Evaluation of Glare as a 

Hazard for General Aviation 

Pilots on Final Approach

Jason A. Rogers1

Clifford K. Ho2

Andrew Mead,3 Angel Millan3

Melissa Beben,3 Gena Drechsler3

1

Greensboro College 

Greensboro, NC 27401

2

Sandia National Laboratories

Albuquerque, NM 87185

3

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

July 2015

Final Report

DOT/FAA/AM-15/12

Office of Aerospace Medicine

Washington, DC 20591
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 thereof.

___________

This publication and all Office of Aerospace Medicine 

technical reports are available in full-text from the 

Federal Aviation Administration website.
i

Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

DOT/FAA/AM-15/12

4. Title and Subtitle 5. Report Date

Evaluation of Glare as a Hazard for General Aviation Pilots 

on Final Approach

July 2015

6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.

RogersJA,

1 Ho CK,2 Mead A,3 Millian A,3Beben M,3 Drechsler G3

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

1

Greensboro College

815 West Market St., Greensboro, NC 27401

2

Sandia National Laboratories

P.O. Box 5800, Albuquerque, NM 87185

3

Federal Aviation Administration, Civil Aerospace Medical Institute

P.O. Box 25082, Oklahoma City, OK 73125

11. Contract or Grant No.

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered

Office of Aerospace Medicine 

Federal Aviation Administration

800 Independence Ave, S.W.

Washington, DC 20591 14. Sponsoring Agency Code

15. Supplemental Notes

Work was accomplished under approved task AM-HRR-521

16. Abstract

Solar power is a growing source of energy for airports and for their communities. While solar power 

panels provide a useful means to generate revenue and to provide energy locally, it does pose a potential 

hazard in the form of glare. In the current study, pilots were exposed to glare during a series of flights in a 

flight simulator, and their perceived impairment was recorded. 

During the approach phase of each flight, we simulated glare from one of four possible angles (0, 25, 50, 

and 90 deg left of straight ahead) and for glare durations of either 0 (no glare control), 1, and 5 s. The glare 

was simulated using halogen lamps that, under the lighting conditions of our lab, approximated the visual 

effect of solar glare. Subjective measures of impairment were recorded for each condition. There was a 

significant main effect of glare duration and a significant main effect of glare angle. 

Impairment was perceived as being worse for glare sources that are straight ahead of the pilot and of 

longer duration, with a gradual decline in impairment as the glare source moves toward the side of the pilot. 

However, there was no significant interaction between glare duration and of glare angle.

17. Key Words 18. Distribution Statement

Human Factors, Aircraft Simulation, Solar Panel Glare, 

Airport, Pilot Hazard

Document is available to the public 

through the Internet:

www.faa.gov/go/oamtechreports

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price

Unclassified Unclassified 15

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

iii

ACKNOWLEDGMENTS

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, 

a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National 

Nuclear Security Administration under contract DE-AC04-94AL85000.

v

Contents

Evaluation of Glare as a Hazard for General Aviation Pilots on Final Approach

Introduction. 

Methods. 

Participants. 

Design. 

Stimuli and Apparatus. 

Glare Experience Questionnaire. 

Pilot Demographics. 

Questions Related to Solar Glare. 

AGARS Flight Simulator. 

AGARS Flight Simulator Host System. 

AGARS Out-the-Window Display System. 

Navigation Map Display. 

Glare Simulation Devices. 

Post-Trial Questionnaire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Procedure. 

Pilot Preparation. 

Familiarization Flight. 

Flight Route. 

Results. 

Glare Experience Questionnaire  

Pilot Demographics. 

AGARS Flight Simulator Data. 

Post-Trial Questionnaire. 

Discussion. 

AGARS Flight Simulator Data. 

Post-Trial Questionnaire  

Conclusions. .

References. .

1

Evaluation of Glare as a Hazard fo

General Aviation Pilots on Final 

INTRODUCTION

Solar power is a growing source of energy for airports and for 

their communities. For example, in 2012 Manchester-Boston 

International Airport completed installation of 42,000 photovoltaic panels (Manchester-Boston Regional Airport, 2012). 

In 2011, private development of a 75-acre solar farm on land 

owned by the Indianapolis International Airport began with 

an expected capacity to generate 15 gigawatts of electricity. The 

airport was collecting approximately $315,000 a year in rent 

for the land on which the solar farm was built (Indianaplois 

Airport Authority, 2011; Swiatek, 2013). The Denver International Airport currently has three separate solar arrays, and in 

June 2014, announced that a fourth solar installation will be 

built and altogether spread over 55 acres (Montgomery, 2012). 

In the same month, General Mitchell International Airport in 

Milwaukee, WI, completed acceptance of requests for proposals (RFP) to “evaluate the feasibility of siting a large-scale solar 

photovoltaic system at General Mitchell International Airport” 

(U.S. Department of Transportation, 2014). It is worth noting that there is no clear indication in the RFP as to how large 

this solar installation will be, but if some of the installations at 

other airports are an indication, it is likely to cover many acres 

in solar panels.

While solar power panels provide a useful means to generate 

revenue and to provide energy locally, they do pose a potential 

hazard to pilots, in the form of glare. For example at the Manchester-Boston Regional Airport, air traffic controllers (ATCs) 

reported significant problems seeing due to glare reflecting from 

the solar panels toward the tower. Aside from the ManchesterBoston Regional ATCs suffering from solar glare, reports from 

pilots flying near the Ivanpah Solar Electric Generating System 

have included complaints about the glare from the facility (Motley, 

2014). Pilots have described the glare as “blinding,” and at least 

one individual reported in the Aviation Safety Reporting System 

(ASRS) database that the glare was “like looking into the sun” 

and that they thought the glare was a hazard because they could 

not see if there was air traffic nearby (ASRS Database, 2013). 

The effect of transient glare from a solar panel can produce 

a sudden increase, or flash of light. Sudden changes in the appearance or the presentation of new stimuli at a point within 

the visual field are known to capture attention (Yantis, 1993a; 

Yantis & Hillstrom, 1994), including interrupting attention 

allocated to another task (Yantis, 1993b). A particularly salient 

cue for the capture of visual attention is a sudden change in 

brightness within a point of the visual field (Theeuwes, 1991; 

Wright & Richard, 2003). The pulling of attention away from a 

primary task (such as flying) produces some level of distraction 

and introduces a secondary task (noting a source of glare) (Lavie, 

2005; Wickens, Sandry, & Vidulich, 1983). Visual distractors, 

both internal and external to a vehicle, have been known to 

influence control (Engstrom, Johansson, & Östlund, 2005; 

Ranney, Garrott, & Goodman, 2000). Flooding the cockpit of 

an aircraft with glare will likely decrease visibility for the pilot 

thereby making it more difficult to control the aircraft. The 

increased difficulty will likely be reflected by increased cognitive 

load as the pilot will now have to work a bit harder to maintain 

visual contact with the runway, instruments, and the management of their aircraft. 

In the current study, pilots were exposed to glare during a 

series of flights in a flight simulator, and their perceived impairment was recorded. During the approach phase of each flight, 

we simulated glare from one of four possible angles (0, 25, 50, 

and 90 degrees left of straight ahead), and for glare durations of 

either 0 (no glare control), 1, and 5 s. The glare was simulated 

using halogen lamps that, under the lighting conditions of our 

lab, approximated the visual effect of solar glare. During the 

flight, the pilots wore an EEG cap to record any changes in 

neural activity that would indicate increased cognitive and visual 

load as a function of glare exposure. An eye tracker was used 

to monitor eye movements to ascertain if they looked toward 

the glare and what compensatory eye movements were made 

in response to glare exposure. The results of the EEG and eye 

tracking will be reported in separate reports. Finally, we asked 

pilots to provide subjective ratings of their own perceptions of 

how the glare affected their ability to fly and to read their instruments. Additionally, we asked them to rate the similarity of the 

simulated glare to glare they have experienced in the real world.

METHODS

This study was completed using the AGARS Simulator (described in detail later) at the Federal Aviation Administration’s 

Aerospace Human Factors Research Lab (AHFRL) at the Civil 

Aerospace Medical Institute (CAMI), which is located at the 

FAA Mike Monroney Aeronautical Center (MMAC) in Oklahoma City, OK.

Participants

All participants in this experiment were federal employees 

recruited via distribution of emails internal to the MMAC facility. 

The experiment was completed as part of the each employee’s 

work activities, which required that the participants negotiate 

the time with their individual managers. Because this study was 

completed as part of the employee’s normal work activities, no 

additional compensation was given. The minimum requirements for this study included having been a certified private 

pilot (though not necessarily current) and normal or correctedto-normal visual acuity. A total of 20 participants coordinated 
2

their time for participation. One was excluded from analysis 

due to early termination of his experiment session, leaving 19 

participants, all male. All participants were required to provide 

their informed consent via two consent forms, one for CAMI 

and one for Sandia National Laboratories, approved by each 

institutions’ Institutional Review Board.

Design

We combined four angles of glare exposure (0, 25, 50, and 

90 deg) and two levels of exposure duration (1 and 5 s) to create eight possible experimental conditions. The durations were 

selected as they represent a range of transit times across solar 

installations at a variety of speeds. Additionally we had the pilots fly a single trial in which no glare was present as a control 

condition, thereby producing a total of nine conditions. Each 

pilot flew one trial of each of the nine conditions. The order 

of trials was randomized for each participant, so the pilot did 

not know if a glare event would occur during any given trial, 

or from what angle. 

Stimuli and Apparatus

Glare Experience Questionnaire

The glare experience questionnaire asked questions about the 

pilot’s experience with solar glare while flying, as well as some 

general demographic questions.

Pilot Demographics

The pilots were asked to indicate their current age, gender, 

how long they have been flying, if they wear corrective lenses 

(and if so what kind), and if they have had vision corrective 

surgery (and if so to indicate how long ago).

Questions Related to Solar Glare

Pilots were asked to provide ratings of their experience related to direct sunlight, glare from solar panels, and glare from 

other objects. For each, they were asked to indicate what stage 

of flight they had their encounter (departure, take-off, cruising, 

approach, touch-down), impairment of ability to fly the plane 

and the impairment to the ability to read their instruments (each 

on a 5-point scale: no impairment, slight impairment, moderate 

impairment, significant impairment, severe impairment), typical 

duration of exposure (less than 1 s, 1-5 s, 5-10 s, greater than 

10 s), and to indicate what compensatory strategies they have 

used (use sun shade, use sunglasses, avert eyes, other). With 

regard to glare from other objects, we asked them to indicate 

the source of the glare. 

AGARS Flight Simulator

The flight simulator used in this study was the Advanced 

General Aviation Research Simulator (AGARS). The AGARS 

is a simulation of a Piper PA-46 Malibu single-engine aircraft. 

Unique features of this simulator include the replacement of 

the hardware-based instrumentation with a touchscreen representation of flight instruments. This was done to mediate 

configurability of the cockpit for use across multiple research 

projects. For this study, we maintained use of the traditional 

round dial configuration.

AGARS Flight Simulator Host System

The AGARS simulation host computer is a custom-built 

system that uses a AMD Opteron 2218 processor with 1Gb of 

RAM. The operating system is Fedora Linux 12 and the simulation software was written by ZedaSoft, Inc.

AGARS Out-the-Window Display System

The AGARS out-the-window (OTW) display system used 

five Sharp Aqous 60-inch LC-60LE835U flat panel televisions 

mounted on stands in front and to the sides of the cockpit, thereby 

creating a segmented display system spanning 180 degrees and 

creating a reasonably realistic OTW scene.

Each of the OTW displays is driven by a custom-built computer. These computers have Intel, Inc. i7 CPUs, 12Gb DDR3 

RAM, and two Sli-connected NVidia GTX 470 video cards with 

128 Mb of memory. The computers are running the 64-bit edition of Microsoft Windows 7 Professional. The image generator 

(IG) software, which is responsible for the OTW scene, is VRSG 

5.7.2 from MetaVR, Inc.

Navigation Map Display

A JeppView FlightDeck 3.5.6 GPS navigation map display was 

positioned above the glare shield and centered in the cockpit near 

the forward windscreen. The JeppView software was running on 

a Dell Optiplex 780 computer with an Intel Core 2 Duo 2.93 

Ghz processor with 4 Gb RAM. The operating system of this 

computer was the 32-bit edition Windows 7 Professional. The 

display was a Faytech 9.5 inch touchscreen (model: FT10TMB).

Glare Simulation Devices

To simulate glare being reflected from solar panels, we used 

a series of four SoLux halogen bulbs (12 V, 50 W, MR16, black 

back) with a 10-d beam spread and a color temperature of 4700 

K to reproduce the full solar spectrum. Each of the lamps was 

mounted atop a Leica Tri 100 tripod. Each light was controlled 

by its own control box, built by Sandia National Laboratories. 

Each control box featured a trigger switch, which, when thrown, 

activated a PTC-1A digital timer manufactured by Omega Engineering, Inc., which determined how long the attached lamp 

would stay on (1 or 5 s). The lamps, tripods, and control boxes 

are collectively referred to as the glare simulation devices (GSDs). 
3

The four GSDs were placed straight ahead of the pilot (0 

degrees), and at 25, 50, and 90 deg away from straight ahead 

on the left side of the simulator cockpit, between the cockpit 

and the simulator OTW view. The distance between the lamp 

and the pilot’s eyes was approximately 0.8 m. Depending on the 

location of the lamp, the measured luminance at the eye was 

between ~1,000 – 2,000 Lux (measured using a digital Lux meter 

LX1330B), which corresponds to a corneal irradiance of ~10 – 20 

W/cm2 (1 W yields approximately 100 lumens of visible light 

in the solar spectrum). The subtended angle of the glare based 

on the bulb aperture of ~0.05 m and a distance of ~0.8 m was 

approximately 0.06 rad. The retinal irradiance was calculated 

from the measured corneal irradiance, subtended glare angle, 

and measured pupil diameter (~5 mm) to be ~0.024 – 0.048 

W/cm2. Together with the subtended glare angle of 0.06 rad (60 

mrad), the retinal irradiance was sufficient to cause a temporary 

after-image, similar to solar glare reflected from flat solar panels 

(Ho, Ghanbari, & Diver, 2011; Ho, 2013).

Figure 1. Placement of two of the Glare Simulation 

Devices are at 5 deg and 50 deg.

Figure 2. Interior view of the AGARS cockpit, with the 0-deg GLD triggered.

Figure 2. Interior view of the AGARS cockpit, with the 0-deg GLD triggered.
4

Post-Trial Questionnaire

Following trials with simulated glare, we asked pilots to rate 

their experience. The three questions and possible responses (on 

a 5-point rating scale) were as follows:

1. Rate the degree of impairment from the simulated glare 

on your ability to fly the plane.

□ 1 = No impairment: Can easily perform functions 

necessary to fly the plane with no noticeable impact of glare

□ 2 = Slight to no impairment: Can still perform 

functions necessary to fly the plane, but glare is 

noticeable

□ 3 = Moderate impairment: Can perform functions 

necessary to fly the plane, but glare required 

some action (e.g., physically blocking glare, averting eyes)

□ 4 = Significant impairment: Difficulty performing 

functions necessary to fly the plane, even after 

performing actions in response to glare

□ 5 = Severe impairment: Unable to perform functions necessary to fly the plane

2. Rate the degree of impairment from the simulated glare 

on your ability to read your instruments.

□ 1 = No impairment: Can easily read instruments 

and values (e.g., altitude, speed) with no noticeable impact of glare

□ 2 = Slight to no impairment: Can still read instruments and values, but glare is noticeable

□ 3 = Moderate impairment: Can read instruments 

and values, but glare required shifting of eyes, 

blinking, or refocusing in order to read values

□ 4 = Significant impairment: Difficulty reading instruments and values, even after shifting of eyes, 

blinking, or refocusing

□ 5 = Severe impairment: Unable to read instruments and values

□ N/A (did not view instruments during or after glare 

event)

3. How similar was the simulated glare to actual glare you 

have observed while flying, if applicable?

□ 1 = No similarity

□ 2 = Slight similarity

□ 3 = Moderate similarity

□ 4 = Very similar

□ 5 = Extremely similar

□ Not applicable

For all trials, we asked the subjects the open-ended question 

“[are there] any additional comments or questions regarding this 

test or your experience that you would like to provide?”

Procedure

Pilot Preparation

Pilots were required to provide their informed consent prior 

to participation. Upon consent, we measured the pilot’s head 

size in order to select the appropriate EEG cap. We then asked 

the pilot to enter the cockpit so that initial eye tracking camera 

calibration and seat position adjustments could be made. The 

pilots completed the glare experience questionnaire. The EEG 

cap was placed upon the pilot’s head and the position and chin 

strap adjusted to ensure proper fit and comfort. Once all EEG 

electrodes indicated good signal, the pilot was reminded not to 

make any sudden head movements and then was escorted to 

and seated in the AGARS cockpit. We asked the pilot to verify 

the correct alignment of the GSDs, and made any minor adjustments that were required to optimize the glare simulation. Final 

eye tracking calibration was then performed.

Familiarization Flight

Each pilot was informed about the performance characteristics 

of the Piper Malibu simulated by the AGARS and was given a few 

minutes to become familar with the location and characteristics 

of the instrumentation. Once the pilot felt ready, we began one 

to three familiarization flights, depending on how quickly they 

became comfortable flying the AGARS. While familiarization 

took place, one of the researchers familiar with flying the AGARS 

remained available to the pilot to answer any questions and to 

guide them along the experimental route .

Flight Route

For all flights, the pilots flew from Max Westheimer Airport 

(KOUN) in Norman, OK, to the GALLY navigation fix, located 

in Newcastle, OK, at an altitude of 2,500 feet MSL (see Figure 

3). From there, they headed north to Will Rogers International 

Airport (KOKC) to land on runway 35R. The pilots were able 

to use the GPS navigation display to maintain spatial awareness 

of their current location in relation to the GALLY navigation fix 

and KOKC 35R. Each flight lasted about 5 min.

Figure 3. Ma

route flown b

was from KO

GALLY wayp

charts) and t

Figure 3. Map of flight route depicting the 

route flown by pilots in our study. Take off 

was from KOUN. Pilots then flew to the 

GALLY waypoint (Stacks on sectional charts) 

and then turned north to KOKC.
5

The radios for AGARS were set to the frequencies for KOKC 

35R automatically. This enabled localizer, glideslope, and distance measuring equipment (DME) instrumentation to work 

appropriately without intervention from the pilot. This was done 

to minimize their workload, particularly because the AGARS 

touchscreens can make manipulation of the radio dials extremely 

difficult, which would dramatically increase pilot workload.

We controlled glare with the GSDs. When a trial called for 

using glare, the appropriate GSD was selected and the exposure 

duration was programmed into the digital timer for that GSD. 

One of the researchers observed a display that replicated the 

DME display from the AGARS cockpit. The trigger for the 

GSD was activated when the DME was 2.6, which places the 

aircraft at 1 mile from the runway threshold, on final approach 

to landing at Will Rogers.

RESULTS

Glare Experience Questionnaire 

Pilot Demographics

Pilots’ mean age was 47.6 years (SEM = 1.88). The mean

flight years was 21.7 (SEM = 2.32). Two pilots had stopped

flying several years prior to participating in this experiment 

(one had ceased five years ago, while the other had not flown 

in 20 years). Both of these pilots demonstrated that their 

flying skills were sufficient for participation. Eleven pilots 

(58%) wore corrective lenses while flying. Of those who wore 

corrective lenses, nine (81%) wore glasses, one wore contacts, 

and one declined to respond. Three pilots had received vision corrective surgery, with a mean of 3.25 years since their 

surgery (SEM = 1.01).

As can be seen in Figure 4, the majority of participants had 

some real world experience with direct sunlight or with solar 

glare reflecting from other objects. From the Figure, it is also 

clear that the majority of encounters with sunlight and glare 

from other objects took place while the pilot was in cruise or 

on approach. Less than a third of pilots had encountered direct 

sunlight during departure or take-off. These results suggest 

that this study design is well-positioned to generalize outside 

the lab, since the experimental design exposed pilots to glare 

during approach, rather than another stage of flight such as 

take off. Of key interest was the low number of respondents 

(two) who had encountered glare from solar installations. This 

was likely due the lack of solar installations in the Oklahoma 

City area, where our subjects were recruited and may have 

spent the majority of their time flying. 

Figure 4. Real-world sources of solar glare that pilots have encountered. Figure 4. Real-world sources of solar glare that pilots have encountered.
6

Figure 5 shows that the majority of our pilots had encountered glare with durations between 1 and 10 s with longer 

durations being encountered for objects other than direct 

sunlight or solar panels. Figure 6 shows that, for most, glare 

emanated primarily from bodies of water. 

AGARS Flight Simulator Data

The lateral deviation from the runway centerline of the initial touch down point was submitted to an analysis of variance 

(ANOVA) for within-subjects designs (a.k.a. repeated measures). 

In this instance, there were two factors (Independent Variables, 

or IVs): 1) duration with two levels (1 s and 5 s) and 2) angle of 

the simulated glare exposure (0, 25, 50, and 90 deg to the left of 

straight ahead). The outcome measure, or Dependent Variable 

(DV), was the lateral deviation of the initial touch-down point 

from centerline. 

Neither duration, F(1,18) = .406, MSe = 5.282, p < .532, ή2

= .022, nor the angle of simulated glare exposure was significant, 

F(3,54) = 1.407, MSe = 3.228, p < .251, ή2 = .073. Likewise, no 

significant interaction was found between these two variables, 

F(3,54) = .451, MSe = 4.046, p < .717, ή2 = .024. 

It should be noted, however, that there were two runway 

impacts (crashes) during the course of the experiment. The first 

took place during a control condition during which no glare was 

present. This pilot, we suspect, may have been testing the limits of 

the simulator, because the pilot appeared to be showing signs of 

boredom, such as making delayed approaches requiring a steeper 

approach angle. Following this impact, the pilot appeared to fly 

much more conservatively. Since this pilot had no difficulty with 

any other landing, it seems more than coincidental that the one 

time he had a problem was also the one time he did not have a 

glare event during the main trials.

The second runway impact took place when the glare was 

presented straight ahead of the pilot for a duration of 5 s. This 

pilot bounced the aircraft twice while landing. The third contact was ultimately registered as an impact (crash). While the 

previously mentioned lack of significant groupwise interaction 

between glare angle and glare duration does not directly support 

causation of this particular impact, that notion is suggestive for 

this one case.

Post-Trial Questionnaire

Pilot ratings of perceived impairment of glare on the ability 

to fly the airplane and to read their instruments, for both the 1-s 

and the 5-s durations, are presented in Figures 5 and 6. 

Figure 6. Frequency of glare from sources other than direct sunlight or solar 

panels.

 Figure 5. Duration of glare from real-world objects encountered 

by pilots.

Figure 6. Frequency of glare from sources other than direct sunlight or solar 

panels.

Figure 6. Frequency of glare from sources other than direct 

sunlight or solar panels.
7

The average results for the 1- and 5-s durations are presented 

in Figure 7. It is obvious by looking at the Figures 7 and 8 that 

impairment is worse for glare sources that are straight ahead of 

the pilot, with a gradual decline in impairment as the glare source 

moves toward the side of the pilot. If we look at the ratings of 

impairment on the ability to fly, we can see that the mean rating, 

for both 1 s (M = 3.16, SEM = 0.23) and 5 s (M = 3.53, SEM 

= 0.16) glare durations at 0 deg is above 3, a rating of moderate 

impairment. At an angle of 25 deg, the mean impairment rating 

for an exposure duration of 5 s (M = 2.89, SEM = 0.20) is just 

below the rating of 3, and the error bar rises above the rating of 

3. This indicates that this particular condition results in moderate impairment of the ability to fly. Also, at the angle of 25 deg, 

the mean impairment rating for a glare duration of 1 s is M = 

2.47, SEM = 0.25, indicating slight to moderate impairment. 

For the control (no glare) condition, all pilots rated the impairment for both the ability to fly and impairment for reading 

their instruments as a 1 (no impairment). This indicated that 

they were able to fly the aircraft and see their instruments with 

no difficulty when glare was not present in a flight. However, 

since the absence of glare uniformly produced a rating of 1 (a 

clear floor effect) we excluded those data from further analysis 

because leaving them in would have automatically led to higher 

statistical significance when glare was present. We instead opted 

to leave those data out and focus solely on conditions in which 

glare was present to determine how those conditions differed 

from each other.

Figure 8. Mean ratings of impairment to read instrumentation based upon the angle and duration of 

simulated glare exposure. Error bars represent the standard error of the mean.

Figure 8. Mean ratings of impairment to read instrumentation based upon the angle and duration of 

simulated glare exposure. Error bars represent the standard error of the mean.

Figure 7. Mean ratings of impairment to ability to fly based upon the angle and duration of 

simulated glare exposure. Error bars represent the standard error of the mean.

Figure 8. Mean ratings of impairment to read instrumentation based upon the angle and 

duration of simulated glare exposure. Error bars represent the standard error of the mean.
8

To isolate the sources of variation in our study, a doubly 

multivariate analysis was conducted. The doubly multivariate 

analysis is an extension of ANOVA for within-subjects designs 

that allows for the measurement of changes in multiple DVs as 

a function of different IVs. This analysis measured three DVs: 

the pilot rating of a) impairment of flying ability, b) impairment 

to read their instruments, and c) how similar the simulated glare 

was to what had been experienced in the real world. Two IVs 

were used in this analysis. The first was the duration of the glare 

exposure with two levels (1 s and 5 s). The second was the angle 

of glare exposure, with four levels (0, 25, 50, and 90 deg to the 

left from straight ahead). Wilks’ λ was used in the multivariate 

testing. Wilks’ λ, also called the maximum likelihood criterion, 

is a multivariate statistic that measures the proportion of variance 

in the DVs that is unaccounted for by the IV(s). Because it is 

measuring the variance that is unaccounted for, a small Wilks’ 

λ is associated with a statistically significant result and therefore 

rejection of the null hypothesis. 

There was a significant main effect of glare duration, Wilks’ ή

= .508, F(9,10) = 9.325, p < .011, ή2 = .492. This indicates that 

there is a difference among the DVs based upon the duration 

of glare exposure. There was also a significant main effect of the 

angle of glare exposure, Wilks’ ή= .106, F(9,10) = 9.325, p < 

.001, ή2 = .894. This indicates that there was a difference among 

the DVs based upon the angle of glare exposure. However, there 

was not a significant interaction between duration of glare exposure and the angle of glare exposure, Wilks’ ή= .711, F(9,10) 

= .452, p < .877, ή2 = .289. 

Given the significant multivariate tests, univariate tests 

were carried out to further parse the relation supported by the 

multivariate main effects. These univariate tests are two-factor 

ANOVAs for within-subjects designs. Each of these univariate 

tests measured the effect that the two IVs had on a single DV 

(the pilot’s rating of impairment on flying ability, the pilot’s 

rating of impairment to read the instruments, and the pilot’s 

rating of how similar the simulated glare was to what they had 

experienced in the real world). 

The first univariate test assessed how glare angle and duration 

affected pilots’ rated impairment of glare on flying ability. This 

test showed a significant main effect of simulated glare duration 

on impairment of flying ratings, F(1,18) = 11.272, MSe = .675, 

p < .004, ή2 = .385, with the 5-s duration having a higher overall 

mean (M = 2.645, SEM = .136) than the 1 s duration (M = 

2.197, SEM = .128). There was also a significant main effect of 

the simulated glare exposure angle on the pilot ratings of how 

it affected their ability to fly, F(1,18) = 32.898, MSe = .675, p 

< .000, ή2 = .646, with an orderly rating of straight ahead as the 

most impairing (M = 3.342, SEM = .171), 25 deg left of straight 

ahead as second most impairing (M = 2.684, SEM = .172), 50 

deg left of straight ahead as less impairing (M = 2.026, SEM = 

.130), and 90 degr to left of straight ahead as the least impairing 

(M = 1.632, SEM = .166). 

To determine if there were significant differences between the 

ratings of how piloting ability was affected for each of the various angles, pairwise comparisons were performed. A Bonferroni 

correction was used to control for familywise error rate inflation. 

The pairwise comparisons of angle of exposure revealed that 

straight ahead was rated as significantly higher than 25 deg to 

the left of straight ahead (p < .038). Likewise, straight ahead 

was found to be significantly higher than 50 deg to the left of 

center (p < .000), and 90 deg left of center (p < .000). Further, 

25 deg left of center was found to result in a higher rating than 

50 deg left of center (p < .001), and 90 deg left of center (p < 

.000). Finally, with regard to the rating impact to piloting ability, 

there was no significant difference found between 50 deg and 

90 deg left of the center (p < .236). 

The second univariate test we conducted assessed how glare 

angle and duration affected pilot ratings of their ability to read 

instruments. We found a significant main effect of glare duration on rated ability to read instrumentation, F(1,18) = 11.046, 

MSe = .572, p < .004,ή2 = .385, with the 5-s duration having 

a higher overall mean (M = 2.132, SEM = .151) than the 1-s 

duration (M = 1.724, SEM = .154). 

Mauchly’s test for Sphericity determines whether the variances 

across the different conditions are equal. When the variances across 

levels are equal, the sphericity assumption of an ANOVA has 

been met and Mauchy’s test for Sphericity will not be significant. 

When Mauchly’s test for Sphericity is significant, it means that 

the sphericity assumption has been violated, which results in a 

greater risk of a Type II error (failure to reject the null hypothesis). 

To compensate for this, the degrees of freedom for the ANOVA 

have to be adjusted; typically by using a Greenhouse-Geisser 

correction. When analyzed for the effect of glare angle on pilot 

ratings of their ability to read their instruments, we found that 

Mauchly’s test for Sphericity was significant, ή2(5) = 12.362, p < 

0.030. The corrected ANOVA showed a significant main effect 

of simulated glare exposure angle on ratings of how it affected 

their ability to read the instruments, F(2.281,46.319) = 13.611, 

MSe = .948, p < .000, ή2 = .646,with an orderly rating of straight 

ahead as the most impairing (M = 2.474, SEM = .189), 25 deg 

left of straight ahead as second most impairing (M = 2.184, 

SEM = .214), 50 deg left of straight ahead as less impairing (M 

= 1.737, SEM = .168), and 90 deg to left of straight ahead as 

the least impairing (M = 1.316, SEM = .159).

To determine if there were significant differences between 

the ratings of how the ability to read instrumentation was impacted for each the various angles of simulated glare, pairwise 

comparisons were performed using a Bonferroni correction. The 

pairwise comparisons of angle of exposure revealed that straight 

ahead is not rated as significantly higher than 25 deg to the left 

of straight ahead (p < 1.000). However, straight ahead was found 

to be significantly higher than 50 deg to the left of center (p < 

.014) and 90 deg left of center (p < .000). Further, 25 deg left 

of center was significantly higher than 50 deg left of center (p < 

.014) and 90 deg left of center (p < .006). Finally, with regard 

to the rating impact to the ability to read instrumentation, it 

was found that there was not a significant difference between 

50 deg and 90 deg left of the center (p < .098). 

The last univariate test assessed how glare angle and duration 

affected pilot ratings of the simulated glare verse glare they had 
9

experienced while flying in the real world. We found no main 

effect of duration on ratings of the similarity of represented glare 

to real-world glare (F(1,18) = .471, MSe = .893, p < .501, ή2 = 

.026). We analyzed the effect of the angle of glare exposure on 

pilot’s ratings of the similarity of the simulated glare to real-world 

glare, Mauchly’s test was again significant( ή2(5) = 11.218, p < 

0.048). Subsequent Greenhouse-Geisser-corrected ANOVA 

was not significant (F(2.117,38.102) = .626, MSe = 1.370, p < 

.549, ή2 = .034). This means that regardless of the duration or 

the angle of the glare, the ratings of how realistic they perceived 

the simulated glare to be remained about the same.

DISCUSSION

AGARS Flight Simulator Data

Results of the landing data showed no significant, systematic 

lateral deviation from runway centerline, regardless of the duration or angle of simulated glare presented to the participant. 

The one case that we considered to be of any potential concern 

was when a pilot crashed during landing with the glare presented 

straight ahead for a duration of 5 s. However, we would suggest tempering any concern by pointing out that if there was a 

problem with that particular angle and duration, we would have 

likely seen more individuals who had crashed. 

Post-Trial Questionnaire

Data from the post-trial questionnaire demonstrate that, 

for the most part, higher glare durations result in greater selfperceived impairment in the pilots’ ability to safely fly an aircraft 

and to read aircraft instrumentation relative to shorter durations. 

Further, as expected, the more forward-facing the glare was, the 

more impairment the pilots reported experiencing. More precisely, we found that when glare was present, the ability to read 

aircraft instrumentation was not statistically different between 

glare that was presented straight ahead and when it was 25 deg 

to the left of straight ahead. Likewise, no statistical difference 

was found between 50 deg and 90 deg of straight ahead. Taken 

together, this suggests that as far as reading instrumentation is 

concerned, two groupings of angles resulted in similar impairment among the member angles: The first grouping included the 

member angles of 0 and 25, and the second grouping included 

the member angles of 50 and 90. While there was a significant 

increase in these ratings, it is still considered to be less than a 

moderate impairment on the ability to read instrumentation. 

Though the rating was, ultimately, below our threshold of “moderate impairment,” one could speculate that longer durations may 

result in higher impairment ratings for reading instrumentation, 

particularly for angles of 0 and 25 deg of straight ahead.

In terms of how glare impacted the ability to fly, we found 

a similar effect of glare duration as described above: A longer 

duration resulted in greater self-reported impairment to the 

ability to land on a runway center. We found that glare from 

the angles of 50 and 90 deg was not statistically different from 

each other with regard to the relative impairment to the ability 

to fly. Interestingly, there is a statistically significant increase in 

the ratings of impairment when glare comes from an angle of 

25 deg, and a still larger increase in the ratings of impairment 

for glare that is straight ahead. Again, the closer the glare was 

to straight ahead, the more likely it became problematic for 

the pilot, and glare toward the side is unlikely to be a problem.

Figure 9 shows that ratings of the impairment to the ability 

to fly for glare from straight ahead were above a rating of 3. Additionally glare from 25 deg for a 5 s duration yielded a rating that 

was, statistically, indistinguishable from a rating of 3. Therefore, 

it is reasonable to say that glare from straight ahead or from 25 

deg (if it is long enough) will result in moderate impairment.

To summarize, the safe course of action would appear to be 

to locate sources of glare such that they do not produce glare 

from angles less than 50 deg from the pilots’ view straight ahead 

on approach to landing.

Figure 9. Mean ratings of impaired flying ability, impaired ability to read instrumentation, and the 

similarity of simulated glare to real glare, as a function of glare exposure angle. Error bars represent 

one standard error of the mean.

Figure 9. Mean ratings of impaired flying ability, impaired ability to read instrumentation, 

and the similarity of simulated glare to real glare, as a function of glare exposure angle. 

Error bars represent one standard error of the mean.
10

CONCLUSIONS

The presence of glare was associated with the most impairment in the pilot’s ability to see their instruments and to fly their 

airplane when the glare was straight ahead, as well as slightly to 

the side. The more forward the glare is and the longer the glare 

duration, the greater the impairment to the pilots’ ability to 

see their instruments and to fly the aircraft. These results taken 

together suggest that any sources of glare at an airport may be 

potentially mitigated if the angle of the glare is greater than 25 

deg from the direction that the pilot is looking in. We therefore 

recommend that the design of any solar installation at an airport 

consider the approach of pilots and ensure that any solar installation that is developed is placed such that they will not have 

to face glare that is straight ahead of them or within 25 deg of 

straight ahead during final approach. 

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