A parametric study of the instantaneous radiative impact of contrails is presented using three different radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm−2 daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net effect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover.

On the Radiative Forcing by Contrails

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The Art Of The Long View

EU ETS versus CORSIA – A critical assessment of two approaches to limit air transport's CO2 emissions by market-based measures

Aviation is an important contributor to the global economy, satisfying society’s mobility needs. It contributes to climate change through CO2 and non-CO2 effects, including contrail-cirrus and ozone formation. There is currently significant interest in policies, regulations and research aiming to reduce aviation’s climate impact. Here we model the effect of these measures on global warming and perform a bottom-up analysis of potential technical improvements, challenging the assumptions of the targets for the sector with a number of scenarios up to 2100. We show that although the emissions targets for aviation are in line with the overall goals of the Paris Agreement, there is a high likelihood that the climate impact of aviation will not meet these goals. Our assessment includes feasible technological advancements and the availability of sustainable aviation fuels. This conclusion is robust for several COVID-19 recovery scenarios, including changes in travel behaviour.

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Evaluating the climate impact of aviation emission scenarios towards the Paris agreement including COVID-19 effects.

Mitigating the Climate Impact from Aviation: Achievements and Results of the DLR WeCare Project

Estimating the direct operating costs (DOC) is a common way to assess new technologies and aircraft designs. In aircraft technology assessment, a variety of DOC methods (i.e. sets of equations relating known aircraft parameters with operating costs) find their application, yet the explanation of choice is usually omitted. Alternatively, life cycle based models can be used, which incorporate the technologys' impact throughout all life phases. However, their usage is less common. The objective of this paper is to analyze the effort and effectiveness of DOC methods compared to the life cycle cost-benefit model developed by DLR. To do so, the first part of the paper deals with the differences of selected DOC models applied on hybrid laminar flow control (HLFC) as a use case. Effort and extent are investigated and sensitivities regarding key parameters (i.e. fuel price and system mass change) are analyzed. In the second part, the life cycle based model is presented and applied on the same aircraft to assess HLFC. After the results in terms of Net Present Value and Internal Rate of Return, the impact on total operating costs as well as on line and base maintenance are shown. Furthermore, sensitivity studies regarding uncertainties are performed, which give a full picture of the economical impact to be expected by applying laminar flow control. While all models yield an economical benefit, the different DOC methods show considerable variations in their results. The life cycle based method requires more detailed information, but provide a detailed breakdown of the economic impact of HLFC.

Comparison of Direct Operating Cost and Life Cycle Cost-Benefit Methods in Aircraft Technology Assessment

In order to reduce operating costs and increase the operational stability, the aviation industry is continuously introducing digital technologies to automate the state detection of their assets and derive maintenance decisions Thus, many industry efforts and research activities have focused on an early state fault detection and the prediction of system failures Since research has mainly been limited to the calculation of remaining useful lifetimes (RUL) and has neglected the impact on surrounding processes, changes on the objectives of the involved stakeholders, resulting from these technologies, have hardly been addressed in existing work However, to comprehensibly evaluate the potential of a fault diagnosis and failure prognosis system, including its effects on adjacent maintenance processes, the condition monitoring system’s maturity level needs to be taken into account, expressed for example through the technology’s automation degree or the prognostic horizon (PH) for reliable failure projections In this paper, we present key features of an automatic condition monitoring architecture for the example of a Tire Pressure Indication System (TPIS) Furthermore, we develop a prescriptive maintenance strategy by modeling the involved stakeholders of aircraft and line maintenance operations with their functional dependencies Subsequently, we estimate the expected implications for a small aircraft fleet with the introduction of such a monitoring system with various levels of technological maturity Additionally, we calculate the maintenance cost savings potential for different measurement strategies and compare these results to the current state-of-the-art maintenance approach To estimate the effects of implementing an automated condition monitoring system, we use a discrete-event, agentbased simulation setup with an exemplary flight schedule and a simulated time span of 30 calendar days The obtained results allow a comprehensive estimation of the maintenance related implications on airline operation and provide key aspects in the development of an airline’s prescriptive maintenance strategy

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Concept and Economic Evaluation of Prescriptive Maintenance Strategies for an Automated Condition Monitoring System

Current practices for investment and technology decision making in aeronautics largely rely on regression-based cost estimation methods. Although quick to implement and easy to use, they suffer from a variety of limitations, both in temporal space and scope of applicability. While recent research and development in this area addresses these to a certain extent, aerospace engineering still lacks a flexible and customizable valuation framework. To this end, a generic environment for economic and operational assessment of aircraft and related products named LYFE is presented. This tool employs a discrete event simulation which models the product life cycle from its order through decades of operation and maintenance until disposal. This paper introduces its key characteristics and default methods alongside its modular program architecture. The capabilities are demonstrated with a case study of on-wing engine cleaning procedures which are triggered by a customized decision making module. Thereby, the impact on engine health, fuel efficiency and overall economic viability is quantified. On the whole, the framework introduced in this paper can be used to analyze not only physical products but also operational procedures and maintenance strategies as well as specified decision making algorithms in terms of their impact on an aircraft’s or system’s life cycle.

A Modular Framework for the Life Cycle Based Evaluation of Aircraft Technologies, Maintenance Strategies, and Operational Decision Making Using Discrete Event Simulation

Introducing variance-based global sensitivity analysis for uncertainty enabled operational and economic aircraft technology assessment

This paper demonstrates the evaluation of a future aircraft concept equipped with natural laminar fow technology (NLF) based on airline network design and fleet assignment
NLF leads to higher fuel efficiency compared to existing state-of-the-art short-to-medium haul aircraft The evaluation approach based on network modeling allows to capture net-
work e�ffects such as fleet utilization Network eff�ects are not captured by a cost bene�fit analysis applied to standard flight missions In this study networks are designed for different air transportation scenarios, whereas the flight schedule of an existing European low-cost carrier serves as candidate flight list Fleet assignment is solved simultaneously by considering a baseline aircraft and the future aircraft concept as candidate fleets The resulting networks are evaluated with respect to global network pro�tability, fuel consumption and fleet composition Results reveal a signi�cant impact of the natural laminar flow performance on fleet deployment and network contribution of the future concept Further, results indicate turn-around time to be an important driver for fleet deployment caused by network e�ffects

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Kai Wicke

Papers

Comparison of Direct Operating Cost and Life Cycle Cost-Benefit Methods in Aircraft Technology Assessment

Concept and Economic Evaluation of Prescriptive Maintenance Strategies for an Automated Condition Monitoring System

A Modular Framework for the Life Cycle Based Evaluation of Aircraft Technologies, Maintenance Strategies, and Operational Decision Making Using Discrete Event Simulation

Introducing variance-based global sensitivity analysis for uncertainty enabled operational and economic aircraft technology assessment

Analysis of Natural Laminar Flow Aircraft based on Airline Network Design and Fleet Assignment