Seat installation

[Salazar.aviation]

Hi all,

We're having an internal debate about seat static test load factors.

Does anyone knows if the 1.33 fitting factor applies to the 4g side load case or is it already included in 4g (3g x 1.33)? This is to substantiate the seat attachment to the aircraft.

Thanks,

Andres

References
TSO-127
AS8049
14 CFR 25.561, 25.785

 

[rb1957]

I would add it, I think the 1.33 already applied (to the load) is a seat factor.

I'm more used to seeing 1.15 as fitting factor.

another day in paradise, or is paradise one day closer ?

 

[Salazar.aviation]

yeah typical fitting factor is 1.15. In this case, per 25.785 (f)(3) 1.33 applies.

It's just not clear if the particular 4g side load case already includes this factor or it needs to be added on top. Typical 25.561 side load is 3g. Hence, for seats, using 4g = 3g x 1.33.

Thanks,

Andres

 

[rb1957]

yeah, that's what I meant with "seat factor". 561 and 785 produce 4g load, then add a 1.15 FF.

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

Concur with RB...

Per MIL-A-8865 seating load factors are ultimate...

Any fitting factor to be applied in the design/analysis [IE: 1.15X, 1.25X, 1.33X, 2.00X(typ for castings), etc] is over/above the ultimate [limit x 1.5] load factor.

Regards, Wil Taylor

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[Salazar.aviation]

the ambiguity here is that the TSO-127 which refers to the AS8049 specifies that for the side load case 4g already includes the 1.33, so no need to go higher than 4g.

The is also specified by EASA in CS 25.785. So it`s still not clear if it should be 3g x 1.33 (=4g) OR 4g x 1.33?

 

[rb1957]

I'd say don't mix your standards. If you're certifying to a TSO then use the 4g load specified. If certifying to the FARs then you have 561 and 785 to give you a 4g (ultimate) load.

When analyzing the fittings I would probably add the 1.15 fitting factor ... sure there's an argument not too, but what's to cost of including it ? <1 lb of Al ??

I would not include Ultimate FoS (as I think Will is suggesting, apologies if I got this wrong) as 561 (and presumably TSO loads) are already ultimate.

another day in paradise, or is paradise one day closer ?