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(q) When the PMS descent is oriented to a bottom of descent (BOD) waypoint, the PMS continuously computes current path deviation from the descent profile path.
(4) At altitudes below 10,000 feet, the PMS automatically commands a speed of 250 knots. Descent continues under PMS control down to a radio altitude of 2500 feet. At this altitude a signal from the low range radio altimeter disengages the PMS from the autopilot-flight director and from the throttle servomotor. The low range radio altimeter (LRRA) signal is also used during the climb mode to prevent PMS engagement prior to 2500 feet.
6. Control Display Unit (Fig. 6)
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A. Basic control of the PMS is obtained by operating keys and displays on the PMS control display unit (CDU). Also the PMS CDU can be used to place the INS in either the PMS waypoint control mode, or the INS waypoint control mode.
B. The CDU contains a power supply, logic circuit cards, a front panel assembly and display assembly. The front panel and display assemblies contain the controls and indicators that are used to insert information into the computer and to display computer unit output data. The logic circuits transform inserted data into serial digital data and serial digital data into illuminated indications consisting of indicating lamps and numerical displays. The logic circuits also provide independent CDU lamp and display testing features.
C. The CDU provides the following capabilities:
(1)
A means for alphanumeric data entry into the PMS computer unit.
(2)
A means of flight mode selection.
(3)
System status annunciation and the performance management of the airplane.
(4)
A PMS display of navigation and guidance data.
D. Input/Output Word Format.
(1)
The data words received from the computer unit are displayed by the CDU as alphanumeric characters on the four-line light emitting diode (LED) display, or as discretes to illuminate lamps on the CDU fault panel.
(2)
The input and output words used, in the CDU to computer interface, are 32 bits in length. Each word consists of a 24-bit data field and an 8-bit label field. The label field determines whether the 24-bit data field is display data or discrete data.
(3)
The input and output data is in RZ (RETURN TO ZERO) self synchronizing format on a two wire interface. The 24-bit data field of a serial data output word consists of keyboard and slew switch encoding.
E. CDU Data Displays and Switch Controls.
(1) The four line data display is composed of 5 by 7 LED dot matrices which provide a maximum display of 24 characters per line. Characters include letters, numbers, mathematical symbols, and punctuation marks. The selection of data for display is controlled by the display selection keys on the left side of the CDU, the slew switch and the STS/TEST key. The top line of the CDU display is a title line giving the page type on the left and the page number on the right. The other three lines provide data displays.
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(2)
The display selection keys (ENG LIM, WPT, PERF DATA, NAV DATA, NAV AID, CLB, CRZ, DES and PLNG) are used to select and indicate the type of data being shown on the CDU display. Depressing one of these keys causes a page of the related data to appear in the display. Climb (CLB), cruise (CRZ), and descent (DES) data displays can also be selected automatically by the computer. In such cases, the mode page is displayed and the line select 1 switch and INSERT keys light simultaneously. The display can then be slewed to the page for the desired option and the INSERT key depressed to command the computer to enter that mode of operation.
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