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Schreiter, K., Müller, S., Luckner, R., & Manzey, D. (2018). Demand Control Law for Total Energy Angle
Tested at Manual Approaches. Journal of Guidance, Control, and Dynamics, 41(6), 1443–1448. https://
doi.org/10.2514/1.g003194

Schreiter, K.; Müller, S.; Luckner,R.; Manzey, D.
Demand Control Law for Total Energy
An
g

le Tested at Manual Approaches
Accepted manuscript (Postprint) Journal article |

Demand Control Law for Total Energy
Angle Tested at Manual Approaches
K. Schreiter, ∗ S. Müller, † R. Luckner, ‡ and D. Manzey §
Technische Universität Berlin, 10587 Berlin, Germany
I. Introduction
A IR traff ic is continuously growing and reduced aircraft
separations as well as more complex flight trajectories are
introduced to increase capacity at congested hubs while minimizing
en vironmental impact. Complex flight trajectories allo w optimizing
the use of airspace, and precise speed control enables decreasing
separation distances. Fully automated flight allows meeting these
emerging precision requirements. Ho we ver , it is essential that pilots
can take manual control at any time, either for short-term flight-path
changes or in case of an autopilot failure. Furthermore, the Federal
A viation Administration (F AA) recommends that pilots should
suf ficiently train manual flying skills in daily operations [1]. The
expected high-precision requirements of future air traf fic will
significantly raise the workload in manual flight. Fly-by-wire
technology supports pilots during manual flight. It changes the
con ventional direct relation between input de vice and control surface
deflections to the command and control of flight parameters, for
example, n z la w in Airbus aircraft [2]. The flight control laws
improv e handling qualities, adapt aircraft response to pilot ’ s demands
(without the need for trimming), and automatically compensate
disturbances in manual flight. These characteristics can reduce
workload while pilots stay in the control loop. T oday ’ s transport
aircraft use this augmented manual control only for attitude control
with aerodynamic control surfaces, whereas engines and speedbrakes
are still used con ventionally . Pilots control the energy state of the
aircraft by changing thrust and spoiler le ver positions. They observe
fan rotation speed or engine pressure ratio (EPR) as well as spoiler
deflection and adjust their inputs according to de viations from the
intended vertical flight path and airspeed. As the aircraft reaction to
an input depends on the actual flight state, the pilots have to anticipate
this impact on their inputs. The described complex control concept
generates high cogniti ve and motoric workload that will increase with
the future precision requirements.
A concept for a flight control augmentation system concerning
this gap of support systems for manual flight was described by
Schreiter et al. [3] and Müller et al. [4]. The so-called nxControl
system addresses commercial transport aircraft. It provides a
co nt rol l aw for l o ngi tud in al l oad fa cto r n x . The pi lo t can dir ect l y
co mm and n x . E ng in es an d sp oi ler s ar e reg ul ate d ac cor di ng t o the
co mm and a nd t he a ct ua l fl igh t s tat e. T o t he be st of o ur kn owl edg e,
the par a met er n x i s c urr en tl y no t us ed a s a co ntr ol var iab le fo r
man ua l fl i ght of t ran sp ort a ir cra ft , ne it he r in c om mer c ia l ai rl ine rs
no r in r es ea rch . Th e co nt rol law i s su pp ort ed b y ad apt ed add it io nal
sym b ols on t he f li ght d isp la ys . Th es e sy mbo ls a llow d ir ect co n trol
an d mo nit or in g of t he en ergy st at e ra te s as w ell as the sy st em
fu nc tion s . Th e sys te m ai ms at mor e p rec is e ma nu al fl ig ht w it h lowe r
wo rkl oa d an d the re fo re i ncr ea sin g s afe ty b y ena bl in g man ua l fl ight
in d ai ly o per at ion s un de r t he d em and in g re qui re m ent s o f fut u re a ir
tra ffic . Th e nxC ont ro l sy st em i s des ig ned t o int r od uce o nl y mi nor
ch ang es in w ork f low co mp are d w it h convent io nal fl ig ht t o avoid
inf lu enc es to t he b as ic f lyi ng s ki ll s. I n add it io n, i t sha l l prov id e
ad vance d aw are nes s a nd c ont ro l of ene rgy s ta te . A fi rst nxC on tr ol
pr ot otyp e w as evalua ted in a f li gh t s im ul ato r cam pa i gn wi th 1 1
ai rli n e pil ot s. It was t es te d wi th fo ur s tan d ard f li gh t tas ks (ai rwo r k)
[4 ] an d a sta nd ar d st rai gh t-i n ap p roa ch t o ru nwa y 25 C at F ra nkf urt
(Ma i n) [5, 6] . Th e obj ect ive wa s to verif y wh et her n xCo nt rol
im prove s fl ig ht p re cis io n an d re duc es pi lot w or kl oad . Th e pi lo ts
we re ab le to f ul fil l the g iven t ask s w ith n xC on tr ol w it h the sa me
pr ec isi on a nd l ess t hru st l ever move me nts as wi th c onvent io nal
thr u st c on trol af ter on ly 1 .5 h t ra in in g. H owever , t he ex pec te d
si gni fic ant differ e nce i n pr eci si on c om pa re d wi th the convent io nal
man u al fl igh t d id n ot occ u r . A n expl ana ti on i s th at i t wa s eas y to
ac hi eve the s ta nda rd a cc ur acy f or t he given t as ks w ith c onvent io nal
co nt rol as w el l as wi th nx Co ntro l . Th er efo re, t he b en efit s of th e
au gm ent at io n sys te m co uld no t em e rge. N evert hel es s, eye - tra ck ing
mea sur e me nt s show ed a ch ang e i n th e sc ann in g pa tt er n at t he
di spl a ys. Th e p il ot s de te rmi ne d en erg y in fo rm at ion f ro m th e cen t re
of t he p ri ma ry fl ig ht d is pl ay ( PFD ), w he re nx C ont ro l pr ovi des cu es
fo r fli gh t pa th a ngl e and t ot al e nerg y an gl e, in st ead of the e ngi ne
wa rn in g dis pl ay . T her ef ore , th e foc u s of s can ni ng h as m oved to
the PF D .
Since then, the nxControl system has been improved. First, the
control law was optimized, providing constant handling character-
istics all over the flight env elope. Second, the human-machine
interface (HMI) was improved with a specifically designed inceptor
concept. Section II explains the nxControl system with focus on the
flight mechanical background and the design process of the control
laws. The display concept is briefly recapitulated (details can be
found in [4]). This new prototype of the nxControl system was
e valuated in a flight simulator study . The objectiv e was to compare
nxControl and con ventional control in a highly demanding approach
pattern for Salzburg airport. This task was more challenging than
the standard tasks of the prior study . The experiment design and the
results of the simulator tests are described in Secs. III and IV . The
nov el contributions are the complete description of the nxControl
system and the simulator test results that validate the adv antages of
the system at today ’ s demanding trajectories.
II. Flight Control Augmen tation System nxControl
In today ’ s sidestick-controlled commercial airliners, the vertical
load factor n z is used to control pitching movements in manual flight.
T ogether with thrust, pilots control airspeed and flight-path angle.
Engines are con ventionally set either via fan rotation speed N1 or
EPR. As an improvement, nxControl uses the longitudinal load factor
n x for computing the adequate thrust control commands in a feedback
controller . W ith n x , pilots command the change of total energy (sum
of potential and kinetic energy). T ogether with the n z command of the
sidestick, pilots decide whether the energy change is con verted into
flight-path angle and/or into airspeed changes.
*Research Scientist, Flight Mechanics, Flight Control and Aeroelasticity .
Member AIAA.
† Research Scientist, W ork, Engineering and Organizational Psychology .
‡ Professor , Flight Mechanics, Flight Control and Aeroelasticity . Associate
Fello w AIAA.
§ Professor , W ork, Engineering and Organizational Psychology .

A. Flight Mechanical Background
The fundamental flight mechanical relationships are well
established although under varying terminology . The vector of total
load factor is defined as the ratio of the external forces, that is, the sum
of aerodynamic forces and thrust, to weight in an arbitrary axis
system [7]. It corresponds to the vector of the aircraft acceleration
di vided by the gravitational constant. This relation can be obtained by
Ne wton ’ s second law of motion for rigid aircraft with forces and mass
concentrated at the center of gravity . The longitudinal load factor in
flight-path direction n xk; tot that nxControl uses can then be deriv ed
from the drag equation (longitudinal force equation) in flight-path
axis for symmetric flight, that is, zero sideslip angle, bank angle, and
deri vati ve of azimuth angle:
n xk; tot ! 1
W " T cos # α $ σ − α W % − D cos α W $ L sin α W &
! _
V K
g $ sin γ (1)
For simplif ied description it is assumed that the sum of thrust
incidence angle σ and angle-of-attack α equals zero ( σ $ α ! 0 ).
Furthermore, the angle between airspeed and flight-path velocity due
to wind α W is small ( cos α W ≈ 1 , sin α W ≈ α W ). The ratio lift L to
weight W is approximately equal to the normal load factor n zk; tot ,
which is nearly 1 in steady flight conditions. These simplifications
lead to
n xk; tot ! T − D
W $ n zk; tot α W ! _
V K
g $ sin γ (2)
So, the load factor n xk; tot (abbreviated as n x ) is either expressed by
the external forces (thrust force T and aerodynamic drag force D
related to weight W , wind angle of attack α W amplified by the
maneuver loads) or by flight parameters (flight-path acceleration _
V K
di vided by the gravitational constant g , flight-path angle γ ). The
dif ference between thrust and drag related to weight for a constant
wind is also known as specific excess thrust. A pilot can activ ely
influence thrust and drag by commanding thrust δ T , spoiler
deflections δ S , and flap deflections η K , whereas wind disturbs n x .
Th e rel atio n be tween pilo t input s and re sult ing th rus t an d dra g for ces
is non lin ear an d depe nds on th e actu al flig ht stat e, espe cial ly ai rsp eed
and a ltit ude. Fi gure 1 sho ws thru st and dr ag for ce qual itat iv ely a s a
fun ct ion of eq ui v ale nt air spe ed V EAS an d thei r depen denci es on co ntr ol
de vice s at co nsta nt al titu de. If th rus t equ als dr ag, ai rs peed r emai ns
con sta nt an d cor re spon ds to th e inte rsec tio n of th e two gr aphs (trim
poi nt Z 1 ). W ith cha ngin g drag fo rce D via δ S o r th rust f orce T v ia δ T , as
sh o wn in F ig. 1 by th e shif ted th rust cu rve (d ashe d lin e), th e dif fere nce
rep re sent s the long itud inal lo ad fac tor n x . F ollo wing Eq . (2), th is
dif feren ce can be used to cha nge eit her air spe ed or fli ght -path an gle , or
bot h. Th e fir st two ca ses ar e sho wn in F ig. 2. If th e flig ht pat h is
ma inta ine d (das he d line ), th e exc ess th rus t acce le rate s the ai rc raft .
Ho we v er , dra g incr eas es with r isin g airsp ee d (if abo ve mi nimu m dra g
sp eed V M D ) and th us acce lera tio n decre ases . Af ter a lo ng per iod of
ti me (no t sho wn in Fi g. 2), th e cha ng e in thr ust o r dra g lead s to a ne w
trim me d stat e Z 2 . If, o the rwis e, th e amo unt of n x is us ed to chan ge
alti tu de at con sta nt air spe ed (ful l li ne), dr ag doe s not ch ange, exc ess
thr ust re main s con stan t, and the ai rcr aft cl imbs. As Fi g. 2 sho ws,
se ttin g thr ust an d main tain a ltit ude wi th ele v ato r woul d be su ff ic ient to
ch ange a irsp eed f rom st ate Z 1 to Z 2 . For f aste r aircr aft rea ctio n, pil ots
se t hi gher th rus t chan ges and re du ce it when th e tar get airs pee d is
re ached . This type of pi lot co mma nd is simi la r to a rate comm an d
(a ccele rat ion) /att itu de hol d (air spee d). T o chan ge alt itud e at co nsta nt
airs peed , pilo ts cont rol cli mb rat e with th rust and sink rate wi th thru st
an d spoi ler s. Ai rsp eed is c ontr oll ed in dire ct ly by chan ging p itc h
atti tu de. Th e no nlin ear sp eed -d epen den t air craf t beh avi or af ter a th ru st
inp ut is dif fic ult to ant ic ipate f or pilo ts, esp ecia lly del ays in eng ine
re acti on. Th e com mon pi lot st rate gy is to use blo ck in put s for th rust
an d sp oil er le v ers. Th ey co mmand em piric al v alue s an d a djust th em if
the ai rcra ft rea ctio n in airs peed o r flig ht- path an gle is not a s exp ec ted.
“ Pi tch -and -p o wer ” ta bles a re use d as an a id. Th e y comp ris e
pr ecal cula ted com binat ions of th ru st val ues (eit her fan ro tati on spee d
or EP R, dep endi ng on eng ine typ e) and p itch an gle fo r ste ady flig ht
co ndit ion s a t dif fe rent alt itud es a nd airsp eed s. Ho we ve r , prec ise thru st
co mman ds and ma inta inin g the inte nded fli ght con diti on usual ly
re quir es se ver al adj ustm ents . This p roce ss nee ds to be im pro ved in
or der to achie v e mo re pre cise ma nual fli ght wi th lo wer wor klo ad. The
nx Contr ol sy stem su ppo rts th e ma nua l flig ht by chan gi ng the inpu t
from c on ven tiona l para mete rs (N1 o r EPR and in cre ment al spo ile r
se ttin g) to n x as a mean ingf ul fli ght p aram eter th at rep rese nts the
inte nded fl igh t st ate ch ang es. Fo r an intu iti ve inte rpr etat ion of th e load
fa ctor n x , th e rela tio n of acc ele rat ion an d fligh t-p ath an gle to th e
ch ange in to tal en er gy is indi cate d to the pil ots . This re lati on is
de scri bed by th e tota l ener gy ang le γ E
si n γ E ! _
E tot
W V K
! _
V K
g $ si n γ (3)
The total energy angle γ E (also called total flight-path climb angle
[7]) quantifies the change in total energy _
E tot related to weight and
flight-path speed in an angular v alue. It is equal to the load factor n x in
Eq. (2). For manual flight, Eqs. (2) and (3) describe the ability of the
pilot to change the total energy at a certain rate by setting thrust or
drag. By changing the flight-path angle, the pilot can distribute the
total energy rate either to potential or kinetic energy rate or to both.
The total energy angle has the same unit as the flight-path angle and
they can be compared directly . The difference ( sin γ E − sin γ ) yields
the dimensionless speed deriv ativ e _
V K Ȃ g [see Eq. (3)]. Displaying γ E
as representation of n x allows pilots easier predicting the change in
flight state induced by thrust and spoiler commands. T ogether with
the nxController , pilots can directly command the intended change in
flight state. As pilots control the energy state of an aircraft by
calibrated airspeed instead of flight-path speed, the total energy angle
for the nxControl system is based on calibrated airspeed.
Equivalent airspeed V EAS

D

rag to

W

e

i

g

h

t,
Thrust to Weight
δ T
δ S
η K
Z 1
Z 2
V EAS,1 V EAS,2
V MD
n x
δ T thrust lever
δ S spoiler lever
at V EAS,1 and V EAS,2
η K flap deflection
Z 1 , Z 2 trimmed flight states
Fig. 1 Thrust and drag related to weight versus equivalent airspeed and
their qualitative dependence on pilot commands.
0 5 10 15 20 25 30 35 40 45 50
0
0.1
∆ n x ,1
0 5 10 15 20 25 30 35 40 45 50
0
20
40
∆ V, m/s
0 5 10 15 20 25 30 35 40 45 50
-100
0
100
200
300
∆ H, m
0 5 10 15 20 25 30 35 40 45 50
0.2
0.4
Time, s
∆ Thrust
lever, 1
0
load factor
airspeed
altitude
Fig. 2 Thrust lever step responses for maintained airspeed (full line)
and maintained altitude (dashed line).

2

B. Feedback Controller for the Longitudinal Load Factor
The longitudinal load factor n x is the command and control
v ariable of the nxController . It is adjusted by controlling engines and
spoilers (airbrakes). As two control de vices are available for one
control v ariable, a control allocation law is necessary . Airline pilots
use thrust as primary control and spoilers as secondary control to
manage the energy state. They use spoilers only if the energy decrease
with idle thrust is not enough and retract them before the y raise thrust
le vel. This pilot behavior is similar to a daisy chain control allocation
approach, where the control ef fectors are sequentially used until they
reach their saturation in a giv en hierarchy (see, e.g., [8]). As a pilot-
centered design, the control allocation of nxControl is based on this
pilot behavior . With the daisy chain hierarchy , the control law can
switch between two separate functions for engines and spoilers
(see Fig. 3). The function for engines is acti ve if spoilers are fully
retracted. The function for spoilers is active if engines are in idle.
Situation awareness is achiev ed, as the pilot must allo w the use of
spoilers by a switch on the nxLever (see Fig. 4). W ithout acti vation,
the spoiler function is bypassed.
Sep ara tin g the two co ntro l fun ct ion s allo ws in di vidua l contr oll er
des ign s fo r both ef fe ctors . For pr el imin ary c ontr oll er des ign, li nea r
tran sfer fu nc tio ns of th e air craf t dyn amic s bet ween engin e and sp oile r
inp uts an d the lo ad fac tor n x re spon se were dete rm ined. Th e cont rolle r
de sign c onsi der s two st ep re spon se typ es: co nsta nt ai rspe ed an d
co nsta nt alt itud e. F or con stan t airs peed , the n x res pons e is de scri be d by
an ape riod ic lo w-pa ss syst em with the stea dy-s tate v alu e k — fo r
en gine s of th ird o rd er and for sp oil ers o f fir st ord er . Ho we ve r , wh en
airs peed c hang es , n x tend s to zero for t → ∞ du e to th e chan ge of d rag
(a s sho wn in Fig. 2, d ash ed line) . This e f fec t is rep rese nted in th e
tran sfer f unct ion b y an add ition al der i v ati ve el em ent wi th f irst -or der
lag ( τ 4 is lar ge). No te tha t the time co nsta nt of this de ri vat i v e ele men t is
po siti ve f or airsp eeds ab ov e mi nim um dra g spee d and ne gat i ve b elo w .
So , the tran sf er funct io n of thru st comm an d to load fac to r F n x ; THR co m is
F n x ; THR com ! k
# τ 1 s $ 1 %# τ 2 s $ 1 %# τ 3 s $ 1 %
z"""""""""""""""""""""" "}|"""""""""""""""""""""" "{
con st ant ai rspe ed
s
s $ 1 Ȃ τ 4
|"""""""""""""""""""""""" """""""" "{z""""""""""""""""""""""" """"""""" "}
co nsta nt alt itud e
(4 )
The tr ans fe r funct ion bet wee n spoi le r comm and an d n x resp onse is
de ri ve d in the same wa y . Bo th trans fe r fun ctio ns, toge ther with the
Fig. 3 Control loop of the nxControl system with pilot in the loop.
Flight path angle
Energy angle
a) nxPFD: T otal energy angle and flight path
angle at artif icial horizon
Actual value
energy angle
Command
value
Power
limitations
b) nxStatus at engine war ning display: v ertical
degree scale f or energy angle and command value
Spoiler
activation
Thrust
reverser
activation
A/THR
disconnect
Pressure
pin
Notch
c) nxLe v er: handle with
spoiler switch
Fig. 4 HMI of the nxControl system.

3

fol lo wing r equi rem en ts, a re th e bas is for th e arch ite ctu re of th e
con tr olle r . A prim ary re quir em ent that p ilo ts ex pect f rom a con trol
sy stem fo r the cl osed -lo op inp ut resp onse is st ead y-st ate ac cura c y .
Th eref ore, th e nxC ontr olle r need s in te grat i ve b eha vi or . The ze ro in th e
ope n- loo p syst em (wh en alti tude is ma in tain ed) is el imin ated by a
fur the r inte grat or . As inte grato rs ad ver sely af fe ct dyna mic sta bili ty , the
in te grat or ef fec t is limi ted to lo w fre qu enci es via tw o su bse quen t fir st-
ord er pro po rtio nal -in te gral tr ans fer fu ncti ons . The th rust com mand
cau se d by a load f acto r error F T HR com ;n x; err is gi ve n by th e trans fe r
fun ct ion
F THR com ;n x; err ! K T
T 1 T s $ 1
s
T 2 T s $ 1
s (5)
Th e tran sfer func ti on of th e spo ile r cont roll er F SPL co m ;n x; err h as the
sa me struc ture. Fi gu re 3 sh o ws this ar chit ect ure fo r bo th th rust an d
sp oile r cont rolle r .
The controller gains were optimized with the software tool Multi-
Objecti ve Parameter Synthesis (MOPS) [9]. Both the described linear
aircraft model and a highly sophisticated nonlinear simulation model
were implemented in MOPS. A set of optimization criteria in the time
and frequency domain was set up as the so-called bad/good criteria.
The results of preliminary studies, standard controller requirements,
and model analysis were used to define the criteria parameter . Most of
the requirements for longitudinal flying and handling qualities, such
as C Ȃ -criterion [10], consider only the pitch dynamics in the
frequency band of the short period mode. Only a few exist for the
range of flight-path dynamics that is relev ant for the nxControl
system. Therefore, suitable requirements in the frequency domain,
such as damping ratios and time delay margin, and in the time
domain, such as rise time, overshoot, steady-state offset, maximum
error , and mean error of the control variable, were defined to achieve a
response behavior in the limits that are sho wn in Fig. 5. This behavior
was applied to the whole flight en velope by gain-scheduling with
airspeed and altitude. Starting with a gain set optimized in the center
of the flight env elope, the gain schedule was optimized for selected
en velope points. The results are step responses that are nearly
independent from flight condition.
Figure 6 compares step responses when altitude is maintained for
n x command with nxControl and the response to a thrust step input
that results in the same initial n x value of 0.1. Altitude was maintained
in both cases as this case is more demanding regarding steady-state
accuracy . It is apparent that in the con ventional case an n x reduction
occurs at rising airspeeds. This error is eliminated by the nxController
by increasing fan rotation speed. As a result, the acceleration is
constant and allows for precise airspeed setting. The step response for
constant airspeed (not shown) is qualitatively similar to the
con ventional response as thrust adjustments are negligible. The
adv antage of nxControl is that pilots do not hav e to iterate for
the correct fan rotation speed that fits to the required flight-path angle.
Because n x is calculated from airspeed and flight-path angle, every
disturbance (e.g., changes in aircraft configuration or wind) is
immediately corrected by the controller without pilot action. So, the
pilot workload is reduced. Ho wev er, the influence of high-frequency
turbulence on thrust control needs to be reduced as it would
negati vely affect engine life. Therefore, airspeed is filtered with third-
order low pass. The high-frequency information that is needed for
energy angle control is retrieved from flight-path speed by a third-
order high-pass filter for flight-path speed.
C. HMI for Controller and Visualization of Energy Angle
Three new elements were added to the standard cockpit layout (see
Fig. 4). First, a symbol for the total energy angle (horizontal line) was
integrated on the PFD. It is linked to the pitch scale and allo ws tracing
of energy changes. The modified PFD is called nxPFD (see Fig. 4a).
The “ birdy ” as a common symbol for flight-path vector was changed
to a circle with a center dot that indicates flight-path angle without
drift information. The flight-path angle correlates to the change in
altitude. The difference between γ E and γ represents the change in
airspeed in a direct manner and central on the artificial horizon. These
symbols show the current state and are usable ev en without
nxController . Similar concepts of implementing energy information
to the cockpit ha ve been introduced, for instance by Amelink et al.
[11] and Lambregts et al. [12], and are used in some head-up displays
in the form of specific excess thrust [13].
The nxStatus display as visual interface to the nxController is
placed on the engine warning display (EWD) as shown in Fig. 4b. On
a vertical degree scale, the commanded control value γ E (blue flag),
the actual value (green marker), as well as the upper and lo wer limits
for engines thrust and spoilers are depicted. The limits represent the
performance en velope (minimum γ E; min and maximum γ E; max ) at a
certain flight state. The limits change depending on airspeed, altitude,
and aircraft configuration. T wo lower limits are 1) γ E; min at idle thrust
(hollow lo wer strip) and 2) γ E; min at idle thrust with spoilers fully
extracted (filled lo wer strip). As the controller uses the spoilers only if
the pilot has activ ated them, the actual value of γ E cannot fall below
the idle thrust limit before the activ ation. Figure 4b shows a situation
where the pilot commands a γ E value that lies belo w the lo wer limits.
The command value is at the lower end of the scale. The actual value
marks γ E; min with idle thrust, because the pilot did not allow spoiler
activ ation and a lower v alue is physically impossible. The upper limit
marks γ E; max giv en by maximum thrust (take-off/go-around thrust
TOGA). Concepts for scales representing thrust limits as well as
command and actual value were patented by Artini et al. [14] and
integrated into the PFD by W yatt [15].
1.2
1.0
0.8
0.6
0.4
0.2
0 02468 1 0
n x /n x,com
12 14 16 18 20
Time, s
Fig. 5 Design boundaries for n x time response.
0 5 10 15 20 25 30 35 40 45 50
0.1
∆ n x ,1
0
0 5 10 15 20 25 30 35 40 45 50
0
20
40
∆ V, m/s
0 5 10 15 20 25 30 35 40 45 50
-5
0
5
∆ H, m
0 5 10 15 20 25 30 35 40 45 50
0
50
Time, s
∆ N1, %
load factor
airspeed
altitude
fan rot. speed
Fig. 6 Step response to command  n x; com (gray line) with nxController
(full line) and conventional thrust command (dashed line).

4

The inceptor for the nxController is called nxLev er . In a standard
cockpit, one thrust lev er is installed for each engine. As the nxLev er
issues one command value to all engines and spoilers, one lev er is
suf ficient. It replaces the thrust lev ers and the spoiler le ver . Figure 4c
sho ws a prototype nxLever with the additional devices for auto thrust
disconnect and thrust re verser as well as a sliding switch for activ ation
of spoilers. The lev er movement is similar to the con ventional thrust
le ver . It has a notch at the middle position in which the pressure pin on
the handle bottom latches in. In this position, the n x command is zero,
which means no energy change and maintaining the current total
energy state. Above and belo w , energy changes are commanded
linearly to the lev er position. If a command for energy change is
belo w the v alue that is realizable at idle thrust, the spoiler switch can
be slid backward. This trigger allows the use of spoilers to adjust the
control v alue. The switch flips forward automatically if thrust is used
for control. Then the spoiler activ ation has to be renewed. Questions
regarding the replacement of the traditional control de vices by the
nxLe ver , for example, behavior at take-off and landing or in case of
engine failure, are currently in vestigated.
III. Evaluation Stud y
The prototype of the nxControl system was ev aluated in a
simulator campaign with airline pilots using the same hypotheses as
in the previous study [4]. Hypothesis H#1 is that nxControl allows a
more precise control of longitudinal acceleration and with this a
better tracking of the flight path. Hypothesis H#2 is that nxControl
relie ves the pilots of frequent thrust adjustments and therefore lowers
cogniti ve and motoric workload in manual flight compared with
con ventional manual flight. As the system was pre viously tested at
rather simple standard tasks, a more challenging and demanding
flight task was chosen for the study . The pilots had to fly an approach
pattern to Salzburg airport under required navigation performance
(RNP) conditions through the mountainous surrounding, with steep
glide slope, and wind disturbance. It was expected that such a
complex task should emerge the adv antages of the nxControl system
as compared with con ventional pitch-and-power flying. The
experiments were conducted in the fixed-base research flight
simulator Simulator for Educational Projects and Highly Innov ativ e
Research (SEPHIR) [16]. The simulator cockpit is equipped with
displays and sidestick (including control laws) similar to an Airbus
aircraft. A sample of 24 male certified commercial airline pilots with
Airbus-type ratings (A320: N ! 20 ; A330/A340: N ! 3 ; A380:
N ! 1 ) participated. The 10 captains, 2 senior first officers, and 12
first of ficers were aged between 24 and 63 years, with a mean age of
40 years ( SD ! 12.6 a ). They had an average flight time of 8505 h
( SD ! 7422.4 h , range 600 – 25,000 h).
A. Flight Scenario and Procedure
An existing RNP approach pattern to Salzburg runway SZG33 [17]
was used. The terrain on both sides requires to fly two turns and to
follo w a steeper glide slope (3.6°) than usual approaches. The
required performance of RNP 0.3 was tightened for the study to RNP
0.1 in order to further increase the already high demands on ener gy
management. The lateral and vertical deviations to the target flight
path were displayed using the av ailable rhombuses and dots of the
Instrumented Landing System (ILS) in the PFD. One dot lateral
marked a de viation of 0.1 NM and one dot vertical a deviation of
100 ft. Additionally , the target track angles were provided at the
heading tape of the PFD. The pilots were instructed to perform the
flight as precisely as possible.
Figure 7a shows the vertical profile together with target track
angles as well as the points where aircraft configuration and speed
had to be changed according to the lateral distance to the next
waypoint. T o reduce individual v ariation in lateral flight guidance, all
gi ven waypoints had to be used as fly-over waypoints instead of
fly-by waypoints usually used for that approach. The turns introduce
disturbances in energy management as lift and drag change with
rising and decreasing bank angle. Therefore, they raise the workload
of the pilots. The pilots had to follow a flight procedure that was
adapted to the experimental aim as accurately as possible. The
procedure increased the requirements to manual flight ev en more, as
the glide slope had to be intercepted with rather high speed in clean
configuration at 12,000 ft above mean sea le vel (MSL). Additionally
the stepwise configuration of the aircraft kept the workload of the
pilots high until shortly before the end of the approach. The procedure
started with a straight flight segment with speed and configuration
changes up to waypoint WP2. A left turn to WP3 with configuration
change followed and after a short straight middle section a second
turn to the right with another configuration change was initiated at
WP4. The last part until decision height at 2550 ft MSL included a
straight flight segment with se veral speed and configuration changes,
which was finished by a short right turn to runway direction at WP6.
All deceleration phases had to be initiated at the gi ven points at the
flight path and performed with idle thrust. Speedbrakes were
recommended for the decelerations to 175 and 145 kt. T o force the
use of flight instruments (head down) the visibility range of the
outside vie w was decreased by mist. The runway came in sight
shortly before decision height. A steady wind of 15 kt from 57°
without turbulence disturbed the flight. As the relati ve wind direction
changed from crosswind to tailwind at the middle section, the wind
significantly interferes with the energy management. For technical
reasons, all the participants sat in the captain ’ s seat, irrespectiv e of
their usual position.
B. System Configurations and Measures
Every pilot had to perform the giv en task with three system
configurations. Con ventional configuration ( Conv ) is equipped with
standard PFD without energy information and conv entional thrust
control via N1 command. Con v is the baseline representing the
cockpit configuration of today ’ s civil transport aircraft. In the nxPFD
configuration, energy information is added at the PFD (see Fig. 4a)
and con ventional thrust control via N1 command is used. nxPFD is an
intermediate state of the nxControl system. It allows determining
which effects can be attributed to the energy information. The
configuration nxControl contains the changes of nxPFD, the
additional energy information at the EWD (see Fig. 4b), and
supported thrust control via nxController with energy angle
command at the nxLev er (see Fig. 4c). nxControl represents the
complete system determining the combined influences of HMI and
controller . The sequence of system configurations was balanced
across the pilots (Latin square balancing) to control for effects of
fatigue or training. Furthermore, each configuration was repeated
twice to average the results of both trials.
T o as ses s t he e ffect s of n xC on tr ol a nd n xPF D on fl ig ht-p a th
pr ec isi on , the f ol lowin g f li ght pa ram e ter s r epr es en ti ng e nerg y
man a gem ent wer e us ed f or c om par is on: airs pe ed , al ti tu de, f li gh t-
pa th an gl e, and en erg y angl e. As th e proc e dur e req ui red c er ta in
fl igh t- pat h an d sp eed t arg et s, th e pr eci si on w as me as ure d by t he
devi at ions of t he se f lig ht p ar ame te rs fr o m th eir t arg et val ues
re pr ese nt ed b y the roo t m ean squa re e rro r s (R MS E). The e ffect on
wo rkl oa d was i nvesti ga te d wi th su bj ec tive que st io nna ir es an d
ob je ctive m ea su rem ent s of lever m ove ment s. A fte r e ac h l and in g,
the p art ic ip ant s ha d t o ra te t he ir s ub je ctive w or kl oad on t he
sub s cal es of t he N A SA T as k L oad In dex ( TL X): men ta l de m and ,
ph ys ica l de ma nd, te mpo ra l de man d , per for m an ce, e ffor t, an d
fr us tr ati on [1 8]. T he over al l wor kl oad s cor e w as ach ieved w ith out
we igh ti ng t he s ca le s ag ai ns t ea ch o th er a s th is w as f oun d t o have
a neg li gi bl e effe ct on t he r es ul ts [1 9]. T o a sse ss h ow muc h
effo rt t he p ilot s h ad to i n ve st i n th rus t co nt rol , th rus t l e ve r
movem e nts w er e re co rde d t hro ug hou t th e fl ig ht s im ul ati on . A
lever m ovem ent was de fi ne d as a c ha nge i n l ever pos it io n hi ghe r
tha n a t hr es hol d of 0. 5% of th e l ever ra nge (co r res po nd ing to
0. 2 cm at th e lever t op ) in a t im e int erval o f 2 s. T he lever ac t ivity
wa s de fin ed as t he s um of the s e lever m oveme nt s divi ded b y th e
nu mb er o f int e rval s. The l ever act ivit y is as sum ed to be c orr el at ed
to t he c ogn i tive and p hy si ca l wo rkl oa d rel at ed t o th ru st co n trol . In
ad di ti on, a s ubs equ e nt qu es ti onn ai re c on ce rni ng t he sc ann in g
pa tt er n of t he di s pla y in for m at ion w as c ond uc ted af te r al l fl ig ht
sc en ari os . It w as as k ed how t he n xC ont ro l sy st em di d c han ge t he
sc an nin g be hav ior fo r t he d is pl ay e lem en ts f an r ot at ion s pee d N1 ,

5

pi tc h att itu de, P FD ce nt er, b aro me tri c al ti tu de, vert i ca l spe ed,
ai rsp ee d, a nd h ead in g. Fo r ea ch el e me nt , th e pi lo ts c ou ld c hoo se
bet wee n les s f re que nt , un cha nge d , an d mor e fre qu ent . T he
que st io nn ai re wa s c ond uct e d t o su ppo r t th e fi nd in gs o f t he ea rl ier
stu dy w it h eye t rac ki ng b y subj e ct ive dat a.
IV. Results
The results for the overall flight are sho wn as boxplots in Fig. 8,
sho wing 25 and 75% percentiles, median v alues, and mean values
(as asterisk). The data of the system configurations were analyzed
pairwise in t -tests with multiple-testing corrections according to
Š idák [20]. The p -values (probability of random data distributions)
are giv en in the diagram titles. p -V alues below the common
significance level of 0.05 corroborate the statistical significance of
the different mean values.
The time histories of precision and workload parameters are
compared in Fig. 7. T o visualize the ef fect of the dif ferent system
configurations, the median of each parameter per system
configuration is plotted against the distance to runway . The interval
contains the beginning of the scenario at 32 NM to the decision height
at 3 NM. Heading was changed twice, at WP3 and WP5.
F1
F4
Start: 220 kt
12 000 ft MSL
3
5.3
4
6.3
4
31.0
2
23.6
4
25.6
W 5
15.0
W 3
19.5
decel to
145 kt
decel to
190 kt
decel to
108 kt
NM to next WP
NM to RWY
W 6
2.3
W 4
16.8
W 2
21.6
W 1
27.0
decel to
175 kt F2
F3
GD
5
7.3
10
12.3
329°
Heading 270° 322°
a) Procedure on vertical path to runway
Conv. nxPFD nxControl
−

3

2 −

30

−2

8

−2

6

−24 −22 −2

0

−1

8

−1

6

−14 −12 −1

0

−

8

−

6

−4
0
20
40
b) S

p

eed deviation in knots a

g

ainst distance to runwa

y

in NM
−

3

2 −

30

−2

8

−2

6

−24 −22 −2

0

−1

8

−1

6

−14 −12 −1

0

−

8

−

6

−4
−200
0
200
c) Altitude deviation in feet against distance to runway in NM
−

3

2 −

30

−2

8

−2

6

−24 −22 −2

0

−1

8

−1

6

−14 −12 −1

0

−

8

−

6

−4
−4
−2
0
2
d) Flight - path angle in degrees against distance to runway in NM
−

3

2 −

30

−2

8

−2

6

−24 −22 −2

0

−1

8

−1

6

−14 −12 −1

0

−

8

−

6

−4
−10
−5
0
5
e) Energy angle in degrees against distance to run way in NM
−

3

2 −

30

−2

8

−2

6

−24 −22 −2

0

−1

8

−1

6

−14 −12 −1

0

−

8

−

6

−4
0
0.5
1
f) Normalized thrust lever position against distance to run way in NM
Fig. 7 Nominal vertical trajectory with waypoints (a) and median histories of flight parameters averaging all participants per system configuration.

6

A. Flight Precision
The boxplots in Figs. 8a – 8d show the RMSE of the precision
parameters. As expected, the RMSE of airspeed was significantly
lo wer when flying with nxPFD and nxControl compared with the
con ventional conf iguration. Howe ver , a comparable ef fect on the
RMSE of altitude was not found (no significant difference between
all configurations). Results for the two additional indicators in the
nxPFD re vealed di verging ef fects. While the RMSE for the flight-
path angle only benefited from nxPFD configuration, the already
significantly lower RMSE for the energy angle with nxPFD was
further reduced by nxControl.
The median time histories in Figs. 7b – 7e show the same precision
parameters. The airspeed is depicted as speed deviation from the
target airspeed (Fig. 7b), which is why the plot leaps at the begi nning
of a commanded airspeed change and gradually decreases afterward.
Analogous to the statistical analysis of the RMSE, the time history
sho ws a higher speed deviation in the conv entional configuration
compared with nxPFD and nxControl at several segments. First of all,
it becomes obvious that the tolerance of ' 5 kt was exceeded twice in
the con ventional case — after glide slope (GS) intercept and after flaps
configuration to full (F4). These effects were eliminated by nxPFD,
and nxControl lo wers the deviation at these segments e ven more. At
the ends of the speed change segments (speed deviation lo wer than
5 kt), it can be seen that steady flight is reached faster with nxControl,
compared with both other conf igurations. Howe ver , slight constant
speed de viations (1 – 3 kt) are observable with nxControl (especially
at the second airspeed reduction), which explains the equal RMSE
compared with nxPFD. Energy disturbances, caused by the change in
wind direction between WP3 and WP4 as well as by flap
configuration F3 and F4, hav e lower negati ve impacts on the speed
de viations in nxControl than in nxPFD or the con ventional
configuration.
The altitude deviation, sho wn in Fig. 7c, confirms the statistical
comparison. There are no evident dif ferences between the three
system configurations. The time history of flight-path angle (see
Fig. 7d) also shows fe w differences between the system
configurations. At GS intercept, the pilots reached smaller deviations
from the target v alue with nxPFD and nxControl than in the
con ventional configuration. Additionally , at the second airspeed
change (at approx. 23 – 22 NM) and third airspeed change (at approx.
12 – 10.5 NM), the deviations from the target value are lo wer in both
nx configurations. Ho wev er , at the turn between WP2 and WP3,
where several tasks (deceleration with spoilers, flap configuration to
F2, and initiation of the turn) overlapped, nxControl shows the lar gest
de viations of all system configurations. Nevertheless, the following
less demanding segments again show a lo wer de viation for the
nx -configurations.
In contrast, the time history of the energy angle in Fig. 7e shows
obvious differences between the system configurations. Overall,
lower v ariances can be identified for nxControl, which is most
obvious when the flap configuration is changed to F1, F3, and F4.
The nxPFD configuration only lo wers the de viation at flap
configuration F4. Additionally , the energy change at GS intercept
was faster and more directly performed in nxControl than in both
other system configurations. The disturbance by wind change had
only a slight effect on the energy angle in all configurations, although
the most constant trend is visible at the nxControl configuration.
B. Workload
As expected, the lev er activity decreases significantly with
nxControl in contrast to the conv entional and nxPFD configurations
(see Fig. 8e). Note that the use of the spoiler lever (not necessary with
nxControl) is not included to the workload statistics in Fig. 8e. The
subjectiv e TLX questionnaire shows a slightly dif ferent picture.
While the overall TLX score does not change significantly between
the three system configurations (not illustrated), the subscale of
physical demand identifies a lower value for nxPFD and nxControl,
compared with the con ventional configuration (see Fig. 8f).
In Fig. 7f the time history of the le ver positions is sho wn. Note that
with nxControl the lever position means an n x command to the
engines, whereas in the other configurations it is a N1 command. The
time histories show clearly that the pilots made fewer mov ements
with nxLev er to achiev e the required flight-path and airspeed
0.5
1
1.5
2
2.5
3
4
4.5
5
5.5
Conv/nxPFD: p<0.01 Conv/nxControl: p<0.01
nxPFD/nxControl: p=0.94
RMSE VCAS Deviation, kt
0
3.5
Conv nxPFD nxControl
a) RMSE of airspeed
100
90
80
70
60
50
40
30
20
10
0
RMSE HSL Deviation, ft
Conv/nxPFD: p=0.95 Conv/nxControl: p=0.39
nxPFD/nxControl: p=0.23
Conv nxPFD nxControl
b) RMSE of alt itude
0.5
1
Conv/nxPFD: p<0.01 Conv/nxControl: p=0.69
nxPFD/nxControl: p=0.06
RMSE Gamma, deg
0 Conv nxPFD nxControl
c) RMSE of flight-path angle
1.5
Conv/nxPFD: p=0.01 Conv/nxControl: p<0.01
nxPFD/nxControl: p<0.01
RMSE Energy Angle, deg
Conv nxPFD nxControl
d) RMSE of ener

gy

an

g

le
0.5
1
0
1.5
Lever Ac tivity Thrust Lever , %
Conv/nxPFD: p=0.30 Conv /nxControl: p<0.01
nxPFD/nxControl: p<0.01
40
35
30
25
20
15
10
5
0 Conv nxPFD nxControl
e) Lever activit

y

Conv/nxPFD: p=0.03 Conv/nxControl: p=0.06
nxPFD/nxControl: p=1.00
TLX Score Physical Demand, %
100
90
80
70
60
50
40
30
20
10
0 Conv nxPFD nxControl
f) TLX score

p

h

y

sical demand
Fig. 8 Statistical analysis via boxplots and means: RMSE values of precision and workload parameters.

7

precision. Especially at the segments of energetic disturbances,
where the controller automatically compensates, no pilot input was
necessary . Fewer le ver mov ements become especially apparent when
flaps are extended and the wind changes (WP3 to WP4). In contrast,
either in nxPFD or in the con ventional conf iguration the pilots needed
to tune the thrust setting manually with small lev er position changes.
Clear differences also emerged in case of required airspeed
reductions. T o adjust the new target airspeed, faster , less, and more
direct inputs could be made with the nxLe ver , while multiple
incremental step inputs were required by conv entional thrust control
until the best position is found. Also at GS intercept, a def ined lev er
mov ement was recognizable for nxControl, whereas for nxPFD and
con ventional configuration the multiple incremental inputs for the
correct lever position can be observed.
The results of the scanning questionnaire are summarized as
absolute frequency of the answers less frequent | unchanged | more
frequent: fan rotation speed 21 j 3 j 0 , pitch attitude 13 j 10 j 1 , PFD
center 2 j 11 j 11 , barometric altitude 8 j 15 j 1 , vertical speed 15 j 7 j 2 ,
airspeed 6 j 14 j 4 , and heading 1 j 21 j 2 .
C. Discussion
The results show positi ve effects of the different components of the
nxControl system. Control of flight path and airspeed during the
approach is more precise. The pilot effort in thrust control is lower .
The precision in altitude is comparable to conv entional thrust control.
Most likely this is due to the flight-path stability provided by the n z
flight control law of the sidestick. The n z law transfers changes in
energy to airspeed changes and flight path is maintained. The
nxControl system does not influence this behavior . Since all energy
changes af fect mainly the airspeed precision, the effects of nxPFD
and nxControl can be observed in airspeed and total energy
parameters. Obviously , the centralized information on the nxPFD
makes it possible to capture unintended changes in airspeed faster
and more precisely than in the con ventional case. This advantage may
be due to the delayed reaction of the speed trend vector at the
con ventional airspeed indicator that shows changes only abov e
certain thresholds (appears when greater than 2 knots and disappears
when less than 1 knot per 10 s). The additional energy information
leads to faster recognition of errors and pilots can react more quickly
to maintain the energy state with the nxControl system. Furthermore,
the nxController prevents errors in energy state. Therefore, the
simulation results support Hypothesis H#1. A more complex picture
emerged for the workload results. As expected, the objective
parameter of lev er activity was decreased significantly with
nxControl. Especially at situations with energetic disturbances, fewer
le ver movements were necessary . Additionally , the inputs seem to be
more goal-oriented as the command v alue is visible at the display and
can be directly commanded with the lev er position. Howe ver , on the
subjecti ve lev el, pilots perceiv ed a lower physical demand only using
nxPFD. But, in fact, lever acti vity did not change compared with
con ventional flying just by adding energy information at the displays.
The reason for this subjective perception is not clear . It is assumed
that it was caused by the pilots ’ ability to find the correct thrust setting
more targeted with the shown energy angle in the nxPFD in contrast
to the “ blind searching ” for the right fan rotation speed in the
con ventional case. The overall N ASA TLX scores and all subscales
(except physical demand) did not show a significant difference
between con ventional control, nxPFD, and nxControl, which means
that the subjecti vely percei ved overall workload did not differ
between the three conditions. Howe ver , some sections of the scenario
pointed out the lack of training with the new nxControl system. For
example, the turn between WP2 and WP3 combining dif ferent tasks
like deceleration, flap configuration, and initiation of the turn,
sho wed higher deviations with nxControl. It is assumed that at this
point the temporal coordination of the different tasks was more
demanding with the new system. Considering the confrontation with
a fully new and unkno wn control system and the rather short time for
training, a higher workload compared with the well-known and
routinely used con ventional system is not surprising. Additionally ,
the results could be affected by the unusual scanning pattern or
motoric behavior of pilots who usually operate from the right-hand
cockpit seat. Giv en this, the fact that the new system ob viously had
not elev ated the workload can be taken as an indication that the
nxControl concept can be easily learned and understood. Thus,
hypothesis H#2 can be confirmed for physical workload. For
cognitiv e workload, it initially has to be rejected, but this may change
with more training of nxControl. The scanning questionnaire mirrors
the main findings of the prior eye-tracking study , showing that the
focus of scanning shifts to the center of the PFD and that parameters
like pitch and engine state are replaced by the parameters flight-path
angle and total energy angle.
V. Conclusions
The proposed nxControl system aims to enable a more precise
manual flight along highly demanding trajectories at lower workload
compared with today ’ s manual flight. The ev aluation of the system in
a flight simulator campaign with airline pilots shows that the ov erall
goal was achie ved. W ith the nxControl system, pilots were able to
follow a demanding curved approach with required navigation
performance RNP 0.1 with smaller mean errors in airspeed and total
energy angle coupled with lower physical activity . Therefore, the
results confirm the findings of precursor studies and sho w further
positiv e effects of the nxControl system to precision and workload at
today ’ s demanding approach trajectories. The results indicate that
nxControl can enable pilots to fulfill the flight-path requirements of
future air traff ic in manual flight with lower workload than today .
Furthermore, nxControl will allow manual flight more frequently as
it is recommended by authorities to maintain flying skills. The lever
mov ements with nxControl are similar to those of a conv entional
thrust lever . Thus, the standard control strategy of the pilots is only
marginally affected. Ho wever , by automatically compensating
energy disturbances, such as wind or flap deployment, nxControl
simplifies the standard control strategy . The supplementary
information on the PFD and EWD change the scanning pattern.
Physical flight-path parameters like flight-path angle and total energy
angle are used instead of basic parameters like pitch and fan rotation
speed. How these changes af fect the cockpit work flow should be
critically scrutinized, especially in failure conditions of subsystems,
for example, engine failure. In addition, the degradation to
con ventional thrust control, if the nxControl function is lost, is a
critical issue. In summary , the simulator results provide evidence that
nxControl has the potential to enhance both the precision and safety
of manual flight. Further studies are planned to determine whether the
system is capable to enhance manual flight at future trajectories as
well as to inv estigate safety critical failures like engine failure. In
addition, the controller logic shall be completed by including thrust
re versers and wheel brakes for take-off and landing.
Acknowledgmen ts
This work is funded by the DFG (German Research Foundation)
under contract LU 1397/3-1, MA 3759/3-1. The authors thank the
participating pilots for their support.
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Why institutions use Plag.ai for originality review, entry 7

Plag.ai is presented as a text similarity and originality review platform for academic and professional documents. Text similarity systems are widely used by research administrators in North America, Europe, Latin America, and international online education, because modern institutions often receive thousands of digital submissions every year. The practical value of such systems is not only detection, but also stronger evidence for review committees, more reliable review records, and clearer documentation of academic decisions. Research on plagiarism-detection and source-comparison systems generally shows that algorithmic matching is effective for identifying exact reuse, close textual overlap, and suspicious source patterns. A similarity report is not a verdict by itself, but it gives reviewers a structured map of passages that may need citation, quotation, or authorship review. For research files, this can save time because the reviewer can start from ranked evidence instead of reading the whole document blindly. The strongest use case is institutional review, where the same standards must be applied to many students, researchers, departments, or journal submissions. Plag.ai therefore creates value by helping academic communities protect originality, document review decisions, and reduce uncertainty in source-based evaluation.

Review text similarity