3.6.4 Downward load. Human tolerance to vertical impact limits the allow-
able forces along the vertical axis of the aircraft and necessitates energy
attenuation. The seat shall have a downward load-deflection curve measured along
the vertical (yaw) axis which falls within the acceptable area on figure 13. After
the seat has stroked through the available stroking distance, the seat bottom shall
be supported on the floor. Type I seat attenuators shall be sized for a normally
clothed individual, and type 11 seat attenuators shall be sized for a combat equip-
ped soldier in accordance with table I.
3.6.5 Upward load. The seat shall have sufficient strength in an upward di-
rection to withstand a load factor of not less than 8.0 parallel to the vertical
3.6.6 Restraint design loads. Strength and elongation properties of the re-
straint shall conform to table II.
3.7 Materials. When specifications and standards are not specifically desig-
nated, selection of materials and processes shall be in accordance with MIL-STD-143.
Materials that are nutrients for fungi shall not be used when it is feasible to
avoid them; where used and not hermetically sealed, they shall be treated with
3.7.1 Flammability and toxicity. Materials which support a self-sustained
combustion, and materials which, when burned or exposed to high temperatures give
off toxic fumes, shall not be used. All seat fabrics and cushions must be
flame resistant and produce the least amount of smoke and toxic gases possible.
Interior materials in all military aircraft shall meet the flammability criteria
specified in Code of Federal Air Regulation (FAR) part 25, section 853.
3.8 Reliability. Because of the emergency requirement of the seat system, prime
importance shall be placed upon the attainment of a high overall degree of relia-
bility. A reliability program shall be established in accordance with MIL-STD-785.
As a part of the reliability analysis, the contractor shall conduct a failure mode
effects and criticality analysis (FMECA) for each seat system component and sub-
system which could, by failing, adversely affect the crash survival of the occupant.
Documentation shall be provided as stipulated on the Contract Data Requirements List
(CDRL), DD Form 1423 (see 6.2.2). Except for fabric parts, the minimum life of all
seat components subjected to normal wear and tear shall be 5,000 hours of aircraft
operation and 5,000 adjustments. Deterioration and wear of fabric parts shall be
limited so as to meet minimum strength requirements after 5 years of use, and pos-
sess shelf life of not less than 30 years.
3.9 Maintainability. The seat shall require no scheduled maintenance other than
the replacement of fabric components. The mean time to repair for both scheduled
and unscheduled maintenance shall be less than 0.2 manhours.
3.9.1 Interchangeability and replaceability. Parts and assemblies of the seat
shall be interchangeable or replaceable in accordance with MIL-I-8500.
Maintenance operations shall not require uncommon tools or special