Jonathan S. Litt

Glenn Research Center, Cleveland, Ohio

T. Shane Sowers 

Vantage Partners, LLC, Brook Park, Ohio

A. Karl Owen

Motile Robotics, Inc., Joppa, Maryland

Christopher E. Fulton

Zin Technologies, Middleburg Heights, Ohio

Amy K. Chicatelli

Vantage Partners, LLC, Brook Park, Ohio

Flight Simulator Evaluation of Enhanced Propulsion 

Control Modes for Emergency Operation

NASA/TM—2012-217698

September 2012

AIAA–2012–2604
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Jonathan S. Litt

Glenn Research Center, Cleveland, Ohio

T. Shane Sowers 

Vantage Partners, LLC, Brook Park, Ohio

A. Karl Owen

Motile Robotics, Inc., Joppa, Maryland

Christopher E. Fulton

Zin Technologies, Middleburg Heights, Ohio

Amy K. Chicatelli

Vantage Partners, LLC, Brook Park, Ohio

Flight Simulator Evaluation of Enhanced Propulsion 

Control Modes for Emergency Operation

NASA/TM—2012-217698

September 2012

AIAA–2012–2604

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

Infotech@Aerospace 2012 Conference

sponsored by the American Institute of Aeronautics and Astronautics

Garden Grove, California, June 19–21, 2012
Acknowledgments

The authors thank Ten-Huei Guo and Ryan D. May for guidance in the implementation and testing of the yaw rate feedback. The 

authors acknowledge the NASA Aviation Safety Program’s Vehicle Systems Safety Technologies Project for funding this work.

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

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217698 1

Flight Simulator Evaluation of Enhanced Propulsion 

Control Modes for Emergency Operation

Jonathan S. Litt

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

T. Shane Sowers 

Vantage Partners, LLC

Brook Park, Ohio 44142

A. Karl Owen

Motile Robotics, Inc.

Joppa, Maryland 21085

Christopher E. Fulton

Zin Technologies

Middleburg Heights, Ohio 44130

Amy K. Chicatelli

Vantage Partners, LLC

Brook Park, Ohio 44142

Abstract

This paper describes piloted evaluation of enhanced propulsion control modes for emergency 

operation of aircraft. Fast Response and Overthrust modes were implemented to assess their ability to 

help avoid or mitigate potentially catastrophic situations, both on the ground and in flight. Tests were 

conducted to determine the reduction in takeoff distance achievable using the Overthrust mode. Also, 

improvements in Dutch roll damping, enabled by using yaw rate feedback to the engines to replace the 

function of a stuck rudder, were investigated. Finally, pilot workload and ability to handle the impaired 

aircraft on approach and landing were studied. The results showed that improvement in all aspects is 

possible with these enhanced propulsion control modes, but the way in which they are initiated and 

incorporated is important for pilot comfort and perceived benefit.

Introduction

Previous in-flight emergencies in which flight control has been partially or totally lost, have required 

pilots to learn how to fly the damaged aircraft, sometimes requiring innovative approaches. The use of 

differential thrust for maneuvering is an example that has been used successfully on several occasions

(Refs. 1 to 4). Other examples of mid-air or on-the-ground crises, such as accidents caused by runway 

incursions or attempted take-offs from the wrong runway, have not ended well (Refs. 5 to 7). However, it 

has been speculated that in some cases there is a potential safety improvement possible through the 

incorporation of additional propulsion system capability (Ref. 8).

The engines are the most powerful actuators on the aircraft, and have a large role to play in upset 

recovery and accident prevention. For instance, it is possible to use differential thrust to replace or 

augment the function of a damaged rudder and vertical tail. However, when using the engines alone for 

maneuvering, an aircraft can take as much as 5 to 10 times as long to respond compared to using the 

conventional flight control surfaces (Ref. 9). This lag in response is due to the relatively slower engine 
NASA/TM—2012-217698 2

dynamics; additionally, engine placement dictates the control authority the engines have on the aircraft.

Besides the ability to maneuver and land a disabled aircraft, as demonstrated in the UAL 232 Sioux City 

accident (Ref. 1) and the DHL A300-B4 Baghdad event (Ref. 4), there are other more subtle capabilities 

of the flight control system that can be assumed by the propulsion system in case of an emergency, such 

as maintaining acceptable handling qualities (or at least aircraft stability). For instance, Dutch roll is a 

combined roll and yaw oscillation that is normally very lightly damped in swept-wing aircraft such as 

modern airliners. To increase the damping of the Dutch roll oscillations, a yaw damper is installed that 

measures the yaw rate of the aircraft and makes necessary commands to the rudder to compensate. In the 

event of vertical tail damage, the aircraft’s natural tendency to damp the Dutch roll oscillations is reduced, 

and with no rudder, the yaw damper will become ineffective. Previous NASA research aimed at using the 

throttles alone to maneuver an aircraft with no flight control system specifically identified sluggish engine 

response and Dutch roll as problems (Ref. 10). As a result of these findings, follow-on research to 

develop a propulsion-based automatic flight control system known as Propulsion Controlled Aircraft 

(PCA) was pursued (Ref. 11). This system proved successful in both alleviating much of the lightly 

damped aircraft behavior, and in reducing pilot workload.

Another safety-enhancing feature that that has not been previously studied is the ability of the 

propulsion system to provide additional thrust beyond the normal maximum. This capability could be 

used to shorten the required take-off distance, for instance, in the case of an aircraft that mistakenly 

utilizes a runway that is too short.

Research into achieving enhanced engine responsiveness to address these situations has revealed that 

the potential exists to greatly improve engine performance through control system modifications alone

(Ref. 12) albeit with a slightly increased risk to the engine (Ref. 13). This risk is mitigated, however, by 

the overall safety improvement to the distressed vehicle (Ref. 8). In preparation to investigate the 

improvement in controllability and thus safety for the imperiled aircraft, enhanced propulsion control 

modes for emergency flight operation have been developed and demonstrated in simulation (Refs. 13 to 

15). Specifically, the two modes are Overthrust and Fast Response, which relate to emergency situations 

such as runway incursion and loss of flight control effectiveness, respectively.

This paper describes on-going flight simulator evaluation of enhanced propulsion control modes as 

the pilot attempts to complete various tasks with an impaired aircraft, specifically with the rudder stuck in 

the neutral position. The intent is to begin to characterize the limitations of using the standard propulsion 

control available with the nominal or impaired aircraft, and the improvement achievable using the 

enhanced propulsion control modes. The performance improvements enabled by these modes have the 

potential to provide safety enhancements over using the nominal engines, whether for throttles-only 

maneuvering or as part of a specially designed flight control system such as PCA. The enhanced 

propulsion control modes are described in the next section. The remainder of the paper describes the 

results of several tests used to evaluate the effectiveness of the enhanced propulsion control modes, and 

their integration into the aircraft for ease of use. Based on these results, conclusions are drawn.

Simulator and Enhancements

The enhanced propulsion control modes were implemented for the engines (Ref. 12) of a nonlinear 

simulation of a four-engine transport aircraft. The engine performance is representative of actual engines 

in their thrust class (Ref. 16), and the enhanced control modes are realistically achievable. This simulation 

was incorporated into a fixed-base flight simulator that was developed to evaluate the impact of 

propulsion control innovations on flight operation. The cockpit (Figure 1) has two throttles which are 

used for the left and right side engines, meaning that the inboard and outboard engines on each side are 

always at the same power setting. The pilot has switches in the cockpit to turn the Overthrust and Fast 

Response modes on and off individually. The pilot can set the flaps and landing gear. The cockpit also has 

rudder pedals and a stick. There are no other controls. No wind was included in these tests.
NASA/TM—2012-217698 3

Figure 1.—Flight simulator setup.

Overthrust

The impact of the Overthrust control mode is shown in Figure 2. The throttle position, which 

corresponds to the thrust setpoint, is moved higher than the normal 100 percent, and control limits that 

might otherwise be hit are relaxed to enable the engine to produce thrust beyond its normal maximum. In 

the figure, the initial power level corresponds to 100 percent thrust. At 10 s, Overthrust mode is initiated, 

resulting in the various overlaid transients up to higher thrust levels. Here each higher thrust level 

corresponds to a different level of risk of engine failure as the engine is pushed harder and harder.

Fast Response

The impact of the Fast Response control mode is shown in Figure 3. In this case, the engine is more 

responsive to large throttle changes because the limits that restrict acceleration have been adjusted to 

allow faster command following. The thrust response of an engine is typically restricted to accommodate 

the worst case stack-up of detrimental effects (inlet distortion, engine deterioration, engine-to-engine 

variation, Reynolds number effects, etc.) to avoid stall and surge (Ref. 9). If one is willing to accept 

higher risk of surge, or knows with certainty that the worst case situation does not exist, the engine can be 

allowed to accelerate more rapidly.

Yaw Rate Feedback

For some of the testing, a yaw rate feedback controller was implemented to aid or potentially replace 

the rudder function automatically, as opposed to manual manipulation of the throttles (Refs. 15 and 17).

The approach taken was similar to that in Reference 15: Multiply the measured yaw rate signal by a gain 

k after it passes through a washout filter, and sum the result with the pilot’s pedal inputs. This signal is 

subsequently applied to the throttle settings differentially, as shown in Figure 4. (Note that the throttle 

setting is sometimes called Power Lever Angle or PLA.) This setup allows the pilot to maintain control 

over yaw rate using the pedals, and commands zero yaw rate when they are not depressed, which 

corresponds to a coordinated turn. As can be seen in Figure 4, the yaw rate error is applied to the engines 

on each side with equal but opposite magnitudes. On one side the throttle is increased, on the other it is 

decreased by the same amount. This maintains approximately the same total thrust, but applies a yawing 

moment to the aircraft, which can be used to help maneuver, or to oppose an undesired yaw rate 

disturbance.
NASA/TM—2012-217698 4

Figure 2.—Examples of Overthrust operation. 

Thrust levels reach various values above the 

normal maximum level as the setpoint is 

raised above 100 percent. The higher the 

thrust, the greater the risk of engine failure.

Figure 3.—Fast Response transient 

showing the ability of the engine to 

accelerate more rapidly than normal 

when controller limits are relaxed.

Figure 4.—Yaw rate feedback to differential throttle, where r is yaw rate and 

PLA is Power Lever Angle or throttle position.

Results

Three types of tests were conducted. The purpose of the first type was to evaluate the reduction in 

required takeoff distance obtained using Overthrust for a runway incursion scenario. The second type of 

testing involved turning with the rudder locked, using nominal and enhanced engine responses, with and 

without yaw rate feedback. The purpose of these tests was to evaluate Dutch roll damping and the ability 

to achieve a desired heading. Finally, the third type of testing assessed approach and landing attempts

with a disabled rudder, again using a variety of control techniques.

Runway Incursion

For consistency during these tests, and to eliminate pilot anticipation, runway incursions were not 

simulated. Since runway incursions are relatively rare events, the pilot would not generally be expecting 

another aircraft to cross its path during takeoff. However, since the pilot knew it would happen here, even 

if the tests were randomized, it was decided to eliminate the human factor as much as possible and just 

begin the takeoff roll with Overthrust mode active. Thus from engine spool-up, the highest throttle setting 

corresponded to higher than normal takeoff thrust. It is intuitively clear that the required takeoff distance 

will be shorter with additional thrust, so the focus was on testing the improvement achievable through the 

use of this emergency control mode, and learning how to ascend in the shortest distance. In this scenario, 

three types of propulsion control were applied from the start of each respective run: Standard (not 

enhanced), Overthrust, and a combination of Fast Response and Overthrust. Piloted evaluation showed a 

clear improvement with Overthrust versus standard control, while the addition of Fast Response made no 

significant difference, which is to be expected since the fast response reduces the engine spool up time by
NASA/TM—2012-217698 5

Figure 5.—Comparison of takeoff trajectories with standard 

control and enhanced control (Overthrust mode enabled).

about 1 s (Ref. 13) over the approximately 40 s takeoff roll. Figure 5 shows a comparison of the results 

for standard control and enhanced control in terms of altitude vs. distance. While there is variation within

each group of takeoffs, they are distinct groups with the required takeoff distance shorter by about 1000 ft 

for the set that used enhanced control.

In an emergency situation, the pilot would have to determine the feasibility of using this control 

mode. If the plane has already reached takeoff decision speed (V1 speed) and cannot stop before impact, 

its use would be appropriate. In that case, however, the enhanced control mode would be initiated well 

into the takeoff roll and the distance advantage it provides would be less than seen in this study. On the 

other hand, under those circumstances, Fast Response might show more of a benefit than it did here.

Turns

Turns were used to evaluate the stability and controllability improvements made possible through the 

use of enhanced propulsion control. Two types of test were performed, one to assess Dutch roll damping,

and the other to determine the pilot’s ability to achieve a desired heading.

Turns Using Stick—Dutch Roll Damping

The objective of this test was to evaluate the aircraft’s ability to damp Dutch roll without pilot 

intervention. For each trial, the pilot initiated the Dutch roll using the following procedure. He trimmed the 

aircraft at the desired altitude and speed, moved the stick hard over to the right and banked to 40°, turned 

right maintaining the roll angle, then rolled out at a desired heading by moving the stick hard over to the left, 

and then releasing with wings near level, thus causing the Dutch roll. There was some variation from trial to 

trial, but the starting point after Dutch roll initiation was similar in all cases. The cases included:

• Nominal aircraft, no damage

• Rudder stuck in neutral position with no compensation

• Rudder stuck in neutral position with yaw rate feedback and nominal engines

• Rudder stuck in neutral position with yaw rate feedback and fast-responding engines

Some results are shown in Figure 6 and Figure 7. The trials performed at 5000 ft, 200 kn (Figure 6), 

show that using yaw rate feedback provides a significant improvement in damping over the stuck rudder 

case with no yaw rate feedback, although none are as damped as the nominal case. There is no noticeable 

difference in the ability to damp between the fast-responding and nominal engines using yaw rate 

feedback, indicating that the nominal engines are fast enough. However, at 20,000 ft, 300 kn (Figure 7), 

while the extremes are the same, the fast-responding engines demonstrate a significant improvement in 

damping over the nominal engines when yaw rate feedback is used. This reveals that the nominal engines 

are not fast enough to damp the Dutch roll oscillations effectively in this case.
NASA/TM—2012-217698 6

Figure 6.—Yaw rate at 5000 ft, 200 kn demonstrating similar yaw 

damping with nominal and faster engine. The pilot initiated a Dutch

roll by using the stick to bank and turn, then roll out rapidly.

Figure 7.—Yaw rate at 20,000 ft, 300 kn demonstrating improved yaw 

damping with faster engine. The pilot initiated a Dutch roll by using 

the stick to bank and turn, then roll out rapidly.

0 10 20 30 40 50

-10

-5

0

5

10

Time, s

Yaw Rate, degrees/s

Yaw Damping

Baseline

Stuck Rudder

Yaw Rate Feedback, Fast Response

Yaw Rate Feedback, Nominal Engines

0 10 20 30 40 50

-5

0

5

10

Time, s

Yaw Rate, degrees/s

Yaw Damping

Baseline

Stuck Rudder

Yaw Rate Feedback, Fast Response

Yaw Rate Feedback, Nominal Engines
NASA/TM—2012-217698 7

Turns Using Rudder Pedals

The purpose of this test was to evaluate the controllability of the aircraft by testing the ability to 

maintain a desired heading when rolling out of a turn. For this test, the pilot used the stick together with 

the pedals, when the yaw rate feedback to the throttles was engaged, to bank and turn, then roll out at the 

desired heading. Figure 8 shows the results in heading and roll angle for the four cases. As usual, the 

nominal aircraft was very controllable and smooth, and the aircraft with the disabled rudder was much 

more oscillatory. When using yaw rate feedback to the throttles, the behavior is a little more oscillatory 

than for the nominal aircraft, regardless of engine response speed, particularly in roll, but is very 

controllable. The hunting at the end of the run for the final heading is mostly due to the pilot having to 

anticipate when to apply rudder to stop the turn; the faster engine stopped it too soon, while the nominal 

engine stopped it too late.

Using the pedals seemed more successful in controlling heading than the use of yaw rate feedback 

without the pedals. This is likely due to the size of the command that the pilot was able to give with the 

pedals, and the speed with which he could modulate it, as well as his ability to anticipate. Although the 

pilot seemed to have good control during this maneuver when yaw rate feedback was engaged, he said 

that he was not comfortable using the rudder pedals in that way. He said that using the stick without the 

rudder pedals felt more natural, while using yaw rate feedback did not feel right dynamically. The pilot is 

used to nearly instantaneous response from the rudder, and although the engine response can be sped up, 

the inherent delay cannot be avoided altogether. He did not use rudder pedals for any other tests.

Landing

Several methods of testing landing were evaluated with the stuck rudder; the landing gear started in 

the lowered position in all cases. The pilot flew using the standard controls with compensation for the 

stuck rudder, and he used a throttles-only technique. All testing began from a trimmed condition. Locking 

the rudder in flight in such a case did not cause an upset and was transparent to the pilot.

Landing Using Stick

In this scenario, the crippled aircraft started out in stabilized flight pointed in the general direction of 

but offset laterally from the airport. The objective was to maneuver to the airport (Figure 9) and land 

(Figure 10). 

Figure 8.—Roll out at a heading of 270° after a bank and turn accomplished using rudder pedals and stick. These 

tests were performed at about 3000 ft, 250 kn.

70 75 80 85 90 95

260

262

264

266

268

270

272

274

276

278

280

Heading

Heading, deg

Nominal

Stuck Rudder

Stuck Rudder, Yaw Rate Feedback

Stuck Rudder, Yaw Rate Feedback, Faster

 

 

70 75 80 85 90 95

-10

-8

-6

-4

-2

0

2

4

6

8

10

Roll

Time, s

Roll, deg
NASA/TM—2012-217698 8

The pilot flew using the stick; he did not attempt to use the rudder pedals. The flaps were set at 

50 percent. The tests included:

• Rudder stuck in neutral position with no compensation

• Rudder stuck in neutral position with yaw rate feedback and nominal engines

• Rudder stuck in neutral position with yaw rate feedback and fast-responding engines

These were blind randomized tests, during which the pilot did not know the type of engine response or 

feedback in use. He was very cautious about making or unwilling to make last minute corrections; he flew 

very conservatively. His comments after each flight indicated that he felt most comfortable without yaw rate 

feedback because he could better anticipate how the aircraft would react. He seemed to feel least 

comfortable with yaw rate feedback and fast response. These impressions are particularly interesting 

because in the best no-yaw-rate feedback case, when he was able to avoid initiating any significant 

oscillation, the results were no less oscillatory than the cases with yaw rate feedback and faster engines, and 

generally the compensation reduced oscillation significantly. Additionally, yaw rate feedback with faster 

engine response always provided the most damping and the smallest oscillations, while nominal engines 

with yaw rate feedback were often the least damped after the second turn. Figure 11 and Figure 12 show 

typical results for roll rate and yaw rate. What is clear is that after the first large turn, in the cases with yaw 

rate feedback the oscillations damp out much more quickly than without. After the second large turn, 

however, damping for the cases with yaw rate feedback with nominal engines was often worse than for the 

other cases. In all cases without significant oscillation, on final approach there is a persistent small Dutch 

roll, probably maintained by the tiny corrections required to land. Apparently, lining up with the runway 

was tricky in these runs, and poor orientation after the second turn often resulted in a difficult approach.

Landing Using Throttles Only

This scenario was the same as the previous one (Figure 9), except for the following: The pilot used 

throttles alone to maneuver, the flaps were set at 65 percent, and there was no yaw rate feedback. He did 

not use the stick, even though only the rudder was stuck. Landings were attempted with nominal and fast 

engines, and the pilot was aware of the control mode. The pilot flew conservatively, and was able to line 

up with the runway without too much difficulty in all cases. This difference in ease of lining up from the 

previous test using the stick is due to the slower, more sluggish behavior with throttles-only maneuvering 

that eliminated the tendency to over-control. With throttles only, final approach was much harder than 

initial alignment with the runway because the flight path adjustments had to be finer, and the pilot was

careful not to overcompensate or accidentally initiate a large oscillation. He was able to achieve manageable 

roll and yaw rates (Figure 13 and Figure 14), although they were larger than he would have preferred. The

Figure 9.—Ground track of impaired aircraft flying toward 

airport (CLE).

Figure 10.—The pilot's view toward the airport (CLE) on 

approach.
NASA/TM—2012-217698 9

pilot felt that the faster engine response provided an advantage for fine tuning. Figure 15 and Figure 16 bear 

out the pilot’s claim. These figures show the time derivative of the throttle movements for similar 

approaches to emphasize the adjustments the pilot made. Though true for both throttles for the runs shown, 

for right throttle in particular (Figure 16), it is clear that the pilot made fewer, faster adjustments with the 

more responsive engines, while he made gentle adjustments more often with the nominal engines. Thus the 

faster engines provided about the same level of flight control with lower pilot workload. As with the other 

tests, skill tended to improve with practice.

Figure 11.—Roll rate for landing trials using the stick.

Figure 12.—Yaw rate for landing trials using the stick.

0 50 100 150 200 250 300

-15

-10

-5

0

5

10

15

20

25

Roll Rate

Time, s

Roll Rate, deg/s

nominal engines, no yaw rate feedback

nominal engines with yaw rate feedback

fast engines with yaw rate feedback

0 50 100 150 200 250 300

-5

-4

-3

-2

-1

0

1

2

3

4

5

Yaw Rate

Time, s

Yaw Rate, deg/s

nominal engines, no yaw rate feedback

nominal engines with yaw rate feedback

fast engines with yaw rate feedback
NASA/TM—2012-217698 10

Figure 13.—Roll rate on final approach for throttles-only landing.

Figure 14.—Yaw rate on final approach for throttles-only landing.

160 170 180 190 200 210 220 230 240 250 260

-4

-3

-2

-1

0

1

2

3

Roll Rate on approach

Time, s

Roll Rate, deg/s

nominal engines

fast engines

160 170 180 190 200 210 220 230 240 250 260

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

Yaw Rate on approach

Time, s

Yaw Rate, deg/s

nominal engines

fast engines
NASA/TM—2012-217698 11

Figure 15.—Time derivative of movement of left PLA on approach for 

throttles-only landing.

Figure 16.—Time derivative of movement of right PLA on approach for 

throttles-only landing. It is clear that the pilot made fewer, faster 

corrections with the faster engines, and smaller adjustments more often 

with the nominal engines.

160 170 180 190 200 210 220 230 240 250 260

-200

-150

-100

-50

0

50

100

150

200

250

300

Time, s

d(PLA)/dt, %/s

d(PLAL)/dt on final approach

nominal engines

fast engines

160 170 180 190 200 210 220 230 240 250 260

-200

-150

-100

-50

0

50

100

150

200

250

300

d(PLAR)/dt on final approach

Time, s

d(PLA)/dt, %/s

nominal engines

fast engines
NASA/TM—2012-217698 12

The pilot seemed more comfortable using the throttles for fine tuning than attempting to fly normally 

with yaw rate feedback to the throttles. This preference was a result of the relatively slow engine response 

when compared to the rudder; the delay in engine response made small adjustments particularly difficult 

to accomplish.

The general observations were that there is a clear learning curve in all cases. With practice the pilot 

was able to land safely more consistently, however, there was greater improvement when using the

enhanced control modes. When the pilot had the ability to turn on and off the enhanced control modes, he 

tended to use Overthrust during flare, which he stated was very useful. Increasing power during flare was 

used to reduce sink rate. Normally, the stick would be pulled back to settle on the runway, but increasing 

power caused a similar effect. Therefore, Overthrust capability is considered generally useful for flying, 

not just for takeoff, when incorporated intelligently or when the pilot knows when to take advantage of it. 

This is the type of unanticipated benefit exposed by the creativity and resourcefulness of the pilot, and is 

reminiscent of what happened during the Baghdad event, in which the pilots of the disabled aircraft 

increased thrust during flare to obtain positive pitch (Ref. 4). 

General Impressions

The pilot had several observations:

• He preferred the throttle to the pedals because he felt he had finer control with the throttles.

• He would have liked to have a sideslip indicator, which is not currently in the simulator’s 

instrumentation. The pilot might have been more willing to use pedals if there had been one 

available.

• His assumption is that landing on airport grounds is as good as landing on a runway. The ground

is hard-packed and relatively obstacle free. In real life, the landing gear may be torn off, but a 

survivable landing on the aircraft’s belly should be possible.

• When landing, it is more important to keep wings level and hit a grassy area than try to maneuver 

onto a runway. Usually, maneuvering would result in an oscillatory behavior that continued until 

touchdown, resulting in a crash.

• He tried to have a shallow approach under the glide slope. Steep approaches were harder to 

control and usually resulted in a crash.

• Throttles-only control needed to be initiated from a stabilized and trimmed condition. 

Controllability depended on being able to adjust speed to climb or descend.

• If the aircraft is not trimmed, it is very difficult (or impossible) to control the aircraft. Throttles 

alone cannot easily recover an unstable aircraft.

• The goal was to land on a specific runway, but on approach he tried to minimize changes to flight 

path, so if another runway was more achievable, it would become the target.

• It is important to watch airspeed during approach. If speed drops off and the aircraft enters into a 

stall, recovery is not possible because the aircraft is too low. This point is crucial because glide

slope is controlled by airspeed.

• Increasing power during flare was used to reduce sink rate. Normally, the stick would be pulled 

back to settle on the runway. Increasing power caused a similar effect, although more delayed so 

it requires more anticipation.

• With Fast Response and Overthrust together, landings are easier because the flare is easier to time 

and to get the necessary power to reduce the sink rate. 

• Overthrust was hard to judge and control when used during flight. The difference in the 

sensitivity to pilot input between when it was on or off was more noticeable than for Fast 

Response. However, it is good for getting power during climb out, slowing sink rate during 

landing, and increasing speed when entering into a stall condition. The pilot’s difficulty with 

Overthrust mode during flight was due to its integration into the simulator. The throttle was 

rescaled for Overthrust to allow for a wider power range over the same range of throttle 
NASA/TM—2012-217698 13

movement. Because of this, the power level changed for a given throttle position with the mode 

on or off, and moving the throttle a fixed amount resulted in a different change in thrust. This 

took some getting used to. The implementation is a result of hardware limitations; it is not the 

desired approach. More instrumentation and more practice would be helpful with this mode in its 

current implementation.

• There were no unusual dynamics reported as a result of turning the enhanced control modes on and 

off. The Fast Response mode only impacts engine transients, so its effect is not obvious unless the 

throttle is moved. Overthrust causes a rescaling of the throttle setting in the current implementation, 

which can result in a small transient when it is initiated, but since its purpose is to increase the high 

power setting, its use was most often in conjunction with a desired thrust increase.

• Fast Response had a positive effect on control. Reducing the time lag associated with engine 

response makes it easier to control the aircraft by alleviating the need to anticipate as much.

• There was trouble flying the simulator due to lack of visual cues and feel. There was no stick 

shaker to warn of the approach of stall, no ground effect during landing, no sound, and little 

instrumentation. In general, “sensing” of the aircraft was missing.

• The aircraft was difficult to slow down so the speed needed to be kept low. At lighter weights 

there was not enough control authority in the throttles to slow it down because power was already 

reduced. Having a heavier aircraft helped because the throttles had to be set higher, providing 

more ability to retard them.

• Fast Response has little benefit to improving performance during take-off, although its value is 

likely to increase the later into the takeoff roll it is initiated. It is most beneficial during throttlesonly flight control.

• Overthrust was most beneficial during take-off and flare. It had limited benefit during throttlesonly flight control.

Conclusions

On-going piloted flight simulator evaluation of enhanced propulsion control modes was described. 

The development and testing of these control modes is in response to the shortcomings of throttles-only 

flight control identified previously by NASA researchers. The engine performance obtained using the 

enhanced control modes is representative for engines of this thrust class and is considered to be 

realistically achievable. Overall the piloted test results were very promising. The enhanced control modes 

showed benefit in multiple scenarios. Although the pilot had some reservations, it is important to realize 

that the purpose of these evaluations was to characterize situations in which the enhanced control modes

would be useful, and ways of implementation that will take advantage of them without being detrimental 

to handling qualities. In addition to the use of enhanced propulsion control modes here, the testing 

performed under this effort differs from the previous work with throttles-only control and Propulsion 

Controlled Aircraft (PCA) in another way. Here only the rudder was failed so other surfaces were 

functional. The current problem is easier from that point of view, but the yaw rate feedback to the 

throttles combined with the remaining flight control system resulted in some uncertainty for the pilot that 

made the final approach difficult. He seemed to prefer no feedback during the fine tuning on approach as 

long as he was very careful not to excite oscillations. A yaw rate feedback implementation that is better 

integrated with the rest of the flight control system should improve pilot satisfaction. Additional work 

should include more tuning of feedback gains around the flight envelope to optimize performance, and 

evaluation of the resulting system in landing scenarios with crosswind conditions.

All aircraft types and configurations respond differently, and behavior varies around the flight 

envelope. During this testing it was shown that fast responding engines were clearly better than nominal 

engines in some cases (e.g., Dutch roll damping at high altitude). It is likely that the benefit would be 

extended to a wider portion of the flight envelope, particularly landing, for some aircraft. A more 

intelligent and natural incorporation of these enhanced propulsion control modes is required so that the 

pilot is not surprised by performance changes. It may not be necessary to go to the extent of developing a 
NASA/TM—2012-217698 14

complete flight control system in the manner of PCA, but handling qualities should not worsen when the 

enhanced modes are initiated, and any risk accrued by their use should be more than offset by improved 

overall safety.

References

1. National Transportation Safety Board, “Aircraft Accident Report, United Airlines Flight 232, 

McDonnell Douglas DC-10-10, Sioux Gateway Airport, Sioux City, IA, Jul. 19, 1989,” PB90-

910406, NTSB/AAR-90/06, 1990.

2. National Transportation Safety Board, “Aircraft Accident Report: American Airlines, Inc. McDonnell 

Douglas DC-10-10, N103AA. Near Windsor, Ontario, Canada, June 12, 1972,” PB—219 370, 1973.

3. Faith, N., “Black Box: Why Air Safety Is No Accident,” Zenith Press, 1997, pp. 157-158.

4. Lemaignan, B., “Flying with no Flight Controls: Handling Qualities Analyses of the Baghdad Event,” 

AIAA–2005–5907, AIAA Atmospheric Flight Mechanics Conference and Exhibit, San Francisco, 

CA, Aug. 15–18, 2005.

5. National Transportation Safety Board, “Aircraft Accident Report: Attempted Takeoff From Wrong 

Runway Comair Flight 5191 Bombardier CL-600-2B19, N431CA Lexington, KY, Aug. 27, 2006,” 

NTSB/AAR-07/05, PB2007-910406, 2007.

6. Job, M., and Swift, S., “JAL123, JAL123 ... uncontrollable,” Flight Safety Australia, July-August 

2005, Vol. 9, No. 4, pp. 28-33.

7. National Transportation Safety Board, “Runway Collision of USAIR Flight 1493, Boeing 737 and 

Skywest Flight 5569 Fairchild Metroliner, Los Angeles, CA, Feb. 1, 1991,” PB91-910409, 

NTSB/AAR-91-08, 1991.

8. 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, 

MO, Mar. 29-31, 2011.

9. Litt, J.S., and Guo, T.-H., “Fast Thrust Response for Improved Flight/Engine Control under 

Emergency Conditions,” AIAA 2008-6503, AIAA Guidance, Navigation and Control Conference and 

Exhibit, Honolulu, HI, Aug. 18-21, 2008.

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

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

11. Tucker, T., “Touchdown: The Development of Propulsion Controlled Aircraft at NASA Dryden,” 

Monographs in Aerospace History #16, NASA History Office, 1999.

12. Csank, J.T., Chin, J.C., May, R.D., Litt, J.S., and Guo, T.-H., “Implementation of Enhanced 

Propulsion Control Modes for Emergency Flight Operation,” AIAA-2011-1590, Infotech@Aerospace 

2011, St. Louis, MO, Mar. 29-31, 2011.

13. 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, Apr. 2011.

14. May, R. D., Csank, J. T., Guo, T-H., Litt, J.S., “Improving Engine Responsiveness during Approach 

through High Speed Idle Control,” AIAA 2011-5973, 47th AIAA/ASME/SAE/ASEE Joint 

Propulsion Conference & Exhibit, Jul. 31-Aug. 3, 2011, San Diego, CA.

15. Urnes, J.M., and Nielsen, Z.A., “Use of Propulsion Commands to Control Directional Stability of a 

Damaged Transport Aircraft,” AIAA- 2010-3470, Infotech@Aerospace 2010, Atlanta, GA, Apr. 20-

22, 2010.

16. May, Ryan D., Csank, Jeffrey, Lavelle, T. M., Litt, Jonathan S., and Guo, Ten-Huei, “A High-Fidelity 

Simulation of a Generic Commercial Aircraft Engine and Controller,” AIAA-2010-6630, 46th 

AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Nashville, TN, July 25-28, 2010.

17. May, R.D., Lemon, K.A., Csank, J.T., Litt, J.S., and Guo, T.-H., “The Effect of Faster Engine 

Response on the Lateral Directional Control of a Damaged Aircraft,” AIAA 2011-6307, AIAA 

Guidance, Navigation & Control Conference, Portland, OR, August 8-11, 2011.

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Flight Simulator Evaluation of Enhanced Propulsion Control Modes for Emergency 

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14. ABSTRACT

This paper describes piloted evaluation of enhanced propulsion control modes for emergency operation of aircraft. Fast Response and 

Overthrust modes were implemented to assess their ability to help avoid or mitigate potentially catastrophic situations, both on the ground 

and in flight. Tests were conducted to determine the reduction in takeoff distance achievable using the Overthrust mode. Also, 

improvements in Dutch roll damping, enabled by using yaw rate feedback to the engines to replace the function of a stuck rudder, were 

investigated. Finally, pilot workload and ability to handle the impaired aircraft on approach and landing were studied. The results showed 

that improvement in all aspects is possible with these enhanced propulsion control modes, but the way in which they are initiated and 

incorporated is important for pilot comfort and perceived benefit.

15. SUBJECT TERMS

Flight simulation; Propulsion control 

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