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their aircraft.
As far as circuit breaker inspections are concerned (for loose, broken, incorrect or
misapplied termination hardware, overheating and electrical arcing), Airbus has already
initiated the process of developing an Enhanced Zonal Analysis Procedure (EZAP) for all
their aircraft types (ref. SIL 20-013). EZAP is a logic process to be applied to all zones
containing wiring that allows determination of a need for tasks to minimize the presence of
combustible material (cleaning tasks); and the need for either standalone General Visual
Inspections or dedicated Detailed Inspections of specific wiring installations.
The new tasks generated by application of the procedure will be added in the Maintenance
Review Board (MRB) report and the Maintenance Planning Document (MPD) will be
updated to reflect MRB Report revision.
Airbus will ensure that application of EZAP will consider circuit breaker panels to permit
visual inspection of circuit breakers.
As far as cycling of circuit breakers is concerned, and based on the lower and higher current
overload results, it can be concluded that cycling the breaker on and off will improve the
voltage drop rated current and circuit breaker’s current overload characteristics.
Airbus is therefore in agreement with this recommendation and then recommends that
operators perform an initial manual cycling of all thermal circuit breakers on and off at least
one time under no power within an initial 24-month period and thereafter at intervals not to
exceed 36 months.
This repetitive task will be included in the next MPD revision (not later than end of 2005),
with the SIL referenced as the source document. Pending the issue of that revision,
operators may use the following allocated MPD task numbers in their approved
maintenance programmes:
- A300: 240000-0503-2
- A300-600: 240000-03-1
- A310: 240000-04-1
- A318/A319/A320/A321: 240000-17-1
- A330/A340: 240000-01-1
Airbus A320 Braking as Predicate-Action
Diagrams
Peter B. Ladkin
Universit¨at Bielefeld, Technische Fakult¨at
Postfach 10 01 31, D-33501 Bielefeld
ladkin@techfak.uni-bielefeld.de
http://www.techfak.uni-bielefeld.de/~ladkin/
Abstract
We use the Predicate-Action Diagrams of Lamport to express the de-
scription of the operation of the Airbus A320 braking systems contained
in the Flight Crew Operating Manual. This helps identify ambiguities
and incompleteness.
1 Introduction
On September 14th, 1993, a Lufthansa Airbus A320 landed at Warsaw Airport
in Poland in a thunderstorm. It overran the end of the runway, surmounted an
earth bank, and came to rest on the other side. Two people died and others
were injured in this accident, which began to interest us and others in the design
of the A320 braking system [FI.93a, FI.93b, FI.93c]. This paper analyses the
specification of the A320 braking system contained in the Flight Crew Operat-
ing Manual [FCOM], and rewrites it in Predicate-Action Diagrams of Lamport
[Lam94b]. A fuller version of this work containing an analysis is [Lad95].
Flight crew should have a complete, accurate high-level specification of sys-
tem operation from which to work. This may be provided using predicate-action
diagrams, with advantage over the Boolean logic expressed in English that is
currently used. This is in line with current thinking, for example by the task
force studying controlled flight into terrain – “a factor that often crops up when
crashes are analysed is the failure of the pilot at the controls to stick to standard
flight procedure. But that is not necessarily the pilot’s fault: [...] Or perhaps
poor descriptions mean the procedure is misunderstood.” [Eco94].
The Braking System Design of the A320. The braking system design
of the A320 is described in the A320 Flight Crew Operating Manual [FCOM].
There are four main components of this system, of which the two primary com-
ponents are the brakes and anti-skid. The other two are the spoilers (which
destroy lift from the wings) and the thrust reversers (which divert engine ex-
haust to thrust in a forward direction). The brakes and anti-skid system are
described in [FCOM, 1.32.30: Landing Gear: Brakes and Anti-Skid]; the spoiler
activation in [FCOM, 1.27.10: Flight Controls Description, P11]; the thrust
reverser actuation in [FCOM, 1.70.70: Power Plant: Thrust Reverser System].
1
Predicate-Action Diagrams and TLA+ Specifications. A predicate-action
diagram is a simple state diagram in which the states are given by the values of
chosen state predicates (conditions which have values), and transitions between
these states, indicated by labelled arrows, are actions of a given type. Predicate-
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