HIC and setback
HIC and setback
(OP)
Hi,
I'm engineer in a company in France which provides modification and certification on aircraft.
For a Cabin Modification on an Emb175, we installed a table in front of a VIP Seat.
We place the table in accordance with the Seat Install Manual :
I quote :
" For double seat, installation aft of any monument must have a minimum setback of 22.86" in case no HIC substantiation is available. For Setbacks below 22.86", installer must provide substantiation for 14 CFR 25.562(c)(5) compliance. This setback accounts for the 50th %ile ATDs"
So we kept a setback of 24" for the installation.
But, when we sent our certification program to EASA, we receive this answer :
"The supporting data they obtained from the seat manufacturer lists a set-back for seats behind interior installations (use for front row seats). The data is only covering 50%tile occupant size. The seat behind a table is not accepted as a front row seat. The clearance shown in the drawings is 24 inches while the minimum acceptable would be 25.86inches."
Can someone explain me why should we take a setback 3"-superior to the setback in the Installation Manual ?
What are these 3" ??
Thank you.
I'm engineer in a company in France which provides modification and certification on aircraft.
For a Cabin Modification on an Emb175, we installed a table in front of a VIP Seat.
We place the table in accordance with the Seat Install Manual :
I quote :
" For double seat, installation aft of any monument must have a minimum setback of 22.86" in case no HIC substantiation is available. For Setbacks below 22.86", installer must provide substantiation for 14 CFR 25.562(c)(5) compliance. This setback accounts for the 50th %ile ATDs"
So we kept a setback of 24" for the installation.
But, when we sent our certification program to EASA, we receive this answer :
"The supporting data they obtained from the seat manufacturer lists a set-back for seats behind interior installations (use for front row seats). The data is only covering 50%tile occupant size. The seat behind a table is not accepted as a front row seat. The clearance shown in the drawings is 24 inches while the minimum acceptable would be 25.86inches."
Can someone explain me why should we take a setback 3"-superior to the setback in the Installation Manual ?
What are these 3" ??
Thank you.





RE: HIC and setback
Quando Omni Flunkus Moritati
RE: HIC and setback
Why whould we use the 95% tile for this installation ?
And as we have only the setback for the 50% tile, there is a regulation which says we have to add 3in ?
Thank you.
RE: HIC and setback
2) it might be defined in the EASA ACs.
3) it is why you talk to your authority before you complete the project (the cert. plan is there to make these rulings ahead of time, so you don't get surprised.
4) using the 95%-ile (or whatever) is probably defined in the AC.
5) you can always placard the seat "suitable for passengers less than X'(Ym) tall".
Quando Omni Flunkus Moritati
RE: HIC and setback
this may or may not help with EASA. EASA should have their own guidence material.
Quando Omni Flunkus Moritati
RE: HIC and setback
Means if your case would have been accepted to fall under "front row seat" category you might be fine with 24" as per installation manual clause you quoted. But because it is behind table the quoted paragraph does not apply and you should fall into another clause, which by the way you should look for in the installation manual, that dictates a different requirement, namely the minimum of 25.86".
I am not from the field at all, so pardon me if my answer is not relevant.
Just tried :)
"If you want to acquire a knowledge or skill, read a book and practice the skill".
RE: HIC and setback
The cited section of the CFR requires substantiation and test with a 50% percentile test dummy. You have provided data accordingly.
Challenge the ruling.
RE: HIC and setback
The AC defines very specifically the head strike zone.
this is all FAA ... EASA has their own take on things. "challenging the ruling" is like "arguing with the
wifereferree" ... "i disagree. sure, disagree, but i'm not changing my mind". but you can ask how they came up with such a specific dim'n. (i think 3" is the difference between 50%-ile and 9x%-ile)Quando Omni Flunkus Moritati
RE: HIC and setback
Both the 25.562 head trajectory and 25.785 35" arc must be complied with, they are often confused together.
RE: HIC and setback
By the way, we have move the table forward, but for my personnal knowlegde, I search the reason for it.
RE: HIC and setback
I am back to you with an answer, and another question about HIC.
Concerning the 3 additional inches : on AC25-562-1b (page 48), it is mentionned " Adding 3 inches to the 50th percentile ATD head path is typically acceptable to account for the 95% occupant head path".
I don't have yet read all the Advisory Circular, but it is a first answer.
Then, a new question now.
I have to install a FC Seat on an Embraer 135. In the seat install manual, there is many case shown with setback, but the case "Forward Facing Seat aft a Monument higher than 17in" is not shown.
So, I can't install my seat aft a wardrobe or a galley in my aircraft.
I'm forced to install my seat Aft-Facing.
Is it possible to justify a position with the headpath given in Install Manual or cases not shown in Install Manual is simply not allowed.
I'm surprised that a seat can be forbidden in this position.
Thank you.
RE: HIC and setback
another day in paradise, or is paradise one day closer ?
RE: HIC and setback
The setback dimension should not limit what type of monument is placed in front of the seat. If it's an aft-facing seat, then there will have to be some necessary space to allow for deformation, unless you want to experience the fun of load sharing.
If you have a headpath applicable to your seat, then you are pretty far ahead. It's pretty rare to get those for airliner seats. Also check that it does not conflict with setback dimension ("applicability"). Some seat manufacturers, unfortunately, charge extra for data to support alternate installations. So you might be forced to pony up more money and incorporate a service bulletin to install a new data plate, change the dash number, etc., and not do any significant changes to the seat. Their right, I guess.