November 6th, 2001

Anthropometry and Ergonomics in Airline Seating

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A recent study concludes that economy-class air passengers do not have adequate space to assume a correct “brace” position for emergency landing, and the seats themselves can be obstacles to quick emergency evacuation of the cabin.

The purpose of the study was to ensure that seating standards are such that passengers would be able to quickly evacuate an aircraft in the event of an emergency. Thus, the study considered seating accommodation against expected population body dimensions. The health implications of aircraft seating were also considered, specifically the occurrence and prevention of Deep Vein Thrombosis (DVT). Comfort aspects of aircraft seating did not form part of the research study.

The study “Anthropometric Study to Update Minimum Aircraft Seating Standards” was initiated by the Joint Aviation Authorities (JAA) under the United Kingdom (UK) Civil Aviation Authority (CAA) funding. It found that the current minimum spacing and design standards for transport-category aircraft allow for too-tight seating, and new standards are needed regarding minimum seat width and a minimum area for feet. Specifically it cites that the CAA’s minimum dimensions need to be expanded by at least 3 inches in terms of seat pitch, or the space between rows of seats, and by as much as 10 inches to more adequately accommodate tall people.

The CAA is currently the only regulatory body to prescribe minimum seat-space dimension. The U.S. Federal Aviation Regulations (FAR) contain requirements for head impact protection, maximum G- loading, damage tolerant single load paths and so forth – but no minimum seat spacing requirements. CAA Airworthiness Notice 64 (AN64) “Minimum Space for Seated Passengers” regulates the minimum seat space dimensions for all UK registered aircraft over 5700kg MTWA which carry 20 passengers or more. Minimum safety requirements were set out using anthropometric data for 5th percentile female and 95th percentile male values which aimed to minimize the effects of lower seat pitches upon the quality of seat occupancy and the ease of egress from the seats. AN64 includes 3 minimum space requirements:

Dimension Description Minimum
A The minimum distance between the back support cushion of a seat and the back of the seat or other fixed structure in front 26 inches
(660mm)
B The minimum distance between a seat and the seat or other fixed structure in front. 7 inches
(178mm)
C The minimum vertically projected distance between seat rows or between a seat and any fixed structure forward of the seat. 3 inches
(76mm)

While AN64 is definitely going in the right direction, the study found it deficient. Finding that dimensions A, B and C are critical, but the current minima need to be increased. As AN64 is based on the 5th-95th percentile of passenger sizes, at least 10% of passengers will not be accounted for. When designing a seating system for safety, the minimum dimensions should account for the 1st – 99th percentile of passenger sizes. Even this range would not include children, people with disabilities, and it would “design out” about 1-in-100 passengers.

The study finds:

The current requirement for dimension A will only accommodate up to 77th%ile of the European population (based on buttock-knee lengths). Dimensions B and C will accommodate even fewer passengers (based on whole-body depth measurements).”

It is recommended that dimension A (seat back cushion to back of seat in front)
be increased to at least 711mm (28.2″) to accommodate up to the 95th %ile
European seated passenger (minimum recommendation). The ideal recommendation would be to increase dimension A to at least 747mm (29.4″ – 99%ile world).”

Dimensions B (seat base to back of seat in front) was also found to be inadequate for both larger and smaller passengers.
The depth of a 95%ile passenger’s thighs is greater than the 178mm (7″) current minimum and the vertical clearance of 76mm (3″) requires that passengers move in a semi-crouched, unbalanced, posture increasing the likelihood of tripping especially when trying to move from the seat quickly. The smaller passenger may be disadvantaged because Dimension B does not allow sufficient clearance for their lower buttocks.
Dimension B may be better expressed as two separate values. Between 230mm
and 255mm (9 and 10 inches) would be an acceptable minimum for dimension B
at armrest level and a minimum of 210mm (8.3″) would be acceptable at cushion
level.

Dimension C would need to be increased from the current 3″ (75mm) to 12″ (305mm) to permit a 95%ile passenger to stand upright.

Foot space, foot rests, alternative seat design, seat cushions, armrests, and tray tables were also addressed.

To meet the report’s recommended standards, entire rows of seats on current aircraft would have to be removed and, depending on the aircraft, at least one seat per row would have to be removed to provide adequate seat width. One account suggests that as many as 100 seats would have to be removed from the economy sections of airplanes now in service, particularly those aircraft – primarily in charter service – featuring “high density” seating.

A single row of six seats in an aircraft, with four of them filled on average per flight, can generate up to $8 million in ticket revenue over a 20-year period. Consequently, if seats were removed to meet expanded minimum space requirements, ticket prices might increase upwards of 25 percent. The counter argument is that while passengers are attracted to low fares, these fares are only made possible by a seating density that could compromise safety.

The full report, “Anthropometric Study to Update Minimum Aircraft Seating Standards,” can be found at http://www.ice.co.uk/transport/pubs.htm .



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