DOT/FAA/AM-97/9

Office ofAviation Medicine

Washington, D.C. 20591

Effects of Mild Hypoxia

on Pilot Performances at

General Aviation Altitudes

Thomas E. Nesthus

Ladonna L. Rush

Steven S. Wreggit

Civil Aeromedical Institute

Federal Aviation Administration

Oklahoma City, Oklahoma 73125

April 1997

Final Report

This document is available to the public

through the National Technical Information

Service, Springfield, Virginia 22161.

19970515 023

©

U.S. Department

of Transportation

Federal Aviation

Administration

DTCC qUALm DJ3FECXED 1
NOTICE

This document is disseminated under the sponsorship of

the U.S. Department of Transportation in the interest of

information exchange. The United States Government

assumes no liability for the contents or use thereof.
Technical Report Documentation Page

1. Report No.

DOT/FAA/AM-97/9

2. Government Accession No.

4. Tide and Subtide

Effects ofMild Hypoxia on Pilot Performance at General

Aviation Altitudes

7. Auttior(s)

Nesthus, T.E., Rush, L.L., and Wreggit, S.S.

9. Performing Organization Name and Address

FAA Civil Aeromedical Institute

P.O. Box 25082

Oklahoma City, OK 73125

3. Recipient's Catalog No.

5. Report Date

April 1997

6. Performing Organization Code

8. Performing Organization Report No.

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

12. Sponsoring Agency name and Address

Office ofAviation Medicine

Federal Aviation Administration

800 Independence Ave., S.W.

Washington, DC 20591

13. Type of Report and Period Covered

Final Report

14. Sponsoring Agency Code

15. Supplemental Notes

16. Abstract

General aviation pilots may fly continuously at altitudes up to 12,500 ft. without the use ofsupplemental oxygen.

However hypoxia is a condition that can develop at altitudes under 12,500 ft. Research has shown highly variable

tolerance and performance ofindividuals during low altitude laboratory exposures with simple and complex tasking.

This study evaluated the physiological and subjective responses, as well as the simulated flight performance of general

aviation pilots during a cross-country flight scenario.

Ten pilots of a mild hypoxia group were compared with 10 pilots of a normoxic control group. Measurements or flight

performance from the Basic General Aviation Research Simulator (BGARS) and of flight-following procedures were

gathered during a 3-day, 2 hr. per day, cross-country flight scenario. Determined by group membership and terrain

elevation during the cross-country flight, subjects breathed either oxygen mixtures simulating sea level, 8,000 ft., lU.OUU

ft., and 12,500 ft. altitudes or compressed air, throughout. -^ , \ n_m\ J

The physiological measures of oxygen and carbon dioxide partial pressures (PtcC>2 and PtcC02), heart rate (HRj, and

blood oxygen saturation (Sa02), provided significant results differentiating the 2 pilot groups and the 4 altitude

conditions ofthe hypoxia group. No significant deviations from assigned altitude, VOR radials, or heading were found

during cruise flight. However, significandy more procedural errors were committed by the hypoxia group during cruise

flight at 10,000 ft. and during the descent and approach phases offlight from 10,000 ft. on Day 3 and during descent

from 12,500 ft. on Day 4. Subjective measures ofsymptoms, workload, and stress provided limited evidence of hypoxic

effects, although the hypoxia group reported significantly greater demands on their time during flight, compared to the

control group. Also, significant group differences were found in flight following procedural errors, particularly during

the descent and approach phases offlight. Recommendations are made to encourage GA pilots to plan their descents

from flights above 10,000 ft. to allow sufficient recovery time as a routine precaution to the often undetectable effects of

mild hypoxia.

7. Keywords

Hypoxia Simulated Altitude

Supplemental Oxygen Requirement

Flight Performance Simulated Flight

18. Distribution Statement

Document is available to the public through the

National Technical Information Service

Springfield, Virginia 22161

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21 No. of Pages

43

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
FOREWORD

This study was conducted as a part of the FAA

Civil Aeromedical Institute (CAMI) general aviation (GA) human factors research program whose

efforts support the mission to:

Conduct applied human factorsresearch in the laboratory

and in the field on carefully selected GA problems, to

obtain objective, scientifically derived datawhichwill aid

in identifying affordable options for reducing the risk

exposure, and number ofincidents and accidents in the

general aviation community, and which will serve to

enhance GApilot performance under non-routine flying

conditions.

The CAMI General Aviation Human Factors

Research Program is consistent with the FAA policy

statement on general aviation, promulgated by the

Administrator in 1993, and the goals of the Flight

Standards General Aviation Action Plan, distributed in 1992. Development of the program was

coordinated with AFS-800, AFS-200, AIR-3, ACE100 and with guidance by the General Aviation

Coalition, accident prevention, and pilot training

working groups. FAA human factors program management coordination was provided by AAR-100.

This report resulted from a FY95-96 effort considering the issue of hypoxia during flights in

unpressurized general aviation aircraft below ehe

altitude requiring use of supplemental oxygen (i.e.,

12,500 ft. and under). Sponsorship for the study

was provided by the Office of Aviation Medicine

(OAM), and the Aviation Flight Safety Program

Branch (AFS-810). Also, through continued coordination of hypoxia research with CAMI's Aeromedical Research Division (AAM-600), this study

provided information pertaining to regulatory questions in partial fulfillment of efforts originating in a

research project initiative with Aircraft Certification (ACE-100) in 1992.
ACKNOWLEDGMENTS

Several individuals contributed significantly to

this research project and should be recognized for

their support. Dr. Dennis Beringer (AAM-510)

made an assortment of modifications to the Basic

General Aviation Research Simulator (BGARS) to

meet our specialized requirements and also, assisted

in the fine-tuning of the flight scenario. Dr. Scott

Mills (AAM-510) developed the Automated Air

Traffic Control (Auto ATC) system for the study,

which has since been extremely useful in several

other projects. He also developed the software

interface for the physiological measurement system

for data acquisition and real-time monitoring of our

subjects during their reduced oxygen exposures.

Delbert Marsh, II (OMNI Corp.) was extremely

helpful in assisting Dr. Wreggit (AAM-510) in the

development of the flight scenario and the ATC

scripts employed in the study. He also supported

the data acquisition phase of the study by familiarizing many of our pilot subjects to the simulation

environment during Day 1 and manning the BGARS

experimental work station during Days 2-4.

Charles Chittum (AAM-630) designed and wired

the solenoid valve system and remote switching

mechanism used in this study to control the simulated altitude/breathing gas administration system.

Dr. Robert Garner, Joseph Mandella, and Richard

Murphy (AAM-623) performed all of the pulmonary function testing (PFT) sessions with our pilot

subjects. Dr. Garner also assisted in interpretation

of the PFT and physiologic data of the study. Dr.

R.E. Blanchard (AAM-510), managed the CAMI

GA Human Factors Research Program and contributed to all phases of this project.
TABLE OF CONTENTS

Page

INTRODUCTION *

Background ^

Purpose ^

METHODS 3

Subjects *

Simulated Altitudes 3

Measures ^

Physiological variables 3

Flight performance 4

Scenarios and procedural errors 4

Subjective questionnaires 6

Training Procedure "

Experimental Procedure 6

ANALYSIS AND RESULTS 7

Physiological Data '

Flight and Performance Data 9

Altitude data 10

VOR tracking error 10

Heading data 10

Procedural error data 11

Questionnaire data *4

DISCUSSION 14

Recommendations 16

REFERENCES 17

APPENDICES

A. Experimenter's Checklist and ATC Script Al

B. Descriptions of Subjective Measures Bl
EFFECTS OF MILD HYPOXIA ON PILOT PERFORMANCES

AT GENERAL AVIATION ALTITUDES

INTRODUCTION

Federal Aviation Regulation (FAR) 91.211 states:

(a) General. No person may operate a civil aircraft ofUS

registry— (1) At cabin pressure altitudes above 12,500

feet (MSL) up to and including 14,000 feet (MSL)

unless the required minimum flight crew is provided

with and uses supplemental oxygen for that part ofthe

flight at those altitudes that is ofmore than 30 minutes

duration...

However, hypoxia is a condition that can occur

during flights at 12,500 ft. (Mean Sea Level) and

below, exposing general aviation (GA) pilots to differing degrees of hypoxia that could compromise flight

safety as they fly continuously up to that ceiling

altitude without supplemental oxygen.

Background

Hypoxia is a state of oxygen deficiency in the

blood, cells, or tissues of the body sufficient to cause

an impairment offunction. In aviation, a reduction in

total atmospheric pressure occurs with increasing altitude. This change produces a reduction of oxygen

partial pressure (PQ2) and hence, a reduction of alveolar oxygen pressure andthe pressure gradient between

the alveoli and mixed venous blood in the pulmonary

capillaries. By breathing the "ambient air" of a reduced pressure environment, less oxygen diffuses across

the alveolar-capillary membranes into the blood stream

and to the tissues of the body.

Among the various tissues ofthe body, neural tissue

is particularly sensitive to reduced oxygen tension.

Normal brain functioning requires a relatively constant and high supply of oxygen. The brain consumes

almost one-fifth of the total oxygen uptake of the

body at rest, even though it comprises only 2% ofthe

body's weight (Ernsting, 1988). Lipton and

Whittingham (1982) stated that a low oxygen tension

condition profoundly disturbs cerebral functioning.

Their work concentrated on certain aspects of neuronal transmission and neurotransmitter metabolism

in the brain during hypoxic exposures. They reported

on neurological dysfunctioning at pressure-altitude

equivalents comparable to the range ofGA altitudes of

interest in this study.

The human body is quite effective in compensating

for the hypoxic condition experienced in aviation, but

only up to a certain point (Ward, Milledge, and West,

1995; Van Liere and Stickney, 1963). Physiological

compensation occurs in the body to optimize the

amount of oxygen available for the tissues by modulating respiration and circulation. Breathing faster

and deeper raises the availability of oxygen for diffusion into the circulatory system that also increases in

flow rate and volume. Hyperventilation, however,

causes a loss of too much carbon dioxide from the

body and creates other problems that can also impair

a pilot's performance. According to Ernsting, Sharp,

and Harding (in Ernsting and King, 1988), the body's

ability to compensate for hypoxia during flights above

the altitude range of 8,000 and 10,000 ft. (MSL) is

compromised by the antagonistic effects of the reduced oxygen tension and hyperventilation.

Factors such as the rate of ascent, the maximum

altitude attained, and the duration of flight at that

altitude interact with personal factors, such as physical fitness and activity, mental health, and the use of

medications and drugs to influence a pilot's tolerance

to hypoxia (USAF Physiological Training Pamphlet,

1976). After the pilot reaches higher altitudes, however, the body's ability to compensate for the hypoxia

condition is eventually exceeded, and significant physiological disruption occurs. The higher altitudes are

also where significant subjective symptoms and behavioral effects occur.

The minimum altitude at which cognitive and

psychomotor performance becomes significantly impaired has been, and remains, a controversial issue

with important implications for flight safety. Tune
(1964), in a review ofthe hypoxia literature between

1950 and 1963, concluded that 10,000 ft. was the

minimum altitude at which significantly degraded

perceptual-motor performance occurred. Denison,

Ledwith, and Poulton (1966) found that decremental

performance occurred in their study at 5,000 and

8,000 ft., though later, it was believed thatthe performance effects were due to such factors as the novelty

of the Manikin task they used, combined with the

physical exertion of pedaling an ergometer at a low

workload level of 27 watts. Fiorica, Burr, and Moses

(1971), in a study of simple vigilance performance,

found no differences between a well-oxygenated group

and a group performing the task for 4 hrs. at 11,500

ft. in a hypobaric chamber. Other research has been

rather equivocal in identifying hypoxia-related performance task impairment at GA altitudes under

12,000 ft. (Crow and Kelman, 1971,1973; Green and

Morgan, 1985; Kelman and Crow, 1969; Kelman,

Crow, and Bursill, 1969).

Fowler, Paul, Porlier, Elcombe, and Taylor (1985)

re-evaluated the question concerning the minimum

altitude at which hypoxia-related performance decrements could be found. In experiment 1 oftheir study,

they found no slowing of reaction times to a spatial

transformation task during the simulated 8,000 ft.

condition. However, in experiment 2, they found

slower reaction times of the spatial transformation

task and attributed them to an accompanying decrease

in blood oxygen saturation (Sa02) values. They explained the decrease in Sa02 to a combination of

hypoxia, exercise, and hypoventilation caused by the

breathing resistance of their simulated altitude system. In another study, Fowler, Elcombe, Kelso, and

Porlier (1987) modulated the breathing mixtures of

subjects to reduce their Sa02 values in 2% steps

between 86% to 76% and found that response times

slowed in a step-dependent manner. Their results

identified an SaOa threshold, an equivalent altitude

estimate of9750 ft., for which performance decrements

were found and influenced by a disruption of vision.

A recentstudy evaluating perceptual-motor performance during hypobaric chamber exposures at pressure-altitude equivalents of 7,000 and 12,000 ft.

found thatsignificantly slower response times occurred

during both altitudes, compared with a sea-level

control, and a significant difference in stimulus discrimination accuracy was found in performance during the 12,000 ft. condition, compared to the sea level

condition (McCarthy, Corban, Legg, and Faris, 1995).

Comparisons ofthe discrimination accuracy for the 4

stimulus types showed that subjects had difficulty

with digits and ellipses during the 12,000 ft. condition compared to the sea level and 7,000 ft. conditions. Research conducted by the FAA's Civil

Aeromedical Institute found that complex task performance was significantly affected by exposures to a

simulated altitude condition equivalent to 12,500 ft.

(Mertens and Collins, 1986, 1985; Mertens, Higgins

and McKenzie, 1983; and Higgins, Mertens,

McKenzie, Funkhouser, White and Milburn, 1982).

Other studies that have incorporated complex or

multiple, time-shared tasks or simulated flight activities in their designs (Denison et al., 1966; Frisby et al.,

1973; Gold & Kulak, 1972; Ledwith & Denison,

1964) produced equivocal results at the altitudes

between 8,000 and 12,500 ft. In explanation of this

ambiguity of results, Fulco and Cymerman (1987)

have suggested that many different factors can influence the performance results of studies on hypoxia,

including the interindividual variability of personality traits, motivation, and attentiveness. If these factors are notwell controlled for during experimentation,

consistent results are not often found.

Purpose

FAR 91.211 clearly states that supplemental oxygen is required for use by pilots in general aviation

above 12,500 ft. MSL. Hypoxia, however, occurs

during flights below the pressure altitude of 12,500 ft.

Research shows that a significant physiological threshold is reached between 8,000 and 10,000 ft., whereby

the body's ability to compensate for the condition is

diminished and that neurological functioning may be

compromised. Individual tolerance to hypoxia is extremely variable and influenced by multiple environmental and personal factors. This interaction of

environmental/personal factors with widely variable

individual tolerances to hypoxia can either attenuate

or accentuate performance degradation. Many research studies of hypoxia have used simple performance tasks and testing procedures. Other research
studies have employed more complex tasks and procedures. However, results from studies evaluating the

range ofaltitudes under 12,500 ft., are rather ambiguous and inconclusive about performance degradation.

Flight safety remains a significant matter of concern

during any flight producing hypoxia, particularly at

altitudes between 10,000 and 12,500 ft. MSL.

This study was developed because research has

indicated significant physiological evidence of hypoxia during exposures to altitudes between 8,000

and 12,500 ft. but ambiguous evidence oftask performance impairment at similar altitudes. The study was

designed to evaluate complex pilot performance during simulated flight because comparatively less research has been conducted on hypoxia in a flight

simulation environment. Simulated flightin this study

required GA piloting skills during a 3-day crosscountry scenario. Flight at altitudes of8,000,10,000,

and 12,500 ft. was required in the scenario by the

changing terrain elevation enroute. Differential effects on performance were anticipated for the hypoxia

and control groups ofsubjects.

METHODS

Subjects

Twenty private pilot subjects (17 males, 3 females)

were recruited as paid volunteers from a local Part 141

flight training school with national and international

clientele. The subjects varied in age from 19-32 {M=

22.5, SD = 3.5), with an average of 186 total flight

hrs.; during the last 90 days they averaged 91 hrs. All

subjects performed a pulmonary function test (PFT)

to determine normal lung functioning. Ten subjects

were randomly assigned to either a hypoxia group or

a control group. The hypoxia group breathed altitudeequivalent oxygen mixtures to simulate environmental flight conditions in the research simulator. The

control subjects breathed compressed air throughout

the experiment.

Simulated Altitudes

Various reduced oxygen breathing mixtures (Primary Standard purity, ± .05 %) were used to simulate

the following altitudes:

• sea level (SL) = 21% oxygen, balance nitrogen

(Grade E Compressed Air)

• 8,000 ft. (2438 m) = 15.5% oxygen, balance nitrogen

• 10,000 ft. (3048 m) = 14.3% oxygen, balance

nitrogen

• 12,500 ft. (3810 m) = 13.0% oxygen, balance

nitrogen.

The use of premixed reduced oxygen breathing gas

has been found to be an acceptable simulation of

altitude (Baumgardner, Ernsting, Holden, and Storm,

1980; Baumgardner and Storm, 1980), and was the

only method logistically possible in our flight simulation environment.

Each breathing gas was administered to the subject

from high pressure cylinders. Regulator valves (2

Matheson Model 9-580, 2 Victor Equipment Company Model VTS 450 D) reduced cylinder pressures

to the inlet 60-100 psi required ofthe USAF CRU-68/

A demand, oxygen breathing regulator (ARO Corp.)

that was set in the nondilution mode to deliver 100%

ofthe source gas. Subjects breathed the oxygen conditions via a Scott Aviation Model 358-1540V quickdon, pressure-demand oxygen mask assembly.

Selection of each oxygen condition was controlled by

a manual remote switch box that electronically actuated 1 of4 (ASCO® normally closed) solenoid valves.

High-pressure lines connected each of the oxygen

cylinders to the 4 solenoid valves. High pressure

outlet lines connected the 4 valves to a single line to

the CRU-68A breathing regulator. The 4 solenoid

valves were secured to a metal box placed within an

acoustical attenuation enclosure. An internal fan provided cooling for the valves. The cylinder pallet and

the valve system were located adjacent to the BGARS

behind acoustical panels and out ofsight and sound of

the pilot subject. The CRU-68A breathing regulator

was located to the left of the pilot's seat. Remote

switching from one valve, and hence oxygen mixture,

to another by the experimenter was unnoticed by the

subject.

Measures

Physiological variables. Four physiological variables were measured:
1) oxygen partial pressure (Ptc02) (Radiometer

TCM-3)

2) carbon dioxide partial pressure (Pt<C02) (Radiometer TCM-3)

3) heart rate (beats per minute) (Nelcor Pulse

Oximeter Model 200)

4) blood oxygen saturation (Sa02) (Nelcor

Pulse Oximeter Model 200)

These 4 measures were displayed on a CRT for

near-real time monitoring of each subject and stored

on a 486 personal computer (PC). Data were stored as

ASCII files for post-study analysis.

Pulmonary Function Testing (PFT) was conducted

prior to the training session for each subject in the

study. This testing was conducted by the Environmental Physiology Laboratory staff (AAM-623) with

a spirometer (Sensormedics Model 922). Increased

risk, associated with the reduced oxygen conditions of

our study, prohibited subjects with significantly outof-range PFT results from participating in the study.

Flight performance. This study used a flight simulator that was modular by design with simulation

software emulating flightinstrumentation and a popular single engine general aviation aero-model. The

Basic General Aviation Research Simulator (BGARS)

employed use of high-fidelity analog controls with

damped self-centering yoke and throttle quadrant,

gear, flap, and trim controls, as well as navigation

radios and frequency select controls. Combined with

a large front projection screen for the forward view

(50° ofvisual angle) and 2 19" CRT monitors for 45°

and 90° left views of the outside world, the BGARS

was considered operationally realistic and required

complex piloting tasks during flight. Additional information concerning the BGARS is found in Beringer

(1996).

Sixteen flight performance variables were collected

at 0.2 Hz. with an aero-model emulating a Beech

Sundowner aircraft. The sixteen variables included:

1. Sample number

2. Longitude

3. Latitude

4. Altitude

5. Airspeed

7. Magnetic Variation

8. Gear

9. Flaps

10. Airway marker

11. Outer marker

12. Middle marker

13. Glide slope altitude

14. DME

15. Localizer error

16. Event marker

Two hours offlight data were recorded for each day

ofthe cross-country scenario. Videotape recordings of

the cockpit environment (including audio), indexed

to DME, were made for each day. Digital audiotape

(DAT) recordings were also made of all communications for post processing. The DAT-based pilot voice

wave profiles will be analyzed for evidence ofaltitude/

hypoxia effects at Brown University (Lieberman,

Protopapas, and Kanki, 1995; Lieberman, Protopapas,

Reed, Youngs, and Kanki, 1994).

Scenarios and procedural errors. Figure 1 represents a scenario timeline and altitude profile ofthe 4-

day study. Each day's flight required ascent to the

targeted altitudes ofthe study due to changing ground

elevations. Cruise flight segments of approximately

45 min. duration were designed for each targeted

altitude as a minimum exposure necessary to produce

hypoxic effects on performance. Twenty-knot winds

were designed into each day's flight in a manner that

provided a similar, but opposite, crosswind component. The scenario checklist and Air Traffic Control

(ATC) scripts for each day are provided in Appendix

A and a summary ofthe scenario timeline and altitude

profile depicted in Figure 1 is as follows:

Day 1: Study overview, signed consent, PFT, 1.5

hr. mask assembly adaptation and BGARS familiarization flight with sea level breathing conditions.

Day 2: Ryan Field to Phoenix Sky Harbor Airport.

Under ATC flight following, subjects were instructed

to fly the first cruise segment at 4,000 ft. (while

breathing compressed air). Midway, subjects were

instructed to climb to 8,000 ft. (switched to breathing

15.5% 02).
BGARS Hypoxia Study-Timeline

Day 1

Training

Don mask

Day 2

45 mins

Don mask, instrumentation

Day 3

Day 4

Don mask, instrumentation

SL

45 mins

8K

Don mask, instrumentation

45 mins

10K

Sea Level

- 45 mins

8

Remove mask, instrumentation

-45 mins

10K

Remove mask, instrumentation

-45 mins

12.5K

Remove mask, instrumentation

Figure 1: BGARS hypoxia study scenario timeline and altitude profile.
Day 3: Phoenix Sky Harbor to Gallup Airport

(New Mexico). Flight following instructed subjects to

fly at 8,000 ft. during the first cruise segment (breathing 15.5% 02). Midway, subjects were instructed to

climb to 10,000 ft. (switched to breathing 14.3% O ).

Day 4: Gallup Airport to San Luis Regional Airport

(Colorado). Subjects flew the first cruise segment at

10,000 ft. (while breathing 14.3% 02), as directed by

ATC under flight following conditions. Midway,

subjects were instructed to climb to 12,500 ft.

(switched to breathing 13.0% 02).

All subjects were under ATC flight following rules

and were provided with instructions via a pre-scripted

automated ATC voice system. This system was designed to provide the same scenario script for all

subjects with different voices for each different controller as the flight progressed from ground communicationsto departure, enroute, and tower on approach

when available. Instructions were provided for pilots

to change headings, change radio frequencies, change

transponder frequencies, intercept very high frequency

omnidirectional range (VOR) system radials, report

heading and altitude information, and to report intercepts and other flight relevant information. Because

ofthese numerous requests, opportunities for pilots to

commit "procedural errors" were frequent and available for measurement during the cross-country flight.

The procedural errors were important additional

measures ofpilot performance during the 4-day study.

Subjective questionnaires. Several standardized

mood and subjective state questionnaires were utilized to identify changes perceived by the subject over

the course of each session. Pre- and post-flight measures included: Mood II scale, the Stanford Sleepiness

Scale (SSS), and the Environmental Symptoms Questionnaire (ESQ-III). The NASA TLX survey measured perceived workload and was presented only

during the post-flight questionnaire session. Brief descriptions ofthese measures are provided inAppendix B.

Training Procedure

The first day was devoted to providing subjects

with information concerning the experiment and

equipment, reading and completing the informed

consent form (as directed by the CAMI Institutional

Review Board), conducting the PFT, and a familiarization/training flight with BGARS (refer to Appendix A

for details). The introductory flight required the pilot

to perform simple and basic flight maneuvers, both

without and with a 20-knot wind (e.g., standard rate

turns and pattern work), operate navigation and communications radios, intercept VOR radials, and

become familiar with the automated ATC system

used for all air traffic transmissions and scenario flight

following procedures. Also during the training flight,

subjects became accustomed to using the oxygen mask

assembly, Peltor headphones, and simulated altitude

delivery system. Subjects wore the quick-don oxygen

mask and breathed room air throughout the 1.5 hr.

training flightto become accustomed to the breathing

resistance and the general distractions imposed by the

system. Upon conclusion ofthe training day, subjects

landed at Ryan field in Arizona and were briefed in

preparation for the continuous 3-day cross-country

flight across Arizona, New Mexico, and into Colorado.

Experimental Procedure

Upon arrival for each experimental session, subjects completed a daily health and sleep survey and the

pre-flight subjective symptom and mood questionnaires. A short pre-flight briefing was provided before

the subject reviewed the chart(s) and general course

for the day. Subjects recorded all NAV/COM frequencies and other information that they believed

pertinent for the flight. Each session involved approximately 2 hrs. of continuous flight; therefore,

subjects were given a short break before electrode

application and donning ofthe mask and headphones.

Following equipment setup, subjects breathed compressed air until a required change in altitude occurred.

Once the physiological measures stabilized, pilots

provided a read-back ofselected letters ofthe phonetic

alphabet for the daily baseline DAT recording. The

flight scenario began with the pilots listening to Automated Terminal Information System (ATIS), contacting ATC for instructions and/or announcing their

intentions on the traffic advisory frequency, when

applicable, before take-off. Once airborne, subjects

requested flight following to their destination airport

or field. The experimenter followed a daily scenario

script to activate data markers and trigger specified
Auto-ATC voice files for proper sequencing of communications (detailed in Appendix A). After pilots

were instructed to climb or descend to different altitudes, the experimenter manually switched a remote

controller to introduce the appropriate breathing gas

condition as the subject passed through an altitude of

1000 ft. below, when climbing and above, when

descending to each targeted altitude.

ANALYSIS AND RESULTS

Analyses for this study were conducted using the

Statistical Analysis System (SAS) General Linear Model

(GLM) procedures for the parametric data and the

Statistical Package for the Social Sciences (SPSS) for

all nonparametric analyses.

Data reduction and calculation ofmeans, standard

deviations, and Root Mean Square Error (RMSE)

were completed using Microsoft Excel V6.0. Event

markers were inserted into both the BGARS and

physiological data at times when subjects were asked

to climb, descend, complete particular tasks, and

when the breathing mixture was switched by the

experimenter. Insertion of the markers allowed for

precise partitioning of the data during the reduction

process. Because stabilization ofthe subject's physiology was importantin evaluating the effects ofhypoxia

on performance, only data corresponding to the approximately 45 min. cruise-altitude segments for both

the physiological and BGARS data were analyzed.

The between-subjects factor was Group (hypoxia

or control). The within-subjects factors were Cruise

segment (1-6) for the initial series of analyses and

Altitude condition (SL, 8K, 10K, 12.5K ft.) for the

final series. Initial analysis procedures evaluated the 6

cruise-altitude segments for evidence of sequential

trial effects and/or evidence of time-on-task effects,

particularly the early vs. late conditions of the 8,000

ft. and 10,000 ft. altitudes. No such effects were

found in the results of this series of analyses, so, the

early session/late session altitude data were combined

and a final series of analyses were performed. The

results ofthese analyses are presented in the following

sections for the physiological, BGARS, procedural

error, and subjective survey data.

Physiological Data

Means and standard deviations ofthe 4 physiological measures are shown in Table 1 for the hypoxia

group and control group for each altitude condition.

The 8,000 ft. and 10,000 ft. columns in the table

labeled 8K and 1 OK, represent mean values ofthe two

cruise altitude exposures for those conditions, respectively (refer to Figure 1).

Table 1: Means and standard deviations of the 4 physiological variables.

SL 8K 10K 12.5K

Ptc02

Hypoxia 73.36 42.51 32.64 23.15

(13.60) (10.12) (9.56) (8.96)

Control 71.60 69.91 70.37 68.72

(12.00)

99.00

(14.65)

95.53

(19.32)

92.78

(25.42)

Sa02

Hypoxia 89.01

(0.68) (2.53) (2.54) (4.78)

Control 97.24 98.00 98.70 98.96

(2.59)

46.14

(2.24)

45.22

(0.87)

44.28

(0.82)

PtcC02

Hypoxia 42.43

(1.92) (2.19) (2.31) (2.19)

Control 43.27 42.94 43.45 43.44

(3.94)

80.39

(3.90)

86.72

(4.14) (4.68)

Heart Rate Hypoxia 88.82 89.60

(7.55) (8.93) (9.72) (9.87)

Control 88.56 85.44 83.35 83.35

(14.15) (14.03) (11.49) (10.67)
Significant results of the analyses of the oxygen

partial pressure measure (Ptc02) included a between

group effect, F(l,18) = 25.14, ^.0001, an altitude

effect, F(3,54) = 24.08, /<.0001, and a group by

altitude interaction effect, F(3,54) = 20.12,/><.0001.

These effects were anticipated and Ryan-EinotGabriel-Welsch (REGW) Multiple Range Tests

showed that the oxygen level in the tissues was different between the experimental hypoxia group and the

control group and that the tissue oxygen level decreased as altitude increased.

One-way ANOVAs were conducted to analyze further the interaction effect and revealed that tissue

oxygen for the hypoxia group changed significantly

with increasing altitude but remained the same for the

subjects ofthe control group. Figure 2 presents means

and standard errors of the P(c02 variable for each

group across the altitude conditions.

Analyses of the blood oxygen saturation measure

(SaO ) yielded results quite similar to those of P O ,

[c 2

as we expected. The results demonstrated a between

group effect, F(l,18) = 27.57, /x.0001, an altitude

effect F(3,54) = 16.33, /x.0001, and a group by

altitude interaction effect F(3,54) = 34.02, p<.0001.

Post-hoc testing showed that Sa02 for the hypoxia

group decreased in value with increasing altitude but

remained the same for the control group because they

breathed compressed air throughout the experiment.

Figure 3 presents the Sa02 means and standard errors

for each group across the altitude conditions.

Tissue Oxygen Partial Pressure

CM

OO

-•— Hypoxia

-m— Control

8000ft. 10000ft.

Altitude

12500ft.

Figure 2: Tissue oxygen partial pressure changes for each group and altitude condition

Blood Oxygen Saturation

CM

on

CO

- Hypoxia

- Control

8000ft. 10000ft. 12500ft.

Attitude

Figure 3: Blood oxygen saturation changes for each group and altitude condition
Analyses of the carbon dioxide partial pressure

measure (PtcC02) yielded an altitude effect F(3,54) =

6.57,/><.0007, as well as a group by altitude interaction effect F(3,54) = 10.09,/><.0001. ANOVAsimple

effects analyses for the interaction terms showed that

P CO for the hypoxia group decreased across altitudes, whereas the control group showed no change.

Means and standard errors of the PtcC02 data are

shown in Figure 4.

Results ofthe analysis ofthe heart rate data showed

a group by altitude interaction effect F(3,54) = 9.95,

/K.0001. No significant effects were found in the oneway ANOVAs conducted for simple effects. Heart

rate means and standard errors are portrayed in Figure 5.

Flight and Performance Data

Sixteen measures were collected with BGARS to

assess pilot performance and capture flight information. Data for each variable were measured and recorded every 5 seconds during the data collection

flight. For this study, only the altitude and heading

measures and VOR tracking error were deemed relevant and reduced for analysis. Event markers were

used to signify various points in the data when subjects climbed, descended, or completed particular

tasks, and when the breathing mixture was changed by

the experimenter. Means and standard deviations are

shown in Table 2 for the 3 BGARS measures for each

group across the altitude conditions.

Tissue Carbon Dioxide Partial Pressure

47

46

45

CM 44 - O

Ü 43 o

S. 42 +

41

40

39

- Hypoxia

- Control

SL 8000ft. 10000ft.

Altitude

12500ft.

Figure 4: Tissue carbon dioxide partial pressure changes for each group and altitude condition.

Heart Rate

E

Q. ffi

n

(T

t

a

4) X

Hypoxia

Control

SL 8000ft. 10000ft. 12500ft.

Altitude

Figure 5: Heart rate changes for each group and altitude condition.
Table 2: Means and standard deviations for the BGARS variables.

Variable Group

ALT RMSE Hypoxia

Control

VOR RMSE Hypoxia

Control

HEADING

RMSE

Hypoxia

Control

SL

37.41

(16.63)

53.87

(48-59)

8K

33.06

(12.28)

36.51

(14-72)

1146.46 1801.91

(543.92) (1597.52)

1652.24 1503.27

(1479.16) (1140.32)

5.34 5.97

(2.03) (6.37)

5.98 12.53

(2.73) (9.09)

10K

30.70

(16.46)

32.39

(13.51)

1554.18

(1376.26)

1710.07

(1471.89)

5.53

(0.99)

5.95

(1-33)

12.5K

25.98

(14.32)

32.84

(13.56)

1288.38

(1179.85)

1498.61

(1004.42)

3.90

(0.69)

4.72

(1-63)

Altitude Data. Aircraft altitude measures were

sampled once every 5 seconds with the BGARS. Only

data following the event marker, when subjects reported being level at assigned cruise altitudes, were

used for comparisons. Ifthe aircraft was ascending or

descending, these data were parsed from the cruise

segments and not used in the analysis. Root Mean

Square Error (RMSE) was calculated for each cruisealtitude segment for each day. RMSE was obtained by

using the following formula for each subject on each day:

l2j(Xi~ criterion )

2

(n)

Whereiis the sa.mp\e,criterion is the assigned altitude,

and « is the total number of samples for a given

segment.

Results ofthe analysis of altitude RMSE found an

altitude effect, F(3,54) = 4.49, /><.007. No other

effects were found. Ryan-Einot-Gabriel-Welsch

(REGW) Multiple Range Tests found mean altitude

RMSE to be greater during the SL altitude condition,

compared to all other conditions. Further investigation found an outlier value in the control group data

that dramatically affected the mean value for the

analysis.

VOR Tracking Error. VOR tracking error was

reduced and RMSE was calculated for each assigned

radial during each cruise altitude. More attention was

needed to reduce these data because some cruise

segments required both intercepting and flight over

more than 1 VOR radial. To investigate accurately the

effects of the altitude conditions on tracking error,

only data from the cruise segments when subjects were

level at a particular altitude and were flying a particular radial, were used. Segments of flight when the

aircraft was ascending, descending, or turning to

intercept another radial, were omitted. This allowed

for a proper between-group comparison of performance for each altitude condition.

The BGARS calculates tracking error data (in feet)

from the radial vector that is dialed in on the navigational radio no. 1 (NAV1; subjects were instructed to

use this radio as their primary navigational radio).

The tracking error output was equivalent to having

already computed thevalue ofthe above RMSE calculation; therefore, the error scores were squared and

summed, then divided by« to complete the computation. The results of the analysis for the VOR RMSE

measure found no significant effects.

Heading Data. Wind conditions were designed

into the BGARS flight scenarios so that each day there

would be some degree of dynamic perturbation and

challenge for performance. As configured, winds of20

knots were selected to produce differential crosswind

effects for the cruise segments each day. Because ofthe

variability in the direction of the winds and flight,

different crab angles were required to maintain accurate flight along each radial vector. The degree ofwind

correction (or crab angle) necessary to maintain a

given radial varied between +5° and -9°. Wind correc10
tion angle was calculated using a Jeppesen model CR3

computer for analysis.

Heading RMSE was calculated for each requested

cruise heading. These calculations were computed

using the same formula for RMSE as was used with the

altitude data. Cruise segments for heading error were

broken down by altitude in the same manner as the

Localizer Error data. The analysis of heading RMSE

yielded no significant results.

Procedural Error Data

Pilot procedural errors and other pilot behaviors

were recorded during each session by the experimenters. These data were not explicitly captured by the

BGARS measures but were collected as additional

indices of pilot performance. These measures were

classified into 12 error categories and were based

mostly on scripted opportunities related to ATC flight

following procedures, requested activities, and routine and unexpected events, including:

1. Misdialed Frequency or Transponder Codes

2. Failed to use Reciprocal value when setting OBS

for the inbound Radial

3. Failed to report radial intercept, level at altitude,

etc., as previously instructed by ATC

4. Deviated from course by inattention or distraction (e.g., reading chart, dropping chart)

9.

Failed to follow ATC instruction

Landed downwind

Crashed on landing attempt

Failed to recognize airport (even after reporting

"in sight")

Missed approach (did not land on initial attempt,

had to go around)

10. Premature maneuver or radio contact

11. Landed in wrong location

12. Dialed incorrect OBS setting (unrelated to inbound reciprocal)

The procedural error records were reviewed and

categorized by the experimenters. The approach used

to evaluate the error data was to parse the data by (1)

error category, (2) altitude, (3) cruise segment, and

(4) phase of flight; then, with a nonparametric test,

the data were analyzed for group differences. First, the

data were summed over subjects by group for each

error category. This characterized the errors committed by each group, as shown in Figure 6. A MannWhitney nonparametric test oferror category resulted

in significant group differences for the Did not seel

recognize airport category, U(l,19) = 30,p = .03, and

theFailedto use reciprocal category, U(l,19) = 29.5, p =

.05. Visual inspection of all the data suggested general

group differences.

0)

o

L.

Ill

o

Ima

Q

E

3

Z

Total Procedural Errors

I Hypoxia

I Control

Figure 6: Total number of procedural errors for each group by error category.

11
Next, the approach was to sum and average errors

across altitude condition for each group. These data

are presented in Figure 7. Visual inspection, again,

suggested group differences. The Mann-Whitney

nonparametric test results, however, were not found

to be statistically significant at the 0.05 level.

Errors were summed across subjects within each

group for each cruise-altitude segment and are presented in Figure 8. A Mann-Whitney nonparametric

test for cruise-altitude segment was again computed

and indicated significant group differences at 10,000

ft. during the first cruise segment at that altitude,

£/(l,19)=18,/>=.010.

The last step in the analyses ofthe procedural error

data was to evaluate the errors summed across subjects

within each group for each phase offlight. These data

are presented in Figure 9. A Mann-Whitney nonparametric test was conducted to determine whether group

differences were present during certain phases offlight.

A significant difference between groups was found for

the first 10,000 ft. cruise segment on Day 3

(t/(l,19)=25,/»=.03), confirming the previous analysis. Also, significant differences were found between

groups on the descent phases of flight for both Days

3and4(C/(l,19)=30,/>=.03and£/(l,19) = 30,/>=.029)

and a trend for Day 2. The descent phase of flight for

Procedural Errors

20

Hypoxia

M Control

8000ft. 10000ft.

Altitude

12500ft.

Figure 7: Number of procedural errors for each group and altitude condition.

Procedural Errors

Hypoxia

@ Control

8000ft 8000ft 10000ft 10000ft 12500ft

Cruise Altitude Segment

Figure 8: Number of procedural errors for each group and cruise altitude segment.

12
Procedural Errors for Each

Phase of Flight on Each Day

By Group

Day 2

Day 3

Day 4

4 5 6 7

Number of Errors

Hypoxia

B Control

Figure 9: Number of procedural errors for each phase of flight on each day by group.

13
this study also included the approach to landing

segment of flight. The results of these analyses indicated that the hypoxia group committed significantly

more procedural errors, compared to the control group,

during descent to landing.

Questionnaire Data

The subjective questionnaire data were collected

during pre- and post-flight sessions on each of the 3

experimental days. No statistically significant effects

were found to differentiate the hypoxia group from

the control group for the 9 factors ofthe Environmental Symptoms Questionnaire (ESQ-III), the 6 subscales

of the Mood II questionnaire, or for the Stanford

Sleepiness Scale.

The NASA TLX workload scale was completed

only during the post-flight session each day. The

results ofthe analysis found a group by day interaction

effect and significant differences between the hypoxia

group and the control group for the temporal stress

subscale. Figure 10 depicts the mean TLX score for

each subscale by group. The results show that the

hypoxia group provided ratings of greater temporal

stress than did the control group; they felt a greater

demand on their time while completing the required

tasks during the flight.

DISCUSSION

An experimental group of 10 pilots, breathing

reduced oxygen concentrations to simulate GA altitude flight conditions, was compared with a control

group of 10 pilots breathing a sea level concentration

ofoxygen (i.e., 21% 02). The premise tested was that

differential changes in physiologic, subjective, and

performance measurements proportional to the simulated altitude conditions, would occur with the hypoxia group, whereas the control group would show

no significant changes.

Analysis of the physiological data clearly demonstrated the predicted differential effects of the simulated altitude conditions. Group by altitude interaction

effects were found for all 4 physiologic measures,

indicating that the simulated altitude conditions of

the study were consistently achieved for the hypoxia

group and significantly different for the control group.

Limited supporting evidence of perceived hypoxic

changes for the experimental group was provided by

the subjective questionnaire results. Though the critical respiratory index factor of the ESQ III demonstrated a unique trend for the hypoxia group; these

subjects appeared to have experienced greater respiratory distress, compared to the control group. Also,

NASA TLX

Hypoxia

Ü Control

S

Figure 10: NASA TLX workload subscales by group.

14
anecdotal reports given by the hypoxia group during

the final debriefing session indicated that they had

noticed subtle changes that were consistent with hypoxia but had not realized their importance until after

leaving the laboratory.

Simulated flight performance with the BGARS

showed no statistically significant differences between

groups across the altitude conditions in the cruise

phase of flight. The BGARS represented a medium

fidelity task environment within which it was anticipated that group differences would be found during

flight. The most reasonable explanation for not finding significant flight parameter effects, concerned the

routine and relatively uneventful cruise phases of

flight. While the overall scenario provided the requirement for multiple operations, and the crosswinds provided a challenge for accurate VOR tracking

performance, the task loading of each cruise-altitude

segment appears to have been insufficient to influence

the measures of performance associated with the hypoxia conditions. Only an occasional request to report heading and altitude were made during each

cruise segment. The pilot had little else to occupy his/

her time during these segments and maintaining

straight-and-level flight was relatively easy. However,

pilots in the hypoxia group rated greater temporal

stress on the NASA TLX workload scale as it applied

to their BGARS flight performance. Although this

result was not clearly tied to any specific segment of

flight, the elevated scores for this group, compared to

the control group, reflected a perception of greater

demands on their time while performing flight activities.

Another measure ofpilot performance in this study

revealed hypoxia-related effects. All pilot-subjects were

under ATC flight-following procedures throughout

the cross-country scenario. These procedures provided control and consistency in the activities of the

flight scenarios. Effectively, the procedures determined what activities would happen when and what

responses were expected to occur. Observed details of

each pilot's behavior were recorded throughout the 3-

day cross-country flight and captured whether or not

they responded appropriately to the ATC requests

including: changes of frequencies, VOR intercepts,

reports of heading and altitude changes, and other

scripted (and all unscripted) activities. Opportunities

for failing to respond appropriately were, therefore,

scheduled and fairly frequent. Since all subjects were

exposed to the same requests and flight activities at

approximately the same times during the 3-day scenario, procedural errors were considered important

measures of performance for comparisons between

groups.

Statistically significant group differences were found

in the number of errors committed during flight over

the 3-day scenario by nonparametric tests. Reduced

by phase of flight, significant group differences were

found during the cruise phase at 10,000 ft. and during

the descent phase from 10,000 ft. on Day 3, and

during the descent phase from 12,500 ft. on Day 4. A

nonsignificant trend ofincreased errors also occurred

on Day 2 during descent from 8,000 ft. The descents

and combined approach phases ofthe study occurred

at the end ofthe daily flight that were also, at the end

of each 2-hr. session. Subjects in the hypoxia group

had, therefore, been breathing reduced oxygen for up

to 2-hrs. at the time of descent which is an important

point, because it is consistent with flights in the "real

world". Flights at GA altitudes for any length oftime

are followed by descent, approach, and landing phases

of flight. Some aircraft accident data suggests that,

compared to the amount of time spent in various

phases offlight, a moderate proportion ofconsequential events occur during descent and approach (Baker

et al., 1996; Boeing, 1994). These data highlight the

criticality of committing errors during the end of any

flight and demonstrate the need for careful piloting

performance.

The results of our data suggest that the duration of

the hypoxic (reduced oxygen) exposure and/or the

mild hypoxia condition, itself, significantly affected

the number of procedural errors committed by the

subjects of the experimental group, compared to the

control group. The control group (breathing compressed air throughout the flights) committed only 3

errors during descent from 8,000 ft. on Day 2 and no

errors during descents from 10,000 ft. on Day 3 or

from 12,500 ft. on Day 4.

In a break-down of the types of errors that were

committed by the hypoxia group during descent, the

following was found:

15
1. Four different pilots on Day 2 initiated premature flight maneuvers (changing heading and/or

altitude before instructed).

2. One different pilot on each day misdialed a radio

frequency.

3. One different pilot during Days 2 and 4 failed to

follow ATC instructions.

4. Two different pilots flew a missed approach on

Days 2 and 4.

5. One pilot crashed while descending on Day 3 (he

failed to check ground elevation on the chart).

6. Four different pilots misreported seeing the airport or field on Days 3 and 4 and required

additional instructions.

The last error in the above list, was of interest

because all subjects were requested to report when the

airport was in sight and each of the 4 hypoxia group

pilots making the error reported sighting the airport

but continued their flights over the field even with the

centerline clearly visible in the display. Each ofthese

pilots maintained their headings well beyond the field

and eventually requested ATC assistance and vectors

back toward the field. None of the control group

subjects had difficulty identifying the airports. Some

aspect ofreduced vision may have been a factor for the

hypoxic subjects to overfly the field, or, perhaps a

form of behavioral fixedness could have occurred in

these subjects to maintain their last given heading.

Regardless, after reviewing the physiological data,

subjective reports, procedural error data, and laboratory notes for these subjects, it was concluded that

subtle effects ofhypoxia were observed in the experimental group. Unsafe and high risk piloting behaviors

were recorded during the final phases of flight for

many subjects ofthe hypoxia group, particularly from

the 10,000 ft. and 12,500 ft. altitudes. Subjects ofthe

control group, though not error-free over the 3 days,

generally exhibited deliberate and cautious behaviors

during the last critical phases of flight; often asking

for additional weather and field-condition information. Some of the control group pilots were also

observed to descend slowly outside of the landing

pattern and only entered the pattern after their intentions were announced. Few, if any, ofthe experimental subjects conducted their descents and approaches

in this manner. Hurried and precipitous behavior was

often seen during descents for many pilots of the

hypoxia group.

Recommendations

In summary, this study did not provide unequivocal evidence of detrimental flight performance due to

the mild hypoxia found during the cruise segments at

8,000, 10,000, and 12,500 ft. simulated altitudes.

However, observed performance during the descent

and approach phases of flight was considered to be

generally unsafe with potentially deleterious outcomes.

Because ofthe known individual variability in tolerance to hypoxia, erring on the side of caution is

recommended from the results ofthis study. Descents

from GA flights of greater than 2 hrs. at these commonly flown altitudes should proceed slowly and

cautiously. Heightened awareness of the potential

risks ofmaking critical errors following flights atthese

altitudes should foster the routine practice of planning a slow descent with enough time at a nominally

lower altitude (e.g., 7,000 ft. or 6,000 ft., when

possible) for physiologic recovery before the approach

and landing phases offlight are continued. Symptoms

ofmild hypoxia may not be perceived by pilots at the

time of their descent procedures, but this should not

suggest to the individual that hypoxia is not present.

Even subtle effects can have unanticipated influence

on the pilot preparing for approach and landing at

uncontrolled fields.

To further research the question of GA pilot performance and the detrimental effects of hypoxia, it is

recommended that a more advanced GA research

simulator be used, such as the Civil Aeromedical

Institute'sAdvanced GeneralAviation Research Simulator, which offers higher sampling rates for all flight

performance measures, greater visual resolution, and

more demanding flight scenarios. Also suggested is an

increase in the sample size of pilots, and the use of

longer hypoxic exposure durations for each altitude

condition studied.

16
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APPENDIX A

EXPERIMENTER'S CHECKLIST

&

ATC SCRIPT

Al
DAY 1 - PRACTICE

WIND: NONE

AMfe* Tucson ATIS: Tucson International, Information Delta, one five zero zero [1500] zulu

weather, temperature eight one [81], dew point six six [66], wind two six eight [268] at

two zero [20], altimeter two niner niner two [29.92]. Advise on initial contact you have

Information Delta.

(Time = 8:00 a.m.) [Freq. = 123.8]

PM^ Tucson ATIS: Tucson International, Information Delta, one niner zero zero [1900] zulu

weather, temperature eight one [81], dew point six six [66], wind two six eight [268] at tw<

zero [20], altimeter two niner niner two [29.92]. Advise on initial contact you have

Information Delta.

(Time = 12:00 p.m.) [Freq. = 123.8]

^ Aircraft ready on Runway 29L (Tucson International) Runway Altitude 2641

• Aircraft Cruise = 2450 RPM / Rotation Speed = 60K / Approach Speed = 65-70K / Climb

Speed = 70

• Take off from Tucson and fly two LEFT-turn patterns at 3500'.

^ Second pattern to full stop. (Land on Runway 29L)

• Experimenter: Go over OBS and VOR NAV Radio use with the subject.

Discuss Outbound vs. Inbound (inbound is reciprocal).

BEGIN FLIGHT

• Take off from Tucson International. (Check Flaps)

• Fly out on the TUS 308 Radial Outbound [Frequency = 116.0] (Alt = 4000).

«" At 13.0 miles NW of TUS VOR Avra Valley will come into view.

• Review Common Traffic Advisory (CTAF) use. Report downwind, base, and final legs of

pattern.

Example "Alameda traffic, Piper 5280 Tango, entering downwindfor runway one sevenfull

stop, Alameda."

• At 18.0 miles from TUS VOR turn right heading 330 to clear Avra Valley traffic.

• At 21.5 miles from TUS VOR (past airfield turn left heading 300 entering into left upwind for

Avra Valley

• Descend 3200' for approach pattern - Pilot calls in downwind, base, andfinal leg on CTAF

123.0

• Land at Avra Valley (Land on Runway 30) [Runway Alt. = 2415].

A3
SET WIND: 20 knots, 268° (where the "W" on the compass card is)

PRESS M (start data collection) |

• Instruct pilot to listen to Tuscon ATIS on 123.8

• Pilot calls CTAF on 123.0 with departure intentions (Check Flaps)

• Take off from Avra Valley maintaining heading of 290 until level at 4,000.

• Instruct Pilot to performs left and right standard rate turns.

• Instruct Pilot to intercept the Stanfield One Two Zero [117] radial inbound (Freq = 114,8,

Heading = 297)

AUTOMATED ATC TAKES OVER

Q Pilot calls Albuquerque Center on 123.5for FLIGHT FOLLOWING to RYANAIRPORT

hypdiooi Albuquerque Ctr: Beech One Niner Two Golf Bravo, Albuquerque Center. Squawk two

one one five [2115] - IDENT.

Q Pilot IDENTs

hypdioo2 Albuquerque Ctr: Two Golf Bravo, radar contact, intercept the Tucson Three Zero Eight

[308] radial inbound. Report when established (heading = 128).

Q Pilot reports established on the 308 inbound

hypdioo3 Albuquerque Ctr: Two Golf Bravo, maintain present track

Q Pilot responds

At 28 miles to TUS

hypdiooB Albuquerque Ctr: Two Golf Bravo, report heading and altitude.

Q Pilot reports heading and altitude

'we»«© Albuquerque Ctr: Roger Two Golf Bravo, contact Tucson Approach on one two five point

one [125.1]

when two zero [20] miles from the Tucson VOR.

At 20 miles to TUS

Q Pilot contacts Tucson Approach on 125.1

A4
hypdiocw Tucson Approach: One Niner Two Golf Bravo, expect heading for Ryan Airport.

Q Pilot responds

At 15 miles to TUS

hypdioo.-) Tucson Approach: Two Golf Bravo, turn right immediately heading one eight eight [188].

Expect Ryan Airport in niner [9] miles. Contact Ryan Tower on one two

five point eight [125.8].

Q Pilot responds

Q Pilot calls Ryan Tower on 125.8

h>Pdioo6 Ryan Tower: One Niner Two Golf Bravo, wind two six eight [268] at two zero [20],

altimeter two niner niner two [29.92], cleared for landing on Runway Two

Four [24].

Q Pilot responds

Q Pilot lands at Ryan —

| PRESS M (stop data collection) 1

Training Flight Ends

A5
DAY 2 - "Sea Level" to 8,000

(Taking off from Ryan)

WIND: 20 knots, 119°

AMP Tucson ATIS: Tucson International, Information Tango, one five zero one [1501] zulu

weather, temperature eight zero [80], dew point six six [66], wind one one niner [119] at

two zero [20], altimeter two niner niner two [29.92]. Advise on initial contact you have

Information Tango.

(Time = 8:01 a.m.) [Freq. = 123.8]

PMP Tucson ATIS: Tucson International, Information Tango, one niner zero one [1901] zulu

weather, temperature eight zero [80], dew point six six [66], wind one one niner [119] at

two zero [20], altimeter two niner niner two [29.92]. Advise on initial contact you have

Information Tango.

(Time = 12:01 p.m.) [Freq. = 123.8]

Q Aircraft ready on Runway 24

Q Pilot listens to INFORMATION - TANGO (Tucson -123.8)

Q Pilot calls tower on 125.8 and informs tower that INFORMATION -TANGO (Tucson) was

heard.

hypd2ooi TOWER: Roger Beech One Niner Two Golf Bravo, Clearance is as follows; Maintain

runway heading, climb to four-thousand [4000], departure frequency is one two

four point five [124.5], squawk two five one three [2513]. (Initial Squawk)

Q Pilot reads back correctly

hypd2oo2 TOWER: Roger Two Golf Bravo, cleared for take off runway two four [24].

Q Pilot Responds

Aircraft lifts off runway

hypd20O3 Pseudo Pilot: Ryan Tower, Cessna Two Seven Six Alpha, ready for takeoff, runway two four [24] left.

hvpd2004 TOWER: Cessna Two Seven Six Alpha, cleared for take off, runway two four [24] left. Traffic is a Beech Sundowner

departing to the southwest.

faypd2005 Pseudo Pilot: Roger, Two Seven Six Alpha.

hvpd2oo6 TOWER: Two Golf Bravo, contact Tucson Departure on one two four point five [124.5]

Q Pilot contacts departure

hypd2oo7 Departure: Beech Two Golf Bravo, Tucson departure - IDENT.

Q Pilot IDENTs

A6
hypd2oos Departure: Two Golf Bravo, radar contact. Climb to four thousand [4000]. Intercept the

Stanfield one three zero [130] radial and report when established inbound.

(Frequency = 114.8) [heading = 310]

Q Pilot responds

Q Pilot reports established

PRESS DATA MAKKKK

hyPd2oo9 Departure: Two Golf Bravo maintain inbound track. Contact Albuquerque Center on one

two three point five [123.5]

Q Pilot responds

Q Pilot contacts Albuquerque Center

hyPd2oio Albuquerque Ctr: Beech Two Golf Bravo, squawk two two four six [2246] - IDENT.

(Early Alt. #1 Squawk)

Q Pilot IDENTs

hypd2oii Albuquerque Ctr: Two Golf Bravo, radar contact. Maintain present track. Report Stanfield

Station passage.

Q Pilot responds

hypd20i2 Pseudo Pilot: Albuquerque Center, Cessna Two Seven Six [276] Alpha with you at four thousand five hundred.

hypd20i3 Albuquerque Ctr: Roger, Seven Six [76] Alpha, IDENT (Pause 5 seconds). Seven Six Alpha, radar contact. Turn right

zero three zero [030], climb and maintain niner thousand [9000].

hypd20i4 Pseudo Pilot: Seven Six Alpha turning right zero three zero [030], climb and maintain niner thousand [9000].

25.0 miles to (sw) Stanfield VOR

bypd2ooT Albuquerque Ctr: Two Golf Bravo, report heading and altitude.

Q Pilot responds

hvpd2oou Albuquerque Ctr: Double Click

Q Pilot reports Stanfield Station passage

A7
hypd2oi5 Albuquerque Ctr: Two Golf Bravo, intercept the Buckeye One Two Zero [120] radial and

report when established inbound. (Frequency = 110.6) [heading = 300]

PRESS DATA MARKER

Q Pilot responds

hvpdZOie Albuquerque Ctr: Seven Six Alpha, climb and maintain one zero thousand five hundred [10,500].

hypd20i7 Pseudo Pilot: Seven Six Alpha, out of niner thousand [9000] for ten thousand five hundred [ 10,500]

hypd20i s Albuquerque Ctr: [Double Click the Mic]

Q Pilot reports established

PRESS DATA MARKER

hypd2oi 9 Albuquerque Ctr: Two Golf Bravo, maintain inbound track.

Q Pilot responds

23.5 miles to (sw) Buckeye VOR

hypd202o Albuquerque Ctr: Two Golf Bravo, squawk two five seven three [2573] - IDENT. (Late

Alt. #1 Squawk)

Q Pilot IDENTs

hypd202i Albuquerque Ctr: Two Golf Bravo, radar contact, climb and maintain eight thousand.

[8000]. Report level at eight thousand [8000]. Report Buckeye Station

passage.

Q Pilot responds

PRESS DATA MARKER

Q Pilot reports level at 8000

PRESS DATA MARKER

hypd2022 Albuquerque Ctr: [Double click mic]

Q Pilot reports Buckeye Station passage

hypd2023 Albuquerque Ctr: Two Golf Bravo, continue outbound track.

A8
Q Pilot responds

15 miles from (nw) Buckeye VOR

hypd2024 Albuquerque Ctr: Two Golf Bravo, turn right immediately to intercept the Phoenix Two

Seven Zero [270] radial inbound. Report when established, [heading =

090] (Frequency = 115.6)

PRESS DATA MARKER

Q Pilot responds

Q Pilot reports established on Phoenix 270 radial inbound

PRESS DATA MARKER

hypti2&25 Albuquerque Ctr: Two Golf Bravo, continue inbound track.

38.0 miles to (west) Phoenix VOR

bypdawv Albuquerque Ctr: Two Golf Bravo, report heading and altitude.

Q Pilot responds

hvpd2oow Albuquerque Ctr: Double Click.

32.0 miles to (west) Phoenix VOR

hypd2026 Albuquerque Ctr: Two Golf Bravo, contact Approach with intentions on one two four point

niner [124.9]

Q Pilot responds

Q Pilot contacts Approach on 124.9 and states intentions - ifintentions are stated skip to 2028 -

ifno intentions are stated go to 2027

intern Approach: (If no intentions) Beech One Niner Two Golf Bravo, what are your intentions?

Q Pilot responds

hypd2028 Approach: Roger, One Niner Two Golf Bravo, squawk two two four six [2246] - IDENT.

(Alt. #2 Squawk - this could be thought ofas an "extra")

Q Pilot IDENTs

A9
h>pd2029 Approach: Two Golf Bravo, radar contact, turn right heading one zero zero [ 100].

PRESS DATA MARKER

18 miles to Phoenix

iiYPd203o Approach: Two Golf Bravo descend and maintain three thousand [3000] .

PRESS DATA MARKER

Q Pilot responds

16.0 miles to Phoenix

hypdHBi Approach: Two Golf Bravo, squawk two five one three [2513] - IDENT. {Late Alt.

#2 Squawk).

Q Pilot IDENTs

hyPd2032 Approach: Two Golf Bravo radar contact,expect heading to Phoenix Sky Harbor.

When pilot approaches 08 Right ILS extended line (apx. 0.5 miles from line)

hypd2033 Approach: Two Golf Bravo, turn left heading zero eight zero [080]. You are cleared

for Runway Zero Eight [08] right approach. Contact tower on one one eight

point seven [118.7] at seven [7] miles to Phoenix VOR.

Q Pilot responds

Q Pilot contacts tower at outer marker

hypd'034 TOWER: Beech One Niner Two Golf Bravo, cleared for landing runway zero eight

[08] right.

Q Pilot lands airplane at Sky Harbor - Phoenix

| Save Data File i^^^^^^^^l

A10
DAY 3 - 8,000 to 10,000

(Taking off from Sky Harbor - Phoenix)

WIND: 20 knots, 237°

AMP Phoenix ATIS: Phoenix Sky Harbor International, Information Papa, one five three zero

[1530] zulu weather, temperature seven eight [78], dew point six six [66], wind two three

seven [237] at two zero [20], altimeter two niner niner two [29.92]. Advise on initial

contact you have Information Papa

(Time = 8:30 a.m.) [Freq. = 121.2]

PMP Phoenix ATIS: Phoenix Sky Harbor International, Information Papa, one niner three zero

[1930] zulu weather, temperature seven eight [78], dew point six six [66], wind two three

seven [237] at two zero [20], altimeter two niner niner two [29.92]. Advise on initial

contact you have Information Papa

(Time = 12:30 p.m.) [Freq. = 121.2]

Q Aircraft ready on Runway 26Right

Q Pilot listens to INFORMATION - PAPA [121.2] (as per experimenter instruction)

Q Pilot calls tower on 118.7 and informs tower that INFORMATION -PAPA was heard.

hypcBooi TOWER: Roger Beech One Niner Two Golf Bravo, Clearance is as follows; Maintain

runway heading, climb to four-thousand [4000], departure frequency is one two

four point seven [124.7], squawk two four one three [2413]. (Initial Squawk)

Q Pilot reads back correctly

hypd3oo2 TOWER: Roger Two Golf Bravo, cleared for take off runway two six [26] right.

Q Pilot Responds

Aircraft lifts off runway

hypd3003 Pseudo Pilot: Sky Harbor Tower Beech Niner Eight Seven Zulu ready for takeoff, runway two six [26] right.

hypd3004 TOWER: Beech eight seven zulu, cleared for take off, runway two six [26] right. Traffic is a Beech Sundowner

departing to the west.

hypd3005 Pseudo Pilot: Roger, Niner Eight Seven Zulu.

hypd3oo6 TOWER: Beech Two Golf Bravo contact departure on one two four point seven [124.7].

Q Pilot contacts departure

hypd3oo7 Departure: Beech Two Golf Bravo, Phoenix departure - IDENT

Q Pilot IDENTs

All
hypccoos Departure: Two Golf Bravo, radar contact. Climb and maintain eight thousand [8000].

Expect right turn to intercept Phoenix three five niner [359] radial outbound.

{Frequency = 115.6)

5.0 miles from (west) of Phoenix VOR

hypd3oo9 Departure: Two Golf Bravo turn right heading zero three zero [030] to intercept Phoenix

three five niner [359] radial outbound. Report when established.

Q Pilot responds (to departure)

PRESS DATA MARKER

hypeöoio Pseudo Pilot: Phoenix Departure, Beech Niner Eight Seven Zulu with you at three.

hypeBOi 1 Departure: Roger eight seven zulu, IDENT (PAUSE 5 seconds). Eight seven zulu, radar contact. Turn right heading

three four zero [340], climb and maintain five thousand [5000],

hypd.3012 Pseudo Pilot: Eight seven zulu turning to three four zero [340], climb and maintain five.

Q Pilot reports establishing Phoenix 359 radial outbound

hypd3ooA Departure: Double Click

PRESS DATA MARKER

20.0 miles from (north) of Phoenix VOR

hypd3oi3 Departure: Two Golf Bravo contact Albuquerque Center on one two three point five

[123.5].

Q Pilot contacts Albuquerque Center on 123.5

hyPd3oi4 Albuquerque Ctr: Beech Two Golf Bravo, Squawk Two Seven Four Zero [2740] - IDENT

(Early Alt. #1 Squawk).

Q Pilot IDENTs

hypd3oi5 Albuquerque Ctr: Two Golf Bravo, radar contact, maintain outbound track, expect Victor

Airway Five Six Seven [567] at FERER Intersection.

48 miles from Phoenix VOR

hypdsoie Albuquerque Ctr: Two Golf Bravo, cleared to Winslow via the Winslow two one zero [210]

radial inbound. Report when established. (Frequency = 112.6for Winslow

VOR) [heading = 030]

Al 2
PRESS DATA MARKER

Q Pilot reports established

l'KKSS DA JA MARKLK

hypd3oi7 Albuquerque Ctr: Two Golf Bravo, Maintain inbound track

45 miles to (sw) Winslow VOR

hypd3ooY Albuquerque Ctr: Two Golf Bravo, report heading and altitude.

Q Pilot responds

hypcnooz Albuquerque Ctr: (Double Click)

15 miles to (sw) Winslow VOR

hypd3oi8 Albuquerque Ctr: Two Golf Bravo Squawk two four seven three [2473] - IDENT {Late Alt.

Q Pilot IDENTs

hyPd3oi9 Albuquerque Ctr: Two Golf Bravo, radar contact, climb and maintain one zero thousand

[10,000]. Report level at ten thousand [10,000].

Q Pilot responds

PKKSS DATA MARKER

Q Pilot reports establishing 10,000feet

PRESS DATA MAKKKR

hypcB02o Albuquerque Ctr: Two Golf Bravo, report Winslow station passage.

Q Pilot responds

Q Pilot reports Winslow station passage

hypdso2i Albuquerque Ctr: Two Golf Bravo, turn right to intercept the Gallup two four two [242] radii

inbound. Report when established. {Frequency = 115.1 for Gallup VOR)

[heading = 062]

PRESS DATA MARKER

Q Pilot responds

A13
Q Pilot reports established on GUP 242 inbound

PRESS DATA MARKER

hypd3022 Albuquerque Ctr: Two Golf Bravo, maintain inbound track.

50 miles to (sw) Gallup VOR

hypd3ooc Albuquerque Ctr: Two Golf Bravo, report heading and altitude.

Q Pilot responds

hypd3ooD Albuquerque Ctr: (Double Click)

12 miles to (sw) Gallup VOR

hypd3o?.3 Albuquerque Ctr: Two Golf Bravo, Squawk two one four zero [2140] - IDENT. {Late

Alt. #2 Squawk)

Q Pilot IDENTs

hyPd3024 Albuquerque Ctr: Two Golf Bravo, radar contact, maintain inbound track.

6.0 miles to (sw) Gallup VOR

hypd3025 Albuquerque Ctr: Two Golf Bravo, Gallup is at your 11 o'clock in ten [10] miles.

Advise when airport is in sight.

Q Pilot reports seeing Gallup Airport

hypdso26 Albuquerque Ctr: Two Golf Bravo, Albuquerque wind is two three seven [237] at

two zero [20], altimeter two niner niner two [29.92]. Gallup traffic

advisory is one two two point niner five [122.95]. Flight following

is discontinued.

Q Pilot lands airplane at Gallup Airport - Runway 24 (upwind)

I Save Data File

A14
DAY 4-10,000 to 12,500

(Taking off from Gallup)

WIND: 20 knots, 231°

NO TOWER at Gallup

AMP ABQ ATIS: Albuquerque Information Bravo, one five twofive [1525] zulu weather,

temperature sevenfive [75], dew point six six [66], wind two three one [231] at two zero

[20], altimeter two niner niner two [29.92]. Advise on initial,contact you have Informatior

Bravo.

(Time = 8:25 a.m.) [Freq. = 118.0]

PMP ABQ ATIS: Albuquerque Information Bravo, one niner two five [1925] zulu weather,

temperature seven five [75], dew point six six [66], wind two three one [231] at two zero

[20], altimeter two niner niner two [29.92]. Advise on initial contact you have Information

Bravo.

(Time = 12:25 p.m.) [Freq. = 118.0]

Tell pilot before takeoff:

Q Aircraft ready on Runway 24

Q Pilot should call ABQ ATIS

Q Pilot should announce intentions on COM frequency 122.95

Q Once aircraft lifts offpilot should contact ABQ Cntr. for FLIGHT FOLLOWING on 123.5

Aircraft lifts off runway

hyjxHOOi Pseudo Pilot: Gallup traffic, Beech Four Seven Foxtrot taxiing into position for runway two four [24],

hypd4002 Pseudo Pilot: Four Seven Foxtrot rolling on runway two four, will be departing straight out.

Q Pilot contacts Albuquerque Center on 123.5 and asksforflightfollowing

hypd4oo3 Albuquerque Ctr: Beech One Niner Two Golf Bravo, Albuquerque Center. Squawk two

five one three [2513] - IDENT {Initial Squawk)

Q Pilot IDENTs

hypd4ooA Albuquerque Ctr: Two Golf Bravo, radar contact. Turn right, fly heading zero one zero

[010]. Climb and maintain one zero thousand [10,000]. Report level at ten

thousand.

Q Pilot responds

Q Pilot reports level at 10,000

Al 5
hypd-HXH Albuquerque Ctr: Two Golf Bravo, turn right, heading zero niner two [092] to intercept

Gallup Zero Five Five [055] radial outbound. Report established

outbound. {Frequency = 115.1 for Gallup VOR).

Q Pilot responds

hypd4005 Pseudo Pilot: Albuquerque Center, Beech Four Seven Foxtrot passing through eight thousand, climbing to niner,

request flight following.

hypd4006 Albuquerque Ctr: Roger Four Seven Foxtrot, IDENT (PAUSE 5 seconds). Four Seven Foxtrot, radar contact. Turn right

heading three five five [355], climb and maintain niner thousand [9000].

hypd4007 Pseudo Pilot: Four Seven Foxtrot is turning to three five five [355], climbing and maintaining niner thousand feet.

Q Pilot reports establishing Gallup 055 radial outbound

PRESS DATA MARKER

hyPd4oo8 Albuquerque Ctr: Two Golf Bravo. Maintain outbound track.

Q Pilot responds

At 50.0 from (ne) Gallup VOR

hypd40(» Albuquerque Ctr: Two Golf Bravo, squawk two two four six [2246] - IDENT. (Early Alt.

#1 Squawk)

Q Pilot IDENTs

hypd4oio Albuquerque Ctr: Two Golf Bravo, radar contact, maintain outbound track.

70.0 miles from (ne) Gallup VOR

hypd4ooY Albuquerque Ctr: Two Golf Bravo, report heading and altitude.

Q Pilot responds

hypd4<x)E Albuquerque Ctr: Double Click

96.0 miles from (ne) Gallup VOR

hypdwii Albuquerque Ctr: Two Golf Bravo, turn left to intercept the Alamosa two zero three [203]

radial inbound. Report established inbound. (Frequency = 113.9)

[heading = 023].

PRESS DATA MARKER

Q Pilot responds

A16
Q Pilot reports established on two zero three [203] inbound [heading = 023]

PRESS DATA MAKKKK

hyp<Moi2 Albuquerque Ctr: Two Golf Bravo climb and maintain one two thousand five hundred

[12,500]. Report level at twelve five.

Q Pilot responds

PRESS DATA MARKER

Q Pilot reports establishing 12,500feet

PRESS DATA MARKER

hyPd4oi3 Albuquerque Ctr: Two Golf Bravo, contact Denver Center on one two eight point three

seven [128.37].

Q Pilot responds

Q Pilot contacts Denver Center on 128.37

hypd4oi4 Denver Ctr: Beech Two Golf Bravo, squawk two five seven three [2573] - IDENT (Early

Alt. #2 Squawk)

Q Pilot IDENTs

hypd4oi5 Denver Ctr: Two Golf Bravo, radar contact, we are temporarily rerouting you due to

airborne fire fighting activity, turn right to intercept the Taos Two Four Zero

[240] radial inbound. Report when established, [heading = 060].

Q Pilot responds

Q Pilot reports established on the Taos 240 radial inbound

hyjxMozz Denver Ctr: Double Click

25.0 miles from (west) Taos VOR

hypd4oi6 Denver Ctr: Two GolfBravo, turn to heading three three zero [330] to intercept the Alamosa

two zero three [203] radial inbound. Report when established.

A17
PRESS DATA MARKER

Q Pilot responds

Q Pilot reports established on the Alamosa 203 radial inbound

PRESS DATA MARKER

hypd4on Denver Ctr: Two Golf Bravo, maintain inbound track.

7.5 miles to (se) Alamosa VOR

hjrpcwois Denver Ctr: Two Golf Bravo, Squawk two two four zero [2240] - IDENT {Late Alt. #:

Squawk)

Q Pilot IDENTs

6.5 miles to (se) Alamosa VOR

hyPd402o Denver Ctr: Two Golf Bravo, turn to heading three five five [355], airport is in ten [ 10]

miles. Advise when San Luis Regional Airport is in sight.

PRESS DATA MARKER

Q Pilot reports seeing San Luis Valley Regional Airport

bypd402i Denver Ctr: Two Golf Bravo, wind is two three one [231] at two zero [20], altimeter

two niner niner two [29.92]. San Luis Valley Regional Airport traffic

advisory is one two two point eight [122.8]. Flight following is

discontinued.

Q Pilot responds

Q Pilot lands airplane at San Luis Valley Regional Airport - Runway 20

I Save Data File ^^^^^

Al 8
APPENDIX B

DESCRIPTIONS OF

SUBJECTIVE MEASURES

Bl
NASATLX

Participants were asked to rate subj ective workload levels by using the NASA Task Load Index

(TLX; Hart & Staveland, 1988). The TLXmeasures subjective workload by requiring the participant

to rate the experience ofworkload on six subscales: Mental Demand, Physical Demand, Temporal

Demand, Performance, Effort, and Frustration. These ratings are averaged to produce a single

workload score ranging from 0 (very low) to 100 (very high). The TLX has been used successfully to

assess workload in a variety oflaboratory and field settings (Hart & Staveland, 1988).

Environmental Symptoms Questionnaire (ESQ-III)

The ESQ was originally designed to measure symptoms in subj ects at high altitudes (Kobrick &

Sampson, 1979). It has since been modified to assess symptoms occurring during other Stressor

conditions (ESQ—III; Sampson &Kobrick, 1980). The ESQ-III consists of68 adjectives. During

administration subj ects were asked to rate how applicable each termwasto howthey felt at that

moment. Six responses were possible from the lowest, 1: {Not atAll), to the highest, 6: {Extremely).

Factor analysis conducted inpreviousresearch identified 9 factors describing an intercorrelational

patternthat appearsto reflect environmental and organismic conditions consistentwith exposuresto

altitude (Sampson, Cymerman, Burse, Maher, & Rock, 1983; Shukitt, Banderet, & Sampson, 1990).

The 9 factors included: cerebral Acute Mountain Sickness (AMS); respiratoryAMS; Ear, Nose and

Throat(ENT); cold stress; distress; alertness; exertion stress; muscular discomfort; and fatigue. Cold

stress symptoms were nonexistent during this study and essentially summed to zero. Hence, it was

dropped from our analysis. Item weights determined bythe previousresearch were applied to our

ESQ data and a severity index score was computed for both the cerebral and respiratory AMS factors

as defined in Sampson et al., (1983).

MOOD II

The automated MOOD II scale comprises 36 itemsfrom the following six subscales: activity, anger,

happiness, fear, depression, and fatigue. As in the ESQ-III, subjects were asked to respond to a list of

adjectives asto howwell each described their current feeling. Possible responsesranged from 1 {Yes

or Mostly) to 3 {No, Not atAll). The MOOD scale was originally developed by Ryman, Biersner,

and LaRocco (1973). The automated version used in this studywas derived from the WalterReed

Performance AssessmentBattery (Thorne et al., 1985).

Stanford Sleepiness Scale

The Stanford Sleepiness Scale consists of7 statementsthat describe different levels ofsleepiness,

ranging from 1 {Feeling very alert, wide awake, and energetic) to 7 {Sleep onsetsoon, losing

struggle to remain awake). Subj ects were asked to select the statement that best described their

currentfeeling. The scale was originally developed byHoddes, Zarcone, Smythe, Phillips, andDement

(1973). The automated version used in this studywas derived fromthe WalterReed Performance

AssessmentBattery (Thorne et al., 1985).

B3 -&U.S. GOVERNMENT PRINTING OFFICE: 1997 - 559-079/40083