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Airliners and charter jets, operating under Part 121, 135, or their foreign equivalents, fall under regulations to ensure accessible exits, 16g seats, and other aspects of occupant safety.

Private aircraft, not holding out, don't need to follow these rules and can have extravagant interior layouts. I'm interested in which regulations or guidelines is the interior designer still expected to follow.

Can the plane be filled with bar stools, rocking chairs, etc., or are there provisions under which something absurd, like a swimming pool on a 737 BBJ, would be denied an airworthiness certificate?

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2 Answers 2

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Emergency exit and seating design is controlled by the aircraft certification process, not through the operating certificate. Operators may not exceed the certified seating capacity. Part 25 covers larger commercial aircraft including the BBJ and similar. Part 23 covers general aviation. Here are excerpts:

Part 25

14CFR25.807g Type and number required. The maximum number of passenger seats permitted depends on the type and number of exits installed in each side of the fuselage. Except as further restricted in paragraphs (g)(1) through (g)(9) of this section, the maximum number of passenger seats permitted for each exit of a specific type installed in each side of the fuselage is as follows: Type A 110, Type B 75, Type C 55, Type I 45, Type II 40, Type III 35, Type IV 9.

Exit type in Part 25 is specified by door size and location.

Part 23

§ 23.2315 Means of egress and emergency exits. (a) With the cabin configured for takeoff or landing, the airplane is designed to: (1) Facilitate rapid and safe evacuation of the airplane in conditions likely to occur following an emergency landing, excluding ditching for level 1, level 2, and single-engine level 3 airplanes. (2) Have means of egress (openings, exits, or emergency exits), that can be readily located and opened from the inside and outside. The means of opening must be simple and obvious and marked inside and outside the airplane. (3) Have easy access to emergency exits when present. (b) Airplanes approved for aerobatics must have a means to egress the airplane in flight.

Part 23 was rewritten to be objective oriented rather than regulated by specific design. The means of compliance now contains all the specifications that used to be in the regulation. The original regulation may be used in many cases but alternate means of compliance can also be proposed and used if approved. Getting approval for a means of compliance is not trivial, so it can be easier just to use the original reg.

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  • $\begingroup$ Thanks. So I guess capacity is locked. Any idea if anything applies to what the seats can be, or is it just the total count? $\endgroup$
    – Therac
    Apr 17, 2023 at 12:40
  • $\begingroup$ @Therac There is a maximum capacity for any given certification but you can put as few seats as you like. There are several rules about width of space between rows and seat clearance at the exits. There are separate certification rules for seats, as for side facing 'couch' type seats and upper body restraints to keep heads from bashing into things. A Supplemental Type Certificate (STC) is used to create a permanent approval for a particular modification to all listed aircraft and form 337 is used to get approval for a particular modification to one aircraft. The lines are not always clear. $\endgroup$
    – Pilothead
    Apr 17, 2023 at 15:26
  • $\begingroup$ @Therac There is a distinction between a seat used for takeoff and landing and some other piece of furniture. Your barstool might be ok for inflight use (no turbulence) but would not be allowed for TO/L. $\endgroup$
    – Pilothead
    Apr 17, 2023 at 15:36
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It seems like you’re talking more about the composition of the seating and not the actual amount of seats, as well as amenities. For that you need to look at CFR § 25.853 I would additionally look at AC 25.853-1 which covers flammability testing. Basically even just refitting the existing seats with a nice leather material may involve expensive testing of the material to ensure it doesn’t burn. Also anything wood is basically out.

The whole sub part D would probably be worth looking at. It includes things like:

§ 25.601 General.

The airplane may not have design features or details that experience has shown to be hazardous or unreliable. The suitability of each questionable design detail and part must be established by tests.

§ 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.

Which I think would be a non starter for the ideas provided, at least in the United States.

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  • $\begingroup$ Thanks. Yes, I'm mostly looking for what regs the seats on a Part 91 bizjet have to comply with. How to quickly tell complete non-starters from something that needs testing. $\endgroup$
    – Therac
    Apr 17, 2023 at 17:08
  • $\begingroup$ My answer applies to aircraft standards so it wouldn’t matter if it’s your own plane or American Airlines they would need to meet these standards. $\endgroup$ Apr 17, 2023 at 17:16

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