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Assessment (FHA), the Preliminary System Safety Assessment
(PSSA) and the System Safety Assessment (SSA). The ultimate
aim is a regime in which no change to the ATM system can be
made before it has first been shown that it will not result in
an unacceptable level of risk of an accident.
The FHA is carried out right at the beginning – when a new
system is being defined or when a change to an existing system
is contemplated – with the objective of determining exactly
how safe the system needs to be. The process identifies
potential hazards and assesses their consequences for the
safety of operations. It then specifies safety objectives: that is,
the safety levels to be achieved by the system.
The PSSA runs in parallel with the design of a new system or
a modification to an existing design and is intended to show
whether the architecture can reasonably be expected to
achieve the safety objectives set by the FHA. It translates
safety objectives into safety requirements and specifies the
maximum contribution to risk to be achieved by each
element of the system. If it is found that parts of the
architecture are incapable of offering an acceptable
contribution to risk, additional mitigations such as back-up
equipment, new procedures and additional training may be
SAM is now being
applied in practice by
EUROCONTROL itself
and by many individual
national Air Navigation
Service Providers
T specified or changes to the proposed design may be required.
In the final stage, at the beginning of implementation of a
new system or a modification, the SSA poses the following
question. Does the system, as implemented, offer acceptable
levels of risk? This stage is designed to verify that past
assumptions remain valid before implementation gets under
way. Its measures are also designed to be applied throughout
the life of the system, to ensure that risks remain acceptable
until the system is decommissioned.
SAM is now being applied in practice by EUROCONTROL itself
and by many individual national Air Navigation Service Providers.
EUROCONTROL is using SAM for developing the required
safety assurance of EATM programmes according to
EUROCONTROL Safety Regulatory Requirement ESARR 4 – Risk
Assessment and Mitigation. ANSPs are as such benefiting from
a harmonised safety case that can be further used and
validated using the local conditions.
National service providers already using SAM, or an adapted
version of SAM tailored to suit their particular circumstances,
include those of Germany, Belgium, Sweden, Norway,
Denmark, Ireland, the Czech Republic, France, Slovakia,
Romania, Bulgaria, Italy, Portugal, Malta, Austria and
Switzerland. Anne Paylor’s article, ‘The perspective of ANSPs
on safety and risk management’, in section one, examines the
tools and programmes being implemented to enhance safety
in greater detail.
Several ANSPs have learned a number of lessons about the
practical application of SAM. “Usually nobody seems to have
a problem with the FHA phase – it’s a creative process to
identify hazards and that is always done well enough,” says
Patrick Mana the EUROCONTROL Safety Assessments
EUROCONTROL AND ACI EUROPE EXPERTISE: CONTRIBUTION TO IMPROVING AVIATION
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Co-ordinator. “The PSSA phase turns out to be much more
difficult because it is less systematic and we do not have
that many tools and guidelines yet. So we are trying hard to
find a more systematic approach.” The culminating System
Safety Assessment (SSA) is comparatively straightforward,
according to Mana: “It’s mostly covered by the software
tools we use.”
Mana is keen to make it clear that the SAM process does
not end with the System Safety Assessment at the time of
switching to operations. “We require every safety
assessment to be followed up periodically, typically every
year,” he says. “The experts should check whether all the
assumptions and results are still valid. Are there new
hazards? Have the probabilities changed?” ANSPs should
also have a formal safety monitoring and control process –
based mainly on incident reports but also on a regular
analysis of system performance data – as well as a system of
regular audits of operational units.
Patrick Mana also says, “Some parts of the methodology
are already very mature and some are still being developed,
but I think most of the work has been done and the first
elements of SAM have been applied very successfully.”
At this point he can see only one possible brake on
　
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