Stephan J. Speth, Director
Vehicle Compliance & Safety Affairs
800 Chrysler Drive CIMS 482-00-91
Auburn Hills, MI 48326-2757
Dear Mr. Speth:
This responds to your recent correspondence regarding the telltale requirement in S19.2 of Federal Motor Vehicle Safety Standard No. 208, Occupant crash protection (FMVSS No. 208). Specifically, you ask whether S19.2 permits a compliance alternative other than the passenger air bag telltale to prove that an the air bag is suppressed when an automatic suppression systems sensor does not detect the presence of a child restraint but the system deactivates the passenger air bag whenever the suppression system perceives that the seat is empty. While not constituting a compliance alternative, S19 does permit a device other than a telltale to indicate that the automatic suppression system has deactivated the air bag in those instances where the suppression system perceives the seat as empty.
In your letter you note that in some vehicle seat designs the car bed is too wide to be sensed by the automatic suppression systems sensor. Instead, the sensor perceives that the seat is empty and suppresses the air bag. Because the seat appears to be unoccupied, the telltale does not illuminate.
On May 12, 2000, the National Highway Traffic Safety Administration (NHTSA) published a final rule requiring advanced air bags in all passenger cars, multi-purpose passenger vehicles, buses and light trucks with a gross vehicle weight rating (GVWR) of 8,500 lb or less starting September 1, 2003, (65 FR 30680). The issue raised in your letter was discussed in the preamble of that final rule.
S19.2.2 requires that each vehicle equipped with an automatic suppression system have at least one telltale that emits a light when the air bag is deactivated and does not emit a light when the air bag is activated, except when the passenger seat is not occupied. The telltale must meet certain requirements further detailed in S19.2.2. As discussed in the preamble to the final rule, NHTSA noted that manufacturers could choose not to illuminate the telltale when the passenger seat was unoccupied, even though the air bag has been deactivated. The final rule specifically provides manufacturers with the option of either deploying or suppressing the passenger air bag when the passenger seat is unoccupied. Suppressing the air bag may be advantageous for various reasons. First, the passenger seat is often unoccupied. Deploying an air bag in front of an empty seat would be both costly and unnecessary. Second, suppressing the air bag in all instances below a certain weight threshold could result in a more robust system that, at lower weight levels, automatically assumes any item or occupant on the seat will not benefit from a deploying air bag. NHTSA decided to allow manufacturers to design telltales that do not emit light, even though the air bag is suppressed, because such a requirement would mean that the telltale would be on more often than it was off in vehicles with these types of designs. Since the point of the telltale is to alert the driver of the vehicle that the air bag has been suppressed in the presence of a child, NHTSA was concerned that overuse of the telltale could dilute the telltales important safety message. Accordingly, the regulation specifically permits non-illumination of the telltale in the event that the seat is unoccupied.
However, NHTSA also contemplated a rare situation in which the suppression systems sensing mechanism reads the passenger seat as unoccupied even though a child could be in the seat. Such a situation should occur only when the weight of the child or test device is so slight as to prevent a sensing system from detecting the occupant. Within the context of the tests in the automatic suppression options of the advanced air bag rule, we believe such circumstance is probably limited to a car bed bridging the seat-based sensing system  or the three-year-old child dummy sitting on the forward edge of the seat, since in both of these instances the level of weight and/or its distribution on the seat may be sufficiently low to prevent a sensing system from detecting the occupant. Because of the possibility that this could occur under limited circumstances, we added S19.2.3, S21.2.3 and S23.2.3 which require some mechanism that definitively indicates whether the air bag is suppressed. In the preamble we stated that" [I]n order to accommodate a design where the telltale was not illuminated when the seat was empty, but still allow for compliance testing of all of the proposed child seating positions, some of which could look to a suppression system like the seat was empty, we added a requirement that the vehicle come equipped with a mechanism that would indicate under all circumstances whether the air bag was suppressed." 65 FR 30723. The mechanism need not be located in the occupant compartment unless the required telltale serves that function.
While this approach has the disadvantage of sometimes not notifying a parent or caregiver that the automatic suppression system has suppressed the passenger air bag, we balanced this concern against competing concerns that the telltale may be disregarded due to overexposure or that a sensing system may be unable to detect the presence of a child under certain real world operating conditions. In the event that a manufacturers suppression system is unable to always detect the presence of a child for whom the system is designed to suppress the air bag, this information must be included in the owners manual so that a parent or caregiver is aware that the telltale may not always illuminate in the presence of a small child. Such information is already required to be provided pursuant to S4.5.1(f)(2)(iv) of the standard.
I hope this letter addresses your concerns. Please feel free to contact Rebecca MacPherson of my staff at (202) 366-2992 should you have any additional questions.
 The car bed is unique among child restraints because it is installed sideways across the seat, it is designed to accommodate only very small infants, and the seat belt is not cinched down when testing the suppression system. This combination of factors could reasonably result in the car bed placing virtually no weight on a seat-integrated sensing system.