Seat dynamic evaluation acc. to FAA Advisory Circular

[Chinit0]

Hi everyone, I am reading the FAA Advisory Circular 25.562-1B for dynamic evaluation of seats.
Could someone tell me if the 10°Pitch and 10°Roll deformation of the tracks described in the document is applicable for the wing center tracks too? I am not able to visualize that kind of pitch deformation in a massive beam as in the 747...

Thank you and BR

 

[rb1957]

I think the AC is trying to say that the dynamic loading is such that the the seat attmts have to survive those rotations.

Now remember an AC is (usually) guidance (rather that statutory), it is a generally acceptable method of showing compliance.

If you're saying I've got a situation where these rotations (of the support structure (more on this later) are unreasonable, then propose some alternate demonstration of compliance, like an LS-Dyna analysis and/or full-scale test.

Now I don't know the AC intimately nor the B747, but I'd imagine the the B747 is typical in that it has brownline track attached to some support beam. The rotations I believe apply to the brownline track and not the support beam, or possibly to the seat post that is attached to the brownline track. These sound more realistic deformations.

Now (2) one thing that may happen is because you're talking about the overwing region of the B747, the FAA may say because your massive support beam may/would attract load from the crash itself then they might want to see the combined effect of the MLG crash loads and the 16g dynamic seat. Yes, I understand this is "unusual".

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

 

[der8110]

Yes the requirement applies to all Part 25 aircraft with Certification Bases Amendment 25-64 and after. And most airliners with earlier Cert Bases used in Part 121 operations (date thresholds apply).

As a practical matter, a seat manufacturer is not going to design different seats for above the wing box, and for elsewhere ahead and behind in the cabin.

The requirements were developed as a result of actual crash investigations where floor deformations caused seat legs to fail, injuring passengers and/or trapping them after what was otherwise a survivable accident. The 10 degree pitch and roll of the seat tracks under test is not meant to represent any particular location on an aircraft, or any particular model. Or the 16g-14g-0.09 sec-44 fps requirements; but, they are based on science.

The good news is, most seat manufacturers have features like clevises or U-joints, so the 10 degree deformations hardly strain the seat structure at all. A much higher success rate compared to the very first dynamic seats.