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Introduction
BACKGROUND
In Section 577 of the Federal Aviation Administration (FAA) Reauthorization Act of 2018,1 Congress directed FAA to issue safety regulations specifying minimum dimensions for passenger seats in transport category aircraft, including minimums for seat pitch and width.2 Seat width is measured according to the distance between the armrests of a seat, while seat pitch is the distance between two successive rows of seats, measured from the same points on two seats, one in front of the other. For FAA to regulate seat dimensions, a safety-related reason must be established. It is therefore notable that in Section 337 of the same act, Congress directed FAA to review recent incidents in which passengers evacuated from aircraft to assess the procedures used for evacuation certification demonstration, including the treatment of changes in an airplane’s seat width and pitch.
To respond to Section 337, FAA chartered the Emergency Evacuation Standards Aviation Rulemaking Committee (ARC) consisting of experts and interested parties and charged with reviewing and advising on evacuation system design, testing, and procedures. The ARC conducted its review during late 2019 and early 2020 and issued a final report to
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1 Public Law 115-254.
2 There are no FAA regulations or regulations in other countries requiring compliance with seat dimension minimums. See Porta, J., Saco-Ledo, G., and Cabañas, M. D. (2019). The Ergonomics of Airplane Seats: The Problem with Economy Class. https://www.sciencedirect.com/science/article/abs/pii/S0169814117305607.
FAA in May 2020.3 At about the same time, the Human Protection and Survival Research Laboratory at FAA’s Civil Aerospace Medical Institute (CAMI) initiated a research project at its testing center in Oklahoma City to measure the body size (anthropometry) of a sample of Americans, test their ability to sit in passenger seats configured with different seat pitches, and record the amount of time they required to evacuate from a simulated narrow-body (single-aisle) airplane cabin during a series of trials involving different seat widths and seat pitches. The research project obtained data from measurements and testing of a maximum of 775 people, including 12 days of evacuation trials in the cabin simulator. In January 2021, CAMI documented this research in the report Effects of Airplane Cabin Interiors on Egress I: Assessment of Anthropometrics, Seat Pitch, and Seat Width on Egress4 and accompanying datasets5 and video recordings.6
The specific influence of seat width and seat pitch on an airplane evacuation had not been studied in previous research projects. However, based on consultations of findings from past evacuation research (as explained in the CAMI research project’s documentation submitted to FAA’s Institutional Review Board [IRB] [see Appendix B]), the CAMI researchers hypothesized that seat pitch and width should not affect the time to fully evacuate the cabin because crowding and queuing in the main aisle and at the exit door would be more significant factors. They further hypothesized (in page 1 of the IRB document) that “so long as it was possible for passengers to get into and out of the seat, the rate at which passengers can move from their seats into the main aisle is ultimately immaterial to the evacuation.” CAMI refers to a passenger’s “ergonomic minimum” as the lowest seat dimensions in which the passenger can fit, which can be viewed more practically as the passenger “body size maximum” for the passenger seats in airline service. Because airlines must serve a customer base whose ability to fit into seats of different dimensions will vary widely, the airlines will select a set of dimensions that will accommodate as many passengers as possible when balancing the economic implications of adding more seats to an airplane while not losing too many paying customers.
CAMI reasoned that all passengers, having been able to traverse to and sit in their seats, should also be able to exit the seat and row, and any effect seat width and pitch may have on the time for an individual to exit their seat and row in an emergency will not be relevant to the time required
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3 See www.faa.gov/regulations_policies/rulemaking/committees/documents/media/Emergency%20Evac%20Standards%20ARC%20final%20report%20final%20(5-26-2020).pdf.
4 Weed, D. B., et al. (2021). Effects of Airplane Cabin Interiors on Egress I: Assessment of Anthropometrics, Seat Pitch, and Seat Width on Egress. https://www.faa.gov/sites/faa.gov/files/2022-04/Effects_of_Airplane_Cabin_Interiors_on_Egress_I.pdf.
to fully evacuate the cabin due to the bottlenecks arising from these other queues. This hypothesis ultimately shaped CAMI’s design of the experiments and the analyses of the collected data. Based on the experiments, CAMI concluded that if passengers can sit in their seats, then a transport airplane’s seat pitch and width should not influence the flow of an airplane’s evacuation as a whole. Furthermore, based on the results of these experiments, CAMI researchers extended the scope of the conclusions to include 99% of the U.S. population, stating that “this study examined the previously mentioned ergonomic minima and found that the experimental seat pitches, which are similar to the seat pitches currently found on flying commercial large transport category aircraft, should provide protection and not impede egress for 99% of the general U.S. population.”
In addition, CAMI maintains that this conclusion is consistent with results from previous evacuation research examining airplane interior configurations.
In March 2022, FAA issued a report to Congress responding to the Section 337 directive.7 The report, which was informed by the results of the ARC review and CAMI research project, includes the following observations:
- With respect to evacuation certification of transport-category aircraft, there have been no relevant changes to passenger seating configurations, including changes to seat width, padding, reclining, size, pitch, leg room, and aisle width; and,
- With regard to assumptions and methods used in evaluating evacuation standards, regulatory standards that have prescriptive or dimensional requirements may become out of date as population demographics or technologies evolve.8
In response to Section 577’s directive for FAA to issue safety regulations specifying minimum dimensions for passenger seats, FAA also issued a request for comments in the Federal Register, titled “Minimum Seat Dimensions for Safety of Air Passengers (Emergency Evacuation).”9 Specifically, the public was invited to consider both the ARC review and the CAMI research report when commenting on whether the width, pitch, or other dimensions of airline seats could adversely affect the ability of passengers to safely evacuate an airplane during an emergency. Following a 3-month
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7 Report to Congress: Aircraft Cabin Evacuation Procedures, FAA Reauthorization Act of 2018 (Public Law 115-254)—Section 337, March 31, 2022. https://www.faa.gov/sites/faa.gov/files/2022-03/PL-115-254-Sec-337-Aircraft-Cabin-Evacuation-Standards.pdf.
8 See page 6, https://www.faa.gov/sites/faa.gov/files/2022-03/PL-115-254-Sec-337-Aircraft-Cabin-Evacuation-Standards.pdf.
9 See https://www.regulations.gov/document/FAA-2022-1001-0001.
comment period, FAA received more than 26,000 comments to the notice, including many comments raising concerns about the research protocols, particularly the composition of the study test group used in the evacuation trials.10
Comments about the CAMI research methods and conclusions were both supportive and critical. The airframe manufacturer Airbus maintained that the research results were consistent with its experience conducting evacuation tests for certification purposes, which the company reported had not shown that variations in seat width and pitch (as low as 16.5 inches and 28 inches, respectively) affect the ability of passengers to move into the longitudinal cabin aisle for evacuation. Likewise, Airlines for America, an airline trade association, commented that CAMI’s findings were consistent with reports of industry evacuation tests showing that the time required for passengers to get out of their seats, even when seats are relatively narrow and close together, is shorter than the time required for the emergency exits to begin functioning and for the line that forms in the aisle to clear by exiting passengers.
Many of the commenters who were critical of the CAMI research questioned the selection of the study test group that participated in the evacuation trials. Six U.S. Senators maintained that the group did not accurately represent the flying public because recruited participants were limited to able-bodied 18- to 60-years-olds. Likewise, 24 members of the U.S. House of Representatives raised concern about the eligibility age limits and the study test group’s lack of participants who are extremely overweight and have disabilities. The Paralyzed Veterans of America, the Human Factors and Ergonomics Society, and several unions representing airline pilots and flight attendants questioned the omission of participants who are older than 60 or under the age of 18, have mobility and sensory limitations (sight, hearing, cognitive), or are severely obese. These and other commenters also pointed to other realistic conditions not considered in the CAMI research that could interact with seat pitch and width to affect evacuation times, including passengers sustaining impact injuries, the presence of service animals and pets in the cabin, the obstacles created by personal items, reclined seats, and varied footwear.
Some commenters also questioned CAMI’s decision to exclude from the evacuation trials recruited participants who were judged based on pre-trial seat experiments that they could not sit in a seat configured with a 28-inch seat pitch, which was the narrowest used in the trials. These participants were disqualified because they would not be able to sit in the seats configured at this pitch during the evacuation trials and under the assumption that they, likewise, would not be able to sit in a seat having this pitch if
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10 See FR Doc. 2022-16565.
encountered in an actual airplane. Regarding this pre-trial testing, the Airline Pilots Association commented that passengers are not screened in advance for their ability to sit in an airplane’s seats, while the Airline Flight Attendants Association pointed out that large passengers do find a way to sit in narrow seats, even if with considerable difficulty.
In correspondence with members of Congress, the FAA Administrator acknowledged that the CAMI trials relied on able-bodied adult subjects under age 61, consistent with safety and ethical standards for human subjects testing, and thus characterized the research as providing “useful, but not necessarily definitive information, regarding the effects of seat dimensions on safe evacuations for all populations.”11
Regarding the 2018 law’s Section 577 directive for FAA to issue regulations specifying minimum seat dimensions, the agency had not made a final determination based on the ARC review and CAMI research when the next FAA Reauthorization Act was enacted on May 16, 2024. It is therefore notable that in Section 365 of the more recent act, Congress again directed FAA to study the effectiveness of existing evacuation certification test procedures for assessing the ability of passengers to evacuate from a transport-category airplane. The law calls for FAA to consider a range of factors that may be relevant to such a study, including passenger age, weight, and height; travelers with disabilities; and passenger space and seat size and pitch.
REQUEST FOR THIS REVIEW OF CAMI’S RESEARCH
A few months after the enactment of the FAA Reauthorization Act of 2024, CAMI’s leadership asked the National Academies of Sciences, Engineering, and Medicine to convene an expert committee to conduct an independent peer review of its evacuation research project, as documented in the 2021 report, datasets, and video recordings. Specifically, CAMI requested a review that would first consider the goals and objectives of the research and then assess whether the experimental research methods, design, and procedures were appropriate to meet those goals and objectives, including the research team’s selection of a study test group and choices about the seat pitch and width dimensions for testing. CAMI also wanted this peer review to consider whether the conclusions reached from the research are supported by the evidence, and whether the research adhered to accepted scientific principles, including for human subjects research. Based on this review, the committee was asked to make recommendations to FAA, as
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11 Steve Dickson, FAA Administrator, correspondence with Senator Maria Cantwell, Chair, Committee on Commerce, Science, and Transportation, March 31, 2022. https://www.faa.gov/sites/faa.gov/files/2022-03/PL-115-254-Sec-337-Aircraft-Cabin-Evacuation-Standards.pdf.
appropriate, regarding the interpretation and use of the research data and analytic results. The specific language of this study charge, or Statement of Task, is provided in Box 1-1.
STUDY APPROACH AND REPORT ORGANIZATION
To conduct the requested study, the National Academies convened a committee of six experts in experimental design, human factors, ergonomics, anthropometry, human subjects research, and aircraft evacuation testing. The committee was expected to review the published report, video recordings, and other documentation from the CAMI research project, meet with the principal investigators from the institute’s Human Protection and Survival Research Laboratory who designed and conducted the research, and consult the technical literature and research reports on airplane evacuation testing and demonstration.
This report documents the committee’s assessment. In keeping with its charge, the committee first reviewed the research project’s stated objectives, or questions to be addressed, for clarity and coherence. These objectives were then considered given CAMI’s research hypothesis, as stated in IRB documentation, that an airplane evacuation flow as a whole should not
BOX 1-1
Statement of Task
An ad hoc committee will conduct a peer review of the Federal Aviation Administration’s (FAA’s) report and accompanying data, including videos, documenting tests performed during 2019 and 2020 to determine the effect of passenger seat pitch and width on the egress time of cabin occupants during an emergency evacuation of a commercial airplane.
The committee will review the goals and objectives of the research, and then consider whether:
- The experimental research methods, design, and procedures were appropriate and sound, including how tested individuals and passenger seat dimensions were selected given the anthropometric makeup of air travelers and actual seat dimensions in commercial airplanes.
- The conclusions drawn and reported in the research documentation are supported by the test results.
- The research adheres to accepted scientific principles to include requirements for human subjects research.
The committee will issue a report on its review and may make recommendations to FAA, as appropriate, regarding the use of the experimental research.
be affected by seat width and seat pitch when these dimensions do not violate the “ergonomic minimums” of passengers, which is interpreted by CAMI as the ability of a passenger to sit in a seat, or alternatively (when considered in terms of the seats available on the airplane), the maximum body size that a given seat dimension can accommodate. Consideration is then given to the composition criteria for the single study test group that was formed for the project’s data collection experiments, each of which is then reviewed in detail. In keeping with the Statement of Task’s interest in advice “regarding the use of the experimental research,” the committee offers its thoughts on how well the project’s design satisfies the interests of policymakers who are concerned that seat space on airplanes is becoming too small as Americans are becoming larger to the potential detriment of airplane evacuation performance.
The remainder of this report is organized into three chapters. Chapter 2 provides background information and a descriptive summary of the CAMI research project’s stated objectives; study design for data collection, presentation, and analysis; reported results and conclusions, and acknowledged limitations. Chapter 3 provides the committee’s critical review of the research. The review seeks to fulfill the study’s charge, which calls for an assessment of whether the project’s objectives and research methods, design, and procedures are appropriate and sound. Because the charge also calls for the committee to consider how the results of CAMI’s experimental research may be used, the chapter concludes by assessing the project’s usefulness for addressing the policy and legislative interests that prompted FAA to commission the work in the first place. Key findings from the critique that pertain to the request in the Statement of Task are summarized in Chapter 4 followed by recommendations on steps that CAMI should take to analyze the collected data in ways that may yield additional insights, as well as ideas for extracting more information from the project’s raw data, conducting supplemental experiments, and designing of subsequent studies that could be helpful for assessing the effects of seat width and pitch on airplane evacuations.
Before proceeding, it merits noting that the committee was confused by uses of the terms “egress” and “evacuation” almost interchangeably and without distinction in the CAMI report. A key distinction, in the committee’s view, is that “egress” is akin to the normal exiting of passengers from an airplane cabin, whereas “evacuation” implies exiting during an emergency. For this reason, “evacuation” is used throughout this report (e.g., referring to “evacuation time” rather than “egress time”), except when text is quoted directly from the CAMI report or when egress is used in reference to something other than an evacuation (e.g., egress space between seats).
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