Optimized fuel values for emission reduction

Aviation is an integral and vital part of modern society. The growth over the last decades has consequences for greenhouse gas emissions and reducing this through efficiency within the same framework is difficult. Precision flight planning is crucial for reliably and optimized real environment aircraft operation. The presented study gives an overview of the status of the legal requirements for flight planning under the current fuel requirements of the European Union Aviation Safety Agency (EASA) and the emerging opportunities for fuel savings. As part of the larger study, planned and actual fuel figures of an international cargo airline were statistically analyzed. The overall analysis showed that there was no significant deviation between planned and consumed fuel. Based on the results, an adjustment of the planned alternative fuel quantity can be considered within the framework of an individual fuel plan. The possible savings potential using the example of Destination Alternate Airport fuel is presented.


Introduction
In the 100 or so years since the first powered flight, the aviation industry has experienced rapid growth [1].Fuel needed to operate thousands of flights worldwide every day is one of the most important cost factors in the airlines' business.According to the International Air Transport Association (IATA) report on the economic performance of the airline industry, global fuel costs were predicted to be $206 billion in 2019, later estimated to be around $188 billion in the 2019 end-of-year report.For 2020, the same report predicted fuel costs to fall to $182 billion, equivalent to 22.1% of average operating costs [2]. Figure 1 shows a corresponding chart by Airbus [3].
Aviation emissions have a climate impact, which came more and more into focus.In 2020 almost every commercially used aircraft still has a propulsion system based on fossil fuels.Emissions from aircraft are greenhouse gases and noise.Fuel costs are therefor not the only driver for reducing the amount of fuel consumed.In recent years, the impact on the environment has become more and more important.The high traffic volume is associated with an enormous demand for aviation fuel and the associated high emissions on the other side.Lee et al. provide an overview of CO 2 and other related emissions and impacts of aviation on the climate [4], likewise Fleming and Ziegler [5] and Filippone [6] -to name just a few examples.Reducing the effects of global warming due to emissions has become a goal.As a result, reducing emissions has become an important issue.The commercial aviation industry has already developed and implemented many techniques to reduce fuel consumption for reasons of economy and efficiency.On the operator side, these are mostly operational improvements, such as reducing the weight of on-board equipment or using a fixed ground power supply instead of the aircraft's auxiliary power unit on the ground.Airlines are searching fuel-efficient routes or flight profiles for most of the time.Measures to reduce noise and pollution are taken by airlines, airports and air navigation service providers in their daily operations [7].
Regulators to reflect the development of emission reduction and fuel saving.ICAO published Doc 10013 -Operational Opportunities to Reduce Fuel Burn and Emissions.It supposes the most effective way to minimize emissions: via the amount of fuel used [8].For a given route fuel burn depends, if environmental aspects like weather or routing are said to be the same, on the weight of an aircraft.Specific range, flying at given altitude, temperature and speed, depends on aircraft mass.It is the physics of flight, that for an aircraft to fly it must generate lift to overcome its weight.The generation of the required lift and the movement of the airframe through the air create drag.The engines generate the necessary thrust to overcome this drag and enable the movement to generate lift (figure 2).The heavier the aircraft, the higher the fuel consumption.Fuel consumption, for carrying extra weight or extra fuel, is called Fuel Carriage Penalty (FCP).EASA gives a value of about 3 % difference in fuel consumption per kg and flight hour for additional weight [9].ICAO Doc 10013 gives a value of 2.5 -4.5 % additional fuel consumption, depending on the characteristics of the aircraft [8].In addition, fuel savings can be made during climb since the lighter aircraft would reach it's optimal flight level earlier [10].
To minimize fuel burn it is most economical to carry the minimum required fuel for the sector.
New regulations will also be applied in the area of European regulations in 2022.EASA Figure 2. Elementary forces on an airframe [10].
published Notice of Proposed Amendment (NPA) 2016-06, which follows a performance-based approach by updating the regulatory requirements for fuel planning, selection of aerodromes and in-flight fuel management, thus aims to increase operational efficiency and to have cost and environmental benefits [9].This proposal to amend the regulations was followed by ...to ensure that every flight carries sufficient fuel for the planned operation and reserves to cover deviations therefrom [12].
The fuel policy is transferred to the so-called Fuel Schemes.The consequences are illustrated below with the use of an example.

Methods
Fuel data of an operating airline were examined to explore a statistical background.The airline utilizes Boeing B777-200 aircraft in a freighter version.The operated network contains large airports, together with some local airports.The network destinations result in a mix of short, medium and long-haul flights.Planning and actual consumption were also evaluated.Here, two periods were considered in two steps: a five-year period covering all flights operated and a one-year period for extremely long long-haul flights with high loads.
In order to use the optimization possibilities in the area of fuel planning, which would be possible from 30 th October 2022, the corresponding prerequisites must be met.The GM2 to CAT.OP.MPA.180 of Regulation (EU) 965/2012 shows a non-exhaustive list of safety performance indicators (SPI) that can be used to measure safety performance [13].This served as the reference point for the statistical fuel data evaluation.
In order to illustrate the possible optimisations, using the example of alternate fuel, the legal situation up to 30 th October and thereafter is compared below.
CAT.OP.MPA.150Fuel policy, which will be omitted in the future, requires: ...(c) The operator shall ensure that the pre-flight calculation of usable fuel required for a flight includes: ...
(3) reserve fuel consisting of: ... (ii) alternate fuel, if a destination alternate aerodrome is required ... [14] Additional information on compliance with the implementing rules can be found in the Acceptable Means of Compliance (AMC).AMCs are non-binding standards adopted by EASA to illustrate means of determining compliance.Furthermore, there is Guidance Material (GM), as non-binding material for explanation and interpretation.So, in AMC1 CAT.OP.MPA.150further explanations are given, regarding the content of the fuel policy: ... ( 4) Alternate fuel, which should: (i) include: 4 (A) fuel for a missed approach from the applicable DA/H or MDA/H at the destination aerodrome to missed approach altitude, taking into account the complete missed approach procedure; (B) fuel for climb from missed approach altitude to cruising level/altitude, taking into account the expected departure routing; (C) fuel for cruise from top of climb to top of descent, taking into account the expected routing; (D) fuel for descent from top of descent to the point where the approach is initiated, taking into account the expected arrival procedure; and (E) fuel for executing an approach and landing at the destination alternate aerodrome;... [14] Figure 3, figure 4 and figure 5 illustrate the possible consequences of the regulatory changes and optimisation options.
Figure 3 shows the missed approach procedure for Runway 26L of the instrument approach for Leipzig Airport (EDDP).In the event of a missed approach, the blue dashed path should be flown, highlighted in green.The corresponding description of the instrument flight procedure   [15].can be found in figure 4. As can be seen above, according to the current requirements, the complete missed approach must be taken into account in the planning -here this is approx.45 -50 nautical miles, or approx.12 minutes flying time, to the start of the new approach.
In practice, however, it must be taken into account that, in the event of a missed approach, radar guidance is usually quick and the entire track is not usually flown.In only a few cases does a missed approach occur at all.In the case of a missed approach to the destination alternate airport, this airport may be located in a completely different direction, so that the aircraft would fly directly in this direction after a missed approach.Figure 5 shows an example of such planning.Here, the approach to Leipzig is planned in a westerly direction.The alternate airport is also in a westerly direction, it is Erfurt (EDDE).Unless a new approach is attempted in Leipzig, the direct route to Erfurt will certainly be chosen Figure 5. Erfurt as Alternate Airport [16].
without flying the entire missed approach.For these three reasons (infrequent need for a missed approach, often shorter route in the case of a second approach, and a more direct route in the case of a diversion under certain circumstances), a reduction of the fuel required in the planning can be considered.The regulatory basis is presented next.
As mentioned above, the fuel policy will be converted into a fuel scheme.The requirements for this can be found in CAT.OP.MPA.180Fuel/energy scheme -aeroplanes.
(a) The operator shall establish, implement, and maintain a fuel/energy scheme that: (1) is appropriate for the type(s) of operation performed; (2) corresponds to the capability of the operator to support its implementation; and (3) is either: (i) a basic fuel/energy scheme, which shall form the basis for a basic fuel/energy scheme with variations and an individual fuel/energy scheme; the basic fuel/energy scheme derives from a large-scale analysis of safety and operational data from previous performance and experience of the industry, applying scientific principles; the basic fuel/energy scheme shall ensure, in this order, a safe, effective, and efficient operation of the aircraft; or (ii) a basic fuel/energy scheme with variations, which is a basic fuel/energy scheme where the analysis referred to in point (i) is used to establish a variation to the basic fuel/energy scheme that ensures, in this order, a safe, effective, and efficient operation of the aircraft; or (iii) an individual fuel/energy scheme, which derives from a comparative analysis of the operator's safety and operational data, applying scientific principles; the analysis is used to establish a fuel/energy scheme with a higher or equivalent level of safety to that of the basic fuel/energy scheme that ensures, in this order, a safe, effective, and efficient operation of the aircraft.
In the associated GM1 to CAT.OP.MPA.180explanations are given on the AMC to be applied.In principle, an operator may choose between three different fuel schemes.The following AMCs apply to the development of each fuel scheme: (a) Basic fuel scheme: all the AMC that apply to the basic fuel scheme.(b) Basic fuel scheme with variations: when an operator decides to deviate fully or partly from the basic fuel schemes, the AMC for basic fuel schemes with variations apply to the specific deviation.(c) Individual fuel scheme: when an operator wishes to apply an individual fuel scheme, the AMC for the individual fuel scheme apply; for the part of the scheme where the operator still follows the basic fuel scheme, the operator should apply the AMC referred to in (a) and (b) [14].
Depending on the chosen level of the scheme, different AMCs, if any, are applied.As previously in CAT.OP.MPA.150, in future in CAT.OP.MPA.181Fuel/energy schemefuel/energy planning and inflight re-planning policy -aeroplanes the requirements for the destination alternate fuel are listed: (4) destination alternate fuel/energy: (i) when a flight is operated with at least one destination alternate aerodrome, it shall be the amount of fuel/energy required to fly from the destination aerodrome to the destination alternate aerodrome; or... [14] However, the supplementary AMC1 to CAT.OP.MPA.181only refers to the basic fuel scheme for Performance Class A aeroplanes.Performance Class A refers to multi-engine aircraft powered by turbojet or turboprop engines that can carry more than nine passengers or weigh more than IOP Publishing doi:10.1088/1755-1315/1254/1/0121397 5 700 kilograms.In terms of content, the requirements in point (d) corresponds in principle to AMC1 of CAT.OP.MP.150 (see above).However, if companies choose a basic fuel scheme with variations or an individual fuel scheme, the AMC is not applicable.As a consequence, consideration could be given, for example, to reduce the amount of alternative fuel, e. g. based on statistical experience.This can result in savings, which are presented below.
The examples shown below are based on statistical fuel data from a globally operating cargo airline.Boeing 777 freighter aircraft are used.For the statistical evaluation, various information was provided via the reporting system.Numerous information can be condensed from the reports.Over a period of five years, for which the data were available, the following points were especially found: • 187 flights, equals 0.59% of 31 315 flights, where planned with no alternate (fuel), • six flights, out of 39 467 flights, could be identified as have to be diverted, which gives a diversion rate of 0.015%.
This information shows the rare event of landing at the alternate airport and the equally rare legal possibility of planning without an alternate airport (where additional fuel must be planned for 15 minutes of flight time).As shown above, when using a basic fuel scheme with variations or an individual fuel scheme, the AMC1 to CAT.OP.MPA.181 is not necessarily applicable.Airlines could, based on statistical data and a corresponding risk assessment, make a reduction in the planned alternate fuel compared to the current planning/requirement.
In the following it is assumed that a reduction of the alternative fuel by 5 minutes is possible.This corresponds to a value of approx.700 kg of fuel for a Boeing 777-200 freighter examined.This value can be derived from the final reserve fuel plan -which provides for 30 minutes of flight time at 1500 feet above the airfield.In figure 6 and figure 7 an excerpt from the operational flight plan is presented, in particular the fuel planning and the mass and loading.Figure 6 shows the comparison of fuel planning for a flight from Hong Kong to Leipzig.Since the current approved planning program does not allow a reduction of the alternate fuel, the value of 5 minutes of fuel was included as additional fuel, for comparison.On the left is the original plan, on the right the plan with 5 minutes more fuel.
The values for alternate and final reserve fuel shown in figure 6 do not correspond to those that would result from an actual reduction of the alternate fuel by 5 minutes.The 700 kg / 5 minutes in the right column only affects trip and contingency fuel, but not per legal requirements needed alternate and final reserve fuel.With a real alternate fuel reduction, these values would also be lower and would lead to a more significant reduction in trip and contingency fuel.Therefore, the resulting delta, in this case an additional consumption of 257 kg, is lower than the actual savings would be.This would be possible in the case of alternate fuel reduction.But the trend and thus a rough figure for evaluation is evident.The average additional consumption for this route is 21.34 kg/flight hour, i.e. this would be the savings potential.In the lower part, the corresponding weight information is also listed as a comparison.As can be seen, 700 kg of extra fuel led to a reduction of the maximum possible load from 1 548 kg before to 589 kg after.Here too, a reduction of the alternate fuel would be correspondingly positive.Figure 7 shows the same considerations for the route Hong-Kong to Cincinnati.Here, the difference in fuel, i.e. the savings potential, is 364 kilograms.The average additional consumption for this route is 25.1 kg/flight hour, i.e. this would be the savings potential in this case.
Both examples show the savings opportunities.A single aircraft, with an average flight time of 15 hours, would consume something like 300 kg less fuel per day.Even if these savings seem small, already with a relatively small fleet of only 20 aircraft, the total value is correspondingly high.A conservative projection of 20 kg/flight hour and 15 hours flight time per day with twenty aircraft results in potentially 6 000 kg fuel saving per day.The associated savings in emissions of carbon dioxide are ∼18 900 kg, water ∼7 500 kg and 30 to 150 kg nitrogen oxides per day  -for a fleet of 20 aircraft.These figures are based on the indication that carbon dioxide and water vapor are the most abundant products of jet fuel combustion, with emission indices for CO2 and H2O of 3.15 kg/kg fuel and 1.26 kg/kg fuel burned [17].These considerations are conservative and do not consider all the other advantages of a lighter aircraft.The values of IOP Publishing doi:10.1088/1755-1315/1254/1/0121399 21 -25 kg of additional fuel consumption determined above correspond to a fuel penalty factor of approx.3%.In the further consideration of the savings effects, the savings of the 5-minute fuel weight (here 700 kg for 5 minutes) and the additional consumption added up per flight hour must also be considered as freight delta cumulatively.For the two flights examined above, this results in approx. 1 000 kg difference for freight at take-off.

Results
As part of an overarching study, statistical flight data of an airline were analysed over a period of five years.In the first step, information on individual fuel components was examined.In the second step, long flights with high freight volumes were examined in more detail with regard to planning and actual consumption.Analysis of the fuel data has shown that consumption in planning and in practice is at a high and reliable level.As a result of this evaluation, an approach to reducing the alternative fuel consumption is possible.This is based on changes in the underlying operational regulations.
A reduction of fuel has an impact on overall fuel and emission reduction.On this basis, it is recommended that airline operators may evaluate their operational procedures, managementand safety system in preparation of the implementation of a choose a basic fuel scheme with variations or an individual fuel scheme.This allows the planning of lower fuel quantities, reducing emissions.
Evaluation in Piano-x and further reduction of other fuel values possible.Figure 8 shows almost no difference for an single flight, in the end the results are quit clearly, seen over a year.

Discussion
The above proposal is the starting point for consideration.Improved risk assessment, calculations based on better data and better decision-making can optimise the amount of additional fuel needed without compromising safety levels.Aviation remains committed to progress towards climate-neutral aviation by 2050 [18].New concepts are also necessary for this.Further research is needed to identify safety and performance indicators.An in deep evaluation of planning and used alternate fuel figures is recommended.Reducing the fuel components can

Figure 8 .
Figure 8. Impact of 5 minutes of fuel.