Flight Instruments, Displays -Electronic Flight Instrument System
EFI Transfer Switch and EFIS Light Sensors

Electronic Flight Instrument (EFI) Transfer Switch
NORMAL – Captain’s and First Officer’s EFIS displays are generated from their
related symbol generators.
BOTH ON 1 – Both EFIS displays are generated from the No. 1 symbol generator.

Flight Instruments, Displays -Electronic Flight Instrument System 737 Operations Manual

BOTH ON 2 – Both EFIS displays are generated from the No. 2 symbol generator.

Remote Light Sensor
Provides automatic adjustment of EFIS EADI and EHSI display brightness as a function of ambient light coming through the associated forward window.

Integral Light Sensors
Provide automatic control of EFIS EADI and EHSI display brightness as a function of ambient light striking the face of the display units.

Instrument Transfer Switch (INSTR SWITCH) Light
ILLUMINATED–one or both of the instrument transfer switches (EFI or IRS) has been moved out of the normal position.
Copyright . The Boeing Company. See title page for details.
10.30.68  August 1, 2003

737 Operations Manual

Introduction
The electronic flight instrument system (EFIS) consists of two symbol generators (SGs), two control panels (CPs), two electronic attitude director indicators (EADIs or ADIs), two electronic horizontal situation indicators (EHSIs or HSIs), and ambient light sensing units. The EFIS utilizes information provided by a variety of aircraft systems to generate the appropriate visual presentations on the EHSI and EADI. Data relating primarily to navigation is provided by aircraft systems such as the navigation radios, flight management computer (FMC), and the inertial reference systems (IRSs). Data relating primarily to automatic flight is provided by the flight control computers (FCCs), the autothrottle (A/T), and the FMC. Data which is used to display current aircraft state information is provided by the air data computers (ADCs) and the IRSs. Automatic adjustment of the display intensity for each display unit is provided by the ambient light sensing units. flight crew control of the EFIS displays is accomplished by positioning the various controls on the respective EFIS control panels to the desired settings.
EFIS Failure Flags and Annunciations
In addition to the normal EFIS displays, various failure annunciations, flags, or indications may be displayed on the EADI or EHSI.
The location of the different failure flags and annunciations is depicted in the EADI and EHSI SYSTEM FAILURE FLAGS AND ANNUNCIATIONS figures included in the EFIS controls and indicators section.
Not all EFIS displays will be replaced by a failure flag or annunciation if the signal from the sending unit has failed. In theses instances, failure is indicated by removal of the data or the affected portions of the display.
Note: The EFIS displays respond to a VHF NAV receiver failure by removing the
associated magenta deviation bar and/or pointer. In response to an ADF
receiver failure, the associated display symbol(s) (ADF pointers or
vectors) are removed from the EHSI.
EFIS Symbol Generator
Two symbol generators form the heart of the EFIS. The SGs receive inputs from various aircraft systems, then generate the proper visual displays for the related EADI and EHSI.
Flight Instruments, Displays -EFIS System Description 737 Operations Manual

EFIS Control Panels
Each SG is connected to an EFIS control panel. Using the related EFIS control panel, a flight crew member can select the EHSI display mode, the EHSI display options, the EHSI display range, the EADI decision height reference, and the EHSI weather radar display option. The EFIS control panels also allow the flight crew to adjust the EADI, EHSI, and weather radar display brightness levels.
Electrical Power
The electronic flight instrument system operates on 115 volt AC power. With loss of all airplane generators, the Captain’s and the First Officer’s EFIS are inoperative. The standby Instruments provide a backup source of information in this event.
On some airplanes, with the loss of all airplane generators, the First Officer’s EFIS becomes inoperative, but the Captain’s primary EFIS displays receive power from the standby AC bus.
The EADI can display pitch and roll attitude (without background color), localizer and glide slope deviation and airspeed on the speed tape. The EHSI can display heading, track, localizer and glide slope deviation, ADF bearing, selected heading, selected course, and course deviation.
Electronic Attitude Director Indicator
The EADI presents conventional EADI displays for attitude (pitch and roll), flight director commands, localizer deviation and glide slope deviation. In addition, the EADI displays information relating to autoflight system mode annunciations, airplane speed (Vmo/Mmo, minimum speeds, CAS, placards, V1, Vr, etc.) (airplanes with speed tape installed), pitch limit, Mach, ground speed, decision height, radio height alert (on some airplanes), and radio altitude.
　
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