Aviation Investigation Report A98H0003

1.6.5  Electronic Instrument System

The MD-11 EIS consists of six display units (DU) mounted in the instrument panel. DUs 1, 2, and 3 are on the left side; DUs 4, 5, and 6 are on the right side (see Figure 11). The captain's DUs (DUs 1, 2, and 3) receive display information from display electronic unit (DEU) 1, and the first officer's DUs (DUs 4, 5, and 6) receive information from DEU 2. DEU 3 (auxiliary) is continuously available as a spare and may be selected for use by either pilot through the EIS source input select panel.

DUs 1 and 6 normally display primary flight information, such as heading, attitude, airspeed, barometric and radio altitude, vertical speed, vertical and lateral deviation, aircraft operating limits, configurations, and flight modes.

DUs 2 and 5 are normally navigation displays (ND). The ND has four modes of operation as follows:

  • MAP mode – Displays the active flight plan referenced to the aircraft position and heading in the form of a pictorial representation; this is the mode normally used with FMS navigation.
  • PLAN mode – Displays the flight plan only, with the aircraft symbol centred on the next waypoint.
  • VOR mode – Displays a compass rose, two bearing pointers (for non-directional beacons (NDB) and very high frequency omni-directional range (VOR)), a course deviation indicator (for VOR navigation and approaches), headings, ground speed, true airspeed (TAS), distance measuring equipment, and weather information; this mode is normally used for conventional (NDB and VOR) navigation and approaches.
  • APPR mode – Displays the same information as the VOR mode, except that the course source is an ILS receiver instead of a VOR; this mode is used for ILS front-course and back-course approaches.

All the modes display wind, clock, and next waypoint information.

DU 3 is normally used to show the engine and alert display (EAD), which includes information such as engine pressure ratio (EPR), exhaust gas temperature, N1,[23] N2,[24] fuel flow, and alert messages. DU 4 is used for the system display (SD), which normally shows either secondary engine data (i.e., engine oil temperature, pressure and quantity), or aircraft systems synoptic pages.[25] The synoptic pages display the configuration and status of the hydraulic, electric, air, and fuel systems. They also include a configuration page, miscellaneous page, systems status page, and a consequence page (see Table 6).

Electrical power is supplied by the left emergency 115 volts (V) alternating current (AC) bus for DUs 1 and 3; by the right emergency 115 V AC bus[26] for DUs 4, 5, and 6; and by the 115 V AC Bus 1 for DU 2. If all three engine-driven electrical generators were to fail, DU 1 and DU 3 would automatically receive electrical power from the aircraft battery. When the air-driven generator (ADG) is deployed and selected to the electric mode, DUs 1, 3, 4, 5, and 6 can be powered, and the aircraft battery charge will be maintained.

lf flight information data to the DU is invalid, that information is removed from the screen and replaced by either a red or amber "X" symbol covering the area of removed data. A red "X" requires immediate flight crew action to restore the lost data. If the "X" is amber the flight crew can decide to delay action to restore the data. A failed DEU is indicated by a red "X" displayed across the entire black screen of the DU. The loss of electrical power to a DU will result in a blank screen. The loss of any DU would cause the remaining DUs to reconfigure automatically. The priority logic used in reconfiguring is to keep a primary flight display (PFD) available at all times; that is, if only one DU were functioning, it would maintain the PFD. In the failure priority logic, the second-to-last operating DU would display the EAD.

[23]    N1 is the rotational speed of the low-pressure compressor and the low-pressure turbine.

[24]    N2 is the rotational speed of the high-pressure compressor and the high-pressure turbine.

[25]    A synoptic page contains a detailed summary of the status of a particular aircraft system, showing all normal or abnormal indications, and is viewed on the system display.

[26]    The report refers to the left and right emergency 115 volts (V) alternating current buses as the left and right emergency AC buses respectively.

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