Aviation, like any other form of mass transport,
suffers from environmental issues aroused from its operations.

  Demand for air
transportation is constantly growing, adapting the present industry to meet the
market demand implies costs to be accepted by the society (noise, pollution,
climate change, etc). Improving aviation’s sustainability is the short-medium term goal to meet
long-term achievements making the industry even more sustainable and reliable. (Eurocontrol, 2017)

  Aviation’s sustainability is
met by constant studies and improvements along the whole industry through successful
collaborations and workshops to share a common vision between institutions for
more sustainable aviation. (Eurocontrol, 2017)

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  Environmental
Management System (EMS) is the most efficient method utilized by companies to meet
their environmental challenges. It is defined by the Transport of Canada as “…A systematic approach
for organizations to bring environmental considerations into decision making
and day-to-day operations. It also establishes a system for tracking, evaluating
and communicating environmental performance. An EMS helps ensure that major
environmental risks and liabilities are identified, minimized and managed. …” (ICAO, 2012)

  Analyzing each
opportunity to minimize negative impacts utilizing every resource available is
the key driven to understand and improving the industry, creating and operating
more efficient air transport management (ATM) systems, technology and
equipment. (Eurocontrol, 2017)

 

 

 

 

1.0   LOW-LEVEL ENVIRONMENTAL ISSUES FOR AVIATION

 

  The aviation
industry allows everyone to reach quickly almost every corner of the globe,
while also linking companies and their products into the global economy.
However, the demand should be weighted and implemented considering who live
near the airports and their rest and protection, people and local fauna. (BDL, 2015)

  Noise has been
along the years the principal environmental issue for low-level operations.
Noise creates adverse effects which are easily observed and documented on
airport’ proximities while
noise itself is difficult to be measured in all of its forms and effectively
cope with them. Documented effects on people are: sleep disturbance,
cardiovascular and psyco-physiological effects, etc. (Eurocontrol, 2017)

  Commercial
aircraft are subjected to a continuously tightened certification standards
adopted to protect airports surrounding areas. These certifications are stated
on the Civil Aviation Organization’s (ICAO’s) noise
certification standards (1971), applied on aircraft design and types when they
are first approved for operational use. (Eurocontrol, 2017)

  From the early
1990s, EMSs started to provide organizations with proactive, systematic an
approach for managing the environmental consequences derived by their
operations. Nowadays, the most commonly used framework is the one based on the
International Organization for Standardization’s (ISO’s) ISO
14001:2004 EMS standard. (ICAO, 2012)

 

 

 

 

 

 

ISO 14001:2004
Framework.

Figure 1. Source: (ICAO, 2012)

 

The elements constituting the model are:

 

·      Environmental policy: the
organization establishes environmental policies reflecting its vision and
framework for environmental management into it;

·      Planning: the organization
identifies how its operations are impacting the environment, setting
objectives, targets and programs to reduce it;

·      Implementation and operation: the organization
implements the systematic measures to manage the operations and lower the
environmental impacts along all levels and functions of its operations;

·      Checking: the organization assess
its performance and effectiveness of the management system;

·      Management review: adjustments
derived from the internal assessment of the implemented systematic measures,
these are focused on promoting continual improvement. The EMS itself moves in a
continual improvement cycle, providing to the company the possibility implement
and adapt its operations to the dynamic nature of the operations and external
conditions; and

·      Continual improvement: process by
which the company refines its EMS improving its environmental performance based
on feedback received through monitoring and assessment processes.

(ICAO, 2012)

 

  An example may
be found on the environmental initiatives of the Dallas/Fort Worth International
Airport (DFW), which launched an Airport-wide sustainability program in 2008,
designed to positively affect the environment, the community, the Airport and
its employees. The model focuses on innovative solution using modern
sustainable approaches and building standards for facility design,
construction, and maintenance. DFW’s environmental success earned the Airport membership in the U.S.
Environmental Protection Agency’s former
National Environmental Performance Track Program and the Texas Commission on
Environmental Quality’s Clean
Texas Platinum Award, recognizing the excellence on the environmental
leadership and performance.  (FAA, 2013)

 

 

 

 

 

 

 

 

Sustainability
indicators.

Figure 2. Source: (Dallas/Fort Worth International Airport, 2016)

 

 

 

 

 

2.0  UNDERSTANDING THE SOURCES OF NOISE

 

  Aircraft noise
is a major issue below 10,000ft, where is producing significant noise impact.
Evaluating the noise footprint is not easy since it’s not following a single model, basically it’s affected by weather
conditions, topography and other factors. (Eurocontrol, 2017)

  Noise levels evaluation
methods are standardized by the International Civil Aviation Organization
(ICAO) and globally agreed using standard computerized models simulating
aircraft performing airports operating procedures, such as the widely used “International Noise
Model”. These programs are
helpful to understand the noise footprint in each area around the airport
applying some variables, such as track dispersion, which are represented as
contours on a map. Commonly used are average weather conditions, which rarely
occur and so the noise contours are only indicative of a typical noise impact. (Eurocontrol, 2017)

  Community
noise has two main sources: airframe noise and engine noise. Airframe noise is
produced greatly by the airflow around the aircraft’s landing gear, and around high-lift devices such as
flaps and slats. The main sources of engine noise are the low-pressure (LP) fan
and the jet downstream. There is a factor of mixed flows, called installation
noise, which is the noise derived from the interaction between the engine’s jet downstream and
the main landing gears interacting with the components of the high-lift devices
on the wing (Aerospace & Defense
Technology, 2017)

 

 

 

 

 

 

Flow structure
visualization around the wind of an Embraer regional jet in high lift
configuration.

Figure 3. Source: (Aerospace & Defense Technology, 2017)

 

  The most
widely used unit for measuring noise levels is dB(A), the A-weighted scale in
decibels, which is the attempts to reflect human reaction to “loudness”. Other dB based measurement units are related
to aircraft, which is less relevant than the perceived impact on local
communities.

  The perceived noise (PNdB) and
effective perceived noise (EPNdb) scales reflect the various frequencies and
duration of noise patterns, resulting from various speeds and modes of
operation of aircraft. (Eurocontrol, 2017)

  The International Civil Aviation
Organization uses the EPNdB concerning its noise certification standards while
the European Community proposes “Lden” as the common unit for measure the
transport noise. The European Community unit is, day-evening-night level
(Lden), is based on Leg over a whole day considering a penalty of 10 dB(A) for
night time noise (22:00-07:00)
and an additional penalty of 5 dB(A) for evening noise (i.e. 19:00-23:00). (Eurocontrol, 2017)

 

 

 The noise level
can be categorized as:

·      Normal conversation 50-60 dB(A)

·      A loud ratio 65-75 dB(A)

·      A busy street 78-85 dB(A)

·      A heavy lorry about 7 meters away
95-100 dB(A)

·      A pig house at feeding time 110
dB(A)

·      A chain saw 115-120 dB(A)

·      A jet aircraft taking off 25 meters
away 140 dB(A)

(Eurocontrol, 2017)

  An increase in
passenger number doesn’t not
necessarily lead to an increased aircraft noise. New technologies allow modern
aircraft to be ever quitter and their noise footprint are significantly below
the permissible limits imposed by the authorities. (BDL, 2015)

3.0  AIRCRAFT STRUCTURAL AND OPERATIONAL
NOISE MANAGEMENT

 

  Aircraft
manufacturers face the necessity to adopt stringent standards for reducing
community noise.

  Over the past
20 years, wind tunnel and empirical methods were used even more to understand
the aerodynamics and the noise itself, this until the computerized era when
more noise sources and solutions were discovered and tested on various
software. (Aerospace & Defense
Technology, 2017)

  Aircraft
development methods based on engineering experience, past designs and flight
testing were not sufficient to meet actual and future targets on noise
abatement and reduction. Computerized software, such as Computational Fluid
Dynamics (CFD) based on the Reynolds-averaged Navier-Stokes (RANS) methods,
have revolutionized aerodynamics engineering helping on coping the noise issue. (Aerospace
& Defense Technology, 2017)

  The greatest
challenge of the new computer technology was representing all the parts and
variables at high fidelity in a simulated model, from the smallest part to the
whole aircraft and the interactions among all the components. This was the
challenging task along the years for the traditional RANS-based CFD model.

  Accurate
predictions shown that even small parts geometry details ca be significant
noise contributors. (Aerospace & Defense
Technology, 2017)

 

Flow structures around
the nose landing gear of a business jet, highlighting the main noise sources.

Figure 4. Source: (Aerospace & Defense Technology, 2017)

 

 

 

 

 

 

5.0  NOISE REDUCTION INITIATIVES.

 

  The best way to reduce the noise pollution is
solving the problem at the source, on the airplane and engines design. Along
the years many improvements were made on engine technology, having a reduction
of over 25 decibels since the introduction of jet engines (corresponding to an
80% noise reduction). Concerning the aircraft design, most of the aviation
industry design was crystalized till the adoption of composites and more
advanced designs. (Vetterlein, 2017)

  In February 2014 Lufthansa became the first
company in the world to take delivery of an Airbus A320 equipped with vortex
generators. A total of 157 aircraft in the present fleet will be equipped with
the advanced technology noise-reducing component allowing quitter operations. (Lufthansa Group, 2017)

  The Vortex Generator consist in a small metal
device placed in front of metal cavities that modifies the airflow reducing the
approach noise from 2 dBs to 6 dBs. (LAX Community Noise Roundtable,
2016)

Principle of vortex generator.

Figure 5. Source: (BDL, 2015)

  Many researches had been financed from
worldwide governments and institutions like the European union with the Clean
Sky project, a financial support aimed to improving the noise abetment and
prevention. Companies such as Airbus and Saab are developing a ten-meter long
wing tip which is aerodynamically more efficient with significantly reduced air
resistance leading to a reduction in noise emissions. (Vetterlein, 2017)

  NASA is testing a new solution on engine
noise reduction utilizing acoustic liners installed around the turbofan rotor,
a complex study to analyze and discover the most efficient installment of this
technology (Heidman, 2017)

  Another NASA research is focused on the
airframe noise reduction, studying innovative trailing edge flap device capable
to reduce noise without compromising cruise efficiency or landing lift and
stall characteristics, this technology is calles FLEXSEL (flexible side edge
link).

  The demonstrated benefits are reduced noise
at landing without compromising cruise or high-lift aerodynamics and marginal
weight penalty. (NASA, 2017)

 

FLEXSEL-Integrated Airframe in Deployes
Configuration. Image credit: NASA Langley.

Figure 6. Source: (NASA, 2017)

 

  The International Civil Aviation Organization
(ICAO) has always been the biggest promoter of airplane progress, financing and
studying possible projects and alternatives.

  The 33rd ICAO Assembly adopted the
Resolution A33/7 introducing the concept of a “balanced approach” to noise
management, establishing guide lines on approach paths and operations. The “balanced approach concept”, also known as continuous descend approach, found on
ICAO’s Doc 9829, is made by four principal elements like reduction of aircraft noise at
source, land-use planning and management measures, noise abetment operational
procedures, and operating restrictions. (Eurocontrol, 2017)

 The European Union incorporated the Balanced
Approach into its legislation as Directive EU EC/2002/30. (Eurocontrol, 2017)

 

  Other commonly applied noise management
measures include:

·      Drawing noise abetment routes on a
map that avoid residential areas as much as possible,

·      Avoid overflying sensitive locations
like hospitals of schools;

·      Ensuring that the optimum runway(s)
and routes are used;

·      Flying continuous descent approaches
and departure associated with noise abetment technique;

·      Avoiding over usage of the auxiliary
power unit (APU) when at the stand;

·      Building barriers and specified
engine test-pens to contain and deflect the noise around the airports;

·      Towing aircraft instead of taxying
with own power;

·      Reducing night operations;

·      Manage and limiting operations on
critical noise contour areas;

·      Providing noise insulation for
houses located in the critical areas or severely affected;

·      Charging different fees in respect
of the noisiness of the aircraft listed on the certification data card;

·      Monitoring all the areas concerning
noise levels and penalizing any breach.

(Eurocontrol, 2017)

Continuous
descent approach reduces aircraft noise.

Figure 7.
Source: (German air traffic control, 2015)

6.0  CONCLUSIONS

 

  An increase in passengers and air movements
don’t necessarily lead to an increase in
aircraft noise. The devotement of new managerial solutions based on previous experience
and implemented by advanced software allow to better predict and reduce noise
pollution.

  Modern aircraft are becoming ever quitter setting
their noise emission well below the permissible limits imposed by the authorities.
(BDL, 2015)

  ICAO policy concerning aircraft noise, ICAO
Doc 9829, contains the details on all the elements employable to achieve noise
reduction, Balanced Approach to Aircraft Noise Management.

  The final aim is to identify the
noise-related measures to achieve the maximum environmental benefit and most
cost-effective using objective and measurable criteria. (Eurocontrol, 2017)

  EMS will be the key driven for the next
generation improvements along the aviation industry to make a greener sky while
expanding the global service. Targeting to the weaknesses and opportunities
creating an efficient industry able to be quitter and even more reliable. (ICAO, 2012)

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