Consensus Study Report

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Suggested citation: National Academies of Sciences, Engineering, and Medicine. 2026. Health and Safety Impacts of Aircraft Cabin Temperatures. Washington, DC: National Academies Press. https://doi.org/10.17226/29472.

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COMMITTEE ON HEALTH AND SAFETY IMPACTS OF AIRCRAFT CABIN TEMPERATURES¹

DAVID H. WEGMAN (Chair), University of Massachusetts Lowell

FABIANO AMORIM, University of New Mexico

CATHERINE BURNETT, Federal Aviation Administration (retired)

SARA CZAJA, Weill Cornell Medicine

BYRON JONES, Kansas State University

W. LARRY KENNEY, The Pennsylvania State University

EILEEN MCNEELY, Harvard University

KIMBERLY MEIDENBAUER, Washington State University

PAUL MORELL, Morell Consulting, LLC

ZACHARY SCHLADER, Indiana University

SHALINI H. SHAH, Boston Children’s Hospital, Region I Pediatric Environmental Health Specialty Unit

DAVID SPACE, Boeing Commercial Aircraft (retired)

MILLENNIA YOUNG, NASA Johnson Space Center

National Academy of Medicine Fellow

ROXANA CHICAS, Emory University Nell Hodgson Woodruff School of Nursing

Study Staff

AUTUMN DOWNEY, Study Director, Biomedical and Health Sciences Program Area

ASHLEY BOLOGNA, Research Assistant, Biomedical and Health Sciences Program Area

BRADFORD CHANEY, Senior Program Officer, Committee on National Statistics

JOSHUA LANG, Program Coordinator, Board on Human Systems Integration (until July 2025)

ALEXANDRA MCKAY, Research Associate, Biomedical and Health Sciences Program Area (from March 2026)

LYDIA TEFERRA, Research Associate, Biomedical and Health Sciences Program Area (until October 2025)

TOM MENZIES, Senior Director, Consensus and Advisory Studies Division, Transportation Research Board

___________________

¹ NOTE: See Appendix D, Disclosure of Unavoidable Conflict of Interest.

EMANUEL ROBINSON, Director, Board on Human Systems Integration

CLARE STROUD, Senior Program Director, Biomedical and Health Sciences Program Area

Consultants

BARRAK ALAHMAD, Harvard T.H. Chan School of Public Health

MAARTJE WOUTERS, Wouters Writing

Reviewers

This Consensus Study Report was reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise. The purpose of this independent review is to provide candid and critical comments that will assist the National Academies of Sciences, Engineering, and Medicine in making each published report as sound as possible and to ensure that it meets the institutional standards for quality, objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process.

We thank the following individuals for their review of this report:

Although the reviewers listed above provided many constructive comments and suggestions, they were not asked to endorse the conclusions

or recommendations of this report nor did they see the final draft before its release. The review of this report was overseen by ERIC LARSON, University of Washington, and DEB NIEMEIER, University of Maryland. They were responsible for making certain that an independent examination of this report was carried out in accordance with the standards of the National Academies and that all review comments were carefully considered. Responsibility for the final content rests entirely with the authoring committee and the National Academies.

Acknowledgments

The committee would like to thank the Federal Aviation Administration for its sponsorship of this study and for the data analyses it provided to the committee to inform the development of this report. Special thanks are also due to all the others who provided information to inform the committee’s efforts—whether by participating in public sessions, sharing data, or submitting responses to committee information requests—including those representing flight attendants and pilots, airlines, aircraft manufacturers, and the Department of Transportation’s Office of Aviation Consumer Protection.

The committee would also like to express its appreciation to all of the National Academies staff who supported the committee across the phases of its work: Autumn Downey, Ashley Bologna, Bradford Chaney, Joshua Lang, Alexandra McKay, Stephanie Puwalski, Lydia Teferra, Anne Marie Houppert, Christopher Lao-Scott, Rebecca Morgan, Christie Bell, Lori Brenig, Samantha Chao, Emanuel Robinson, Tom Menzies, Clare Stroud, and the team at the National Academies Press. The committee is also grateful to Roxana Chicas, National Academy of Medicine Fellow, for her contributions to this report.

Contents

PREFACE

ACRONYMS AND ABBREVIATIONS

SUMMARY

1 INTRODUCTION

Study Context

Study Origin and Scope

Study Approach

Report Organization

References

2 THERMAL CONTROL IN THE AIRCRAFT CABIN ENVIRONMENT

Aircraft Operating Environments

Contributors to the Aircraft Internal Thermal Environment

Aircraft Environmental Control System and Its Role in Thermal Control

Ground-Based Air Conditioning Systems for Thermal Control of Aircraft

Challenges with Thermal Control on Aircraft

Concluding Remarks

References

3 PHYSIOLOGICAL, COGNITIVE, AND BEHAVIORAL EFFECTS RELATED TO THERMAL EXPOSURE

Effects Related to Heat

Effects Related to Cold

Factors that Affect Risks from Thermal Exposure

Concluding Remarks

References

4 APPLYING STANDARDS AND GUIDELINES FOR THERMAL COMFORT AND HEAT AND COLD STRESS TO AIRCRAFT CABIN OCCUPANTS

Thermal Comfort Standards

Heat Stress Guidelines and Standards

Cold Stress Standards

Application of Thermal Comfort and Heat and Cold Stress Standards and Guidelines for Aircraft Cabin Settings

Concluding Remarks

References

5 EVIDENCE ON HEALTH AND SAFETY IMPACTS OF CABIN TEMPERATURES

Direct Evidence of Temperature Impacts on Health and Safety of Cabin Occupants

Indirect Evidence of Temperature Impacts on Health and Safety of Cabin Occupants

Assessing the Magnitude of the Problem

Addressing Current Data Limitations

References

6 STRATEGIES FOR MANAGING CABIN TEMPERATURES AND ASSOCIATED HEALTH AND SAFETY RISKS

Standards

A Systems Approach to Mitigation

Concluding Remarks

References

APPENDIXES

A Study Approach and Methods

B Supplemental Data and Analyses

C Committee, Fellow, and Staff Biographical Sketches

D Disclosure of Unavoidable Conflict of Interest

Boxes, Figures, and Tables

BOXES

S-1 Recommendations Aligned with Stakeholders

1-1 Statement of Task

2-1 ECS Performance Degradation and Maintenance for Aging Aircraft

3-1 Flight Attendant Fatigue as an Aviation Safety Issue

3-2 Acclimatization and Habituation

5-1 ASHRAE Research Project 1262

6-1 Engineering and Management Practices for Mitigating Extreme Cabin Temperatures and Associated Health and Safety Impacts

6-2 Recommendations Aligned with Stakeholders

A-1 Definitions of Terms Used in Thermal Boundary Calculations

FIGURES

S-1 Thermal response zones from the application of thermal comfort and heat and cold stress standards and guidelines

S-2 Expected physiological, cognitive, and behavioral effects across the temperature spectrum

1-1 Load factor for U.S. air carrier domestic and international scheduled passenger flights, 2004–2024

1-2 Map of FAA regions

1-3 Age profile of flight attendants, 2023

1-4 Physical environmental factors influencing the health, safety, and comfort of the cabin environment

1-5 Multiple stakeholders share responsibility for ensuring a safe thermal cabin environment

2-1 Simplified environmental control system schematic

2-2 Schematic representation of a typical aircraft engine bleed-air system

2-3 Schematic of a representative aircraft air conditioning pack and cabin air distribution system

2-4 Schematic representation of typical cabin airflow

2-5 Representative flight-deck interfaces from Boeing 737 aircraft showing flight crew controls for cabin and flight-deck temperature setpoints used to manage thermal comfort

2-6 Preconditioned air unit attached to a jet bridge

2-7 Frequency of equipment issues noted in NASA ASRS reports, stratified by season

2-8 Examples of kinked hoses connecting preconditioned air units to aircraft

2-9 Example of a PCA hose reel

3-1 Expected physiological, cognitive, and behavioral effects across the temperature spectrum

4-1 Thermal response zones from application of thermal comfort and heat and cold stress standards and guidelines for Case 1—busy flight attendant and typical clothing (2.3 MET; 0.6 clo)

4-2 Thermal response zones from application of thermal comfort and heat and cold stress standards and guidelines for Case 2—seated passenger or flight attendant and typical clothing (1.2 MET, 0.6 clo)

4-3 Comparison of comfort zones for Case 1 (high activity, 2.3 MET) and Case 2 (low activity, 1.2 MET)

4-4 Comfort zones for case scenarios 3 through 6 involving different activity and clothing levels, demonstrating how the two factors can offset each other

5-1 Percentage of 2Hot2Cold reports within each temperature category indicating the provision of medical or first aid

5-2 Distribution of in-flight temperature and humidity data from three independent datasets

5-3 Percentage of reports from aviation industry reporting systems citing cabin temperature issues, categorized by temperature range and data source

5-4 Comparison of the distributions of in-flight cabin temperatures observed/reported during typical flights, 2Hot2Cold reports, and NASA ASRS reports

5-5 Comparison of the distributions of on-ground cabin temperatures observed during typical flights (from Nicholls and Vink study), 2Hot2Cold reports, and NASA ASRS reports

5-6 Thermal response zones from the application of thermal comfort and heat and cold stress standards and guidelines for a scenario involving an active flight attendant in typical clothing (2.3 MET, 0.6 clo)

5-7 Comparison of in-flight cabin temperature and humidity data from three independent datasets (Nicholls and Vink, ACER, ASHRAE 1262) overlaid on thermal response zones for case scenario 1—active flight attendants in typical clothing (2.3 MET, 0.6 clo)

5-8 Comparison of in-flight data from three independent datasets (Nicholls and Vink, ACER, ASHRAE 1262) overlaid on thermal response zones for case scenario 2—passive seated passenger or flight attendant in typical clothing (1.2 MET, 0.6 clo)

5-9 Boarding conditions from Nicholls and Vink data overlaid on thermal response zones for case scenario 1—active flight attendants in typical clothing (2.3 MET, 0.6 clo)

5-10 Effect of activity level on the fraction of cabin conditions falling within each thermal zone, based on combined data from ACER, ASHRAE 1262, and Nicholls and Vink

6-1 Comparison of measured aircraft cabin temperatures with ANSI/ASHRAE Standard 161-2023 limits

6-2 Thermal response zones from application of thermal comfort and heat and cold stress standards and guidelines for moderate activity levels typical of a busy flight attendant (2.3 MET) and moderate clothing (0.6 clo)

6-3 Thermal response zones from application of thermal comfort and heat and cold stress standards and guidelines for low activity levels typical of a seated passenger or flight attendant (1.2 MET) and moderate clothing (0.6 clo)

B-1 Percentages of safety incident reports and complaints, by season

B-2 Monthly scheduled passenger enplanements (domestic and international) from January 2022–July 2025 showing increased levels during summer months

B-3 Modeled marginal means and 95 percent confidence intervals by season (winter, spring, summer, fall) and flight phase (boarding, in flight, after landing)

B-4 Distribution of cabin temperatures during boarding and 1 hour after flight

B-5 Distribution of 2Hot2Cold reports across different operational phases

B-6 Temperature range by phase of flight for 2Hot2Cold reports

B-7 NASA ASRS reports by flight phase, stratified by temperature categories

B-8 Effect of delays on aircraft cabin temperatures

B-9 Plots of cabin temperature by aircraft manufacturer during boarding and flight

B-10 Cabin temperature ranges from 2Hot2Cold dataset by airline category

B-11 Cabin environment conditions for Flight F073

B-12 Cabin environment conditions for Flight F031

B-13 Cabin environment conditions for Flight F005

B-14 Cabin environment conditions for Flight F015

B-15 Cabin environment conditions for Flight F009

B-16 Cabin environment conditions for Flight F130

B-17 Cabin environment conditions for Flight F047

B-18 Cabin environment conditions for Flight F018

TABLES

1-1 Changes in Passenger Enplanements by FAA Region, 2004–2024

1-2 OACP and FAA Authorities Related to Safety and Health of Cabin Occupants

2-1 Aircraft Cabin Temperature Design and Operating Requirements

2-2 Contributions of Different Equipment Issues to Thermal Complaint Data from NASA ASRS Reports (1990–2025) and 2Hot2Cold Reports (2018–2025)

3-1 Environmental and Personal Factors that Influence Risks from Thermal Exposures

3-2 Examples of Common Chronic Medical Conditions and Disabilities that Influence Risks from Thermal Exposures

4-1 Subjective Thermal Comfort Scale

4-2 WBGT Adjustment Values for Clothing

4-3 Clothing and Metabolic Rate Values for Case Scenarios Used to Calculate Comfort Limits and Thermal Stress Limits

5-1 Characteristics of Evidence Sources Used by the Committee

5-2 Physical, Cognitive, and Behavioral Symptoms Reported in NASA ASRS Reports

5-3 Summary of Cabin Temperature and Humidity Data from Published Studies

5-4 Summary of Datasets with Raw Cabin Temperature and Humidity Data

6-1 Summary of Factors Affecting Applicability and Feasibility of Existing Temperature and Humidity Standards

A-1 Overview of Committee Information Requests to Aviation Industry Stakeholders

A-2 Overview of Aviation Databases Containing Data Used by the Committee

A-3 Flight Attendant Duties and Metabolic Equivalents Across Flight Phases

A-4 Air Temperature (T_air) and Relative Humidity (RH) Values for Case Scenario 1 Representing a Busy Flight Attendant in Typical Clothing (2.3 MET, 0.6 clo, 0.2 m/s)

A-5 Air Temperature (T_air) and Relative Humidity (RH) Values for Case Scenario 2 Representing a Largely Sedentary Seated Flight Attendant or Passenger in Typical Clothing (1.2 MET, 0.6 clo, 0.2 m/s)

A-6 Upper and Lower Air Temperature (T_air) Limits for Given Relative Humidity (RH) Values for Case Scenario 1 Representing a Busy Flight Attendant in Typical Clothing (2.3 MET, 0.6 clo, 0.2 m/s)

A-7 Upper and Lower Air Temperature (T_air) Limits for Given Relative Humidity (RH) Values for Case Scenario 2 Representing a Seated Flight Attendant or Passenger in Typical Clothing (1.2 MET, 0.6 clo, 0.2 m/s)

A-8 Upper and Lower Air Temperature (T_air) Limits for Given Relative Humidity (RH) Values for Case Scenario 3 Representing a Busy Flight Attendant in Warm Clothing (2.3 MET, 1.0 clo, 0.2 m/s)

A-9 Upper and Lower Air Temperature (T_air) Limits for Given Relative Humidity (RH) Values for Case Scenario 4 Representing a Seated Flight Attendant or Passenger in Warm Clothing (1.2 MET, 1.0 clo, 0.2 m/s)

A-10 Upper and Lower Air Temperature (T_air) Limits for Given Relative Humidity (RH) Values for Case Scenario 5 Representing a Busy Flight Attendant in Cool Clothing (2.3 MET, 0.4 clo, 0.2 m/s

A-11 Upper and Lower Air Temperature (T_air) Limits for Given Relative Humidity (RH) Values for Case Scenario 6 Representing a Seated Flight Attendant or Passenger in Cool Clothing (1.2 MET, 0.4 clo, 0.2 m/s)

A-12 Air Temperature Values Calculated Using ISO Standard 11079 for Different Levels of Metabolic Activity and Relative Humidity

B-1 Summary of Cabin Temperature and Humidity Data from Published Studies

Preface

Well over a century ago, the Wright brothers proved that heavier than air, self-propelled machines could successfully fly. That event in 1903 was followed just over a decade later by the first commercial air flight. Granted, that flight was only 23 minutes long, but it occurred between St. Petersburg and Tampa, Florida, and greatly reduced the 2-hour time it took for an automobile to travel between the two cities. In the following years, commercial air travel developed rapidly, and by 1930 Boeing introduced the first female flight attendant. Ellen Church had convinced the airline of her added value as she was a nurse and could add comfort to the uncertain flying public. Today commercial air flights are so common it is hard to believe that little over a century ago this convenience was a novelty.

Along with the evolution of commercial airflight, there were important risks to consider for both crew and passengers. Among these were risks concerning the air cabin climate (cold temperatures were common and sometimes even heat proved problematic), excessive noise, turbulence, insufficient oxygen along with uncertain air pressure equalization, and, worst of all, fatal equipment failures that resulted in crashes and death. Toward the beginning of commercial flight in the late 1920s there was approximately 1 fatality per million miles flown.

Since those times, the growth of the air industry has been accompanied by a great reduction in these risks. Temperatures are generally comfortable, barometric pressure and oxygen supply are maintained at levels appropriate for human physiology, noise has been markedly reduced, and fatalities have been almost eliminated, being reduced by 99 percent by the late 1950s and by another 99 percent by the early 21st century.

Modern air travel by and large occurs in a well-controlled environment. That environment, however, has been under greater scrutiny as air quality and the overall environment have gained increasing public interest. Earlier this century the National Academies of Sciences, Engineering, and Medicine (the National Academies) was asked to examine air quality in the cockpit and in the cabin for commercial aviation. In the report, recommendations were made on a wide variety of environmental exposures that might present risks to crew or passengers. Interestingly, one environmental topic not addressed in that report was that of temperature extremes, a problem that has become of greater concern as both average temperatures and the frequency of extreme temperature events have been increasing across the United States.

In light of the fact that there has been little organized information about the frequency and degree of exposure to unsafe temperatures during air flight and the possible risks to the public and the cabin crew that might be associated with these exposures, Congress instructed the Federal Aviation Administration (FAA) to commission a National Academies study to address the issue. This report is the product of that effort.

The committee that undertook the FAA’s charge included 13 members selected to represent a broad range of expertise, including mechanical and systems engineering, air cabin health and safety, human systems integration, human physiology, psychology, occupational and pediatric medicine, gerontology, and statistics. The committee had the added advantage that several of its members had experience in the airline industry and were able to bring their practical experience and insights regularly into the discussions. Further, the National Academies provided its own expertise in several areas related to the charge, both through its staff and a National Academy of Medicine fellow, Roxana Chicas. Throughout the committee’s deliberations, there was a willingness on the part of all members to learn from one another, which proved essential as the committee had to chart some new territory in addressing its charge. Ultimately, the committee operated with the wisdom so well-articulated by the eminent epidemiologist and statistician, Sir Austin Bradford Hill:

___________________

¹ Hill, A. B. 1965. The environment and disease: Association or causation? Proceedings of the Royal Society of Medicine 58:295-300.

The committee meetings and deliberations were held entirely virtually, certainly a new experience for me. I had some concerns about chairing a committee entirely online; however, the task became quite a pleasure as a result of the friendly and supportive atmosphere of the meetings. Members volunteered readily for subgroup work, and the collaborative atmosphere greatly benefited the final product. Chairing this committee has been both an education and a rewarding experience.

The committee benefited greatly from the knowledge, administrative skills, and high-quality inputs from the National Academies staff. I know I speak for the committee that this work would not have been possible without the essential organizational inputs and gentle guidance of the study director, Autumn Downey. She was accompanied by a very able staff and their unfailing efforts to assist at every turn.

I want to end this preface with great thanks to and acknowledgment of my fellow committee members, all of whom gave generously of their time in addressing a stimulating and challenging task. We all look forward to ongoing efforts to attend to the health and safety needs of air cabin passengers and cabin crew.

David Wegman, Chair
Committee on Health and Safety Impacts of Aircraft Cabin Temperatures
May 2026

Acronyms and Abbreviations