B737 passenger seats
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From: UK
B737 passenger seats
This question relates to Boeing 737 passenger seats. Does anybody know if the seat backs are designed to stay rigid or crumple forward on impact? Or does it vary from aircraft to aircraft within the B737? Any info would be much appreciated. Thanks, Russell Eaton
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From: various places .....
A little more complex than your question might suggest.
While your interest is in the wonderful fluf machine, the certification considerations, except for minor variations associated with Type and Model specific envelope loadings, are common to airline aircraft seating generally.
Older seats on airline aircraft often had a seatback "break forward" capability controlled by a torqued friction washer assembly or similar to reduce headstrike impact levels on a rather arbitrary basis. In addition, layers of crushable or otherwise deformable load spreading structure (typically high density foam assemblies and referred to as "delethalisation") similar to what one might find on the dashboard of a motorcar were used to reduce head loading a little further.
The problem with this stuff is that the force-deflection characteristics are generally non-linear with the cushioning effect reducing as the impact severity increases .. the reverse of what would be desirable. Some of the crushable foil assemblies were far more linear in their characteristics.
Smaller GA Types, especially, often had rigid backs with delethalisation padding. Many such aircraft were, and still are, nightmares from the point of internal survivablility.
Structural assessment for the older standards was based on static load carrying capabilities and determined by a combination of calculation and test. Survivability considerations were not all that high on the agenda.
Current standards follow the motorcar dynamic impact requirements with a definite interest in survivability and, in respect of blunt impact to the head, there is a formal requirement to assess such impacts on a rational, quantitative basis. While the specifics differ according to the class of aircraft, the basic philosophy is common.
There may be specific design aspects (including things like crush, plastic deformation, and stroking elements) to the seat which are critical to successful test performance and, more importantly, the upholstery and the total relationship of the seat and its surroundings (including the seat or the bulkhead in front of the passenger) becomes a part of the design compromise process.
A significant maintenance problem arises now, in that the current standard seat requires detailed attention to maintenance to maintain the crashworthiness inherent in the design. If you replace the upholstery, for instance, with an assembly having different impact characteristics then that might invalidate the original test results upon which the certification is partly based as loadings on the test dummy are critical to the assessment.
Current seat designs are subject to quite a severe dynamic impact test regime which is particularly critical in the case of lapbelt restraint only ... the usual marketing limitation imposed for the design of most seats in aircraft. Upper body restraint makes life a bit easier for the manufacturer in some aspects but doesn't cause the problems magically to disappear.
While your interest is in the wonderful fluf machine, the certification considerations, except for minor variations associated with Type and Model specific envelope loadings, are common to airline aircraft seating generally.
Older seats on airline aircraft often had a seatback "break forward" capability controlled by a torqued friction washer assembly or similar to reduce headstrike impact levels on a rather arbitrary basis. In addition, layers of crushable or otherwise deformable load spreading structure (typically high density foam assemblies and referred to as "delethalisation") similar to what one might find on the dashboard of a motorcar were used to reduce head loading a little further.
The problem with this stuff is that the force-deflection characteristics are generally non-linear with the cushioning effect reducing as the impact severity increases .. the reverse of what would be desirable. Some of the crushable foil assemblies were far more linear in their characteristics.
Smaller GA Types, especially, often had rigid backs with delethalisation padding. Many such aircraft were, and still are, nightmares from the point of internal survivablility.
Structural assessment for the older standards was based on static load carrying capabilities and determined by a combination of calculation and test. Survivability considerations were not all that high on the agenda.
Current standards follow the motorcar dynamic impact requirements with a definite interest in survivability and, in respect of blunt impact to the head, there is a formal requirement to assess such impacts on a rational, quantitative basis. While the specifics differ according to the class of aircraft, the basic philosophy is common.
There may be specific design aspects (including things like crush, plastic deformation, and stroking elements) to the seat which are critical to successful test performance and, more importantly, the upholstery and the total relationship of the seat and its surroundings (including the seat or the bulkhead in front of the passenger) becomes a part of the design compromise process.
A significant maintenance problem arises now, in that the current standard seat requires detailed attention to maintenance to maintain the crashworthiness inherent in the design. If you replace the upholstery, for instance, with an assembly having different impact characteristics then that might invalidate the original test results upon which the certification is partly based as loadings on the test dummy are critical to the assessment.
Current seat designs are subject to quite a severe dynamic impact test regime which is particularly critical in the case of lapbelt restraint only ... the usual marketing limitation imposed for the design of most seats in aircraft. Upper body restraint makes life a bit easier for the manufacturer in some aspects but doesn't cause the problems magically to disappear.
Last edited by john_tullamarine; 9th April 2002 at 00:34.
