARO correction inputs (range -1000 to +50,000 feet).
(c)
The altitude rate is derived from pressure altitude. Its range is from -20,000 fpm to +20,000 fpm.
(d)
Computed airspeed is computed from a combination of calibrated pitot and static pressure inputs. The static pressure has been corrected for static pressure source errors. Computed airspeed range is from 30 to 450 knots.
(e)
MACH number is computed from the same inputs as computed airspeed. Range is from 0.1 to 1.0 MACH.
(f)
True airspeed is computed from a combination of MACH and static air temperature (SAT). Range is from 100 to 599 knots.
(g)
Static air temperature is computed from a combination of MACH and total air temperature. It ranges from -99°C to +60°C.
(h)
Total air temperature is computed from the analog output of the TAT probe. TAT ranges from -60°C to +99°C.
(i)
Impact pressure is derived from the difference between total pitot pressure and indicated static pressure. Its range is from 0 to 372.5 millibars.
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747-400 MAINTENANCE MANUAL
(j)
Total pressure is derived from the calibrated pitot pressure input that has been compensated for ambient temperature. The range is from 135.5 to 1354.5 millibars.
(k)
Maximum allowable airspeed (Vmo) (display output) is computed from altitude, airspeed, MACH data and stored Vmo reference data. Reference data for 16 airplane types can be stored in memory. Selection of the correct reference data is made by the program jumper. Mmo is derived from Vmo reference data. The Vmo range is 150 to 450 knots.
(l)
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