Jeffrey T. Csank

Glenn Research Center, Cleveland, Ohio

Ryan D. May

ASRC Aerospace Corporation, Cleveland, Ohio

Ten-Huei Guo and Jonathan S. Litt

Glenn Research Center, Cleveland, Ohio

The Effect of Modifi ed Control Limits on

the Performance of a Generic Commercial

Aircraft Engine

NASA/TM—2012-217261

January 2012

AIAA–2011–5972
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Jeffrey T. Csank

Glenn Research Center, Cleveland, Ohio

Ryan D. May

ASRC Aerospace Corporation, Cleveland, Ohio

Ten-Huei Guo and Jonathan S. Litt

Glenn Research Center, Cleveland, Ohio

The Effect of Modifi ed Control Limits on

the Performance of a Generic Commercial

Aircraft Engine

NASA/TM—2012-217261

January 2012

AIAA–2011–5972

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

47th Joint Propulsion Conference and Exhibit

cosponsored by AIAA, ASME, SAE, and ASEE

San Diego, California, July 31–August 3, 2011
Acknowledgments

The authors would like to thank Diana Drury of ASRC Aerospace Corporation, who handled the version control system

for C-MAPSS40k. Our thanks also go to the NASA Aviation Safety Program’s Integrated Resilient

Aircraft Control Project for funding this work.

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Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217261 1 

The Effect of Modified Control Limits on the Performance of a 

Generic Commercial Aircraft Engine 

Jeffrey T. Csank 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Ryan D. May 

ASRC Aerospace Corporation 

Cleveland, Ohio 44135 

Ten-Huei Guo and Jonathan S. Litt 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

This paper studies the effect of modifying the control limits of an aircraft engine to obtain additional 

performance. In an emergency situation, the ability to operate an engine above its normal operating limits 

and thereby gain additional performance may aid in the recovery of a distressed aircraft. However, the 

modification of an engine’s limits is complex due to the risk of an engine failure. This paper focuses on 

the tradeoff between enhanced performance and risk of either incurring a mechanical engine failure or 

compromising engine operability. The ultimate goal is to increase the engine performance, without a large 

increase in risk of an engine failure, in order to increase the probability of recovering the distressed 

aircraft. The control limit modifications proposed are to extend the rotor speeds, temperatures, and 

pressures to allow more thrust to be produced by the engine, or to increase the rotor accelerations and 

allow the engine to follow a fast transient. These modifications do result in increased performance; 

however this study indicates that these modifications also lead to an increased risk of engine failure. 

Nomenclature 

50 hr 50 Hour Engine (new) 

Accel Acceleration Limit (RPM/s) 

C-MAPSS Commercial Modular Aero-Propulsion System Simulation 

C-MAPSS40k Commercial Modular Aero-Propulsion System Simulation 40k 

EGT Exhaust Gas Temperature (°R) 

EOL End-of-Life Engine 

EPR Engine Pressure Ratio 

MAS Modified Acceleration Schedule 

Mid Mid Life Engine 

Nc Core Speed 

Nf Fan Speed 

PI Proportional Integral 

Ps3 max Maximum Combustor Static Pressure

Std Standard Day Temperature (59 °F) 
NASA/TM—2012-217261 2 

1.0 Introduction 

There is interest in the ability to use an aircraft’s engines to stabilize and control a distressed aircraft. 

It has been previously shown that in some emergencies the engines can serve as flight control actuators to 

improve the capabilities of the aircraft (Refs. 1 and 2). The ability of the aircraft’s engines to produce 

thrust beyond their current limitations and to respond more quickly to the pilot’s throttle command may 

result in an even greater likelihood of the recovery of a distressed aircraft. However, achieving elevated 

engine performance is complex due to limits that protect the mechanical system from severe structural 

damage such as rotor disk burst, and operability limits that ensure safe aero-thermal engine operation such 

as avoiding compressor surge. A risk performance study is conducted using the Commercial Modular 

Aero-Propulsion System Simulation 40k (C-MAPSS40k) to determine the tradeoff associated with 

extending or removing the engine controller’s limits and allowing the engine to operate beyond its 

nominal design range. This performance/risk study addresses two types of engine performance 

enhancements: 1) overthrust, where limits are relaxed/removed to allow the engine to produce additional 

thrust, and 2) faster engine response, where the limits and the controller bandwidth are modified to 

improve the responsiveness of the engine to the pilot’s throttle command. The two engine performance 

enhancements are in response to different aircraft emergency scenarios; these are not the only possible 

scenarios but are used as examples for these studies. The overthrust enhancement is in response to a 

runway incursion during takeoff, where the available distance for lift-off is suddenly decreased. Ideally, 

the additional thrust will accelerate the vehicle faster allowing the aircraft to takeoff with less available 

runway. The faster engine response enhancement tries to compensate for a rudder/tail failure, where the 

effectiveness of the rudder control surface or vertical stabilizer is reduced. This performance enhancement 

has been shown to enable the engines to behave dynamically as the control surface. More information 

about these scenarios can be found in Reference 3. 

Engine performance is purposely restricted through conservative controller design practices which are 

necessary to provide safe operation and consistent performance throughout the flight envelope and to 

conserve the life of engine components. However, in emergency situations the need to preserve safety 

margins can be traded for increased engine performance, which improves the survivability of the aircraft. 

This type of tradeoff is only considered for high risk situations; situations in which the aircraft is not 

capable of being flown safely. The ultimate goal of this work is to be able to subject the distressed aircraft 

to the minimum risk through the use of the enhanced propulsion control system; this is beyond the scope 

of this paper and more information about this topic is available in Reference 4. This analysis is limited to 

gaining an understanding of how engine risk is affected by changes to the engine controller limits. 

Previous work investigated the ability to obtain additional performance from a commercial aircraft 

engine. Reference 3 described a sensitivity study using the Commercial Modular Aero-Propulsion System 

Simulation (C-MAPSS), a model of a 90,000 lb thrust class engine. Reference 5 contains detailed results 

for a sensitivity study using C-MAPSS40k, a 40,000 lb thrust class engine. For the overthrust scenario, 

References 3 and 5 both conclude that to obtain additional thrust other engine variables will have to 

increase, possibly beyond their limits. However, neither reference identifies a generic tradeoff between 

enhanced engine performance and increased risk of operation. Reference 5 does show a trend based on a 

few flight conditions, but does not capture the entire performance/risk tradeoff that exists with the 

simulation model/risk calculations. Both References 3 and 5 discuss modifications to achieve increased 

engine responsiveness and they identify a subsequent reduction in either closed-loop stability margins or 

high pressure compressor surge margin; however these results are specific to flight conditions and are not 

generic. This performance/risk study attempts to determine the impact on the engine, in terms of risk of 

an engine failure incurred when providing additional performance, either overthrust production or 

increased engine responsiveness. 

This study is performed with the C-MAPSS40k engine. Details of this simulation and an overview of 

the engine controller is provided in Section 2.0. The results of the overthrust scenario are contained in 

Section 3.0, while the faster engine response results are in Section 4.0. Section 5.0 contains general 

conclusions. 
NASA/TM—2012-217261 3 

2.0 Engine Control Overview 

This performance/risk study is conducted using the C-MAPSS40k engine simulation. C-MAPSS40k is 

a 40,000 lb thrust class, two spool, physics-based, component level, high bypass turbofan engine 

simulation with an associated closed loop controller. This engine simulation is modeled in the 

MATLAB/Simulink (The MathWorks, Inc.) environment (Ref. 6). 

The C-MAPSS40k engine control system regulates Engine Pressure Ratio (EPR), which is the low 

pressure turbine exit pressure divided by the engine inlet pressure. EPR is directly related to the thrust 

produced by the engine. The aircraft engine control system converts the pilot’s throttle command from a 

desired thrust level (idle, flight idle, take-off power, etc.) to an EPR setpoint, which is also affected by the 

current flight condition (altitude, Mach, and temperature). A setpoint controller responds to the EPR error, 

which is the difference between the setpoint and sensed EPR feedback, and drives the engine to the 

requested power level. In C-MAPSS40k, the setpoint controller features a Proportional Integral controller 

with integral wind-up protection. The setpoint controller determines the dynamic response of the engine 

to a throttle transient. 

Controller protection logic ensures that the setpoint controller will not cause the engine to violate any 

of its limits. This logic compares select engine sensed measurements against defined operating limits and, 

if necessary, adjusts fuel flow rate to rectify any limit exceedances. The C-MAPSS40k limiters include: 

maximum fan speed, maximum core speed, maximum combustor static pressure, maximum core shaft 

acceleration (based on an acceleration schedule), minimum combustor static pressure, and minimum ratio 

unit (fuel flow rate divided by the static combustor pressure). More information regarding aircraft engine 

control and the scheme employed in C-MAPSS40k can be found in Reference 7. In order for the results of 

this study to have the widest applicability, the study will maintain the existing control system architecture 

and only modify the control limit values. The general method employed in the study is to remove various 

limiters and observe the resulting change in engine performance. 

3.0 Overthrust 

In the overthrust scenario, Reference 3 found that the engine outputs such as rotor speeds, turbine 

temperatures, and compressor pressures, varied nearly linearly with the throttle input, and that the engine 

limits may need to be increased in order for the C-MAPSS engine to meet the overthrust demand. 

Reference 5 found that increasing the thrust demand resulted in a shift in the C-MAPSS40k engine 

outputs, although the shift is not necessarily linear. Reference 5 also found that increasing the engine’s 

thrust output resulted in increasing the risk of an engine failure, which is also dependent on the amount of 

time spent operating at the overthrust condition. An outcome of the Reference 5 study was the addition of 

a turbine temperature limiter designed to allow the temperature limit to be decreased based on the 

expected time of operation. 

In the overthrust scenario, the pilot requests additional thrust from the aircraft’s engines. To facilitate 

this, the EPR setpoints are extended to higher levels. For this study, the EPR setpoints are extended to 

correlate to 120 percent of the maximum rated thrust. In addition, the maximum fan speed, maximum 

core speed, and maximum combustor pressure limits are extended to 150 percent of their nominal values 

to allow the engine to reach the elevated EPR setpoint. A preliminary risk function has been implemented, 

which is similar to the one proposed in Reference 8, to evaluate the change in risk with operating at the 

higher power levels. This risk function, which is a probabilistic model of engine life as a function of 

operating condition, determines the probability of any mechanical engine failure. The engine is designed 

to have a certain life at a given probability of failure based on expected usage, and increasing the 

operating speed and temperature increases the risk of failure. The risk function is based on relationships 

between speed, temperature, and life consumption, and evaluates risk based on the anticipated overthrustrelated operating conditions. As the engine runs, life is consumed increasing the risk of failure, and use of 

an overthrust control mode, because of the increased speeds and temperatures, consumes life significantly 

faster than normal. This reduction in engine life, combined with the current estimate of the engine 
NASA/TM—2012-217261 4 

condition, determines the overall risk of engine failure. The overthrust scenario in this paper concentrates 

on takeoff, therefore the operating time used in the risk calculations is 15 min. 

The risk of engine failure is dependent on the flight condition (altitude, Mach number, and ambient 

temperature) as well as engine deterioration level. Therefore, in this performance/risk study the altitude, 

Mach number, ambient temperature, and engine deterioration level will be varied to determine the engine 

risk factor trends for different power levels. Figure 1 contains risk factor plots for two different airport 

elevations. This includes one airport at 5,431 ft above sea level (elevation at Denver International Airport) 

and a second airport at 2,181 ft above sea level (elevation at McCarran International Airport in Las 

Vegas, NV). Each of these plots show the risk factor for different power level commands (Full Power 

Throttle, %) for a new 50 hr engine, a mid-life engine (Mid), and an end-of-life engine (EOL) on both 

standard days (Std) and hot days (59 and 109 F at sea level, respectively). 

Based on the data shown in Figure 1, generic observations regarding risk/performance tradeoff based 

on flight condition and engine life can be made. First, the elevation at which the power request is made 

plays a major role. This is shown by comparing the risk factor at 120 percent Max Power between the two 

different elevations. At the higher elevation airport (Denver), the risk factor is more than 10 times the risk 

factor at the lower elevation airport (McCarran). This is due to decreased air density at higher elevations, 

which decreases thrust production. Therefore, for the engine to produce the required thrust for takeoff, the 

engine has to operate at higher speeds and hotter temperatures. Another major contributor to the risk of 

engine failure is the ambient temperature. In both plots shown in Figure 1, the shape of the risk curve 

changes based on ambient temperature (comparing the blue lines to the red lines), and the risk at 

120 percent Max Power increases by a factor of 10 or more from a standard to a hot day. This effect is 

again due to decreased air density on hotter days. As the ambient temperature increases, the air density 

decreases. This again requires the engine to operate at higher speeds and temperatures to produce the 

thrust required for takeoff. Increased engine deterioration levels will cause an increase in the risk factor, 

but the increase is rather small compared to the effects of ambient temperature and elevation. As the 

engine degrades, the risk factor increases due to the components reaching their end of life; operating at 

the same altitude, ambient temperature, and EPR results in an increased risk of failure due to the fact that 

much of the component life has already been consumed. Furthermore, a degraded engine runs hotter, 

which also contributes to increased risk. 

Figure 1.—Comparison of risk factor for varying power level, engine life, and temperature, at two different elevations 

(5,431 and 2,181 ft), both at Mach 0.15. 
NASA/TM—2012-217261 5 

Figure 2.—Risk factor for varying takeoff conditions (altitude (ft), Mach number, ambient temperature, and 

engine age) for two power levels (115 percent max power and 120 percent max power). Note that the 

pilots’ predominant control is engine power level, all other parameters (altitude, Mach number, ambient 

temperature, and engine life) are essentially fixed; determined by the takeoff location (airport), the 

current local weather (temperature), and engine age. 

This type of evaluation can be extended to include many different takeoff conditions, by varying 

Mach number, altitude, ambient temperature, and power levels. Figure 2 compares the risk factor (as a 

contour plot) for varying altitude, Mach number, temperature, and engine deterioration level. The two 

plots shown in Figure 2 correspond to different power levels, 115 percent Max Power (left) and 

120 percent Max Power (right). 

The data in Figure 2 again show the effect of the ambient temperature on risk of failure. Comparing 

the two columns for each power level, a large change in the risk factor exists based on the temperature. 

Comparing the power levels, the data show that increasing the power level from 115 percent max power 

to 120 percent max power greatly increases the risk on hotter days, but not as much on standard days. 

Another observation is that at altitudes greater than 5,000 ft, the risk factor is increased drastically more 

compared to the lower altitudes. This suggests that at airports with an elevation of less than 3,000 ft, 

increasing the thrust output of the engine for takeoff maybe very practical due to the relatively low 

increase in risk. However, at higher altitude airports, such as at Denver (altitude 5,431 ft), additional 

thrust may not be justified based on the increased risk level. These plots also indicate, as did the plots 

shown in Figure 1 that the engine life plays a minor role in increasing the risk of failure compared to the 

ambient temperature and altitude. 
NASA/TM—2012-217261 6 

4.0 Faster Engine Response 

Increasing the responsiveness of the engine can be divided into two separate categories, one for small 

throttle transients and the other for large throttle transients. For the small throttle transients, Reference 3 

found that both increasing the controller bandwidth and disabling the controller limits allowed for a 

significant reduction in the settling time. Reference 5 however found that increasing the bandwidth alone 

was enough to increase the engine responsiveness since none of the limits become active for small throttle 

transients in C-MAPSS40k. The difference between these two findings can be attributed to a structural 

difference between the C-MAPSS controller, which was used in the previous studies, and the 

C-MAPSS40k controller protection logic. The C-MAPSS controller has an upper and lower bound on the 

change in fuel flow, limiting the acceleration based on change in fuel flow, whereas C-MAPSS40k limits 

the acceleration based on the current core speed of the engine and the magnitude of the change. 

Regarding large throttle transients, Reference 3 found that relaxing the turbine temperature limit, 

modifying the acceleration schedule, and increasing the controller bandwidth increased the engine 

responsiveness. Reference 5 proposed a Modified Acceleration Schedule (MAS), which is a look up table 

based method where an offset is added to the nominal acceleration schedule. This offset will increase the 

acceleration schedule resulting in a faster responding engine. 

The purpose of the faster engine response operation is to decrease the lag between the pilot’s 

command and engine response. In an emergency situation, such as a rudder/tail failure as the aircraft is 

approaching the runway, the pilot may find it necessary to execute a go around (abort the landing) and 

re-attempt the approach. For this type of maneuver, the pilot will move the throttle from flight idle (very 

low power level used during the approach) to takeoff thrust very quickly. In this type of situation, the 

acceleration schedule commands a conservative engine response to prevent high pressure compressor 

surge. The acceleration schedule in C-MAPSS40k is designed to ensure that the high pressure compressor 

surge margin is greater than 0.0 for a full throttle transient regardless of the flight condition (as long as the 

flight condition is inside the flight envelope) or the engine deterioration level. 

To increase the responsiveness of the engine for this type of command, the acceleration schedule may 

be modified to allow higher core acceleration, resulting in a faster engine response and decreased high 

pressure compressor surge margin. The modification of the acceleration schedule can be done from a 

lookup table that determines the acceleration schedule bias based on the flight condition and the engine 

deterioration level. This look up table method is referred to as Modified Acceleration Schedule (MAS) 

(Ref. 5). The nominal control response, referring to the engine response with no changes made to the 

controller, and MAS control responses to a full throttle transient with a 50 hr engine and an end-of-life 

engine are shown in Figure 3. 

Figure 3.—Engine responses to a full throttle transient for varying ambient temperature and engine degradation. 
NASA/TM—2012-217261 7 

Figure 3 indicates that an increase in the ambient temperature will increase the settling time for the 

nominal control by about 2 sec. Considering the nominal control response between a 50 hr engine and an 

end of life engine for the same ambient temperature, the thrust response is nearly independent of engine 

life. However, a reduction in engine life will decrease the surge margin; in Figure 3 the surge margin is 

reduced by about 4 percent over the entire life of the engine. Since the MAS control method of increasing 

the responsiveness trades surge margin for responsiveness, flight conditions and engine degradation levels 

that have the most surge margin available will be capable of larger thrust response improvements. This is 

very apparent in Figure 3; the condition with the largest surge margin reduction has the greatest 

performance increase. In this example, the MAS was designed such that the resulting surge margin never 

fell below 2 to 3 percent. The MAS was successful in 3 of the 4 scenarios, the surge margin for a 50 hr 

engine on a hot day decreased to below 2 percent, but stayed above 0 percent. This is due to nonlinearities 

in the engine and inaccuracies in the lookup table method. 

One of the uncertainties that the acceleration schedule must account for is normal engine-to-engine 

variation. Since a less than average engine must be able to accelerate safely, the acceleration schedule 

must be designed to accommodate a 3 sigma variation in surge margin to essentially guarantee that no 

engine will surge. If the engine-to-engine variation in surge margin is normally distributed with a standard 

deviation of 1 percent, then in the worst case 99.86 percent of all engines will accelerate safely for a 

3 percent designed minimum surge margin. Any adjustment of the acceleration schedule for faster engine 

response means that the below average engines are more likely to surge. The impact of the 3-sigma 

variation on faster engine response and surge margin in run-time can be seen in Figure 4. Figure 4 

compares the nominal control and MAS control surge margin response for the 50 hr engine on a standard 

day, the same response as shown in Figure 3, but with the 3 sigma variation around the surge margin. The 

lower bound on the surge margin in Figure 4 represents 99.86 percent of all 50 hr engines. By increasing 

the acceleration schedule to allow the surge margin responses shown in Figure 4, it is clear that there are 

50 hr engines in the fleet that would surge. When modifying the acceleration schedule, the risk is 

inversely related to the likelihood that the aircraft’s engines are better than an average 50 hr engine. The 

more likely that the engine is better than average, the greater the available surge margin and the less risky 

is the modification of the acceleration schedule. The second part of the risk is how much to increase the 

Figure 4.—Surge Margin for 50 hr engine undergoing full throttle transient 

with nominal control and MAS control. 
NASA/TM—2012-217261 8 

acceleration schedule, or how low to reduce the surge margin for an average engine. The more confidence 

there is that the engine is an average engine or better, the more the acceleration schedule can be increased, 

decreasing the engine surge margin closer to zero. However, if there is no confidence that the engine is an 

average engine or better, then the acceleration schedule modification may have to be more conservative. 

The C-MAPSS40k setpoint controller for EPR is a PI controller that dominates the response for 

smaller throttle transients that are unaffected by the acceleration limiter. The performance for these 

transients can be enhanced by increasing the bandwidth of the PI controller. The concern with increasing 

the bandwidth of the PI controller is decreasing stability margins (gain margin and phase margin) and 

actually decreasing the performance of the engine. A decrease in the stability margins can result in a 

decrease in performance, in terms of increased settling time, increased overshoot (below 2 percent is 

considered acceptable), and increased rise time. The only performance metric that may not be affected by 

the decrease in stability margins is the delay time, or the time it takes for the engine to respond to the 

throttle command. Figure 5 shows the settling time, percent overshoot, delay time, and rise time 

performance metrics as a function of the PI gain multiplier (bandwidth increase). The data were taken at 

altitudes from 0 to 28,000 ft in 4,000 ft increments, 0.0 to 0.7 Mach in 0.1 Mach increments, on both 

standard and hot days, and for a 50 hr engine, a mid life engine, and an end-of-life engine. 

The data in Figure 5 suggest that the PI controller gains can be increased, but only by a factor of about 

1.5. Increasing the gains by more than this may decrease the performance of the engine, which is shown 

in Figure 5 by the increase in settling time for multipliers greater than 1.5, an increase in the overshoot 

(above 2 percent) for multipliers greater than 2.5, and increased rise times for multipliers greater than 

approximately 1.5. The delay time improves for almost all of the tested data points, but does start to 

diverge after a multiplier of 3. This shows that it is possible to obtain additional performance from the 

engine by increasing controller gains; however there is a risk that the increased controller gains will 

actually decrease the performance of the engine, making the situation worse. 

Figure 5.—Performance for small throttle transients for various PI gain multipliers. 
NASA/TM—2012-217261 9 

5.0 Conclusions 

This paper discussed approaches to achieve enhanced engine performance and showed results from the 

application of these approaches to a turbofan engine simulation, C-MAPSS40k. For overthrust, the 

amount of additional thrust produced by the engine was compared to the risk factor, or the ratio of the risk 

of an engine failure caused by the use of additional thrust to the maximum normal operating risk. This 

study determined that altitude and ambient temperature are the two most significant factors in increasing 

the risk of an engine failure, especially as the amount of overthrust increases. At lower altitudes, even on 

a hot day, there was low to medium increase in risk to produce 120 percent maximum thrust. For the 

faster engine response, there were two different tradeoffs to compare depending on the size of the throttle 

transient. For large throttle transients, which are affected by the acceleration schedule, the acceleration 

schedule may be increased; this results in faster response and decreased settling time, but at the cost of 

decreasing the surge margin, which is directly related to the risk of an engine failure. The maximum 

benefit can be achieved with newer or above average engines, while similar performance improvement is 

much riskier with deteriorated engines. For smaller throttle transients, which are unaffected by the 

acceleration schedule, improved response speed is accomplished by increasing the controller bandwidth. 

However this will actually decrease stability margins to the point where the performance is degraded. 

Based on the observations in this paper, the controller bandwidth can be increased up to 1.5 times the 

current level with little risk of performance degradation. These results show that it is possible, under the 

right conditions, to achieve significantly increased performance with little risk of engine failure, although 

improvement is severely limited without a significant risk increase in other cases. Understanding what the 

capabilities and limitations are can lead to new control algorithms to improve engine performance 

relatively safely. These conclusions are specific to the C-MAPSS40k type engine and controller, however 

the methodology in this paper can be used to evaluate the trade-offs for different engines and different 

controller architectures. 

References 

1. Burcham, F.W., Jr., and Fullerton, C.G., “Controlling Crippled Aircraft - With Throttles,” 

NASA/TM-104238, 1991. 

2. Burcham, F.W., Jr., Fullerton, C.G., and Maine, T.A., “Manual Manipulation of Engine Throttles for 

Emergency Flight Control,” NASA/TM—2004-212045, January 2004. 

3. Litt, J.S., Frederick, D.K., and Guo, T.-H, “The Case for Intelligent Propulsion Control for Fast 

Engine Response,” AIAA–2009–1876, AIAA Infotech@Aerospace Conference, Seattle WA, 

June 6–9, 2009. 

4. McGlynn, G.E., Litt, J.S., Lemon, K.A., and Csank, J.T., “A Risk Management Architecture for 

Emergency Integrated Aircraft Control,” AIAA–2011–1568, Infotech@Aerospace 2011, St. Louis, 

Missouri, Mar. 29–31, 2011. 

5. Csank, J.T., May, R.D., Litt, J.S., and Guo, T.-H., “A Sensitivity Study of Commercial Aircraft 

Engine Response for Emergency Situations,” NASA/TM—2011-217004, April 2011. 

6. May, R.D., Csank, J., Lavelle, T.M., Litt, J.S., and Guo, T.-H, “A High-Fidelity Simulation of a 

Generic Commercial Aircraft Engine and Controller,” 46th AIAA/ASME/SAE/ASEE Joint Propulsion 

Conference & Exhibit, Nashville, TN, July 25–28 2010. 

7. Csank, J., May, R.D., Litt, J.S., and Guo, T.-H., “Control Design for a Generic Commercial Aircraft 

Engine,” AIAA–2010–6629, 46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and 

Exhibit, Nashville, TN, July 25–28, 2010. 

8. Litt, J.S., Sharp, L.M., Guo, T.-H., “A Risk Assessment Architecture for Enhanced Engine 

Operation,” AIAA–2010–3469, AIAA Infotech@Aerospace 2010, Atlanta, GA, April 20–22, 2010. 
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5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Csank, Jeffrey, T.; May, Ryan, D.; Guo, Ten-Huei; Litt, Jonathan, S. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 284848.02.05.03.10 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-18017 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITOR'S

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2012-217261 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Categories: 07 and 63 

Available electronically at http://www.sti.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

This paper studies the effect of modifying the control limits of an aircraft engine to obtain additional performance. In an emergency 

situation, the ability to operate an engine above its normal operating limits and thereby gain additional performance may aid in the recovery 

of a distressed aircraft. However, the modification of an engine’s limits is complex due to the risk of an engine failure. This paper focuses 

on the tradeoff between enhanced performance and risk of either incurring a mechanical engine failure or compromising engine operability. 

The ultimate goal is to increase the engine performance, without a large increase in risk of an engine failure, in order to increase the 

probability of recovering the distressed aircraft. The control limit modifications proposed are to extend the rotor speeds, temperatures, and 

pressures to allow more thrust to be produced by the engine, or to increase the rotor accelerations and allow the engine to follow a fast 

transient. These modifications do result in increased performance; however this study indicates that these modifications also lead to an 

increased risk of engine failure. 

15. SUBJECT TERMS

Control; Propulsion control; Sensitivity analysis 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

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 PAGES

15 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

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b. ABSTRACT

U 

c. THIS 

PAGE

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19b. TELEPHONE NUMBER (include area code)

443-757-5802 

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