Aircraft Design Criteria Consideration

This article discusses the design criteria for aircraft body design, including the use of aluminum alloys and carbon fibre reinforced plastic composite. It also covers structural fatigue and adhesively and bonded repair methods.

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Aircraft design criteria consideration
1. Introduction
Aircraft body design is able to in-cooperate different materials. This ensures that the efficiency
and functionality of the aircrafts is enhances. Composites and metallic parts are widely used
during the design of the aircraft body. Safety considerations are highly considered when
choosing the ratio of the materials to be used for the body design. Aluminum alloys and carbon
fibre reinforced plastic composite are key materials which are used in design of the body of the
aircraft. The considerations for the areas where the different materials are used are able to help in
enhancing the safety of the aircraft. The structural elements of the aluminum based alloys are
enough to help in preventing some of the key accidents. About 61% of the airbus A380 body is
made of the aluminum alloys. The use of the aluminum alloys is important when considering the
structural weight and the corresponding loads which are experienced by the aircraft. The large
size of the airbus A380 needed a strong material in terms of the structural strength. The
aluminum alloy is one of the strongest metals in use and it was able to offer the structural
strength required to overcome the external loads which may hit the aircraft.
2. Design criteria
The aluminum alloys are able to offer the static structural performance which is needed when the
external loads such as the damages which may be caused by bird. Most importantly, the
aluminum alloys are able to offer the damage tolerance when used for the design of the different
parts. Therefore the choice of the aluminum alloys is one of the best structural design material
choices for the airbus A380 (Langewiesche, Drummond, & Hoopla digital, 2009). In addition,
the fracture toughness is another important consideration which the aluminum alloys is able to

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possess. This important aspect is able to prevent the aircraft body from abrasion when it comes
into contact with other loads while in flight. The fracture toughness is a key structural aspect
which was considered for the design of Airbus A380. This was an important aspect which was to
aid the prevention of accidents and scratching by external loads such as being hit by birds. The
choice of the aluminum alloy for the body was therefore a perfect choice in order to prevent such
accidents.
In addition, the size of the Airbus A380 was huge and this had to get a key consideration for the
weight reduction. Aluminum alloys were able to offer the key important aspect of weight
reduction while maintaining the structural strength which is needed to avoid key accidents. From
the previous version of Airbus A340-500/600, the aluminum alloys were able to proof to have
the key structural capacity to avoid the key external loads and maintain the required structural
strength needed (Blackwell, DeVault, Seamans, Lima, Baumhardt, & Fernández-Juricic, 2012 ).
The alloys were able to offer the perfect choice for the Airbus A380 to avoid such accidents and
increasing the fuel efficiency due to the weight reduction. The ribs were the main parts which
used the aluminum alloys to enhance the weight reduction and maintaining of the structural
strength. The high strength was highly needed on the lower wing stringers and the aluminum
alloys were able to provide the required strength.

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Composite materials are other important materials which have been used for the design of the
aircraft. The airbus A380 was able to implement the use of the composite materials. The carbon
fibre reinforced plastic composite is a key composite material which as implemented for the
airbus A380 (Alexander, 2009). The aircraft has been able to implement about 21% of the use of
the carbon fibre reinforced plastic composite. One of the key parts which has been able to
implement the use of the carbon fibre reinforced plastic composite is the central wing box. The
use of the carbon fibre reinforced plastic composite was able to enhance high weight saving and
reduction than when the aluminum alloys were used. About one and half tones were reduced
when the composite material was used (Deskiewicz, & Perz, 2017). This was able to enhance the
efficiency of the aircraft operations. Other important parts which were able to use the carbon
fibre reinforced plastic composite include the deck floor beams and the rear pressure blackhead.
The use of advanced manufacturing technologies for the carbon fibre reinforced plastic
composite are able to enhance the structural performance of the composites (Martinez-Val, &
Perez, 2009). Technologies such as Automated Fibre Placement, Resin Film Infusion, Resin

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Transfer Moulding and Automated Tape Laying are important technologies which were used for
the composite in Airbus A380. These technologies were able to offer the required technological
and structural advancement of the carbon fibre reinforced plastic composite while including key
cost saving mechanisms. Assembling cost, design of huge composite parts and increase of the
volume of the materials produced were some of the key advantages which the carbon fibre
reinforced plastic composite was able to offer to the Airbius A380. Therefore the choice of the
carbon fibre reinforced plastic composite was an important development which did not interfere
with the structural strength design of the Airbus A380 (Avrenli, & Dempsey, 2014). Considering
these facts, the accident cause could not be related or attributed to the use of the carbon fibre
reinforced plastic composite in the aircraft.
3. Structural fatigue
Structural fatigue is an important aspect in aircraft which is able to lead to prevention of key
corrosion cases which will enhance the abrasion when faced with external loads. Fatigue is

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described as a process where cracking is able to occur under the influence of repeated stressed.
The cyclic stresses are usually below the nominal yield strength of the materials which have been
used. The fatigue process is able to go through three key important stages. First, the initiation of
the fatigue is able to happen (Royal Aeronautical Society et al., 2009). This results from the
stress concentration which may due to material defects or even the design criteria. The
propagation of the fatigue crack is the next process which is able to happen. This is usually a
progressive growth of the available crack. Lastly, the sudden failure of the crack is able to
happen. The crack development is able to reach its critical and maximum size and the material is
unable to continue supporting the load imposed.
On December 2011, when Airbus A380 was being repaired after an engine explosion in
Singapore, failures were noticed which resulted from fatigue in fuel line pipe. Visual inspection
was ordered first to analyze the cracks development and causes (Igor, 2015). In addition, in the
examination of the fatigue, high frequency eddy current equipment was employed to aid the
detection of the non visual cracks on the aircraft. This is a key non-destructive evaluation
technique which is used to identify surface cracks. The method is important to ensure that the
structural integrity of the different parts is maintained (Beydoun, Voinov & Sugumaran, 2018).
Next, the quantitative analysis of the cracks due to the fatigue was carried out. This was to aid
the inspection and analysis of the fatigue behavior and nature of the cracks developed. The key
cracks which were investigated were analyzed include the hairline cracks around the fastened
holes. The second type of the cracks which were examined for the fatigue behavior analysis
includes the cracks at the edge of the vertical web of the feet. These are some of the key areas
where the fatigue is able to develop due to the imposed loads.

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The fatigues defects were able to develop on the key areas such as the feet and wind sections on
the Airbus A380. The development of these cracks was able to ensure that most of the airbus
aircrafts were recalled for analysis. EASA officials noted that thorough structural audit and
analysis of the cracks was needed to ensure that the structural failure of the parts does not occur.
EASA recommended on the analysis of the audit of the design mechanisms used for the different
parts (Islam, & Ekekwe, 2012). In addition, audit of the materials was required in order to ensure
that they are able to meet the required structural strength to overcome the external loads such as
the bird attacks. The fatigue also may result from improper distribution of the load of the aircraft.
EASA also offered recommendation on the analysis of the weight distribution to ensure that the
fatigue development issue is resolved. All there recommendations were offered in order to
mitigate the development of the fatigue cracks. Also, EASA official also offered a key repair
procedure which will mitigate any further development of the cracks due to fatigue.
4. Adhesively and bonded repair
Composite matrix has different properties which involves the combination of different properties
from different metals or composites. The composites are able to involve combination of different
materials which ensure that the properties are enhances. For the Airbus A380, use of the
composite materials was able to enhance the performance of the aircraft. Proper adhesive
combination is critical and highly needed when the repairs of the different parts which have
failed do happen (Komorowski, 2011). The use of Carbon fiber reinforced plastics (CFRPs) has
been implementing including the repairs of the parts which fail due to load fatigue. During the
repair of the parts, proper material bonding is required. This integrity of the repaired parts must
be maintained to ensure their failure does not happen. The analysis of the structural integrity of
the repaired part is important to enhance the performance of the aircraft. One of the key

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important characteristic of the carbon fiber reinforced plastics is the combined properties from
the different composite materials. This characteristic ensures that the repair material is able to
bond well with the carbon fiber reinforced plastics. At the end, the repaired part is able to offer
more structural integrity. The combined characteristics are able to enhance the structural parts of
the repair part and ensure that the structure is enhanced in terms of its strength (Türk, Einarsson,
Lecomte & Meboldt, 2018). High strength of the carbon fiber composites is able to ensure that
even after the repair; the structural integrity of the part is well maintained. The material is able to
enhance the operations of the part and able to combine well during the structural repair of the
material.
Most of the fatigue in the Airbus A380 was experienced in the joint sections. These are key areas
which are able to move and the load is able to stress the parts as they clad against each other. The
design criteria of the joint section had to consider the key movement and transfer of the loads
from one section to another. In the consideration, the transfer of the loads had to ensure that
stress from the loading does not stop at one end (Rokni Nutt, Widener, Crawford, & Champagne,
2018). This will at the end be able to cause differential fatigue of the part and lead to cracks
which may lead to failure. The Interference-fit were used to enhance the repair of the failure
section around the joint sections. This is the process through which the fastener holes are made
smaller than the fastener diameter. The offsetting of the tensile stress is experienced when the
Interference-fit are used. This is a key repair types which was used for the Airbus A380 process.
In addition, the use of this repair type is able to lead to an increase in the fatigue life of the repair
part. The Interference-fit process is able to ensure that less fatigue is induced in the joint sections
and thus improving the structural integrity of the parts. In addition, during the analysis, and
repair period, the use of Irwin’s stress intensity is important to identify the crack and the repair

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mechanism which needed. The area around the crack is identified and analyzed in this case for
the repair of the section. Stress component analysis is key to ensure that the base factor and
repair method being applied will enhance the structural integrity of the aircraft part.
In addition, implementation of repairs through joining the flange repair is a common practice
which ensures that the cracks are prevented from further development. The joined parts can be
enhanced through this method and enhancing the rib web. Geometrical consideration of the
different parts is important when using this method for repair (Mahajan, Murthy, Nanda, &
Gopinath, 2018). The integrity considerations are able to ensure that the parts are able to meet
the required important standard. The joined parts area and length are important parameters which
are considered during the repair process. During the repair, the use of chamfered washers is used
for the repair of the parts. Flange aperture effect and moment variations are able to consider the
fastener distances and crack development. These repair process are important and able to
enhance the operations and integrity of the attacked sections by the birds (Préau & Hubert,
2018). Most importantly, the design of the flanges and other important parts are able to enhance
the repair of the fracture parts due to fatigue. The stresses in the airbus A380 were reported to be
higher on several sections such as the corners of the rib feet. These sections were therefore able
to require more repairs in order to avoid the structural failure which may affect the structural
integrity of the aircraft parts.
Additionally, for the small cracks on the surface, use of metallic or carbon fiber composite
pitches is needed. This is a cost effective method which will ensure that the structural integrity is
preserved. Nevertheless, the cracks should be able to bear no structural effect on the aircraft even
when present for this method to be used to repair the surface (Augl & Naval Surface Weapons
Center Silver Spring Md, 2011). Most importantly, another key consideration which may be

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considered during the repair and the effect on the structural integrity is the place where the
cracks are able to appear. The main load bearing structure cracks will require more intense and
repair methods in order to enhance the structural integrity. The cracks on the Airbus A380 due to
the attack of the birds were not able to appear on the main load bearing body and therefore the
structural integrity of the cracks were not experienced.
5. Policies and procedures
After the attack of the births and repair and analysis of the situation, Airbus A380 had to come
up with the procedure in order to ensure the event does not follow the same process in future.
Several policies and procedures were developed in order to enhance the safety operations of the
aircrafts. First, the collaboration and structural investigation between Airbus and EASA was
improved (Meyers, 2012). The two were able to enhance the collaborative working to ensure that
the structural integrity of the body parts is improved. This collaboration is important in
enhancing the minimizing of the bird attack events. In addition, in order to improve the
operations of the aircraft, Airbus has introduced and analysis process where the aircraft is tested
for its integrity before it is released for a flight. The flawless operations on the different sections
of the jest such as on the electric, hydraulic, flight controls and body parts analysis is carried out.
The policy, which is known as “Iron Bird” is used to identify and rectify any defects which may
be found on the aircraft before the flight takes off (Tai-Ting, & Chang, 2017). This is part of the
care and maintenance programme which the Airbus Company has been able to introduce in order
to avoid any cases such as the bird attack.
In addition, use of key non-destructive testing is carried out to ensure events such as the bird
attacks does not interfere with the integrity and airworthiness of the aircrafts. The regulations
developed required that the materials used for the aircraft design have to go through and pass the

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test before they are allowed to use them in the design of the aircraft bodies (Zuniga, Mota &
Garc??a, 2016). Any defects can be therefore detected and the remedies be done before the
aircraft is allowed to fly. The regulation is done to ensure that the materials are able to [posses
the required structural strength regulation which will be able to overcome external loads such as
the birds attacks. The authority regulation requires that during the maintenance period, the
examination of the part be done to ensure that their structural integrity and airworthiness of the
body and aircraft parts is maintained. Depending on the nature of the assessment for the material,
both the metallic and composite materials analysis techniques can be applied (Dafa’Alla, 2016).
Magnetic, dye dependant methods, eddy current methods, ultrasonic method, thermography
methods and X-ray methods are some of the key methods which regulations are able to allow for
the analysis of the different parts.
In addition, the regulating authorizes have also introduced the structure health monitoring (SHM)
process for the aircrafts. This ensures that the state of the aircrafts is done from time to time (Air
Transport Research Society, 2009). The process is able to monitor the airworthiness of the
aircrafts and ensure that only the aircrafts which pass the monitoring tests are allowed to fly. The
SHM technology is able to ensure that the performance of the aircraft with time is monitored.
This helps to determine the airworthiness of the aircraft and recommend any defect regulating
mechanism required.

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In addition, in order to enhance the flight integrity and airworthiness of the aircrafts, the
regulating authorities have also introduced need of key documents from the manufacturers and
certificating authorities. These are used to ensure that the aircrafts are able to meet the required
threshold of integrity before they are released for their flight (In Cottier, & In Nadakavukaren,
2017). Some of the key documents which the regulations require include manufacturer’s
Maintenance Review Board (MRB) report, Certification Maintenance Requirements (CMR) and
Airworthiness Limitations Items (ALI).
6. Conclusion
Airworthiness and integrity of the aircrafts is maintained from the design stage of the aircrafts.
The choice of the materials has to meet the specify requirements which will enhance the safety
measure of the aircraft. The design procedures have to ensure that the materials used for the
different parts are able to meet the required structural strength to overcome external loads. In
addition, repair and bonding issues has to be considered well when repair are being done. This
ensures that the structural integrity of the parts is not compromised. The regulating authorities
have also developed key measures to ensure that the airworthiness and structural integrity of the

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aircrafts is maintained. Different policies and regulations have been developed to ensure that the
different characteristics are maintained.

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