Why aren’t car-like 3 point seatbelts used in planes?
In: 444
In short, as a three-point harness adds proportionally less safety in an airplane as it does in a car, and a proportionally higher cost. The two-point seatbelt provides a very good protection even for fairly high impacts, despite the simplicity and very low weight (mostly of the two very strong mounting points of the seatbelt)
There are two main reasons:
1. Limited added safety from more complex belt, due to different nature of crashes. A typical airplane crash rarely comes as a full surprise. Rather, in most cases there is even time to teach and train the proper brace position (for example, prior to a suspected-to-be bad landing due to faulty landing gear or during the time between all engines failing and the inevitable hard landing to land or water). When implemented correctly, the brace position already suppresses the impact forces faced by the head and the torso, as one leans forward prior to impact rather than letting the head hit the seat ahead at speed (which we know to work based on past crashes, where the two-point seatbelt combined with a brace has been very effective at reducing both fatalities and injuries). A typical car crash comes comparably out of blue, leaving too little time to similarly brace for impact. Additionally, in a car that is crashing, there is much less space in front of you to be had before hitting something very hard*, like the steering wheel or in modern days the airbags (the airbags are very hard to hit, they are not soft cushioned bags of air but rather very taut and nearly solid bags of air; they provide, however, a less angular surface to collide than, say, steering wheel or the B-pilar).
2. It would increase the cost a lot, both initially and during use. A three-point seatbelt would need a third sturdy mounting point up top of the cabin, which would need a major redesign of all airplane interiors, and would also likely add plenty of extra weight per seat, increasing the fuel usage per flight. (*The backrests of regular airplane seats are not sufficiently strong for this purpose, as they are designed to flex upon impact to soften the impact forces of the person behind you, and also impact tested for this. And, neither is the bottom of the overhead compartments strong, not by a long shot. The impact forces taken by the seatbelts are massive, tens of times of your bodyweight. A two-point harness carries these loads conveniently to the floor of the aircraft via the fairly substantial pieces of metal under the seats, both of which are a strong point. Notably, some of the more reclining first-class seats have a three-point seatbelt, as it allows for more comfortable seats that do not facilitate a conventional brace position.)
Latest Answers