Meet Marius Krömer

Marius Krömer is currently finishing his PhD program at the University of Mannheim in Germany. He is the chairman of the local chapter Rhein-Neckar of the association “bdvb” and engages in the society through participating in a leadership role of the local fire department. In our interview with him, we had the chance to get to know his motivation for starting a PhD and his experience in academia. Through his valuable experience he encourages students who are considering a path in academia to use the freedom that this path offers and do not fear transitioning paths. 

Thank you Marius for taking time for us, we are very excited to write an article about you and your curriculum. We think that your curriculum and advice will be very valuable for a lot of students and other readers.   

Let us start with the experience that you already had in the industry. We saw that during your studies you already had three internships. Which of those did you like the most and which experiences were most valuable for you?  

This is an interesting question for the start, as this was at a time, which was before I even knew that I would be a PhD student. Out of my three internships, I most liked the one with Porsche Consulting. The reason for this is that I had an interesting role in a change management project in the maintenance hangar of a British airline. This project also involved me going to Great Britain from Monday morning till Thursday each week of my internship. We usually left from the airport directly to the client hangar and then in the evening to the hotel, in which we stayed the three nights. Through this experience, I was not only able to get involved in the work content of a consultant but also grasp the lifestyle of a consultant. I really appreciate that Porsche saw the value in bringing me to the client facilities. The project itself taught me how hard it is to implement change in a big operational division, in which there may be a lot of people that oppose or hinder change in the first place. 

Thank you for this insight. Could you give us a deeper view into the change management project for the British airline that you were part of during your internship? 

The big airline had some maintenance departments in their operations division; the division we focused on worked on small routine checks and unexpected damages which needed to be fixed quickly. Therefore they needed to be quick to return the aircraft back to service and their specific problem was that the airplanes often have not been delivered back on time. With a wrong prediction about when the airplane would be back in operation after the maintenance, the following flights could not start on time and were delayed. As you can imagine, canceling a big aircrafts flight is quite expensive (up to 500.000 Euros) due to  passenger rebooking and penalties. Therefore each event, in which such a cancellation happened, was really harmful for the company. The change management project, which I worked on, had the goal to make the planning of the maintenance hangar more reliable, in order to make sure that the flight operations department could make better decisions about the availability of a specific aircraft. The project involved for example the standardization of the typical maintenance work. When engines are changed for an aircraft, some of the aircraft maintenance engineers had their own way to do it. As they worked in different shifts, usually each manager had to first spend two or three hours to figure out what had been done by the previous engineers before continuing the work. Therefore, the aim was to standardize the process in order to make the maintenance operation run more smoothly even when shifts change.  

It is really impressive that you already had the chance to get hands-on experience in such an interesting project during your internship. Through our research we stumbled on your interest in airplanes and flying, did this work experience contribute to it or has it been there before? How did it develop?  

My interest in aviation has already accompanied me for quite some time. After school I wanted to become a pilot and already was in the application process for Lufthansa. Unfortunately, they did not take me back then, so I would have had to finance the pilot training on my own. At that time, I just started studying and this was also very attractive for me. Nonetheless, during my studies I always tried to make a connection to aviation, through the thesis that I wrote and the internships I chose.  

How do you outlive this passion now? Have you somehow followed your interest in flying?  

Yes, during my PhD I had quite a lot of freedom in scheduling my week, as you do not have so many fixed appointments as in working in a corporation. I shifted my daily work more to the evening and attended some flight training during the day. I finished my private flying license. Looking back to my experience, this is an advantage of doing a PhD if you do not only want to focus on your research but can also make use of the flexibility of your time.  

Having had experience abroad at other universities, what made you chose pursuing your PhD at the University of Mannheim? 

During my master I was already a student assistant for my current chair. This allowed me to understand a bit better which kind of work the people were doing there and which requirements there are. At the time that I was halfway through my master, I asked myself what do I want to do next and what are the typical next steps that I could seek. Due to the work at the chair, I saw that there are people continuing and doing their Research. “Would that be something for me?” I asked myself and reviewed my qualifications for pursuing a PhD. I acknowledged that I really liked working in the environment of the chair and would be interested in continuing my work with my Supervisor, Professor Schön.  

Would you recommend working as a student assistant before deciding to pursue a PhD? 

Yes, definitely. There are different kinds of jobs available for students; some are more tutoring-focused, some related to research support or even administrative support. In any way it is good to get to know the people from the chair and what they are working on and how it is like to work with the corresponding supervisor.  

Reflecting on your previous experiences and on yourself could you give us an outlook if you consider continuing your Research or are you considering getting some industry experience? 

My decision for the next step is looking for an industry job. There are several reasons for this decision. On the one hand there are very few jobs in academia. It is very competitive to get a job among all of those very smart people, as for example the Post- Doc and Junior Professor positions are very scarce. In order to get a job, you do not only have to show that you are quite smart, but also that you are quite focused on your research. This requires a lot of time as it is a competition among your peers about who does the best research. Personally, I did not always make the decision that I invest all my available time in my research; even though I still spend long nights at the office frequently. Right now, I notice that for the jobs that are available in academia, there are people that are more qualified than I am.

 I rather shift my focus to a broader picture that includes things like my flying and connections to other topics at the university. On the other hand, 

I also quite like the application of my research. My research, compared to other projects in our discipline and faculty, is more focused on the application.

 Therefore, I would like to bring my Operations Research experience into industry. Currently, I am in discussion with a few potential employers how to apply my talents in my next endeavor.  

Thank you for your outlook. Could you maybe give students that are interested in pursuing a similar career or that are considering doing a PhD a tip on how to decide on that?  

The earlier you make your decision, the earlier you can target your life and working style that you seek and get appropriate qualifications. For example, if you have a research project and put some good amount of time into it, you are likely to publish it in a medium ranked journal. But if you want to get a job in academia, you would have to invest even more time and focus on it. Then you may be able to publish it in a higher ranked journal. If you want to pursue an industry career, you just need to have done this project on a certain level to place it well. Therefore, it is very valuable to know beforehand if you may consider choosing the industry path after your PhD and I am thankful to be in an environment where an academic and an industry career is appreciated as the next step.  

As I said previously, I feel like I have a great sense of freedom compared to others due to my PhD program and therefore there is a chance to use this freedom. 

A colleague did an internship during the PhD, in which the working contract with the university has been paused for two months. For a long time, all the empirically-driven students from a PhD have not had so many possibilities in industry jobs like they have now with the current movement into the direction of data science. There are many more jobs that require the skills that you learn during your PhD research.  

Let us have a closer look at your research now. Could you maybe start with a brief overview of what your PhD project is about?

I have three projects and they all involve airline scheduling, meaning the medium to short term planning of an airline. It’s a process of several steps of how airlines sequentially solve decision problems to come up with a final operations plan. One of these steps is schedule design meaning the airline decides which routes of the network to serve at what time. And if the problem of fleet assignment is added, also the decision about the kind of aircraft type operating the flight is included. In one finished project I worked together with my colleague David Topchishvili and my supervisor Prof. Cornelia Schön. We developed an optimization model for this problem and also included several other questions, such as how much aircraft should the airline actually buy for its network, which destinations should be part of its network, and our central research question was: if there is a cap of co2 emissions imposed, how much does the airline suffer from profit loss, how does the route network change et cetera. 

“What we found is that the airline does not suffer as much as expected, especially taking the operating profit into account. With an emission limit the unattractive routes are canceled quite fast.” 

Typical high volume routes, e.g. New York London, are kept and maybe a bit downsized. But something not as frequently flown, such as New York Berlin, is easily canceled. This route is just at break even, but a new constraint on the amount of CO2 emissions changes the situation: This route is then canceled quite quickly as New York to London is way more profitable and there is the need for some flight cuts. The question arises, if it is fair to the people of Berlin that they do not have direct transatlantic flights anymore because of the CO2 emission limit. But I guess some sacrifices need to be made for the climate and this is our prediction of what would be necessary. Project 2 is quite typical for Operations Research as we discuss the general problem of how crews, like the two pilots in the cockpit, are assigned to flights in the monthly schedule of an airline. For example, we have several datasets from 1013 to 7500 flights, where we just need to assign these flights to specific crew members for the scheduling month. And we have a new mathematical formulation of the optimization problem to tackle this task. The third problem targets a similar area; it considers how sleep and specific regulatory rules called flight time limitations influence the crew scheduling and what impact they have. For example, some sleeping models from the field of psychology are included in this project to model the impact of the rules on the sleeping behavior of crews.

 What kind of methods do you use in your analysis? You said you also used Operations Research and combinatorial optimization.

I actually want to emphasize this topic a bit more because in Operations Research, we are kind of using unknown methods compared to our let's say economics or other business scientists – but its state of the art Analytics. Most of the business researchers work by using qualitative methods, doing things such as interviews, or quantitative methods ,analyzing data and statistics. And we also work quantitative, but we use mathematical optimization or other algorithmic approaches, because instead of trying to find out what the data includes, what message it could provide for us, we actually know our determining factors already. And for big planning problems, for example those of an airline (e.g. how to set up millions of prices for a network), we have all the information available, but we have to put it in order so that we can actually make the best decision. And this is how Operations Research is a bit different from all the other disciplines, which are focusing more on the underlying data, but we are more focused on getting the best decision out of the data - then we call this specific decision the optimum. And to dive deeper, I use combinatorial optimization or as it's called, integer or binary problems, where we always have a decision of either 1 (we assign the pilot to the flight, we ship the package from the distribution center c) or 0 (we don't do it). So we always have two options for one single decision but combining many related decisions makes it quite complex as this example shows: If there are thirty pilots and thousand flight paths, we have 30 times 1000 meaning 30,000 decision variables and it results in 2 to the power 30000 solution options. Not all of them must be feasible, but the huge number shows that there are quite many possibilities that you need to check out to see if it is the optimal solution, and that is why it is so hard to make our decisions.

 Do you find your analysis difficult to do, or did you have the proper training for that?=

I have to say with my background, of my master and bachelor in business, I was unfortunately not as qualified as our engineers, who did have the proper math training. During the start of the PhD I tried to work on this weakness with suitable classes from my Graduate School GESS but still today I sometimes have the feeling that our colleagues are more capable of understanding the math part. But then on the other side, sometimes, I do have a better understanding of what the business needs. My model ideas are sometimes closer to the real requirements from the business side. Overall, I would actually recommend to go for the harder, more methodological classes if you want to pursue a PhD or career in academia.

As you are a pilot in training yourself, does that maybe benefit your research in some ways? 

Not as much as I wish. The crew scheduling problem (assigning crews to flights) I work on includes rules which are only valid for commercial operators. For example, for my flight license, I don’t have to adhere to the requirements that I need after 12 hours of rest resulting in the end of my work or flight day. The direct impact is not there, but of course you learn more about system aviation, how issues arise etc. So a bit yes. But I work on the side for a small consultancy focusing on the intersection of safety, aviation and data analytics. And from them I learned quite a lot about things required for my research problem and developed some ideas based on these insights. My project number 3 is strongly influenced by the work I did there.

So there are all sorts of factors in the problems that you try to optimize and the research that you do, such as I have heard, fatigue, cost, sustainability; which factor do you consider most important?

 I would suggest making a difference between the areas of schedule design and crew scheduling. For schedule design, for a long time it has been cost or finding the most profitable schedule, which could mean that your costs are high but revenues are higher in the end. With the current change in our society to consider climate change more, this of course has shifted a bit, and therefore

“ … sustainability becomes more of a factor. But I guess in the end it is still business, so profit is the most important factor, at least for schedule design.”

For crew scheduling, there is no revenue to gain, so the really important factor is cost. But, there are several constraints also playing into that. The regulations are always there, you have to fulfill them so that kind of sets your boundary for your solution and it is not always easy to adhere to the rules for some cases. Furthermore, fatigue is a huge factor in daily operations and becomes more and more a prominent issue. But also the attractivity of a schedule for crew members is more and more discussed, because crews become scarcer and scarcer. So, the tradeoff is: maybe I can use them as much as possible and really have a cost optimal schedule, but then they could be quite annoyed and overworked and may quit my airline. Due to staff shortage, it would hurt my airline as it has to cancel flights or needs to to buy capacity expensively from someone else. But in the end, the determining factors are still cost and profitability these days.

In what way do you think your research benefits science and society?

Our first research project shows what the impact of a CO2- emission limitation would be on the airlines as well as the consumers. It is also a sound basis to estimate the economic impact of new technological advancements to save or even capture CO2- emissions , as these factors could be built into our model and thus provide a scenario with new opportunities for the airline industry. With our crew scheduling projects, we did bring forth trying to give the crew members a schedule they actually like. Of course, if we have good optimization models and results, there will always be a benefit for the airline (higher profit margins) as well as consumers (better connections and products). For the science community, I see some value in the pure methodological advancements of our projects but also a value in my attitude which is maybe not mainstream. Our research is financed by society and therefore we should try to give back. Some researchers focus only on the academic community and celebrate model advancements, but do not undertake any effort or even shy away from bringing their results into society or business. In my opinion, we should proactively address society and corporate beneficiaries in order to create value with our results. I often raise this opinion and hope to motivate other scientists to invest more into this task.

So maybe to come back to the previous question of the various factors of optimization, do you maybe think sustainability should be prioritized over profit in some way?

Definitely! I also like the approach of giving a cost to the environmental impacts, so that you can kind of internalize all the costs arising with a certain consumption. In the field of aviation, there are many scientists working on great ideas, like hydrogen aircraft, conducting flight planning based on the impact factor “cruise altitude” and the type of aircraft to choose for its trajectory (because the cruise altitude also has an influence on how much impact the CO2 emission has for the environment). There is definitely much happening in this field and the industry should get more involved in it. To increase a movement towards sustainability, there must be a change in customer behavior as well. If we look at empirical results from our field, a big majority of possible customers say they would pay more for more sustainable flight options. But in the end, we can still see in various booking data that the environmental options are not taken and most passengers focus instead on the cheapest flight offers. 

So sustainable scheduling involves a component of customer behavior, besides the supply of sustainable options.

Yes exactly. So we always factor customer behavior in our optimization models and the airline often delivers what the passengers want to have or pay for. There is a big group of passengers saying “I want to go as cheap as possible”. As a result, there is an offer with little service, not attractive departure times, long duration, and not a big consideration of sustainability. The passengers or consumers have the chance to play a central role to steer with their demand the actions of the corporate.

So now a more general question: How is your PhD program structured?

Thanks for bringing that up! I am a member of the Graduate School of Economics and Social Science at the University of Mannheim and there in the CDSB program; uniting all their PhDs from the field of business. It is a structured program with 3 semesters of methodological classes to prepare candidates for their PhD and afterwards they switch to a chair or another type of research institution, where they actually conduct their research and are an employee. The program combines the strengths of the US (high research and method focus) and German (broad set of tasks also preparing oneself for an industry career) PhD journey; both can be considered as “extreme”.  In the US, most of the PhD programs work in the start like a master program. PhDs are students with courses and tough exams and they still have to find their supervisor throughout their program. Also, the connection between supervisor and PhD is not super strong… there is definitely a connection between them, but the PHD students are not administratively super attached to their supervisor; she is not their direct boss. On the other end in Germany, we have a chair system, where we have the whole faculty of one area, let’s say the area of business in our case. The faculty chooses chair holders – the professors. Each professor has teaching requirements and a budget to hire employees, which are usually PhD’s, a post-doc, and a secretary. As part of their job, the PhD students conduct their research and teach; the latter is not common in all programs. Teaching takes up 50% of my time, so this is quite a big factor of what I do. Therefore, I can focus less on my research than some people in other programs.

 Do you like teaching?

Yes! Actually I enjoy it a lot, because it is another way to have an impact! Either your research is well received by the research community, then it has a big impact there, or if I have 400 students and I am able to persuade 10% with my vision, then maybe I can have a higher impact by teaching the students than by doing research. So, If I go back to university, my position would be more focused on teaching than actually on research. This chance is also particularly given in the German university system where we have “Universities of Applied Sciences” with professors focusing on teaching.

How much freedom do you have in pursuing your own research interests?

It is a discussion with the supervisor; I could agree with my supervisor very easily, but others have much less freedom of choice. Of course, the own ideas need to fit to the skills and methods the supervisor uses in case you want to collaborate in the project. And in other programs such as in the US, I think it is more flexible, but there PhD students work more independently. My approach is somewhere in the middle as in the first one and a half years, I did a structured program, and then I changed to the chair system. The more structured programs give you more methodological background. Therefore in my opinion you become a better researcher choosing such a program. On the other hand, if you want to get the PhD quickly (because the motivation is to get the title), want to do teaching, or enjoy a broader overview of all the opportunities the organization ”University” offers, maybe then the chair program would be better for you. 

When do you plan to finish your PhD, and what will come after that for you?

Very soon. Hopefully towards the end of the year, if not I will work on it until march. next year. At the end the task will be to combine all three projects as chapters in one big dissertation and this will be the output of my PhD journey. I will look for an industry job where I can apply my skills and insights from my PhD. Opportunities needing my expertise of decision problems such as airline scheduling exist. Frankfurt is quite close from Mannheim, with a large airport and multiple attractive employers located there. Deutsche Bahn has a large location there as well and almost the same operational problems as airlines. There should be many opportunities.

I have one final question for the students:  Do you have a tip on how  to combine studies with the work at your study association and other interests such as your office at the local fire department or your engagement in the study association?

Time Management and active setting of priorities! At some point you have to make the active decision to follow an academic career in order to qualify yourself for research positions. I never decided on going only to academia. If I would have, I probably would have needed to focus a lot more on my research with a lot less things on the side. Instead, I decided to become a better teacher and completed a didactics qualification for university teachers. Additionally, I always had the practical implication of my research in mind so for me it is not a big issue but rather a cool challenge to switch to industry. I look forward to having my impact there and being a good bridge between the academic community and industry. Others really want to focus hardcore on the math problems, then they also need to adapt their lifestyle. That’s definitely a take away from my PhD journey. As a last recommendation, I can encourage you to build a network. As I am a member of the researcher generation of corona, it was hard for me to network at conferences and such. A network is quite important to be successful in academia. Therefore I recommend going to conferences to reach out to others and also other sectors; networking will provide you exciting chances. 

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