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data communications, with the advantages of lower error rates, more timely service, and lower costs. This
started with highly customized ACARS systems for company communications, using VHF frequencies.
The A330/A340 is equipped with a standardized ACARS system that can be used by any customer,
with allowance for each customer to easily introduce his own custom features to reflect his own needs.
These initial ACARS systems have been extended to offer worldwide coverage, even in mid-ocean and
sparsely inhabited areas, using the Inmarsat facilities and HF data link, and to cover not only company
communications but also ATC services, starting with predeparture and oceanic clearances.
On aircraft delivered since 1998, the ACARS unit has been replaced by the Air Traffic Services Unit
(ATSU), which is designed to also accommodate safety-related ATC functions using the Aeronautical
Telecommunications Network (ATN), offering the majority of ATC and other communication services now
using voice, and more importantly, offering profitable migration to the ATN. The ATSU is the first unit to
host software from a number of different vendors. The same ATSU is also used on the A320 family of aircraft.
The ATN upgrade is being implemented to be available when the corresponding communication and
ATC services are in service.
30.12 Flexibility and In-Service Updates
The first generation of aircraft with widespread digital systems, such as the A300FF, A310, and B767,
suffered from some of the same disadvantages as their analogue-system predecessors in that their avionics
were not designed to accommodate unplanned change. Once a design change was made, equipment had
to be removed from the aircraft, program memories had to be reloaded in the avionics workshops
(sometimes by physically changing parts), and the equipment reinstalled. At some point the airframe
manufacturer usually got involved to certify the change. There was an advantage in the avionics shop,
because reloading a program and retesting is a faster and cheaper activity than installing a kit of new
electronic parts, but the major cost of carrying out the change on the aircraft stayed the same.
The A330/A340 systems have to a large extent overcome this disadvantage, in that those digital LRUs
that have been identified as requiring in-service change now have facilities for updates to be included
in
situ
on the aircraft, at greatly reduced cost.
Two techniques are used, depending on the criticality of the LRU concerned, and on other practicalities.
1. On-Board Replaceable Memories (OBRMs) are memory modules that are located on the (accessible)
front panel of an LRU. They come in industry-standard sizes, cost much less than the LRU itself,
and can be “recycled” many times. The visible part of the OBRM contains the LRU’s software part
number section. OBRMs comply with the toughest criticality criteria, enable classic configuration
control of the LRU and require no tools to change. They have been in use on the A320 since 1988.
2. The other technique in use is on-board data loading using 3.5 in. diskettes and other media. These
are a little slower and are even less expensive than OBRMs, but do require a data loader to be
carried to or installed on board the aircraft, and an adaptation to the aircraff ’s classic configuration
control techniques. The same data loader is used for the FMS data base.
Both techniques enable software updates to be carried out overnight on the whole fleet.
Another aspect is flexibility in dealing with airlines’ changing needs. The basic equipment for the
aircraft is designed with a number of pin-programmable features that correspond to frequently requested
airline changes, and other systems like the FMS where the airline loads a database which specifies its own
preferences. These features allow airlines to pool databases and standard spares at outstations and still
obtain the kind of operation that they need. Another feature is partitioned software, where heavily
customized systems like ACARS can be certified just once for all users, with one set of “core” software.
The airline may load its own additional operational software on top of this core to reflect its own needs.
Lastly, certain systems like the optional Aircraft Condition Monitoring System (ACMS) which used
to be heavily customized, use a combination of these techniques to enable an airline to select the features
that it needs out of a very powerful selection which forms a superset of the needs of all the customers.
© 2001 by CRC Press LLC
30.13 Development Environment
The development of each Airbus Industrie aircraft has been supported by an Iron Bird whole-aircraft
systems rig, and by supporting systems rigs that enable work to proceed simultaneously, without mutual
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