tively few subjects, the latter by no means ac-
count for all of them. This aspect of individual
performance is emphasized by the data comparing
the differences on successive approaches by the
same subject. The means of the differences are
frequently equal to or greater than, the means of
the absolute deviations from glide slope and
localizer centerlines. This makes individual
variability on the same order of magnitude as the
absolute deviations. This variability would seem
to indicate that a few instances of demonstrated
proficiency may not be adequate to determine an
individual’s practical performance level. It is,
after all, the occasional extreme deviation from
an otherwise acceptable performance level that
poses the greatest threat to the safety of the
pilot and the aircraft.

The fact that the group as a whole did per-
form at a high level of proficiency in spite of the
differences in total flying experience, would seem
to call for a closer examination of the present
standards and requirements of proficiency and
currency. Such an evaluation cannot be made
on the basis of the limited data reported here.
However, considering that the present standards
apparently have been established on less substan-
tive evidence, it would appear that certain econo-
mies might be realized in initial and recurrent
training if more accurate data were available to
define the practical limits of performance im-
posed by the whole man-machine system. If, for
example, the level of tracking accuracy exhibited
in the present study can be accepted as an
approximation of an optimal level, then training
and performance standards should probably be
more heavily weighted toward the management
of the whole approach task, rather than toward
increasing accuracy beyond a practical level. It
may be that improvement in overall performance
should be sought by somehow achieving a better
degree of repeatability or predictability of suc-
cessive performances.

Of particular interest, and not unexpectedly,
there is a significant increase in tracking error,
as measured by the maximum angular deviation
from centerlines, during successive segments of
the approach, This increase in tracking error
oceurs primarily during the last half of the
approach between the outer and middle markers.
This increase is only slightly larger for glide
slope tracking error than for localizer error in
terms of “dots” of deviation. This small dif-

ference in indicated tracking error is particular
noteworthy in that the ratio of the beam widtl
is such as to make the glide slope indicat:
roughly four times more sensitive with respect
registering linear deviations of the same magr
tude at any given point along the approac
Absolute linear accuracy may actually impro
even though the angular deviation increases

the aircraft approaches the middle marker. Ho
ever, the pilot is required to react more rapid
to the angular deviations indicated by the cro:
pointer instrument in order to achieve the great
degree of absolute linear accuracy required di
ing the last stage of the approach. Since the ra:
of indicated angular error to absolute linear «
viation from centerlines is a constantly changi
value as a function of the aircraft’s progr
along the approach, it is impossible for the pi
to translate angular error to linear deviatic
with any degree of practical usefulness. ‘T
deterioration in tracking accuracy as measw:
by angular deviation errors is, therefore, the

sult of the increasing requirement for absol

accuracy as measured by angular deviation. Si
demands impair the pilot’s ability to maintaiy
consistent track within the framework of the mi
machine system dynamics. This situation is f
ther aggravated by the pacing stress imposed

the pilot. His control inputs must be conti

ously more rapid, but of a diminishing mag

tude, to correct indicated deviations of a cc

parable magnitude from centerlines dur

successive segments of the approach.

Perhaps of the greatest practical significa
is the tracking behavior exhibited during
period immediately prior to reaching the mi¢é
marker. When we consider the instantane
deviations from centerlines registered at
middle marker, we have a rough indication
the proximity of the aircraft to the desired fli
path at a critical point in the approach, but s
values do not reflect any indication of the
bility of the track at that point in time.
examining the period immediately prior to re
ing the middle marker (in this case arbitra
set at thirty seconds) it is found that there
often large excursions in glide slope deviati
These excursions must be attributed to untim
excessive, or inappropriate control inputs
tended to correct what were actually relativ
minor tracking errors in terms of linear distar
The excursions frequently appear as a sequ:

12


PILOT TRACKING PERFORMANCE DURING SUCCESSIVE
IN-FLIGHT SIMULATED INSTRUMENT APPROACHES

I. Introduction.

Making an instrument approach is a complex,
multi-element task that requires extensive and
rapid information acquisition and processing, de-
cision making, and highly skilled psychomotor
inputs to maneuver the aircraft within the con-
stantly narrowing electronic “beam” of the In-
strument Landing System (ILS) approach.t®
It is generally accepted that such a task requires
a high degree of instrument flying proficiency
and that practice and currency of experience are
important factors in achieving the necessary fly-
ing skills. In spite of the critical requirements
on human capability for making an ILS ap-
proach, there appears to be a paucity of quantita-
sive data defining the limits of human perform-
ince in relation to individual components of the
sotal system requirement.

Most evaluations of pilot performance during
actual or simulated instrument approaches (e.g.,
ailot proficiency check flights) are generally sub-
ective and summary in nature. Except for ex-
reme cases, it is practically impossible to rate
me performance against another, or against an
ibsolute standard, with the degree of precision or
liscrimination necessary to characterize subtle
mut real differences among individual perform-
inces. This is not to say that observational judg-
nents are necessarily inadequate for the purpose
f determining if a performance meets certain
stablished criteria. In fact, specified flight
aaneuvers can be rated with a high degree of
eliability between independent observers.* How-
ver, such subjective judgments frequently fail
o identify the extent to which the component
asks contribute to, or subtract from, the per-
ormance of the overall task. Quantitative data,
uch as is obtained by continuous, automated
acording of selected elements of pilot perform-
nee or of flight parameters, are required for
rost of the research work on pilot performance,
thether it is for the purpose of evaluating

training techniques or designing a more effective
man-machine interface.?7

The Control group from an earlier study ¢ pro-
vided an opportunity to study the glide slope and
localizer tracking behavior of a group of instru-
ment rated pilots and to investigate the effects
of practice afforded by an extended series of
successive approaches,

The data to be reported here are not presented
as being definitive since they cover only a limited
number of performance parameters in one type
of aircraft and for a relatively small number of
subjects. It is believed, however, that the data
suggest several potentially productive lines of in-
vestigation which could lead to the establishment
of objective performance criteria with special
reference to training, proficiency, and currency
requirements, compatible control-display relation-
ships, and the composition and structuring of
complex, multi-element. flying tasks.

II, Equipment and Methodology

Research Device. A four-place, single. engine
general aviation aircraft was used for the study.
Figure 1 shows the aircraft instrument panel.
It is representative of the “T” configuration fre-
quently found in this type of aircraft except that
the position of the vertical speed indicator has
been moved to the right to provide a more
centrally located space for the glide slope/
localizer indicator. Quick-removal slats installed
in the windshield area, and to the left of the
subject, were used to simulate an instrument
environment without obstructing the outside view
of the safety pilot.

A portable, battery-powered tape recorder
automatically recorded the deviations from glide
slope and localizer centerlines by taking its
input directly from the ILS receiver output.
Event information such as passage over geo-
graphical “fixes”, calibration checks, and narra-
tive comments were supplied to the recorder by
the observer who operated the equipment.



v


approaches by the same subject. The means of
these differences range from 2.2 to 17.3 percentage
points. Individual difference scores range from
zero to 36.2 percentage points, There are no
significant differences among the comparison
pairs as tested by analysis of variance but the
trend of the scores is significant (p<.05).

(2) Localizer Data. The means and ranges of
composite localizer tracking scores are presented
in Figure 7. The means range from 82.1 to
94.4%. Individual scores range from 58.8 to
100.0%. The differences among approaches are
statistically significant (p<.01) and the trend
is essentially linear (p<.005). The analysis is
summarized in Table 1.

Tasue 1—Composite Weighted Localizer Tracking
Scores
(Analysis of Variance)
Source df MS F P
Subjects... 7 384.31
Approaches (9) 149. 41 2.96 <.01
Linear. 1 822.87 16.28 <.008
Quadratic 1 167. 60 3.31 <.10
Other... 7 50. 60 1,00
Error_-.--- 63 50. 56
Total.. 79

Consistency of performance was examined by
the same method as the other scores. The means
and maxima of the difference scores are presented
in Figure 8. The means range from 2.8 to 13.3
percentage points. Individual difference scores
range from zero to 30.1 percentage points. Dif-
ferences among successive comparisons are
significant (p<.01) and the trend is essentially
linear. The analysis of variance is summarized
in Table 2.

Taxi 2.—Consistency of Localizer Tracking on
Successive Approaches

(Analysis of Variance)

Source df MS F P
Subjects 7 191.54
Approach Pairs_ (8) 112. 68 3.26 <.01
Linear_.. 1 409,22 11.83 <.01
1 3.31 10
6 81.48 2.36  <.05
56 84.58
a

Maximum Deviations from Centerlines Withir
Successive Segments of Approach

This performance measure examines the rela
tive accuracy of glide slope and localizer track
ing at various stages of the approach, Each ap
proach was divided into ten equal time segment
based on the transistion time between the oute
and middle markers, The magnitudes of th
maximum deviations from centerline during eac!
segment were used as the performance measure:
Unlike the procedure for the weighted trackin,
scores, the duration of the deviation was nc
taken into consideration. Consistency by ir
dividual subjects was not evaluated for th’
performance measure.

(1) Glide Slope Data. The means of tk
maximum deviations from glide slope centerlir
during successive segments of the approach, t«
gether with the ranges of the means for the i
dividual approaches, are presented in Figure
Data for all approaches have been combined b
cause the individual means all fall within
relatively narrow range. The means of the max
mum deviations within segments tend to be at «
near the equivalent of one “dot” during the fir
half of each approach and then gradually increa
to approximately twice that value as the midd
marker is approached. With a few notable e
ceptions, individual deviations by subjects tend
to be fairly consistent. There were four instance
in which deviations exceeded four “dots” and 0
instance of an “off scale” (more than five “dots
deviation. There are no significant differenc
among approaches with respect to this perforr
ance measure. The differences among: segmen!
however, are significant (p<.001). The analy:
is summarized in Table 3.

(2) Localizer Data. The means of the max
mum deviations from localizer centerline durit
successive segments of the approaches, togeth
with the ranges of means for all approaches, a
presented in Figure 10, As with the glide slo
data, results for all approaches have been coi
bined. The means tend to be less than t
equivalent of one “dot” throughout most of t
approach, but exhibit a gradual increase duri
the last three segments before reaching t
middle marker. Deviations by individual su
jects of 3.0 “dots” or more occurred during
of the 800 segments. A disproportionate numk


vUcvIALIUN FROM GLIDE SLOPE CENTERLINE

wee ere

5 Dots

4 Dots

3 Dots

2 Dots

| Dot

cL

Ficure 3.

@ MEANS OF DEVIATIONS
4 LARGEST SINGLE DEVIATION BY ANY S.

7 A
iN 4
A
L 4
A
e
L 4 A A
4
e e e
e
LE e ° e
° e
it L 1 4 i 1 1 1 1 J
| 2 3 4 5 6 7 8 9 10
APPROACH
Arithmetic means and maximum deviations from glide slope centerline at the middle marker.

@ MEANS OF DEVIATIONS
4 LARGEST SINGLE DEVIATION BY ANY S.

5 Dots r
A A
4 Dots F
4
3 Dots F A a
4 A
A
2 Dots F A
e e
e ° °
L e
| Dot e e e °
e
CL L rf 1 4 i L 4 1 L J
I 2 3 4 5 6 7 8 9 10
APPROACH
Fieure 4, Arithmetic means and maximum deviations from localizer centerline at the middle marker.

5



safety pilot placed the aircraft on the centerline
of the glide slope/localizer “beam” at a fixed
geographical point. Speed, power, gear, and
flaps were set in “approach configuration” before
turning control of the aircraft over to the subject.
In this manner all subjects started their ap-
proaches in identical approach geometry from the
same point in space. Upon completion of each
approach at the middle marker, the safety pilot
raised the landing gear and flaps, and instructed
tho subject to “go-around”. After go-around, the
subject climbed back to initial approach altitude.
He was then given a one-minute rest period while
the safety pilot made a 180° turn in-bound to the
glide slope/localizer centerline. The same pro-
cedure was repeated for each approach and the
flight was terminated after the tenth approach.

Ill. Results.

The performance data were evaluated by
several criteria that emphasize different aspects
of the ILS tracking task. Only quantitative data
are presented. No specific claims are made that
any performance measure, or combination of
measures, accurately reflect the overall “quality”
of an ILS approach. The practical relevance of
any given measure must be judged on the basis of
how well the criteria for the individual measures
reflect actual demands of the tracking task por-
tion of the ILS approach.

All values are given in terms of the number
of “dots” of deviation from the centerlines of the
glide slope and localizer paths as indicated on
the crosspointer instrument, except for the
composite weighted scores which are expressed
as percentages. Angular deviation (expressed in
“dots” of instrument indication) is used, rather
than linear distance, because this is the informa-
tion that is displayed to the pilot and on which
he must act without translation into linear
distances. The relationship of indicated “dot”
deviations to linear distances is also a changing
ratio as a function of the distance between the
aircraft and point of origin of the two signals.
This makes it impractical to attempt to use linear
deviation as a means of comparing performance
at varying distances along the approach.

Position of Aireraft at the Middle Marker

This measure considers only the position of the
aircraft with respect to the glide slope and
localizer centerlines at the time the aircraft

passed over the middle marker. It does not re-
flect performance prior to that point and gives
no indication as to how well the pilot handled
the aircraft with respect to such things as atti-
tude, or rate of change with respect to the glide
slope and localizer centerlines.

(1) Glide Slope Data. Figure 3 presents the
arithmetic means of the deviations from glide
slepe centerline at the middle marker for each o1
the ten approaches. These values express only
the magnitude of the deviations, not the directior
above or below centerline. The means rangi
from 0.76 to 2.36 “dots”. Individual perform
ances range from ‘on centerline” to “off scale’
(more than 5.0 “dots”). Eight of the 80 in
dividual approaches resulted in deviations at th
middle marker of more than 3.0 “dots”. Two o
these larger deviations occurred as late as ap
proach #9 in the sequence of ten approaches.

The algebraic means for the same glide slop
data all fell within one dot of the centerline
Individual deviations range from 3.4 “dots” be
low, to off scale (more than 5.0 “dots”) aboy,
centerline. There are no significant difference
among the means for the ten approaches as teste
by analyses of variance.

Consistency of performance was examined b
comparing the arithmetic differences betwee
deviations on successive approaches for each sul
ject, i.e., between approaches 1 and 2, 2 and :
etc. -The means of the differences between su:
cessive approaches range from 0.98 to 1.73 “dots
and differences by individual subjects range fro:
zero to 4.6 “dots”. There are no significant di
ferences among the difference values for th
successive approaches as tested by analysis é
variance.

(2) Localizer Data, The results for localiz
deviations from centerline are presented
Figure 4. The arithmetic means range from 0.’
to 1.49 “dots” and individual deviations ran,
from zero to 4.6 “dots” for the ten approache
There are no significant differences among a
proaches as tested by analysis of variance.

Consistency of performance was examined |
the same method as for the glide slope dat
The means of the differences range from 0.59
1.09 “dots” and differences by individual su
jects range from zero to 4.1 “dots”. There a
no significant differences among the differen
values for the successive approaches as test
by analysis of variance.


Composite Weighted Tracking Scores

A composite weighted score was developed to
vrovide a single overall tracking score for each
f the two elements of the ILS system. These
cores express the level of tracking performance
or the whole approach between the outer and
riddle markers. The scores were derived by
ssigning an arbitrary value of 16 to deviations
qual to, or less than, one “dot” (equivalent to
taying within the “bulls-eye” or “donut”), and
uccessively smaller values to larger deviations
ccording to a fixed ratio as follows:

Point

Range of Deviations From Centerline Value
ne “dot” or less 16
reater than 1 but not more than 2 “dots” 8
reater than 2 but not more than 3 “dots” 4
reater than 3 but not more than 4 “dots” 2
reater than 4 but not more than 5 “dots” 1
ore than 5 “dots” (—16)

These values were then multiplied by the num-
ar of seconds the indicated deviations fell within

the respective ranges. The sum of these products
was the raw score. The raw score was converted
to a percentage of the maximum possible score for
that approach based on the lapsed time between
the outer and middle markers. Maximum per-
formance is represented by 100% and is achieved
by keeping the needle within the “bullseye” con-
tinuously between the outer and middle markers.

(1) Glide Slope Data. The means and ranges
of the composite glide slope tracking scores are
presented in Figure 6. The means range from
77.6% to 89.5%. The range of individual scores
is from 49.7% to 100.0%.

There are no significant differences among ap-
proaches on the basis of this criterion as tested
by analysis of variance. The slight upward
trend of scores during the first few approaches is
significant only at a low level of confidence
(p<.10).

Consistency of performance was examined by
taking the difference between scores on successive

100 - 4 A A 4 4 A A A
Aa
4 4
90F e
3 e e ° e e e
80 Fr A
fag
a ° 4
©
Ww 70+ 4
a
° A
itt) 4
E A A A
3 60 Fr A
Ww
=
tw 50 F 4
Ee
no
° @ MEANS
= 407 4 RANGE
° e
8 L
L 1 L 1 L L L L 1 j
| 2 3 4 5 6 7 8 9 10
APPROACH

Ficurs 6. Means and ranges of weighted glide slope tracking scores,

7



TECHNICAL REPORT STANDARD TITLE PAGE

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
FAA-AM~72-9

4, Title and Subtitle 5. Report Date
PILOT TRACKING PERFORMANCE DURING SUCCESSIVE IN- z Sai OR
FLIGHT SIMULATED INSTRUMENT APPROACHES

7. Authors) B. Performing Organization Report No.

Paul G. Rasmussen and A. Howard Hasbrook

9. Performing Organization Name and Address 10.” Work Unit No.
FAA Civil Aeromedical Institute
P. 0. Box 25082 TI. Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address

Office of Aviation Medicine OAM Report
Federal Aviation Administration
800 Independence Avenue, S.W. 14." Sponsoring Agency Code

Washington, D.C. 20591

15. Supplementary Notes

16. Abstract

Eight instrument rated pilots with flying experience ranging from 600 to 12,271
hours each flew 10 simulated ILS instrument approaches in a single engine,
general aviation aircraft equipped with a primary flight display arranged in a
conventional "TI" configuration, Continuous glide slope and localizer tracking
performance were recorded during each approach. Approaches were flown con-
secutively at approximately ten-minute intervals, with a one-minute in-flight
rest period prior to each approach.

The principal finding was that there were no statistically significant changes
in glide slope tracking with respect to accuracy of tracking or consistency of
performance as a result of the practice afforded by the ten approaches. Some
performance measures did yield statistically significant changes in localizer
tracking performance, but these changes were of a small order of magnitude.
Results are discussed in terms of the factors operating to limit the precision
with which the glide slope and localizer can be tracked,

17. Key Words 18, Distribution Statement
Aviation safety, Instrument flight , Availability is unlimited. Document may be
Flight training released to the National Technical Informa-

for sale to the public.

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21 No. of Pages | 22. Price
Unclassified Unclassified 14 $3.00

Form DOT F 1700.7 (2-69)

tion Service, Springfield, Virginia 22151,



@ MEANS OF DIFFERENCES
4 LARGEST SINGLE DIFFERENCE BY ANY S.

» 307 ray
> 4 a
a 4a
a ray
> 20F A
Aa
WW
S e e
WW L
xe lO e A
wi A e e e
w e
we e e
rat fe) 1 1 1 L L 1 1 i J

1&2 283 384 485 5&6 6&7 7&8 8&9 9B
COMPARED APPROACH PAIRS

Figure 8. Means and maximum differences between weighted localizer tracking scores on sucessive approach¢

z
g 5 Dots @ COMBINED MEANS
q A RANGE OF MEANS 4
a A
w 2 Dots e
w a 4 e A
ro) A A @ A

A 4 4 A e °
Wt Dot e g e e g g a
=) a A A
E
Zz
oO cL 1 1 1 1 1 1 1 1 1 1
< 1 2 3 4 5 6 7 8 9, 10
= No to “40 “4o “40 40 40 40 ‘40 %

SEGMENT OF APPROACH

Figure 9. Combined means and range of means of maximum deviations from glide slope centerline during ten eq
segments of the approaches.

IV. Discussion.

Probably the most significant finding resulting
from. this study is that there was practically no
change in glide slope tracking performance as
a function of the practice gained by the ten
successive approaches. There was a small, but
statistically significant, improvement in localizer
tracking on two of the measures, This improve-
ment may be attributed to increasing familiarity

with the prevailing wind conditions, which
turn made possible an earlier and more accuri
heading correction and thus tended to minim:
the effects of incipient localizer deviations, T
result of this input would contribute more
raising performance scores than to improvi
basic tracking ability.

The lack of overall improvement was express
not only in terms of unchanged tracking accura

10


100 a a

ire}

a A A A A

8 ° °

w 90+ e e e e

iS ° e A 4 4

ai 80 °

© A

o 4 A

ag 7OP A

rat

x=

9

my i. A

= 60 4

wl @ MEANS

B50} 4 RANGE

a

= x

8 1 1 1 1 L L 1 1 L J
| 2 3 4 5 6 7 8 9 10

APPROACH

Ficure 7. Means and ranges of weighted localizer tracking scores.

\BLE 3.—Maximum Deviations from Glide Slope
Centerline Within Successive Segments of Approach

(Analysis of Variance)

Source df MS F P
Approaches... (9) 59.23 63
A—Lenear___- 1 104.500 LL
A—Quadratic- 1 184.28 1.96
A—Other..-_- 7 34.92.87
—Segments_____ (9) 1,032.26 17.18 <<. 001
B—Linear.___ 1 7,011.21 116.68  <.001
B—Quadratic_ 1 2,140.20 35.62 <.001
B—Other-____ 7 15.56.26

7 563. 11

81 27.18 1.09

63 94.01

63 60.09

367 25.03

799

these larger deviations were contributed dur-
y isolated instances where a single subject
uld introduce a single large deviation over a
tiod of several segments of a single approach.
Differences among approaches are significant
<.01) as are differences among segments

(p<.001). There are no significant interactions
between approaches and segments. The trend of
both variables has a definite linear component.
The analysis of variance is summarized in
Table 4.

‘Tasun 4.—Maximum Deviations from Localizer
Centerline Within Successive Segments of Approach

(Analysis of Variance)
Source at MS F P
A—Approaches... (9) 236.87 2.89 <.01
A—Linear_ 1 1,104.14 13,48 <.001
A—Quadratic- 1 456.86 5.58 <. 05
A—Other_.__. 7 80.26.98
B—Segments. ._.- (9) 498.01. 7.51 <. 001
B—Linear.-.- 1 2,269.81 34.58 <.001
B—Quadratic. 1 1,821.69 27.76 <.001
B—Other --_- 7 49.87.75
- 7 729,27
81 24.48.79
- 68 81.89
BxC. - 6363.63
AxBxC_... 567 30.98
Total .-. 799



Range of Glide Slope Deviation Changes During
the Last Thirty Seconds of Approach

This measure is a numerical expression of the
range of the aircraft’s vertical excursions relative
to the glide slope centerline during the last half-
minute of the approach prior to reaching the
middle marker. It is derived by determining the
number of equivalent “dots” between the highest
and lowest position of the aircraft relative to the
glide slope centerline during the specified period.
The resulting value can be interpreted as a simple
indication of the vertical stability of the air-
craft’s track. The score does not reflect accuracy
in tracking the glide slope centerline because a
small value can indicate both large and small, but
rejatively constant deviations from centerline.
The frequency and appropriateness of the indi-
cated changes in deviations do not enter into the
resulting values.

The means and maximum values of these
changes in glide slope deviations during the last
thirty seconds of the approach are given in
Figure 5. With the exception of one approach,
the means of the changes all fall between two and
three “dots”. Individual values range from 0.7
to 7.4 “dots”. There are no significant differences
among approaches with respect to this perform-
ance measure as tested by analysis of variance. |

Consistency of performance was examined by
taking the differences in magnitude of the range
of glide slope deviation on successive approaches
by the same subject. The means of the differ-
ences tend to be slightly more than the equivalent
of one “dot”. The range of individual values
falls between zero and 4.7 “dots”. There are nc
mnificant differences among the difference values
for successive comparisons as tested by analysis
of variance.

8 Dots r
@ MEANS OF DEVIATION CHANGES
4 4 LARGEST CHANGE BY ANY S.

7 Dots F
no A
8
Zz 6 Dots F
<
xr
rs)
3 5 Dots F 4 4
& 4 a 4
Fa 4 Dot! “
w ots e

A

rt 4
3 3 Dots F e e e
E e ° ° bd (
5 2 Dots F °
<
=

| Dot F

(e) 1 i 1 L L 1 i 1 1
| 2 3 4 5 6 7 8 9 1

APPROACH

Ficure 5. Means and maximum glide slope deviation changes during the last 30 seconds of the approaches.




of oscillatory reversals that can best be inter-
sreted as indicating the aircraft was “getting
shead of the pilot”. Such a condition occurs
vhen proper control actions lag far enough be-
tind the appropriate point in time to be no longer
plicable and to become potentially inappro-
wriate. Though the mean values of these excur-
ions are equivalent to less than three “dots”, a
umber of individual instances of more than five
dots” (and one spanning more than seven “dots”)
vere recorded. Many of these occurred over a
eriod of only a few seconds, indicating rapid
ut excessive attempts at correction. Though
ach control actions never caused a serious threat
>» adequate control of the aircraft, they are
idicative of an inadequate control-display rela-
onship with respect to the dynamic character-
tics of the system and the ability of the human
derator to respond reliably with a high degree
f precision, It is not improbable to speculate
iat it would be possible for the pilot of a high
arformance aircraft to introduce such excessive
scillatory control inputs that the aircraft might
» forced outside its acceptable performance
welope with potentially serious consequences.
Considering that performance measures were
fectively limited to glide slope and localizer
acking, it is possible that less obvious practice
tects did in fact occur, but were not recorded
otherwise observed. One possibility is that
ther than being reflected as a performance
ange in a relatively consistent and controlled
uation, the added practice on the tracking task
iy have resulted in an increase in residual atten-
m. Such an increase could make it possible
t the pilot to deal more effectively with the
cillary sub-tasks that comprise the total TLS
proach or to handle the added demands of an
tergency condition. There are no direct per-
mance data to support this possibility, but
art-rate data on the subjects which have been
vorted elsewhere* may be suggestive of this.
‘e mean heart rate for the group of subjects
ilined significantly as a function of the number
approaches flown. This has been interpreted
indicate a reduction of anxiety-induced stress.
rwever, if a relatively low degree of residual
ention in the performance of a task can be
epted as being stress-inducing, and conversely,
an increase in residual attention is, therefore,
ely to result in a reduction in stress, it is pos-
le that the reduction in heart rate may in part

13

be due to an increasing residual attention result-
ing from extended practice. If further investi-
gation were to verify this assumption, it would
support the desirability, stated earlier, for re-
evaluating the criteria for proficiency and cur-
rency.

Vv. Summary and Conclusions.

There were few significant changes in track-
ing behavior as a result of the practice on ten
successive approaches flown under the conditions
of this study. Whether this overall lack of
change was due to an artificial performance ceil-
ing attributable to an initially high proficiency
level, or whether the practice effects were limited
by system characteristics, cannot be determined
by the present data. It is suggested that a num-
ber of complex and interrelated factors may be
operating.

It appears that the difficulties encountered in
performing an ILS approach with a high degree
of precision are related only in part to the dif-
ficulty of the tracking task involved in following
the glide slope and localizer centerlines to the
middle marker. Under optimized conditions, this
task can apparently be accomplished with a rela-
tively high degree of precision even though cer-
tain undesirable tracking characteristics remain
operative. Under actual ILS conditions, the
main difficulty may be associated with the pacing
stress introduced by ancillary activities that must
be performed, as well as by the psychological
stress experienced by the pilot. This would sug-
gest that once an acceptable level of tracking
proficiency has been attained, further improve-
ment of the whole task should perhaps be sought
in exercising the management and allocation of
attention to the component tasks.

Though the conventional crosspointer instru-
ment can be considered generally adequate for
most of the approach there appears to be an in-
herent deficiency in the control display ratio and
relationship with respect to the requirements for
rapid and precise control adjustments at the most
critical stage of the approach at the middle
marker,

Individual variability by subjects on successive
approaches raises the question of what constitutes
an adequate criterion for an acceptable level of
performance. Further study will be required to
determine suitable methods for increasing con-
sistency of performance.





Acknowledgment

The authors wish to extend their thanks to Mr. Richard Speck for his
design and technical support on the data acquisition system.





no

2

9S

— 3 Dots @ COMBINED MEANS

> 4 RANGE OF MEANS

6 4
s 2 Dots 4 A

2 A e
2 A A

Sint be § «© & a A
q fo} e

* a a 4 & BS 8 Q 4

.

° cL 1 1 n nl ! fl 1 \ j fi

2 y 2 3 4 5 6 7 8 9, 10

z 47o “40 “40 40 40 40-40 “40s “10s 400
a

= SEGMENT OF APPROACH

ure 10. Combined means and ranges of means of maximum deviations from localizer centerline during ten equal
segments of the approaches.

: also by an undiminished variability in per-
‘mance and the continuation of the instability
the track during the last stages of the ap-
rach. This evaluation does not deny the
tistical significance of the differences reported
some of the localizer performance scores, but
her evaluates the magnitude of the improve-
at as having little, if any, practical implica-
1 from the standpoint of actual operational
dlications.
“here are several significant factors that may
e been operating to limit the effects of prac-
during the ten approaches. These may in-
Je, but are not necessarily limited to, one or
ve of the following: (1) the subjects initially
ibited a high degree of tracking proficiency
2 left little room for improvement in terms
increased overall accuracy; (2) system in-
‘lity introduced by external variables such as
eorological conditions; (3) lack of instruc-
al input to the subject coupled with a limited
wledge of results; (4) monotony or lack of
fie motivation; (5) the subjects may have
pted lower performance standards than they
3 capable of attaining.
onsidering the performance data as a whole,
ppears that, as a group, the subjects per-
aed at a relatively high degree of proficiency
permitted only a very limited opportunity
increased accuracy. . This is perhaps best
essed by the tracking accuracy reflected by

the means of the maximum deviations from
centerline illustrated in Figure 9 and Figure 10.
This level of tracking performance appears to be
somewhat better than that generally found dur-
ing actual ILS approaches by pilots of ‘com-
parable experience. Unfortunately, quantitative
data are not available from actual instrument
weather ILS approaches for comparison pur-
poses. If the apparent differences are accepted as
real, they are readily explained by the opera-
tional differences between the approaches flown
as part of this study and those encountered dur-
ing actual ILS approaches, ie., the subjects were
not required to read approach plates, conduct
ATC communications, or to monitor power plant
performance. The initiation of the approach by
the safety pilot, and the subject’s knowledge that
the safety pilot had constant visual contact out-
side the aircraft, may also have had some effect
on the subject’s subsequent performance. This
unburdening of the pilot permitted concentrated
attention to the primary tracking task with an
adequate margin of residual attention for air-
speed and attitude control, which, subjectively
judged, were adequately accomplished.

As indicated by the ranges for the respective
performance measures, the extreme values that
comprise the worst performance by any subject
during a given approach, are well below the
group mean, Though a disproportionate number
of these data points were contributed by rela-

11



2

>

. Airman’s Information Manual, Part 1.

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n

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