Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

Improving Single Engine Controllability With A Fly-By-Wire 

Flight Control System

Mr. Bret Marks, Carrier Suitability Engineer - The Boeing Company

Mr. Mike Heller, Flight Control System Engineer - The Boeing Company 

Mr. Ricardo Traven, Test Pilot - The Boeing Company

Lt Erik Etz, Test Pilot - United States Navy

Abstract

For conventional multi-engine jet aircraft, single engine minimum control airspeed (Vmc) 

has traditionally been attributed to the ability of the rudder to overcome the yawing 

moment produced by the asymmetric thrust associated with the loss of an engine. 

Consequently, Vmc evaluations have historically focused on thrust configuration 

(distance between engines, engine splay angle, thrust magnitude) and rudder 

effectiveness. However, in establishing Vmc for the Boeing F/A-18E/F Super Hornet, a 

critical connection to lateral control inputs was also revealed. The minimum airspeed at 

which the aircraft was controllable following a simulated dynamic engine failure was 

heavily dependent on the aggressiveness of the pilot in the lateral axis. In addition, by 

automatically commanding full rudder to oppose the thrust-induced yawing moment 

generated by the operating engine, the fly-by-wire flight control system minimized the 

dependency of Vmc on pilot delays in applying full rudder. 

The dependency on lateral stick was accentuated during Vmc flight demonstration 

testing when an unexpected departure occurred at low altitude, nearly resulting in the 

loss of the aircraft. The departure was attributed to loss of directional control resulting 

from excessive lateral stick deflection used in attempting to maintain a wings level 

condition. This event initiated a study to identify candidate control law modifications to 

minimize the potentially harsh consequence of large lateral stick inputs following a 

dynamic engine failure. The result is a revision to the flight control software that virtually 

eliminates lateral stick-induced yaw departures below Vmc, significantly increasing the 

margin of safety in a failed engine, catapult launch scenario. This paper describes the 

mechanics of single engine controllability, flight test results from a severe loss-of-control 

event, the philosophy, implementation and flight demonstrated results of flight control 

system revisions designed to improve Vmc characteristics, and the applicability of these 

efforts to any multi-engine, fly-by-wire aircraft.

Photograph Courtesy of D.S. Groen
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

2

Introduction

Designed to satisfy the U.S. Navy’s need for increased mission and payload flexibility, 

the F/A-18E/F, Figure 1, is an evolutionary upgrade of the combat proven night strike 

F/A-18C/D. The Super Hornet offers greater range and endurance, increased payload 

capability, increased bring back capability, enhanced survivability, and allowance for 

future growth.

Figure 1. F/A-18E/F Super Hornet

Airframe – A larger wing planform area and longer fuselage result in a 33% increase in 

internal fuel capacity over the F/A-18C/D, providing significant increases in mission 

radius and endurance. The addition of two new wing store stations, bringing the total 

number of store stations to eleven, enhance mission flexibility and lethality. Increases in 

wing, wing Leading Edge Extension (LEX) and empennage areas combine to expand 

launch payload capability by 28% and give the E/F three times the bring back ordnance 

capability of the C/D while reducing both launch and recovery Wind Over Deck (WOD) 

requirements. To aid directional controllability in the event of an engine failure, E/F 

vertical tail and rudder areas are 15% and 54% larger, respectively, than those of the 

C/D.

Power Plant – The E/F is powered by two General Electric F414-GE-400 engines 

derived from the highly reliable F404-GE-402 engines utilized by the C/D models. The 

F414s, like their F404 predecessors, employ augmented low bypass, twin-spool 

turbofans with afterburners and Variable Exhaust Nozzle (VEN) geometry. Improved 

engine efficiency is achieved with the addition of a Full Authority Digital Engine 

Controller (FADEC).
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

3

Flight Control System – Improvements in the Super Hornet’s quad-redundant, digital flyby-wire flight control system provide greater reliability and maintainability. Significant 

weight reductions have been achieved by eliminating the mechanical back-up system 

and conventional speedbrake.

Background

During shipboard operations, it is highly desirable to minimize the catapult end airspeed, 

and thus Wind Over Deck (WOD), required to launch an aircraft to safe fly-away speeds. 

Minimizing launch WOD provides greater operational flexibility by lowering ship steaming 

and catapult energy requirements. For the United States Navy, the minimum 

permissible catapult launch end airspeed is established based on the following six 

criteria defined in the Carrier Suitability Testing Manual, Reference 1:

1.) High Angle Of Attack Flying Qualities

2.) Proximity To Or Warning Of Impending Stall (Not To Exceed 0.9*CLmax)

3.) Minimum Level Flight Longitudinal Acceleration Capability (0.065 a/g)

4.) Flight Control Saturation

5.) Aircraft Center Of Gravity Sink Off Bow

6.) Single Engine, Minimum Control Airspeed (Vmc)

The minimum safe catapult launch end airspeed is the lowest speed that satisfies all of 

these criteria. For normal fleet operations, a 15 kt margin is added to the minimum 

launch endspeed to account for variability in catapult performance, WOD and other 

safety considerations. This paper focuses on the Vmc criterion and the significant 

improvements achieved for the Super Hornet with the implementation of flight control 

system revisions specifically designed to improve departure characteristics below Vmc. 

It is important to note that operational endspeeds do not guarantee single engine 

fly-away (positive rate of climb). However, they are intended to ensure adequate 

controllability for all permissible store loadings (symmetric and asymmetric) to enable the 

pilot to safely execute emergency procedures and, if necessary, safely eject from the 

aircraft in the event of a catastrophic engine failure during catapult launch operations.

Maneuver Description

The Vmc characteristics of the F/A-18E/F were established under the Engineering and 

Manufacturing Development (EMD) flight test program. The objectives of the Vmc flight 

testing were to establish full and half flap Vmc for symmetric and asymmetric store 

loadings. The results of this testing were used to establish catapult launch asymmetry 

limits, fleet operational launch airspeeds and recommended emergency launch and 

recovery procedures.

Prior to flight demonstration, the Boeing St. Louis Manned Flight Hardware Simulator 

(MFHS) was used to develop a reliable test technique which was operationally relevant 

and enabled the dependency of Vmc on angle of attack (AOA) and lateral weight 

asymmetry to be quantified. The development of this technique and its relevance to the 

aircraft carrier environment is discussed in Reference 2. The resulting technique is 

described as follows:
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

4

1.) Stabilize the airplane in wings level, steady heading flight at the specified initial 

conditions:

a.) Landing gear extended, full or half flaps

b.) Test altitude +500 ft, airspeed for target AOA, dual engine thrust required for 

slow rate of descent (~1,000 ft/min)

2.) While maintaining wings level, steady heading flight, reduce power on the critical 

engine to Flight Idle and advance the opposite throttle to the desired thrust level 

(Intermediate Rated Power or Maximum Afterburner) while passing through the 

test altitude.

3.) Maintain initial AOA with neutral directional controls. Lateral inputs required to 

maintain a wings level condition are permitted.

4.) Apply recovery controls (rudder to oppose yaw, lateral stick to arrest roll) after 2 

seconds has elapsed (simulated pilot reaction time) or a limiting factor has been 

reached:

a.) 20° Angle Of Bank (AOB) change

b.) 10° Angle Of SideSlip (AOSS) change

c.) Pilot evaluation of yaw / roll rates (pilot comfort)

d.) Full rudder deflection does not result in reversal in yaw rate slope

5.) Re-acquire steady heading flight within 5° AOB into the operating engine.

Dynamic Vmc, as it pertains to the F/A-18E/F catapult launch scenario, is defined as the 

airspeed (target throttle chop speed) below which recovery controls do not prevent AOB, 

AOSS or yaw / roll rates from exceeding the limiting factors defined in Step 4. 

Using this technique, maneuver entry speed for a given test AOA is controlled by varying 

aircraft weight. As fuel is burned and the aircraft becomes lighter, the airspeed required 

to stabilize in wings level flight at a given AOA is reduced. Consequently, the maneuver 

is repeated at successively lighter weights and lower airspeeds until Vmc is established.

Developmental testing conducted in the MFHS revealed that dynamic Vmc was 

extremely sensitive to the magnitude of the lateral stick input used to arrest the 

sideslip-induced roll rate resulting from the throttle split. This characteristic was later 

verified in flight. Overreacting to this initial roll rate was found to aggravate the 

departure. It was found that judicious use of lateral control was required to arrest the roll 

rate without inducing additional sideslip due to the adverse yawing moment produced by 

the ailerons. Attempting to roll into the good engine further aggravated the departure 

since, at the Vmc condition, full rudder deflection is required to oppose the 

thrust-induced yaw combined with the aileron-induced yaw generated by attempting to 

maintain an approximate wings-level condition. Consequently, the rudders are unable to 

generate the additional yawing moment required to coordinate a roll into the good 

engine. Optimal lateral stick position for recovery was determined to be approximately 

1/3 to 1/2 of the allowable travel. The use of full lateral stick at the Vmc condition often 

resulted in a yaw departure.

To quantify the sensitivity of lateral stick deflection on dynamic Vmc, a simple pilot model 

was developed to replicate the pilot technique used to perform the flight test maneuver. 
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

5

This model permitted precise, repeatable off-line simulation of the maneuver for use in 

establishing Vmc sensitivities to variations in atmospheric conditions, angle of attack, 

lateral weight asymmetry, and most importantly for the purposes of this discussion, 

lateral stick input. Figure 2 illustrates the sensitivity of dynamic Vmc to the magnitude of 

the lateral stick input used to arrest the sideslip-induced roll rate. 

Predicted Dynamic Minimum Control Speeds

3 Tank Interdiction Loading, Full Flaps

Standard Day, 14° AOA, 200 ft Hp

120

125

130

135

140

145

0 1 2 3 4 5

Max Lateral Stick Deflection @ Vmc Condition (in)

Minimum Control Airspeed (kcas)

Max Lateral

Stick Travel Increasing Bank

Into Bad Engine

Max Lateral Stick Deflection @ Vmc Condition (in)

Minimum

C

ontrol Airspeed (kcas)

5 kt

Figure 2. Dynamic Vmc Sensitivity To Lateral Stick Input

Simulated engine-out maneuvers were initiated from the symmetric throttle position 

required for 1g, level flight at a given AOA. The throttle on the critical engine was 

reduced to idle one second after a trim condition was established. For symmetrically 

loaded configurations, Vmc is independent of the direction of the throttle split. However, 

for the asymmetrically loaded configurations evaluated to date, the critical engine 

corresponds to the engine on the wing-heavy side of the aircraft. Vmc is greatest for this 

scenario due to the additional aileron bias required to balance the lateral weight 

asymmetry. This was demonstrated with the F/A-18E/F for various store loadings during 

manned simulator and flight demonstration testing.

Full rudder to oppose the thrust asymmetry resulting from the throttle split was initiated 

two seconds after completion of the throttle split. As described in Step 4 of the 

Maneuver Description, this two second delay is intended to account for potential pilot 

delays in recognizing and reacting to a dynamic engine failure and is defined in the 

F/A-18E/F Weapon System Detail Specification, Reference 3. Longitudinal stick was 

input as required to maintain the target AOA throughout the maneuver. Lateral inputs 

required to maintain a wings level condition were permitted in executing the flight test 

demonstration maneuver. However, to simulate a worst case scenario, lateral stick 

inputs were initiated two seconds after completion of the throttle split during off-line 
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

6

simulations. Lateral stick was input as required to attempt to capture and maintain a 5° 

angle of bank into the good engine, the maximum permitted by the Reference 3 Detail 

Specification. The pilot model lateral stick proportional gain was also permitted to vary 

with roll rate to aid in the initial recovery and more accurately reflect the lateral stick 

characteristics exhibited by the test pilots during manned simulation and flight 

demonstration testing. The Vmc impact of pilot aggressiveness in the lateral axis was 

established by varying the pilot model lateral stick proportional gains. 

As Figure 2 illustrates, applying full lateral stick during the recovery increases Vmc by 

10 kt relative to the Vmc obtained when lateral stick inputs are limited to 1/2 the 

available travel. This can have serious ramifications in the catapult launch environment. 

Recall that for normal fleet operations, a 15 kt margin is added to the minimum launch 

endspeed to account for variability in catapult performance, WOD and other safety 

considerations. In the event of a dynamic engine failure at holdback release, the 

catapult end airspeed can be as much as 5 kt lower than the targeted value. This 

reduction in endspeed results from the reduction in total acceleration associated with the 

loss of thrust on the failed engine. In establishing Super Hornet Vmc speeds, lateral 

stick inputs were limited to 1/3 to 1/2 the available travel. Applying full lateral stick to 

oppose the sideslip-induced roll resulting from a catastrophic engine failure at holdback 

release could exhaust the remaining 10 kt of the original 15 kt operational launch 

margin, potentially resulting in an out-of-control departure at an altitude approximately 60 

ft above the water. Consequently, warnings were added to the NATOPS Emergency 

Catapult Flyaway procedure, Reference 4, instructing the fleet pilot to limit lateral stick 

inputs to 1/2 the available travel. The pilot was also warned of the potentially severe 

consequences of applying full lateral stick in conjunction with a catastrophic engine 

failure. This approach had been successfully implemented for other aircraft, specifically 

the F-14, which exhibited similar lateral stick-induced yaw departure tendencies. In all 

likelihood, no further action would have been taken for the Super Hornet had it not been 

for an out-of-control departure experienced during follow-on Vmc demonstration testing 

at an altitude of 2,000 ft.

Vmc Testing Leads to an Out-Of-Control Event

The techniques described above resulted in a very successful program for most of the 

configurations tested. However, one configuration resulted in an unexpected departure 

and is the focus of this paper. The configuration labeled “5-WET” is the F/A-18E/F 

proposed tanker configuration. The 5-WET label represents the 5 five external fuel 

stations loaded on the aircraft, as illustrated in Figure 3.

Figure 3. 5 WET Configuration
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

7

Using the dynamic Vmc technique described previously, the pilot repeatedly executed 

the maneuver at progressively slower speeds as gross weight was reduced in an 

attempt to establish a full flap, 14° AOA, 5-WET Vmc. As the pilot approached this 

speed, execution of the Vmc maneuver and flying qualities were deemed to be excellent. 

There was very little roll-off noted and the pilot was easily able to maintain wings level 

with very little lateral stick (less than 1/3 of that available). Sideslip was contained well 

within the knock-it-off criteria and there was no perception in the cockpit of being near a 

Vmc condition. However, on the event that led to the departure the pilot did experience 

a call from monitoring station that sideslip had exceeded the knock-it-off limit of 10°. The 

pilot reduced AOA and used lateral stick to oppose the sideslip-induced roll-off. As 

sideslip and roll angle continued to build, the pilot instinctively increased lateral stick 

input to hold the wings level. Within approximately 8 seconds from the completion of the 

throttle split, sideslip had built to nearly 30° and the aircraft no longer responded to 

lateral stick input, which by this time had reached the maximum available. The pilot 

experienced a rapid roll reversal opposite to his stick input and an ensuing departure 

that resulted in an inverted position 60° nose low at 2,000 feet. The pilot regained control 

of the aircraft after this snap roll to inverted and was able to roll the aircraft upright and 

avoid impacting the water by approximately 200 ft. Time histories comparing the 

maneuver flown just prior to the event with the actual event are provided in Figure 4. 

The mechanics of the departure can best be explained when viewed from a total 

controllability standpoint. As Figure 4 illustrates, the rudders were deflected to their 

position limits within a very short time of the engine loss, mainly due to the sideslip 

feedback to the rudder in the control laws. The pedal that was applied shortly after the 

engine loss also contributed, however, most of the rudder had already been applied 

automatically by the flight control system. As a general rule, control augmentation is in 

question when a control surface can no longer react to the motion changes it is intended 

to augment, which this incident clearly possessed. 

The presence of the position-limited rudders with increasing lateral stick deflection is a 

bad combination in two ways. First, the directional stability augmentation desired with 

the sideslip feedback can no longer be achieved. Second, the roll coordination function 

of the rudder can not be performed when additional aileron deflection is commanded 

from the lateral stick. The result is an uncoordinated roll input, which in conjunction with 

the inability to contain yaw rate, has the effect of rapidly increasing adverse sideslip due 

to the lateral stick input. Given the stable dihedral effect exhibited by the F/A-18E/F, the 

rolling moment produced by the sideslip growth became large and dominated the other 

moments acting on the aircraft, rolling the aircraft opposite to the pilot input. Alternately 

stated, this was a case of two axes simultaneously desiring, and then overwhelming, the 

same control surface to effectively defeat the basic intentions of that surface. The result 

was a large sideslip excursion that spawned the departure from controlled flight.

Solution

In establishing the Emergency Catapult Flyaway procedure for the Super Hornet, it was 

reasoned that by instructing the fleet pilot to limit lateral stick inputs to 1/2 the available 

travel, sufficient safety margin existed to prevent an out-of-control departure in the event 

of a catastrophic engine failure during launch. Recall that a 15 kt operational margin is 

added to Vmc when establishing target end airspeeds. Furthermore, it was reasoned 

.
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

8

120

130

140

150

0

4

8

12

16

0

20

40

60

-20

0

20

40

-2

0

2

4

-2

0

2

4

-80

-60

-40

-20

0

20

-160

-120

-80

-40

0

40

Calibrated Airspeed ~ kt

T hrottle Handle Angle ~ deg

FCS Angle Of Attack ~ deg

INS Sideslip Angle ~ deg

Longitudinal Stick Deflection ~ in

Lateral Stick Deflection ~ in

Pitch Attitude ~ deg

Roll Attitude ~ deg

Right THA

Left THA

E1, Flight 427, Rec 31 (Easily Controlled)

E1, Flight 427, Rec 32 (Departure)

10 kt

-100

0

100

200

-200

-160

-120

-80

-40

0

-80

-60

-40

-20

0

20

40

-40

-30

-20

-10

0

10

20

-20

0

20

40

60

80

0 2 4 6 8 10 12 14 16

-40

-30

-20

-10

0

10

20

0 2 4 6 8 10 12 14 16

Pedal Force ~ lb Heading ~ deg

Roll Rate ~ deg/sec Yaw Rate ~ deg/sec

Differential Aileron Deflection ~ deg Collective Rudder Deflection ~ deg

Time ~ sec T ime ~ sec

Figure 4. 5 WET Vmc Testing Leads to Out-Of-Control Event
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

9

that by establishing Vmc at 14° AOA, the maximum AOA allowable during catapult 

launch operations, additional margin was built-in to the procedure (Vmc increases 

significantly with increasing AOA). During normal, "hands-off" catapult launch 

procedures at or above the Vmc-based minimum launch endspeed, the flight control 

system is designed to capture and maintain a 12° AOA with only a transitory excursion 

to no greater than 14° AOA during the initial rotation following main wheel roll-off. The 

additional margin results from the unlikelihood that, if the pilot entered the loop, he/she 

would actively maintain a 14° AOA any longer than necessary to arrest the abnormal 

aircraft settle off the bow and establish a positive rate of climb. However, the 

out-of-control event which occurred during Vmc demonstration testing in the 5-WET 

configuration graphically illustrated that attempting to mitigate the risk of a departure 

through pilot training alone was not sufficient. 

As described previously in this paper, the mechanics of the Vmc departure are well 

understood. By limiting lateral stick input, and thus limiting the adverse effects 

associated with large differential aileron deflection at a condition where no additional 

rudder power is available to counter them, the severity of the departure characteristics at 

Vmc can be greatly reduced. However, the use of lateral stick to hold the wings level is 

very instinctive to the pilot. In the end, it was decided that with the digital technology 

available to the F/A-18E/F, it was unreasonable to ask the fleet pilot to act against that 

instinct, particularly when distracted by adverse circumstances, possibly at night in 

inclement weather. The result is a modification to the flight control software, which 

reduces aileron authority when additional rudder deflection is unavailable. 

Modification of the control laws to desensitize the effects of the lateral stick in a 

single-engine situation was viewed as the most robust option for preventing this type of 

incident in the future. There were, however, many issues that required consideration –

most associated with the concern that modifying the control laws at an extremely late 

stage in the development program would change the basic flying qualities and invalidate 

the results that had taken years of development and testing to identify. Given these 

concerns, the goals of the control law modification were:

 Fix the problem, focusing on the higher angle of attack problem area above 12° AOA.

 Don’t affect flying qualities near the most-used flight conditions – on-speed at 8° AOA.

 Don’t affect normal maneuvering during two-engine operation at the higher AOAs.

The solution to the problem focused on the rudder needs of the directional and lateral 

axes during single-engine operation:

Rudder Usage for the Directional Axis - The directional axis is most straightforward, in 

that the rudder is used to offset the asymmetric yawing moment from the single engine. 

Rudder is commanded in two ways within the control laws. First, the pedal commands 

rudder to counter yaw rate – which is the normal pilot control input for the engine-out 

case. And second, sideslip feedback also commands rudder to augment the directional 

stability. In single-engine operation, sideslip generation is normal and rudder is 

automatically applied by the sideslip feedback to oppose it. At low speeds near Vmc, 

practically all of the available rudder deflection is commanded via the sideslip feedback, 

with the pedal application typically making only a minor additional contribution. 

Rudder Usage for the Lateral Axis - The lateral axis requires rudder to coordinate roll 

maneuvers, i.e. keep sideslip small as the aircraft rolls. There are two factors 
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

10

addressing sideslip control. First, the control surfaces used to roll the aircraft (ailerons 

and differentially deflected stabilator) typically possess the side effect of producing 

adverse yawing moments that tend to generate sideslip in the direction to oppose the 

roll. Rudder must be applied with the roll to offset those moments and maintain low 

sideslip. Second, the kinematic effect of the roll itself conducted at higher angles of 

attack generates sideslip, and yaw rate must be generated in the same direction to offset 

this effect when coordinating a velocity vector roll. This additional yaw rate requirement 

makes another significant demand of the rudder at higher angles of attack. The rudder 

deflection required to offset these two factors is automatically applied during lateral stick 

inputs within the F/A-18E/F flight control system via the Rolling Surface to Rudder 

Interconnect (RSRI).

The basis of the control law change is that the rudder cannot perform its intended 

function in either axis if it is unavailable. Therefore, the concept is to give one axis 

priority of the rudder over the other. The control law solution implemented gives the 

directional axis that priority. The reasoning is that the job of constraining the sideslip 

induced by the asymmetric thrust is of primary importance over rolling the aircraft, and 

should be done first.

The priority assignment looks at the total rudder command from the pedal and sideslip 

feedbacks and determines how much lateral authority can be granted given the 

commanded load. For instance, if the pedal and sideslip contributions are small, then 

full lateral authority can be allowed since only the lateral axis is using the rudder. 

However, in the case where directional activity is high, the lateral command must be 

limited to avoid over-saturating the rudder. This is achieved by implementing a variable 

limiter on the lateral command path as a function of the pedal+sideslip feedbacks. The 

computation for the limit is such that the limited lateral command plus the existing 

directional feedbacks will not over-saturate the rudder (some lateral command is always 

allowed). Logic is also included to limit the lateral authority only in the direction that 

adds to the rudder, allowing unlimited command in the opposite direction. In order to 

affect only the higher angles of attack, the added logic was incorporated on an AOA 

schedule so that the limiting would be fully active at angles of attack greater than 12°, 

and inactive at angles of attack less than 10°. This schedule ensures that the on-speed 

flying qualities remain unchanged. A block diagram of the modification is shown in 

Figure 5.

Before the logic was released for flight, several manned simulations were conducted to 

ensure that normal maneuvering was not affected. In addition, the new logic was fed 

into the time histories of previous roll maneuvers to show that the logic would not 

interfere with normal maneuvering. All of these efforts confirmed that the modified 

control laws would not impact normal maneuvering, yet would be invoked as needed in 

the engine-out case.

Vmc Regression Flight Testing With New Control Laws

The new control laws were first evaluated in the simulator. These tests indicated that 

Vmc dependency on lateral stick was eliminated. In fact, full lateral stick inputs at and 

below previously determined Vmc speeds would allow the aircraft to roll in the 

commanded direction without the adverse sideslip build-up that resulted in a yaw 

departure prior to modifying the control laws. Additionally, the simulator was used to 

.
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

11

Rudder Command 

from Pedal

Rudder Command 

from Sideslip



+K2

-K2

+50

-50

RSMAX RSMIN

RSM AX

RSM IN

Roll Command

K1

AOA Schedule

Limiter

Limiter

(K2 < 50)

(K1 > 50)

+

+

+

+

-

+

Prioritized Roll 

Command

Figure 5. Block Diagram of Control Law Modification

ensure that there would be no transient roll "ratcheting" as a result of the gain changes 

at and around 12° AOA regardless of the engine-out situation. The pilots were unable to 

detect any lateral stick gain changes as a result of the new control law architecture even 

when transitioning through the affected AOA range of the modification. Of particular 

interest was the control margin available for roll even with large lateral weight 

asymmetries. This was also found to be acceptable even with an engine out-condition 

on the critical side of the asymmetry. 

Flight testing was then accomplished to verify simulator results and certify the new 

control laws. Flight testing in the clean aircraft showed no degradation in roll control or 

signs of sideslip build-up at high AOA. In the 5-WET configuration, the aircraft was very 

well behaved. Lateral control power was more than adequate for the fly-away task. 

Additionally, full lateral stick inputs were intentionally inserted near Vmc. Prior to the 

control law modification, inputs of this nature near Vmc would result in significant 

adverse sideslip build-up and provoke loss of aircraft control, as the Figure 4 5-WET 

departure illustrates. However, with the control law modification implemented, the 

aircraft remained well behaved with no signs of side force build-up or yaw-induced 

departure noted by the test pilot or indicated in the test data. 

Impact to the Fleet Operator

Arguably, a settle off the catapult during carrier operations at sea is the most critical 

emergency a naval aviator will encounter. Any one of a number of situations may result 

in a settle off the bow of the ship (i.e., “soft” catapult shot, degraded engine 

performance, or total single engine loss of thrust), but all are sensitive to pilot reaction 

time and pilot input in a manner unmatched in most shore-based operations, since the 

aircraft is immediately catapulted at only 60 feet above the water. The carrier 

environment is rarely forgiving of pilot error, and an aviator’s initial response to a settle 

off the catapult has historically been the determining factor as to whether the aircraft flies 

away safely, or impacts the water, with or without the pilot still at the controls. 

Consequently, procedures for a safe “Emergency Catapult Flyaway” are critically 
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

12

important to carrier pilots to ensure aircraft recovery. Priorities during emergency 

catapult flyaway are to establish control of the aircraft, arrest aircraft settle, and 

accelerate for climbout away from the water. In the event the single engine rate of climb 

remains negative, it is highly desirable to at least slow the descent rate and maintain 

aircraft control to accomplish external stores jettison and continue flyaway attempt, or 

perform a safe, upright ejection. 

Although catapult launch bulletins should ensure an endspeed at least 15 knots above 

Vmc, wind over deck variations and loss of thrust may erode that planned margin, and 

the effects of pilot overreaction, both in pitch and roll, cannot be ignored. Years of fleet 

experience and simulator testing have demonstrated that the transition from a 

“hands-off” catapult to immediate “pilot-in-the-loop” control for emergency catapult 

flyaway can lead to an initial over-rotation to AOA’s greater than 14°, primarily resulting 

from instinctive pilot reactions in the presence of extreme "ground" rush. Prior to 

implementation of the Vmc control law modification, this action, coupled with lateral stick 

input of greater than approximately 1/2 stick could have resulted in an immediate 

adverse yaw departure at less than the carrier deck height of 60 feet. A departure at 

that altitude would not have provided any opportunity for controlled stores jettison, or 

ability for safe ejection.

Conclusions

The Vmc control law modification developed for the Super Hornet provides a forgiving 

environment for variances in pilot reaction that may be encountered during single engine 

catapult events. Specifically, at higher AOA’s, the decreased sensitivity to lateral stick 

input will prevent adverse yaw departures. Additionally, it is apparent from simulation 

that at speeds below Vmc, where immediate departure would have been the likely result 

of any lateral stick activity, the modification allows for lateral control of the aircraft to 

accomplish stores jettison or controlled ejection within a safe envelope. Applications of 

up to full lateral stick are now acceptable to attempt to arrest roll rates induced by the 

asymmetric thrust in a single engine failure scenario. The result is a flight control system 

that inspires confidence in the naval aviator in his/her ability to handle a single engine 

failure off the catapult in even the worst environmental conditions, specifically at night in 

bad weather. This Vmc control law modification provides the carrier aviator time to 

procedurally step through a decision matrix that will allow him/her to control the Super 

Hornet with an engine loss at the most critical moment. At the very least, the 

modification will provide a controllable aircraft for a wings-level ejection that will save the 

pilot's life.

Lessons Learned 

Where flight safety is concerned, full advantage should be taken of the digital technology 

available to today's flight control designers. When the critical connection between 

dynamic Vmc and lateral control inputs was first identified during the F/A-18E/F EMD 

flight test program, it was believed that the risk of an out-of-control departure following a 

catastrophic engine failure during catapult launch could be sufficiently mitigated through 

pilot training. However, as the 5-WET departure discussed in this paper graphically 

illustrated, training alone does not adequately protect even the most highly skilled pilot 

when that training requires him/her to act against what is instinctive. For the Super 

Hornet, fly-by-wire technology was successfully utilized to virtually eliminate lateral 

stick-induced yaw departures below Vmc.
Copyright © 2000 by B.A. Marks, M.J. Heller, R.S. Traven, E.O. Etz

13

References

1. SA-FTM-01, “Carrier Suitability Testing Manual,” Revision 2, 30 September 1994.

2. SFTE European Chapter 10th Annual Symposium Proceedings, "Single Engine 

Minimum Control Airspeed Evaluation Of The F/A-18E/F," LCDR Ken Ham, 

Henry Melton, Bret Marks, 14-17 June 1998.

3. SD-565-3-1, "Detail Specification For Model F/A-18E/F Aircraft Weapon System," 

Vol. I, 27 Aug 1993.

4. (DM)A1-F18EA-NFM-000, "Preliminary NATOPS Flight Manual Performance 

Charts – Navy Model F/A-18E/F 165533 And Up Aircraft," 1 March 1999