One main task of ICAO’s Committee on Aviation Environmental
Protection (CAEP) is to identify and carry out analyses of
the future trends and various options available to limit or
reduce the current and future impact of international civil
aviation noise and emissions. The aim of these studies is
to assess the technical feasibility, the economic reasonableness,
and the environmental benefits, as well as the trade-offs
of the options considered. In doing so, CAEP has relied on
the use of a variety of computer-based simulation models and
databases offered by Member States and international organizations
that participate in CAEP.
Over the years, CAEP’s analytical role has progressively
expanded from basic assessment of standard-setting options
to include analyses of policy measures such as the balanced
approach to limit or reduce the impact of aircraft noise
and market-based options (i.e. noise and emissions charges
and emissions trading). As the need for a better informed
policy-making process grows, CAEP’s modelling requirements
in terms of coverage (i.e. noise, emissions, costs and benefits,
etc.) and accuracy increase.
To support the analyses for the eighth meeting of CAEP
in February 2010, a thorough evaluation of the proposed
models and databases was carried out. The goal of this evaluation
was to advise CAEP as to which tools are sufficiently robust,
rigorous, transparent, and appropriate for which analysis
(e.g., stringency, CNS/ATM, market-based measure), and to
understand any potential differences in modelling results.
Evaluation teams were established for each of the modelling
areas: noise, local air quality, greenhouse gas emissions,
and economics. A common methodology was developed to ensure
consistency in the model evaluation process across the four
modelling areas, which included a review of the key characteristics
of a robust model or database.
The models were then used to assess two sample problems:
the effects of reduced thrust takeoff, and the effects of
hypothetical NOx stringency. One of the goals of the sample
problems was to advance candidate model evaluation and development
by practicing on a set of problems that are similar to those
that were considered as part of the CAEP/8 work programme.
The practice analyses were accompanied by a rigorous assessment
process, so that the strengths and deficiencies in the models
could be identified, and appropriate refinements and improvements
implemented. This ensured that the models were sufficiently
well understood and robust to support a broad range of CAEP/8
for use by CAEP/8
Figure 1: Characteristics of a robust
model or database.
Each model and database has its strengths
and weaknesses, and the use of multiple models provided
CAEP insight into sensitivities of the results. Going forward,
the model evaluation process developed for CAEP/8 has established
a framework for the future evaluation of new models and
updates to the existing tools.
Of key importance is the fact that the input databases
were common to all of the models. This allowed, for the
first time, exploration of the interrelationships between
noise, local air quality, and greenhouse gas emissions.
As experience is gained investigating these interdependencies,
and as the models mature further, more advanced decision
making on aviation environmental protection will become