The air bag system: what went wrong with the systems engineering?

The Air Bag System: What Went Wrong with the Systems Engineering?
Dennis M. Buede
Department of Systems Engineering, George Mason University, Fairfax, VA 22030-4444 Received January 16, 1998; accepted March 21, 1998

ABSTRACT
The air bag restraint system in automobiles has received a great deal of attention since the summer of 1996. The purpose of this paper is to review the successes andfailures of the air bag from its introduction in 1988–1996 and to relate these successes and failures to the requirements that led to the current air bag design. The issue addressed in this paper is whether the systems engineering development process that led to the first generation air bag system could be considered reasonably successful. This question is not the same as whether the firstgeneration air bag was better than no air bag system for the spectrum of drivers and passengers in automobiles and light trucks. Rather the issue is whether the first generation air bag system addresses the spectrum of requirements one could expect from such a system. Finally suggestions are made about how the requirements development process can be improved for all systems, considering the obvious andnot-so-obvious mistakes that were made during the development of the air bag. ©1998 John Wiley & Sons, Inc. Syst Eng 1: 90–94, 1998

1. INTRODUCTION
Air bags are safety devices that are used in conjunction with safety belts. In particular, air bags installed in the steering wheel and passenger side dashboard are useful in frontal accidents that cause the driver and passenger to move forward towardthe steering wheel or dashboard and windshield.

1.1. The Year Is 1983
You have been selected to be part of the systems engineering team for a new safety system to be installed on

© 1998 John Wiley & Sons, Inc. CCC 1098-1241/98/010090-05

automobiles, called air bags. You are part of the requirements development effort. The systems engineering team consists of people from government[National Highway Traffic Safety Administration (NHTSA), which is part of Department of Transportation (DOT)] and industry. As background information you find that air bag research has been underway by automobile manufacturers for about 20 years. A 1969 research paper by General Motors [Brown and Skrzycki, 1996a] and a 1974 study by Volvo [Payne, 1996] both concluded that children and small adults weresubject to injury or death during air bag inflation. General Motors actually sold cars with air bags in them from 1974 to 1976, but stopped the experimental program. There are currently about 30,000 people dying each year as occupants in accidents involving passenger cars and light
90

THE AIR BAG SYSTEM

91

Table I. Yearly Fatality Data Year Vehicle miles traveled (VMT, billions)Fatalities (passengers & drives) % Frontal crashes % Seat belt use Fatalities per billion VMT 1983 1700 (estimate) 30,000 60+ 10–15 18 1988 2000 34,000 60+ 25–40 (estimate) 17 1995 2400 32,000 60+ 65–70 13

trucks (see Table I). Over 60% of these fatalities occur in frontal accidents [Traffic Safety Facts 1995—Overview, 1996]. Only 10–15% of drivers and passengers are wearing their seat belts [Steedet al., 1996].

1.2. The Year Is 1988
Driver-side air bags are just now being introduced ahead of the government time line due to market forces. There are now about 34,000 people dying each year as occupants of passenger cars and light trucks; over 60% of the deaths involve frontal accidents. Seat belt use has grown substantially [Traffic Safety Facts 1995 — Overview, 1996]. There has been agreat deal of discussion about air bag effectiveness since 1984, but the requirements have not changed in this time period.

1.3. The Year Is 1995
Air bags have been available for 8 years. During 1995 about 32,000 people died as occupants of passenger cars and trucks; over 60% of the deaths involve frontal accidents. Figure 1 shows a breakdown of traffic fatalities by age group; while the age...