Research

Source3part1.pdf

This chapter summarizes scenarios of how an upcoming more electric aircraft and especially an upcoming electric aircraft would impact current processes and regulations for aircraft operations. Therefore, the following sections address both ground operations and in-flight operations. As these topics are introduced within a mid- to long-term timeframe and as some key questions defining the most plausible path remain unanswered, the following discussion is an attempt to envision future air transport operations with some caveats though.

9.1 Ground Operations 9.1.1 Maintenance—State of the Art Maintenance in aviation covers all tasks ensuring the compliance with Airworthiness Directives including Service Bulletins. These tasks are highly regulated and mainly specified by the Original Equipment Manufacturers (OEMs) in order to guarantee a safe use of every component. The regulations are supervised by national regulation agencies like the Federal Aviation Administration (FAA), Civil Aviation Authority (CAA), or European Aviation

Maintainability and Operational Overview Sven Taubert Lufthansa Technik

C H A P T E R

Thalin, Pascal, et al. Fundamentals of Electric Aircraft, SAE International, 2018. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/dcccd-ebooks/detail.action?docID=28983708. Created from dcccd-ebooks on 2023-02-05 20:18:20.

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Safety Agency (EASA) and internationally coordinated by bodies like the International Civil Aviation Organization(ICAO). To ensure the compliance with these regulations, every maintenance task and every appointed staff has to be licensed. Maintenance is also part of the certification process—during type certificate (TC) or amendments to TC, the maintenance schedule is documented and approved by the certifying authority.

The maintenance market itself is very fragmented. Most of the larger airlines are performing at least some of these tasks themselves. The rest would be subcontracted to either independent Maintenance, Repair, and Overhaul (MRO) companies like Lufthansa Technik, among many others, or the component/aircraft OEMs themselves.

9.1.1.1 Maintenance Planning: Currently, maintenance tasks are often planned far in advance. Most checks are repeated in periodic intervals depending either on the flight hours or cycles. One cycle describes one takeoff and one landing. The main categorization is done in A, B, C, and D checks.

A and B checks are performed in line maintenance, and C and D checks performed in base maintenance. Line maintenance includes minor checks and unscheduled inci- dences, solvable within a few days or which would cause the aircraft to lose its airwor- thiness. Loss of airworthiness or “Aircraft on Ground” (AOG) prohibits flying with immediate effect.

Planned checks are mainly done during night shifts. During daytime, between flights for aircraft in service, the main task for line maintenance is to service and repair “on-wing” as may be necessary. Base maintenance includes major upgrades like installing a satellite communication system, cabin refurbishment, larger inspections, and almost all “off-wing” repairs.

9.1.1.1.1 A Check. The A check subscribes the smallest planned interval. It has to be performed every 400-600 flight hours or every 200-300 cycles, depending on the aircraft type and the components needing maintenance, and can take up to 50-80 man-hours. Normally, airlines will try to complete an A check during one night shift in a hangar (6h-10h). Some of the tasks can also be postponed or even done earlier to ensure a maximized utilization time of the aircraft by a guaranteed safety level. As there are thousands of components in each aircraft, an ingenious maintenance schedule can easily save millions of dollars.

9.1.1.1.2 B Check. The B check has to be performed every 6-8 months and takes 150-200 man-hours. Again, these estimations depend on the type of aircraft and equipment conditions. All tasks can be done within a downtime of 1-3 days. This is widely considered as the maximum time for line maintenance. Using better planning possibilities, more and more MROs divide B checks into several A checks (Checks A-1 through A-10) to avoid daytime downtime and maximize aircraft utilization time.

9.1.1.1.3 C Check. The C check has to be performed every 20-24 months, depending on either actual flight hours (or cycles) or manufacturer Service Bulletins. This check grounds the aircraft for 1-2 weeks and involves up to 6000 man-hours. This includes inspections of a majority of the aircraft systems and components. The C check cannot be subdivided into several B checks, as a lot of components have to be shipped to off-site

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suppliers. Due to the long downtime, the C check can be performed at specialized MRO facilities, which are not necessarily near the airline’s hubs. Most airlines make use of the check to perform upgrades like cabin modifications, installation of connectivity equip- ment, or avionic upgrades. For the Boeing 747-400, the C check itself may cost somewhere between $0.7 million and $1.5 million.

9.1.1.1.4 3C Check. The 3C check, sometimes known as “Intermediate Layover” (IL), is necessary on some aircraft to check structural parts and some high-load parts for corrosion. Similar to the C check it can be combined with major cabin upgrades like class changes with new seats or monuments. The combination of these tasks saves again downtime of the aircraft. The 3C check can be incorporated in several C checks or into one D check. The main reason for that incorporation is an improvement of the reliability due to better corrosion protection.

9.1.1.1.5 D Check. The D check, sometimes known as “Heavy Maintenance Visit” (HMV), has to be performed every 6-10 years. It is by far the largest maintenance check and takes 2-3 months. During the 50,000 man-hours more or less necessary, the whole aircraft is disassembled. All parts have to be checked. For some structural visual inspec- tions, even the aircraft paint has to be removed. As this check is very time consuming and workload intensive, it is often performed in countries with low labor and hangar costs. Such a check may easily cost several million dollars. For example, a Boeing 747-400 has a D check every 72 months (6 years) costing around $5 million. Due to the long downtime, D checks are planned far in advance. It is common to move the inspection ahead in time to perform it during the winter flight plan utilizing a smaller number of aircraft. As the costs are significant, an upcoming D check can cause the phase-out of an aircraft because its residual value may be lower than the check costs. Most of the commercial aircraft undergo three D checks overall.

9.1.1.2 Maintenance Prediction—Condition Monitoring: The advent of computerized control systems gave rise to the concept of condition monitoring, and computing capacity is a key enabler. As the “condition monitoring” term indicates, maintenance tasks here are not based on fixed flight hours, cycles, or time anymore, but on the actual condition of the components. The condition is mainly determined by sensors. Often, the condition has to be defined by multiple indicators, including:

• Pressure • Vibration and sound • Temperature and heat transfer rates • Speed (axial and rotation) • Power consumption, current, and voltage • Stress, pressure, and shock • Overall position • Computer outputs

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Thanks to increased availability of real-time data today, even non-critical systems can feature condition monitoring. The big advantage of such systems is the reduction in maintenance costs they bring. The MRO is able to focus on inspecting and/or changing components with actual defects or find issues much faster, reducing aircraft downtime.

The challenge of condition monitoring is to find the economic balance between the system costs and expected savings. As condition monitoring systems need advanced instrumentation, the initial costs can be significant. Legacy components often lack data or even a power interface, making retrofit scenarios very unlikely. Wireless data commu- nication may ease the situation. An example for this technology is vibration sensing of rotating parts like a turbine shaft or a pump motor.

Analyzing more complex components requires data fusion. The challenge here is to use the right data combination and interpretation to determine the defective compo- nents to be replaced.

One of the hazards of condition-based maintenance (CBM) is the rising complexity of the instrumentation itself. If the sensors are faulty themselves, they may indicate component failures that are inexistent, increasing again the maintenance costs.

All and even more electric aircraft implement electrical systems in lieu of hydraulic and pneumatic systems; all-electric systems also eliminate traditional propulsion systems. Most of the electrified systems require active power control enabled by sensors. So the hardware requirements for condition monitoring may be met. But the difficulty remains in finding what kind of data indicates what kind of failure. This is why data interpretation algorithms often get mature only months or even years down the line thanks to cross-checks of sensor readings with actual maintenance findings.

9.1.1.2.1 Condition-Based Maintenance (CBM) and Predictive Maintenance (PdM). The terms Condition Based Maintenance (CBM) and Predictive Maintenance (PdM) are often used as synonyms. Actually, there is a slight difference, or to be more precise, there is a considerable overlap. PdM uses often the tools and methods of CBM but could also use other data sources to predict life of parts.

CBM should only be performed if the component shows any indication of failure or unacceptable degraded performance. PdM has the goal to predict the failure of a component so that it could be changed or repaired preemptively even if the part is not showing any signs of degradation. Therefore, big data analytics based on statistical principles are used.

As a simple example, let’s take an armrest of an economy class aircraft seat. CBM could monitor the stress curve through the part. If this curve changes to a certain shape, this would be interpreted as reduced performance and the part would be changed. Predictive maintenance would use the same information in the same manner, but it could also consider, for instance, the number of passengers having taken that seat. The PdM model predicts that every 30,000 passengers the armrest has to be changed due to scratches. Scratches cannot be detected by any sensor, making it impossible to track the actual condition. An experi- ence-based model, on the other hand, would give a very good indication when a change should be considered. The classic maintenance schedule is based on “simple” experi- ence-based models. The essential difference with modern predictive maintenance models is combining the experience-based data with live data. This extensive data may reveal patterns indicating failure root causes which were unknown or undetected before.

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Another very important aspect of CBM is the “on-wing” capability. Most inspection technologies perform sensing on components during their operation, making a compli- cated disassembly unnecessary or at least far less mandatory. This is an important factor for cost savings.

Table 9.1 shows the advantages and disadvantages of CBM. To reap the full benefits of a PdM approach, the dataset of each and every aircraft

of an airline has to be connected to a so-called computerized maintenance management system (CMMS). It manages the condition of all components and triggers maintenance tasks and schedules. Otherwise, a fleet with hundreds of aircraft, each with millions of parts, cannot be run efficiently.

To achieve this, several inspection technologies are needed. A part’s condition is nondestructively analyzed by sensors measuring different light spectrums, acoustics, vibration, temperature, speed, power, stress, liquid composition, or computer outputs. Often, not one but several indicators are utilized to determine the condition, both analyzing the equipment and its immediate environment. Especially wireless commu- nication technology kicked off the implementation of sensor networks.

In the following, some of the mentioned technologies are described in further detail:

Visual inspection Visual inspections have been used in aerospace industry for decades. For

example, black light and contrast liquids are used to detect cracks, folds, and corrosion. Endoscopes, mirrors, and lenses help maintenance staff to detect failures on hidden and not easily accessible spots like in the engines. Most of these inspections are performed during maintenance checks by MRO staff, but recent developments in camera sensor technology enabled automated live data collection. As visible light camera sensors need at least 300 lumens to deliver good results, infrared monitoring is utilized for more and more inspections. Its versatile utilization possibilities allow detection of mechanical and electrical failures (Figure 9.1). Due to its low price it is considered as one of the most cost- efficient inspection methods.

Acoustics Sonic and ultrasonic real-time analyses are mainly used for moving parts like

shafts. Sonic monitoring is used in applications that need less accuracy. It is less expensive and can also be detected by trained staff by intent listening with their bare ears. Ultrasound has enough acoustic resolution to inspect even machines

TABLE 9.1 Pros and cons of condition-based monitoring

Advantages Disadvantages Increase of utilization time Increase of CBM-enabled component cost

Improvement of component reliability Risk of increased maintenance tasks due to sensor failureMinimizing AOG time

maintenance cost reduction via optimized maintenance schedules

CBM/PdM is non-invasive. Equipment can be operated during inspection

May generate considerable retrofit effort

Increase of safety levels Unforeseen failures in case of false analytics

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rotating with high frequency like jet engines or turbo pumps. Ultrasonic microphones can “hear” the difference between smooth operation of a rotating machine and one with too much friction or stress by comparing sound profiles. Each type of machine has its own sound profile, similar to an acoustic fingerprint. Changes like friction, stress, or deformation generate additional distinguished sounds visible in the upper ultrasound spectrum. That effect detects an abnormal wear far before visible inspection could. The only comparable method would be vibration analytics. But, unlike the ultrasonic method, there are instances whereby vibration monitoring may fail to distinguish the faulty component from the healthy one (Figure 9.2).

Aircraft OEMs outlined that predictive maintenance based on data analytics and CBM could eliminate all AOG events within the 2025-2035 timeframe. This timeline allows for such advances to be taken into account in future design configurations of the electric aircraft. Meanwhile, implementation of more electric systems, until there is finally a full electric aircraft, will not only benefit the environment but also the main- tenance effort. Until now, modern conventional aircraft have decreased fuel consumption and weight at the cost of more system complexity. This trend of more and more complex system architectures could be totally reversed on an all-electric aircraft, electrification allowing for the removal of the pneumatic, hydraulic, and fuel distribution systems along with traditional propulsion systems.

FIGURE 9.1 Infrared monitoring for failure detection.

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FIGURE 9.2 Vibration monitoring for failure detection (method limitation shown).

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9.1.2 Changes for More Electric Aircraft As a first step, a more electric aircraft may substitute hydraulic and pneumatic systems with electrical ones. Hydraulic systems can distribute large forces over the whole aircraft through cumbersome piping pumps and valves with a huge number of fittings and couplings. However, due to redundancy built into architectures, it is very robust. Unfortunately, it also poses some challenges concerning maintenance. Because of its complexity, leaks are often very difficult to locate. In the meantime the leaking fluid could cause a cascade of other failures. This makes the maintenance of the hydraulic but also pneumatic systems time consuming and expensive.

Hydraulic and pneumatic systems were used because it meant that the actuators supplied by them could be built less complex, lighter, and smaller. As electrical motors made enormous progress in these areas over the past years, this advantage is almost leveled out. Electrical cabling, on the other hand, is far less complex then piping. The functions of today’s hydraulic, pneumatic, and power systems could all be inte- grated into one power distribution network. Instead of maintaining three systems there would be just one. Moreover, cable breakages are much easier to detect than pipe leaks. Wire fault location uses a technology called reflectometry. This consists in sending a discontinued signal into the damaged cable and the break or short would reflect the signal and send it back. The time required for the reflection indicates the distance to the problem.

In general, electric systems are much easier to monitor for health and system status. Even on a more electric aircraft, the reduction in system parts by moving to a primarily electric architecture may be significant. A case in point is the more electric Boeing 787 where the bleedless architecture allows reduction of overall mechanical systems complexity by more than 50% compared to a conventional 767; the elimination of pneumatic systems is a major contributor [9.1]. As a consequence of this reduction in mechanical systems’ complexity, airline operations may get less maintenance inten- sive and more reliable than with conventional systems of bleed architectures, even though the complexity on the electrical side goes up. In fact, the move to electric systems helps in cutting significantly the schedule interruptions compared to a conven- tional aircraft for the systems affected by the no-bleed/more electric architecture. Other benefits include improved health monitoring and greater fault tolerance.

Moreover, the 787 features greatly expanded and improved systems monitoring capability coupled with an advanced onboard maintenance computing system. This capability combined with e-enabling technologies, which make real-time ground-based monitoring possible, significantly aid in rapid, accurate troubleshooting of the 787. Airplane systems information used in conjunction with fully integrated support products help maintenance and engineering organizations quickly isolate failed components and reduce return-to-service times. No-fault-found (NFF) removals are also drastically reduced compared to conventional aircraft, reducing yet another major cost driver for operators. Therefore, thanks to the extensive system electrification on the Boeing 787, even though hydraulics have not been totally removed, airlines have far less maintenance to perform less often than they are used to. This leads to extended check intervals compared to conventional aircraft as shown in Figure 9.3.

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9.1.3 Changes for an Electric Aircraft With an electric aircraft, the complexity of the engine decreases by orders of magnitude. A current jet engine is one of the most advanced combustion machines ever developed. It consists of up to 30,000 parts. The combustion chamber reaches up to 2000°C and even the exhaust gas can still reach 500°C. Therefore, dozens of blades have to be made of ceramics or single-crystal metal or have advanced cooling outlets for cool air shielding. All this makes it not only the most expensive aircraft system at the moment of purchase but also in terms of maintenance. Current jet engines and their support systems have hundreds of thousands of years of service history, while the electric aircraft is still in its infancy state and will take some learning process to get to the current existing aircraft state.

An electric engine for aerospace applications would in contrast probably have only around 250-300 parts. Also, temperature should not be in the same order of magnitude. So, it is obvious that electric engines will have a much lower share of total cost then today’s jet engines.

The electric aircraft also adds a new system: a solid power source. While batteries are already used, the dimension needed for an electric aircraft escalates to an entirely new level. If we imagine batteries, which can store enough energy to use them as primary power source, they would have to be maintained unlike jet fuel today. Battery state of charge and state of health are key measures to ensure safe operations and full battery utilization. That means that it would be mandatory to devise an approach to maintain them. Replacing them after some hundred cycles comparable to today’s smartphones or even cars would not be ecologically and financially sustainable. Furthermore, a lot of current battery technology is based on rare earth materials. How that maintenance service could be offered and by whom is currently not clear. Decisive factors are tech- nical expertise, global capacity, price, but also upcoming regulations.

FIGURE 9.3 C-check interval – long range aircraft [9.2].

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9.1.4 Airport Operations Next to maintenance, airport operations form the other part of ground operations. In the coming sections, topics like infrastructure, aircraft turnaround, and emergency processes will be addressed.

Airports are currently the foundation of aerospace business. Apart from decentral- ized helicopter landing areas (helipads), every aerospace mission starts and ends at an airport. Its infrastructure includes runways, taxiways, aprons, terminals, hangars, traffic control centers, and support infrastructure like fuel reservoirs. International airports facilitate border control and customs checks as well.

9.1.4.1 Infrastructure: One fundamental question remains: which future aircraft concepts need what kind of infrastructure? Looking at long- and short-range more electric and electric aircraft, this will not change. Larger aircraft will always need a certain support infrastructure, especially if international travel is involved. The next section on aircraft handling will go into further detail on this.

Urban air mobility concepts like the Volocopter shown in Figure 9.4 will need a much smaller scale of infrastructure. However, the core functions of an airport have to be covered somehow. A combination of helipads and “vertiports” could be a solution.

Assuming that urban air mobility concepts are more competitive concerning pricing than current helicopter services, the number of missions would be much higher. Therefore, a simple and seamless boarding and disembarking process is manda- tory. Many studies show that security control is currently the pain point number one at airports. Automated or remote-controlled advanced scanner technology in combi- nation with a kind of background pre-screening similar to systems like ESTA in the United States could minimize the effort. As this process should be done within minutes, a large waiting area like in current terminals would not be needed.

The vehicle itself would need a refueling or recharging facility and maybe a small line maintenance station. Depending on the success rate of predictive analytics, the maintenance could be even coupled with similar services at the airport. While urban air transportation is probably offered in larger cities that are already equipped with at least one full-scale airport, the question whether traffic control of low altitude urban mobility would be managed by local airport(s) is still open. A lot of urban air mobility concepts reckon with the fact that air traffic management principles and its responsibility are yet be addressed. On top of the focus on autonomous operation, navigation, sense, and avoid are also key technologies.

However, that would mean that urban air mobility concepts would be mainly point-to-point connections between localities featuring so-called rooftop “vertihubs” or “vertistops” integrated to roads. First test cases support that prediction.

FIGURE 9.4 Example of urban air mobility vehicle (Volocopter) [9.3].

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Future smart ground transportation systems may also be poised to compete directly with urban air mobility concepts. In fact, most of the current ground mobility business models focus on the pain point of gridlocks found in many urban metropolitan areas. Therefore, if autonomous taxi or car sharing concepts were to become reality, with their own traffic management in place, congestion issues would be resolved, and a shadow would be cast on the appeal of air mobility.

From an energy consumption point of view, aerospace applications will always be more demanding and thereby more expensive. Also old applications will have to merge with the new ones seamlessly, which is quite a challenge. In addition, door-to- door transportation depends on ground-based systems to a certain extent. Even if urban air mobility concepts save their customers some time, ground-based solutions offer not only lower prices but also more comfort and onboard infrastructure allowing better utilization of travel time. A similar situation can be currently observed with trains versus aircraft on short-range flights, especially in Europe and Asia.

9.1.4.2 Aircraft Handling: Focusing again on larger electric aircraft concepts, these vehicles would need similar aircraft handling services like today with two exceptions— Refueling/Recharging and Pushback/Taxiing.

9.1.4.3 Refueling/Recharging: As one of the biggest changes of an electric aircraft would be the replacement of the main energy source, the refueling process would have to be completely redesigned. If the new energy source is liquid or gaseous, current processes might not differ much.

Assuming a kind of battery system, there are normally two solutions—recharging or replacing. Recharging would have the main challenge of time. Today, a turnaround of an A320 is between 30 to 60 min. Refueling is only permitted if no passengers are on board or a fire truck is on standby next to the aircraft. But predicting that recharging would be allowed during the whole turnaround time, it is still technically very challenging to recharge the batteries within that timeframe without losing too much battery life. In addition, battery technology would have to improve a lot from a specific energy standpoint.

If the specific energy challenge could be solved but the recharging timeframe could not, a battery swap would be the most likely solution. Some car manufacturers showed already such concepts of fast and automated battery swapping systems.

Both solutions have one common challenge for the airport—standardization. Today, all aircraft f ly with the same fuel. Looking at electric vehicles, there are a multitude of power plug standards. Each car manufacturer defined its own plug with specific standards for voltage and current. For aircraft ground support equip- ment (GSE), there is a standard connector which is the Euro plug. Nevertheless, for future electric aircraft batteries, the existing Euro connectors may not be sufficient. This may require standardization bodies to develop standards for the battery recharging process. Moreover, depending on the aircraft system architecture, different OEMs are likely to come up with totally different power architectures. So, it will be essential for airports to define a very f lexible, but also scalable (up and down), power grid architecture.

Battery pack shapes are mainly driven by the geometry of the powered device/ vehicle. Predicting a variety of configurations could also mean that current geometry

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standards are not useful anymore. For example, the cargo LD-X standard container (Figure 9.5) fits into the cargo hold of almost every long haul aircraft—A380, A350, A330/A340, B747, B777, B787 …. A f lying wing config- uration may waste a lot of space by adapting to that standard, leading to a new type of container.

Accordingly, if all electric aircraft were to have very diverse configurations, airports would have to store large stocks of different kinds of batteries. This would not just mean a storage space challenge but also consequential costs.

This is why standardization bodies like SAE International are already discussing possible solutions with all impacted industry stakeholders to avoid that. The objective is to produce a standard that would minimize variability and provide guidance for standardized design, production, and testing.

Likewise, fuel cell utilization at airports requires storage and/or distribution of hydrogen to airport facilities for aircraft refueling. This requires modifications to infra- structure addressing hazard prevention and safety concerns.

9.1.4.4 Pushback/Taxiing: The increasing awareness and attention to environ- mental concerns drives innovation in aeronautics. One of the issues to be addressed is aircraft maneuvering on ground using jet engines, thus causing a variety of undesired emissions. The general working principle is to use electric vehicles to move aircraft from the gate to the runway and vice versa. For several years, research and demonstra- tions have been carried out in the short-range segment to validate electric taxiing achieved by the aircraft on its own. This solution consists of integrating electric wheel motors in the landing gear which draw electrical power from the APU (or fuel cell) in combination with batteries, if necessary. With the APU being more fuel-efficient than a turbofan engine, this aircraft-based electric taxiing allows for reductions in fuel burn and emissions. Moreover, with this solution, retrofit on legacy aircraft may be possible. Chapter 7 provides a deep insight into this incremental electrification approach of conventional aircraft.

9.2 In-Flight Operations This section discusses both cockpit and cabin implications of electric aircraft concepts, bearing in mind that far more changes are expected for the flight deck rather than the cabin. Starting from pilot licenses, an overview of controversial topics such as single pilot operations, autonomous flight, future urban mobility with pilots akin to drone operators, etc. is openly presented. As a general comment, not all these topics are directly linked to the electric aircraft. But this is the future, so when reading through this visioning exercise, remember that the future is predictable only with limited certainty.

FIGURE 9.5 2 LD-3 containers get loaded into a Lufthansa A380 aircraft.

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9.2.1 Flight Deck Operations With the introduction of electric aircraft there will be at least some changes in the cockpit.

9.2.1.1 Complex Configurations/Licenses: Similar to aircraft certification chal- lenges, pilot licensing will be a topic for electric aircraft operation. Today, pilots need a certificate issued by the Civil Aviation Authority of the country where they want to operate. Despite several attempts, the licensing process is still different from country to country. The most known agencies regulating pilot certification are the Federal Aviation Administration (FAA) in the United States and the European Aviation Safety Agency (EASA) for the European Union and Switzerland.

As there are different aircraft categories and classes, there are different levels of licenses, further distinguished by ratings:

Private and Commercial Pilot License (PPL and CPL) For non-commercial and commercial operation of small aircraft, respectively.

Depending on the country, different sub-ratings are available, for example, complex aircraft, single-engine/multi-engine aircraft (maximum takeoff weight (MTOW) of 2t), etc.

Airline Transport Pilot License (ATPL) This license is required in order to fly commercial planes in the range of those

usually operated by airlines. ATPL is the highest level license covering PPL and CPL. For each aircraft type flown, an additional type rating is required.

Drone operators Some countries start regulating drone operations by requiring a Drone Operator

License. Especially commercial drone operations are covered by these initiatives. However, a structured international standard is currently not available.

Depending on electric aircraft configuration and its TC, the corresponding pilot license is derived. The biggest gap here is within the urban air mobility concepts. These vehicles are often a combination of ultra-light aircraft, helicopters, and drones. There is, for instance, an urban air mobility prototype which is currently applying for an EASA ultra-light certification. The derived ultra-light pilot license would be just valid for Europe and not for commercial use.

The bigger electric aircraft concepts for commercial short-range applications would be certified under CFR Part 25 so that the normal ATP license with a specific type rating would probably be sufficient.

9.2.2 Single Pilot Operations A topic that is currently controversially discussed is large commercial aircraft single pilot operations. It would mark a first step towards autonomous flight. Both automotive and aerospace vehicles powered by fossil fuel would be capable to integrate the necessary technology for (greater) autonomy. However, as the topic of autonomous driving is by public perception linked to electrically powered cars, this impression is transferred as

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well to aerospace. Nevertheless, there are some arguments why an electric aircraft program could foster the implementation of this concept.

As many concepts for even large short-range applications envision multi-impellor or multi-propeller with multi-power sources, thrust control in case of failure is getting much more complex. Moreover, these engines not only produce thrust but also lift or steer the vehicle. It is presumable that, similar to modern unstable fighter jets, these aircraft are not maneuverable without significant computing support. So, as the computer is anyway responsible for a significant portion of flight operation, the question is how effective a human pilot would be interfering in case of a failure. There might be the conclusion that the most effective operation in terms of cost but also safety is an advanced autopilot system supporting one pilot.

The biggest issue in this scenario would be how to compensate the loss of a single pilot in case of medical emergency, for instance. For this particular case, initial studies support a remote pilot solution. As a side effect, these remote pilots could also support aircraft with a twin pilot operation if one of the pilots gets suddenly unfit during flight.

9.2.3 Autonomous Flight Of course, autonomous flight is discussed with even more controversy. Similar to single pilot operation of commercial flights, autonomous flight is not directly related to electric aircraft but is often mentioned in the same breath.

In contrast to single pilot operation, autonomous operation today is mainly driven by smaller electric aircraft concepts like civil drone applications and urban air mobility vehicles. Here, the business case rests on the assumption that autonomous flight is both technically possible and socially acceptable, and is cost-efficient. Urban air mobility may also need autonomous operation to close the business case just because there won’t be enough pilots.

In commercial aviation, autopilot systems have been the norm for years. Automatic landing systems are in place, but the standard procedure is still for the pilot to land the plane manually. Fully autonomous flights were also demonstrated multiple times. In 1988, as one of the most famous examples, Russian spaceship Buran, which looks quite similar to the American Space Shuttle, performed a fully autonomous start, flight in space, and landing. In military drone operations, autonomous or semi-autonomous flights are increas- ingly becoming the standard procedure. With the Northrop Grumman X-47B Unmanned Combat Air Vehicle (UCAV), even automated air-to-air refueling and landing on an aircraft carrier were demonstrated (Figure 9.6).

Note that these flights have been performed on vehicles with no passengers on board, but the tech- nology is mature. Yet, some industry actors, especially airline related, have suggested that autonomous flight in commercial aviation will take more than one gener- ation to become reality. The Aircraft OEMs Boeing and

FIGURE 9.6 UCAV autoland on aircraft carrier [9.4].

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Airbus are more optimistic and want to start trials within months not decades. Both sides have valid arguments.

One of the main arguments against autonomous flight concerns safety. The issue is less on the computing power but more on the generation of intelligent decision trees. In unforeseen events, even Artificial Intelligence (AI) isn’t capable to come up with “inno- vative” ideas to solve the issue. Furthermore, AI needs vast amounts of data to train machine learning for the resolution of problems. It is currently not proven that the available data from, for example, simulator emergency situations is sufficient for that approach.

On the other hand, autonomous driving has gained remarkable traction in its devel- opment, while a car operates in a far less predictable environment than an aircraft. Therefore, problem-solving algorithms from the automotive industry could also help aviation overcome technical challenges. The near future will show if the OEMs can reach mandatory safety levels and prove that autonomous flight is technically feasible on a commercial aircraft. The outlined and published timelines by various startups and OEMs must be treated with some reservation. In the 1980s, visions of the future also predicted that autonomous flights would become reality no later than the year 2000. Like single pilot operation, the development of a complete new aircraft, especially an electric aircraft redefining current standards, would boost technical development and, therefore, the chances of implementation.

Another aspect is the social acceptance of autonomous flight. Whether or not passen- gers would board a self-flying plane is just as hotly debated as technical questions. Similar to trains or nowadays cars and trucks, some people believe in autonomy and others do not. History shows that, while it will take some time, people will get used to the new technology. In several cities, like in Paris, for instance, fully automated subways have been in service for years and passengers readily ride them, often without noticing the absence of a driver. Nevertheless, there are still public transportation providers who are convinced that their customers would not accept a driverless train. Self-driving cars triggered an even bigger discussion. That this debate is not always driven by logical arguments becomes obvious when accidents do happen, especially when there are fatal- ities. Most of these technology demonstrators have theoretically proven that they have much higher reliability compared to human drivers, and the social debate will certainly heat up around whether to adopt the concept or not.

On the other hand, cars with anti-lock braking systems (ABS) or Electronic Stability Control (ESC or ESP) are considered safer, even if this means that a computer overrides the human driver impulse and manages autonomous braking. So, when higher safety levels of an autonomous system compared to a human operator is statistically proven, and the general public is convinced, it could even become a must-have item. Given the emotional rather than logic development of public opinion, it is very hard to predict if or when that will happen.

9.2.4 Pilots as Drone Operators In unmanned military applications, pilots working as single or even multiple drone operators is something which has already been implemented over the years, but for commercial aviation it is still considered as disruptive. The straightforward reason behind this is that commercial aircraft carry passengers, and as such have to comply with stringent safety requirements.

In the early 2000s, the United States developed weaponized drones from a prototype status to what has come to be known as UCAVs. Combat drone operations are becoming

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increasingly commonplace regardless of where around the globe the theater of operation is located. Incidentally, most of the pilots are remotely stationed in Europe (Figure 9.7) or in the United States, sometimes several thousand miles away from combat zones. This distance causes a signal delay of up to a couple of seconds between the time a command is issued to the drone and the time when it is received.

Due to that delay, time critical operations like start and landing are performed by drone operators on location. When the drones reach their operational altitude, there is a handover to the remotely located pilots. As most of these operations are highly auto- mated observation missions, drones operate semi-autonomously, that is, fly without human interaction unless a potential finding requires an operator’s action. This is why drone operators have the capacity to “fly” more than one drone.

Future combat drones may leverage hybrid-electric propulsion for stealthier VTOL operations like with the LightningStrike from Aurora, a Boeing company, wherein vertical takeoff and landing would be possible without a runway. This would stave off the handover constraint making UCAVs operable remotely right from the onset.

Anyway, the handover principle between remote and local control stations used in current UCAV operations could also be adapted for future commercial aviation or delivery drones. For instance, urban air mobility concepts using electric propulsion like CityAirbus shown in Figure 9.8 could operate autonomously until a situation arises

FIGURE 9.7 Remote and local Ground Control Stations part of the Predator Unmanned Aircraft System (UAS) [9.5].

FIGURE 9.8 CityAirbus urban mobility concept vehicle rooftop landing (rendering) [9.6].

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where the system would need human assistance. This would give the concept the possi- bility to utilize all four seats for passengers alone and benefit as well from advanced safety measures. Depending on the upcoming scenarios, there could even be a similar split between local operators and centralized facilities like flight control radio stations. Of course, this infrastructure would also have to support single pilot operation or auton- omous flight of larger airliners.

9.2.5 Cabin Operations The other part of in-flight operations is performed on the other side of the cockpit door: cabin operations. Cabin operations consist of both passenger service—a very important brand experience touch point for airlines—and passenger safety, the more important aspect from a regulatory standpoint.

Passenger service processes will slightly differ depending on cabin geometry and flight profile. However, it is one of the top priorities of every airline to offer a consistent service product. The customer should know what baseline to expect, enhanced by the personal touch of every crew member. The current processes are updated regularly based on experience and driven by changing customer expectations. A more electric or electric aircraft is not likely to have a major impact in this area.

Beyond service, flying personnel are required to guarantee the safety of passengers. An electric aircraft with a different power distribution system or even a different main power source could impact today’s procedures. Today's procedures require aircraft and ground power supplies to be properly grounded in order to ensure their protection against electrical hazards (static electricity and failures) and that of crew, passengers, and maintenance personnel. These procedures have to be revisited with the advent of more electric or electric aircraft due to the presence of more hazardous high voltage within power systems and energy storage.

One of the questions currently open is how to indicate that the aircraft is electrically grounded. This issue could impact the safety of the crew, passengers, but also first responders in case of an emergency landing. The latter case involves potential hazards unique to onboard electrical systems such as electrocution, fire, and battery electrolyte spillage.

A potentially higher explosion risk of batteries could lead to a shorter maximum evacuation time. Therefore, new ways of disembarking would have to be developed.

Looking at urban air mobility concepts, safety in case of emergency landing could also become a key topic. As most concepts plan for autonomously operated vehicles, there is no trained crew to help passengers leave the vehicle in case of emergency. Digital information technology could potentially compensate portions of these tasks, but the physical support assisting injured or movement-restricted passengers is technically challenging to compensate.

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References [9.1] Sinnett, M., “787 No-Bleed Systems—Saving Fuel and Enhancing Operational

Efficiencies,” AERO Magazine Q4, 2007, published by Boeing. [9.2] Boeing, “Airline Economics,” 2016 Airline Planning Workshop, Airports Council

International (ACI), North America, USA, 2016. [9.3] https://www.volocopter.com/en/product/, accessed May 5, 2018. [9.4] https://www.usnews.com/news/articles/2013/06/11/new-military-uav-may-lead-to-

commercial-drone-flights, accessed May 4, 2018. [9.5] https://www.uasvision.com/2011/07/15/view-inside-a-predator-ground-control-

station/, accessed May 5, 2018. [9.6] https://airbus-h.assetsadobe2.com/is/image/content/dam/corporate-topics/

publications/press-release/CityAirbus-01.jpg?wid=3626&fit=constrain, accessed May 4, 2018.

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https://www.volocopter.com/en/product/

https://www.usnews.com/news/articles/2013/06/11/new-military-uav-may-lead-to-commercial-drone-flights

https://airbus-h.assetsadobe2.com/is/image/content/dam/corporate-topics/publications/press-release/CityAirbus-01.jpg?wid=3626%26fit=constrain

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