25.603 in application for secondary structure

[irq]

Hello,

The interpretation of the paragraph § 25.603 Materials regarding primary structure was discussed here: thread2-45169. What about secondary structure like interior: baggage compartments, wall panels, lining panels? Is there 25.603 especially point c) applicable? It says "take into account the effects of environmental conditions, such as temperature and humidity, expected in service". RTCA DO-160 is very often referenced regarding environmental conditions expected in service. The main question - is it applicable to interior panels? Originally the document was aimed to create the environmental conditions for electrical equipments, today it is used as a main standard for all components. The operating conditions like -15° or +55° or in extreme case even -55° to +85° seems to me very critical and unrealistic for interior components.

What approach do you recommend to cover 25.603 c)? Are the material data under RT/Ambient enough for the application I mentioned? Probably not, the certain moisture or elevated temperature impact is still expected. The question is how to quantify them covering the paragraph and not build the parts to heavy. What range of temperatures/humidity conditions should we subjected when components 1)operating (=in flight) 2) not operating (=grounding)?

irq

 

[rb1957]

DO160 is applicable to electricial boxes, not interior components.

your interior components are secondary structure so whilst they don't cerry primary loads they do need to be durable enough for in-service loads. so how do you define in-service loads ? however you want to; if the components degrade and need to be replaced your customer won't be very happy.

of course there are many other requirements of interiors ... flam/smoke, vibration, and general appearance (remember the interior panels are one of the main things that the passengers see ... if they look like crap, well, that doesn't inspire confidence.)

Quando Omni Flunkus Moritati

 

[SWComposites]

Is RTA adequate? Probably not. Call your cert agency and discuss with them. What are realistic temperatures during which critical loads could occur? - you should be able to sort this out or get from the a/c oem.

 

[Sparweb]

You may want to look at Mil-Hdbk-17 anyway, even if the materials you intend to use are probably not in there - it's just to give you an idea what to ask for when talking to your vendor about this. It provides material properties data at various combinations of temperature and humidity, there is much discussion in the preamble/introduction before the data tables.
The RTCA testing standard is really meant for electronics, so it won't help much for structural materials.
Even the related Mil-STD-810 is probably not going to help much, but I'd take a quick look - it is much broader than many other environmental testing standards.

Will the aircraft cargo compartment be heated when flying at altitude? What altitude (implying what ambient temperature it is up there) is its service ceiling? Will the aircraft in question operate north of the arctic circle? Or south of the antarctic? Will it operate between the tropics? The aircraft flight manual will have operating temperature limitations, for a start, and all of the ground conditions have to be realistic, considering the possible locations where the aircraft will take off/land. I've seen enough STC's to have encountered some where temperature limitations were imposed due to the limitations of materials or equipment inside the aircraft. Seen it more than once. You definitely don't want that.

Doesn't the guidance and policy material from the FAA (referenced in the thread you linked) address this subject specifically?


STF

 

[stressebookllc]

§ 25.603 Materials.
The suitability and durability of materials used for parts, the failure of which could adversely affect safety, must—

(a) Be established on the basis of experience or tests;

(b) Conform to approved specifications (such as industry or military specifications, or Technical Standard Orders) that ensure their having the strength and other properties assumed in the design data; and

(c) Take into account the effects of environmental conditions, such as temperature and humidity, expected in service.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-38, 41 FR 55466, Dec. 20 1976; Amdt. 25-46, 43 FR 50595, Oct. 30, 1978]

Wall panels ceiling panels etc. are generally made from honeycomb materials (nomex, aluminum panels etc.) and are not severely affected by normal operating temperatures or humidity. Unless it is totally soaked in water for extended periods of time. In which case there may be appropriate knock down factors for that. Generally these knock down factors are determined by environmental tests. For cargo compartment metal components, mostly made from Al alloys, this should be covered with fitting factors. If you have redundant load path, then B-Basis may be acceptable, otherwise A-Basis is required in addition to fitting factors.

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