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K.
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A
747-400 MAINTENANCE MANUAL
(b) DH Alert 1) Alert is annunciated for radio altitude less than selected decision height.
2) The green colored DH legend and readout are replaced by a large yellow colored DH legend. The yellow DH legend flashes at a rate of four times a second for three seconds.
3) A DH alert is cancelled automatically for radio altitude equal to zero or when the radio altitude is 75 ft greater than the selected decision height. A DH alert can be cancelled manually by pressing the RST switch on the EFIS Control Panel.
(2) Radio Altitude (RA)
(a)
General 1) Displayed by a white colored digital readout for radio altitude less than 2,500 ft. 2) For a radio altitude input of -20 ft or less, the readout will limit and continue to display -20 ft. 3) For NCD (No Computed Data) radio altitude, the readout is removed.
4) For failed radio altitude, the readout is removed and the RA flag (Fig. 10C) is displayed.
(b)
DH Alert 1) Alert occurs when the airplane descends to a radio altitude less than the selected decision height. 2) For alert conditions, the color of the radio altitude
readout changes from white to yellow.Marker Beacon
(1)
The outer marker, middle marker or inner marker is annunciated as OM, MM or IM respectively.
(2)
A marker beacon receiver functional test condition is annunciated as
FT.Pitch Limit
(1)
The pitch limit symbol is displaced vertically along a line through the center of the airplane reference symbol.
(2)
The symbol moves in response to SWC pitch limit data.
(3)
The symbol is removed if the SWC pitch limit or IRU pitch angle is invalid, or if IRU pitch attitude exceeds |90°.
(4)
The symbol is removed if IRU roll angle is invalid.Pitch Indices
(1)
Indices appear at 2.5° intervals from +90° to -90°.
(2)
Positive pitch causes the indices to move down the display relative to the airplane reference symbol.
(3)
Positive roll causes the indices to rotate counterclockwise on the display.
(4)
Indices are removed if IRU pitch or roll attitude are NCD.
(5)
Indices are removed and the ATT flag (Fig. 10C) is displayed if IRU pitch or roll attitude is failed, or if IRU pitch attitude exceeds |90°.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
M. Slip Skid Indicator
(1)
The roll angle pointer is in two sections. The triangular upper section points to the roll indices and indicates roll angle. The rectangular lower section slides along the upper section.
(2)
The lateral displacement of the bottom section relative to the top section indicates airplane body lateral acceleration.
(3)
When the body lateral acceleration equals zero, the two sections will be aligned.
(4)
Positive IRU lateral acceleration causes the lower section of the roll pointer to move to the left.
(5)
The symbol is removed for invalid IRU body acceleration or roll angle.
(6)
The symbol is removed if IRU pitch attitude is invalid or exceeds |90°.
N. Roll Indices and Pointer
(1)
Indicates |40° of roll angle.
(2)
Indices are placed at 10° intervals with a zero degree index located at the center.
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