In accordance with §91.223, if you own or operate a U.S.-registered turbine-powered airplane configured with six or more passenger seats (exclusive of pilot and copilot seating), you must install a terrain awareness and warning system (TAWS) that as a minimum meets Class B TSO-C151 standards. The rule is applicable to airplanes "configured" with six or more passenger seats, not to airplanes "type certificated" for six or more passenger seats, so regardless of what the type certificate says, compliance with TAWS is determined by the actual number of passenger seats in the airplane.
No person may operate a turbine-powered U.S.-registered airplane configured with six or more passenger seats, excluding any pilot seat, after March 29, 2005, unless the airplane is equipped with an approved TAWS.
The FAA, through the Handbook Bulletin for Airworthiness (HBAW) 04-06B, provides guidance to its FSDO inspectors on how to properly evaluate aircraft passenger seating configurations. While the bulletin contains guidance specific to §135.411, the FAA says that the agency will use the criteria contained in paragraphs 6-11 when evaluating aircraft passenger seating configurations for the purpose of determining compliance with TAWS requirements under §91.223.
Certain interior configurations have limited the seating capacity so the aircraft will meet certain operational rules regarding crew rest requirements. AFM supplements or other approved data may list multiple seating capacities that can be changed by designating certain areas as crew use only, by blocking seats with placards preventing passengers from occupying them, or by removing seat belts. These types of arrangements are not acceptable. Installation of bulkheads and doors to separate or restrict access to cabin areas where seats are located will not reduce the seating configuration.
Certain aircraft may have been delivered with, or an STC has been issued to install, a dynamic forward observer seat (jump seats that fold down and are stowed when not in use) or a static jump seat in or near the flight deck area. If these seats are limited in the TC or STC and placarded for "crew use only," then they will not be counted in the passenger configuration of the aircraft. If these jump seats are TC'd or STC'd for crew or passenger use, then they must be counted in the total passenger seating configuration. Refer to the STC to determine the intent of the seat use.
If a normal passenger seat has been placarded or designated as a forward observer seat for the purposes of crew use or en route inspection, then it must be counted as a passenger seat in the configuration of the aircraft.
These approved seatbelt installations will be counted in the total passenger seating configuration if certified to be occupied during takeoff and landing.
Pilot and copilot seats are specifically excluded from the TAWS requirements of §91.223. Accordingly, the passenger use of a pilot seat will not be considered as part of the six seats physically installed in the cabin and will not be counted in the total passenger seating configuration.
If the seat, bench, or divan is side-facing and is not certified for use during takeoff and landing, regardless of how many are installed, it is not counted in the total passenger-seating configuration.
Even though these side-facing seats, benches, or divans may not be certified for takeoff and landing, they may still have a seatbelt (gust belt) installed to protect passengers from turbulence. This is the only acceptable situation in which a placard must be installed through a STC or TC stating that the seat is not to be occupied during takeoff and landing for the purposes of this bulletin.
Note: A review of the STC must be made to determine if the seats do not meet the rule requirements to be certified for takeoff and landing or does the STC merely placard a certified seat for the purposes of reducing capacity. This information should be found in the limitations section of the STC. Contact the appropriate Aircraft Certification Office (ACO) if necessary to help make this determination.