Summary
This report presents a peer review of a research project conducted by the Federal Aviation Administration’s (FAA’s) Civil Aerospace Medical Institute (CAMI) to assess whether airplane evacuation times can be affected by variations in passenger seating space, and particularly the dimensions of seat width and seat pitch. As delineated in the CAMI study, seat width is the distance between the inner edges of the arm rests, while seat pitch is the distance between two seats, one in front of the other, measured from the same point on each seat. CAMI requested this review because of FAA’s interest in knowing whether the project’s results may be informative to pending decisions about whether to regulate the width and pitch of passenger seats. Of concern is that constrained seat space may interfere with cabin evacuations during an emergency, especially because the average body size (e.g., girth, weight) of Americans has been increasing. While FAA has the authority to regulate seat dimensions and configuration for any reason having a safety basis, such as to protect passengers from hazards in flight, this review focuses solely on the CAMI research project and FAA’s interest in understanding whether constrained seat space may impede evacuations for the purpose of informing its regulatory determinations. In this regard, the findings from the review suggest that CAMI’s research project does not provide the information needed for the proposed purpose. The project’s fundamental shortcoming is that it does not directly assess how seat width and pitch interact with passenger body size variables to affect evacuation performance, and especially for plausible scenarios in which the number and concentration of people with large body sizes on a flight may differ from the pattern for the flying public generally.
BACKGROUND AND OVERVIEW OF THE CAMI PROJECT
Concerned that airline passenger seat space may be becoming too small as Americans are becoming larger on average, Congress has on multiple occasions directed FAA to consider prescribing minimums for seat width and pitch, particularly if constrained seat space can be shown to hinder emergency evacuations.1 Indeed, Congress most recently directed FAA to consider such regulatory interventions in the FAA Reauthorization Act of 2024.2
As part of its response to these concerns, FAA commissioned a CAMI research project, which consisted of a series of seat experiments and evacuation trials intended to assess the effects of seat width and pitch on the time required to fully evacuate an airplane cabin. The project’s objectives, methods, and results were documented in the 2021 report Effects of Airplane Cabin Interiors on Egress I: Assessment of Anthropometrics, Seat Pitch, and Seat Width on Egress.3
As a first step in its study, CAMI recruited a test group consisting of 775 individuals intended to be broadly representative of the U.S. public and by inference representative of U.S. air travelers. Researchers took anthropometric, or body size, measurements of participants and then tested them for their ability to sit in a seat configured to the narrowest seat pitch (28 inches) currently in airline service and one that is even narrower (26 inches). The experiments were conducted using 17-inch-wide seats, which survey data indicated is common in airline service, although some seats are deployed with smaller widths (e.g., 16-inch-wide seats). Based on participant feedback from the experiments, CAMI determined that the tested 26-inch pitch would likely be too narrow to be practical for airline service, and thus in subsequent evacuation trials the test group participants were timed on their ability to evacuate a simulated airplane cabin when sitting in seats having a pitch as narrow as 28 inches when compared with seats having larger pitches (32 and 34 inches). Seat widths were varied, with some trials using seats having 18-inch widths and others using seats having 16-inch widths.
Citing previous evacuation research, CAMI hypothesized that the time to fully evacuate the cabin would not be slowed by constrained seat width and pitch because the time passengers spend queuing at the exit door and in the main aisle is greater than the time required for a passenger to exit the seat and seat row. CAMI reasoned, therefore, that because all passengers
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1 Sections 337 and 577 of the Federal Aviation Administration Reauthorization Act of 2018.
2 Section 365 of the Federal Aviation Administration Reauthorization Act of 2024.
3 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.
onboard an airplane could get into their seats, they should be also able to get out of their seats, and that any additional time required to do so because of limited seat space should not affect the evacuation flow overall. After analyzing the trial time data, CAMI concluded that the results were consistent with this hypothesis, finding that variations in seat width and pitch did not affect the time to evacuate the cabin fully even though individual study participants with larger body sizes did tend to evacuate more slowly.
When CAMI’s research report was released and FAA invited public comments, the project’s experimental methods garnered criticism, particularly regarding the composition of the study test group. Although CAMI strived for a test group that was broadly representative of the U.S. public, study safety concerns meant that individuals under the age of 18, older than 60, and with physical limitations would need to be excluded from the evacuation trials. Because individuals having such excluded demographics are common on airplanes, commenters questioned whether the results of the trials were sufficiently relevant to inform regulatory decisions.
FINDINGS AND RECOMMENDATIONS
Because CAMI’s evacuation research project was conducted to inform potential regulatory decisions about passenger seat dimensions, the institute’s leadership asked the National Academies of Sciences, Engineering, and Medicine to convene an expert committee to conduct this independent review of the project and its relevance to such decisions.
The review surfaced several technical issues related to the project’s design, experimental setup, and analytic methods. Some of the identified issues, which are detailed in Chapter 3, can be addressed by reanalyzing the data already gathered from the experiments and by extracting more information from the video recordings of both the seat experiments and evacuation trials. Indeed, the committee recommends a series of steps for this purpose that would not require substantial additional time and effort but could potentially provide researchers with more insight into how seat space and body size may interact to adversely affect evacuation performance. Several steps are recommended for this purpose and detailed in the report’s final chapter, including a reexamination of the results by including the times of participants who were excluded from the original analyses, by comparing the evacuation times for the individuals seated in the same aisle seats during successive trials, and by examining trial data from the first and second trials conducted by each cohort of participants, in all cases looking for patterns related to the demographics and body size of participants. Other recommended steps would involve more granular analyses of the project’s raw data, such as by reviewing the videos to extract information
about the time required for passengers with different body sizes to exit their seats and row, which could be useful to evacuation computer modeling.
However, the benefits from pursuing these recommended steps will be limited and largely prospective by informing and providing data for future research and modeling on evacuation performance and seat design. This is because, as explained next, CAMI’s study was not designed to reveal the effects of passenger body size and seat space on the time required to evacuate an airplane. The study results, even when reanalyzed and augmented with more extracted data, will be insufficient to establish if constrained seat space is immaterial to evacuation performance, but they may be useful for understanding any deleterious effects on evacuation performance. Indeed, the committee finds that the key conclusion in CAMI’s report that current airplane seating configurations should not impede the evacuation of 99% of the general U.S. population is not supported by the design and results of the research project. To make such a definitive claim, CAMI would need to undertake an extensive series of additional evacuation trials or combination of seat row exit trials and computer-based evacuation simulations that specifically take passenger body size into account as an independent variable.
As noted above, soon after the project was completed, the design of the CAMI study was criticized because the test group was intended to resemble the U.S. public generally but excluded individuals having certain demographics (e.g., individuals with disabilities, individuals with mobility limitations, and older than 60 years of age). In the committee’s view, the concerns expressed about the representativeness of the test group are valid, but the exclusions were understandable to ensure participant safety during the evacuation trials and they were supported by CAMI’s Institutional Review Board. Nevertheless, the committee finds that CAMI could have done more to manage demographic biases in the recruited test group, which skewed young. CAMI’s recruitment methods should have been designed to counter such sampling bias, which can arise from the way candidates are identified, approached, and respond to invitations to participate in the research.
It is understandable that CAMI wanted to form a test group that could represent air travelers generally because the seat experiments were aimed at determining the lowest seat pitch that could be practically implemented by airlines serving the general public. Based on these experiments, CAMI justified not including seats configured with a 26-inch pitch in its evacuation trials because about 8% of participants in the seat experiments reported they could not sit in the seat, which suggested that a seat pitch this narrow would not be viable for airline service. While this reasoning may hold, the committee questions the reliability of this experimental method, which involved self-reporting by participants without objective decision criteria or assessments of the videos for verification. Accordingly, it remains an open
question whether the 28-inch pitch tested in the evacuation trials is indeed the practical minimum.
More problematic in the committee’s view is CAMI’s decision to use the same test group for the evacuation trials as the one used in the seat experiments. While the test group was intended to be broadly representative of the public, one might have expected researchers to have employed different criteria for the group participating in the evacuation trials. For example, a test group consisting of a disproportionate number of individuals with large body sizes (even if limited in their age range and mobility levels for safety concerns) would have been more appropriate given the underlying concern that declining seat space and the prevalence of more passengers with larger body sizes could interact to have negative effects on evacuation performance. Evacuation trials using a test group that skewed larger in body size variables such as girth, weight, and height could have stress tested CAMI’s hypothesis that a passenger’s seat and row exit time should not affect an airplane’s overall evacuation time. Such a test group would have also provided opportunities to design trials that not only manipulated seat width and pitch but also that purposefully varied the number and seating locations of passengers with large body sizes.
The committee observes that CAMI’s evacuation trials did indeed indicate that some body size variables (i.e., girth and knee-to-floor distance) can affect individual evacuation times. CAMI acknowledged in the conclusion to its report that even if seat space remains unchanged, passenger size and shape may change enough in the future to become unfavorable to safe evacuation. The implication from this acknowledgment is that if increasing percentages of the passengers on flights have large body sizes in the future, this might lead to interactions by passengers with one another and with seat dimensions that slow evacuation time, an outcome inconsistent with CAMI’s hypothesis that seat and row exit times are immaterial to evacuation flow. However, CAMI should have recognized that the demographic and physical profile of passengers on individual flights will not necessarily match the profile for U.S. air travelers generally, and thus some U.S. flights today may already have these unfavorable conditions.
Accordingly, the committee believes CAMI missed an opportunity to directly address policymaker concerns about the changing body size of Americans in relation to seat width and pitch. While the steps recommended by the committee to reanalyze the results of the research and to extract additional data from the videos could prove useful for informing follow-on research, CAMI’s study design was not suited fundamentally to address these policy interests. Additional and more involved work, potentially using some of the data collected in CAMI’s study, will be needed for this purpose. The final chapter of this report, therefore, describes alternative research designs
for CAMI and others to consider, including designs for small-scale studies and new evacuation trials and computer modeling simulations. Knowing that FAA has an immediate interest in determining whether regulatory interventions for seat space may be warranted, these designs are offered as ideas for CAMI to consider, as opposed to a recommended research agenda, recognizing that additional time and resources would be required to pursue them.
