(b)
Pushing the MTRS button adds or removes the altitude display in meters on the corresponding PFD.
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747-400 MAINTENANCE MANUAL
(c)
The baro set control consists of an outer and an inner concentric knob, the inner knob is also a push button. The outer knob selects the selected barometric reference to be displayed in inches of mercury (IN) or hecto Pascals (hPA) on the corresponding PFD. Pushing the inner knob will select the standard (STD) barometric reference to be displayed on the corresponding PFD. Each time the STD barometric reference is selected, 29.92 IN or 1013 hPa will be displayed just below STD in the preselect readout on the corresponding PFD.
(d)
A preselected barometric reference value can be selected by rotating the inner knob. After a preselected value has been set by rotating the inner knob, pressing the knob will remove the STD barometric reference and replace it with the preselected barometric reference value.
(e)
The altitude in meters and the barometric reference settings can be set using the CDU in the event that the EFIS control panel fails.
(f)
The captain's and first officer's EFIS control panels are located on the left and right sides of the pilots' light shield.
EFIS/EICAS interface unit (EIU)
(a)
The three EIUs receive digital data, on data bus No. 2 and data bus No. 4, and discretes from each ADC. The EIUs process this information to create air data system displays on the PFDs and air data system warning, status, and advisory messages for the EICAS displays.
(b)
The left ADC serves as the primary source for the left EIU and an alternate source for the right and center EIUs. The right ADC serves as the primary source for the right EIU and an alternate source for the left and center EIUs. The center ADC serves as the primary source for the center EIU and an alternate source for the left and right EIUs.
Primary flight display (PFD)
(a)
The PFD is a CRT that provides displays for several electronic systems. The following paragraphs describe the displays for the air data system.
(b)
The altitude tape display presented on the right side of the PFD is an electronic representation of a continuously rotating drum with a fixed readout box in 20-foot increments. The altitude tape displays a full scale range of 825.0 feet at any given time with numeric altitude placed at 200-foot intervals. Indices are placed every 100 feet. Negative values will show a negative sign immediately to the left of the most significant displayed digit. A detected failure of the displayed altitude information is annunciated by removal of the altitude tape and the appearance of a yellow boxed ALT where the altitude tape is normally located.
(c)
Altitude in meters, when selected, equivalent to feet is digitally displayed above the fixed altitude readout box. The metric altitude is rounded to the nearest one meter. The metric readout is removed when an altitude failure is detected.
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747-400 MAINTENANCE MANUAL
The airspeed tape display presented on the left side of the PFD is an electronic representation of a continuously rotating drum with a fixed readout box in 1-knot computed airspeed (CAS) increments. The airspeed tape displays a full-scale range of
123.75 knots at any given time interval with numeric airspeed placed at every 20-knot intervals starting at 40 knots. Indices are placed every 10 knots starting at 30 knots and ending at 420 knots. A detected failure of the displayed airspeed information is annunciated by removal of the airspeed tape and the appearance of a yellow boxed SPD where the airspeed tape is normally located.Current Mach is displayed digitally below the airspeed tape by a period followed by a 3-digit number. A detected failure of CAS will remove the Mach readout. A detected Mach failure and not a detected CAS failure is annunciated by removal of the Mach readout and the appearance of a yellow boxed MACH where the Mach readout is normally located.The maximum operating speed (Vmo) limit barber pole is displayed against the airspeed tape scale. The Vmo speed displayed is the smallest value parameter that is received from the stall warning computer and the air data computer. A detected failure of CAS will remove the Vmo barber pole symbol. A detected Vmo speed limit failure and not a detected CAS failure is annunciated by removal of the Vmo barber pole symbol and the appearance of a yellow boxed SPD LIM near the top, right side of the airspeed tape.The barber pole symbol consists of red squares spaced equally on a black background. The barber pole symbol will extend from Vmo speed limit to the upper edge of the airspeed tape (in the direction of larger airspeed values). If the airspeed values displayed are lower than the Vmo speed limit, the barber pole symbol will not be displayed.Vertical speed is displayed on the right side of the PFD in digital and analog representation. The digital readout appears when the vertical speed equals or exceeds plus or minus 400 feet per minute. If vertical speed is positive, the digital readout appears above the analog display. If the vertical speed is negative, the digital readout appears below the analog display without a minus sign. If the vertical speed exceeds plus or minus 9999 feet per minute, the display will read 9999.The analog display is a fixed scale with a moving pointer. The pointer moves in a windshield wiper manner about a center point located off the display along the PFD horizontal centerline. The pointer indicates the value along an analog scale. The scale is positive for values up from the center line and is negative for values down from the centerline. The scale is linear between numerics. The scale defined for the 2000 to 6000 feet per minute range is extended to the upper or lower display range limit when the vertical speed exceeds the analog display range limit and the pointer parks in view at the upper or lower limit.
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