ARINC CHARACTERISTIC 701 - Page 1
1.0 INTRODUCTION AND DESCRIPTION
1.1 Purpose of this Document
This document sets forth the characteristics of a Flight
Control Computer System (FCCS) portion of the larger
Automatic Flight System (AFS) specifically designed to
provide autoland capability for commercial transport
aircraft.
The intent of this document is to provide general and
specific design guidance for the development and
installation of an FCCS primarily for airline use. This
document will make reference to and state need for
assumptions or prerequisites for the Flight Augmentation
Computer System (FACS), the Flight Management
Computer System (FMCS), and the Thrust Control
Computer System (TCCS), but those elements of the total
Automatic Flight System (AFS) will be defined in separate
ARINC characteristics. As such, this guidance will
include the desired operational capability of the system
and the standards necessary to ensure limited
interchangeability.
Equipment manufacturers should note that this document
encourages them to produce maintenance-free, high
performance equipment rather than that of minimal weight
and dimensions. They are at liberty to accomplish this
objective by means of design techniques they consider to
be the most appropriate, as their airline customers are
interested primarily in the end result rather than the means
employed to achieve it.
1.2 General System Description
The Flight Control Computer System (FCCS) described in
this document is necessarily a subset of the more
extensive overall automatic and manual control system of
the aircraft and, therefore, must have reasonable and well-
defined subsystem boundaries. These boundaries for the
"Basic Autopilot" have an arbitrary aspect and have been
chosen with the objective of attaining the highest integrity
of operation for the overall flight control of the aircraft.
Because of vagaries of airframe design generally, and
honest differences of designers’ opinion in particular,
different configurations of FCCS may be required
although the functions and sensors for the various possible
configurations may be identical.
COMMENTARY
The airlines have indicated that the AFS for the
"next" airplane should automate or eliminate many of
the operating modes and manual mode selections to
reduce cockpit work load, thereby facilitating better
pilot management of the AFS and progress of the
flight. Furthermore, the basic autopilot or building
block of the digital AFS should include the autoland
functions. It is assumed that airframe manufacturers
will build and certify an ICAO Category 3 aircraft,
but the airlines will probably buy a Category 2
version. In addition, certain "outer loop" functions of
the FCCS have been determined by the airlines to be
more properly located in the FMC elements of the
AFS. Thus, the FCCS design is predicated on
installations having an FMC installed. However, it
should be noted that a small but vocal group of
airlines (and manufacturers) desire a more
conventional and self-contained FCCS. The
differences between these concerns will be made
evident elsewhere in this characteristic.
1.3 Elements of Automatic Flight System
The Auto Flight System (AFS) is made up of the
component systems shown in Attachment 1. The Flight
Augmentation Computer System (FACS) provides all the
functions needed to assure suitable aircraft handling
qualities for manual control, i.e., when the "autopilot" is
not engaged. Such functions are obviously unique to a
particular airframe type and may include (but are not
necessarily limited to) pitch trim, stability augmentation,
aileron gain programming and flap load limiting. Its
airframe type dedication makes the FACS less than
amenable to form, fit, and function standardization of the
ARINC type. Only the electrical interfaces for this
system are defined in Attachment 3.
All other AFS functions are distributed between the Flight
Control Computer System (FCCS), the Flight Management
Computer System (FMCS), and the Thrust Control
Computer System (TCCS). The basic FCCS provides the
"basic autopilot" functions and those functions involved in
or associated with landing the aircraft automatically. In
the basic system the remaining AFS functions are located
in the FMCS and TCCS. In this way a failure of a
nonautoland function will not prevent the dispatch of the
aircraft. Further, such failures can be corrected without
the need for autoland capability requalification. The
FCCS, the FMCS, and the TCCS are amenable to form,
fit, and function standardization. ARINC Equipment
Characteristic Nos. 701, 702, and 703 are devoted
respectively to them. The FCCS and TCCS may also be
defined in an expanded configuration which allows either
to be installed and operated independently of an FMCS
which this configuration does not include.
The AFS consists of possible configurations of line
replaceable units (LRUs) as outlined in Attachment 1.
This attachment shows in greater detail the relationships
among the LRUs of the AFS. Note that the glare shield
controller and the mode annunciator panel, if desired,
provide the pilot input/output interface for the whole AFS.
Note also that the FCCU interfaces with the pitch, roll and
yaw servos, even though these units are components of the
FACS. This is made possible by the AFS interface
standardization.
The FMCS consists of the several units described in
ARINC 702. It derives the sensor and other basic data it
needs to perform its functions independently (parallel) of
the FCCU. The FMCS also exchanges data with the
FCCU.
A more detailed description of the possible AFS
partitionings is provided in Attachment 1.
COMMENTARY
Despite widespread airline desire for a "universal" and
"interchangeable" autopilot, the variations in opinions
about modes, functions, and displays which are "basic
to autoflight, along with varying airframe and airline
positions about the amount of desirable
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