SAFETY FIRST. Air bags are installed in the seat belts and shoulder harnesses, and deploy outward from the occupant. Improper use or design of these systems can compromise occupant safety.
The NTSB recently completed a safety study of air bags in general aviation aircraft. It concluded that air bags can reduce or eliminate injuries in survivable accidents where most of the impact force is longitudinal (lined up with the direction in which the aircraft is moving). However, in an aircraft accident, there often are severe vertical and sideways forces acting on the aircraft and its occupants. Aircraft air bags are installed in the seat belt/shoulder harness, and deploy outward from the occupant, rather than being built into the dashboard, steering wheel or sidewall as with cars and trucks. The ability of current designs to afford protection against forces from multiple directions is restricted, unlike some automotive systems where curtains of airbags surround occupants. The NTSB's researchers found that improper use, adjustment or design of restraint systems can compromise occupant safety.
The Safety Board noted that air bags were first certificated for pilot and copilot seats on general aviation aircraft in 2004. In 2005, Mooney, Cessna and Cirrus began offering air bags as standard equipment on their GA aircraft. As of August, 2010, they had been installed in more than 7,000 aircraft. In 2006, the NTSB began its study to see whether air bags actually worked to reduce injuries in general aviation accidents. During the next three years, researchers were notified of 145 accidents or incidents involving airplanes that had air bags. Ten of those accidents fit the study criteria and received in-depth treatment. The 10 accidents were severe enough to expect that the air bags should deploy, and they worked in all 10 cases. Despite detailed documentation of damage to the aircraft and injuries to occupants, the researchers didn't uncover evidence that the air bags reduced the severity of injuries in all cases. They were able to conclude, however, that the air bags didn't make things worse.
The Safety Board previously noted that tests showed air bags would help reduce head injuries in general aviation accidents. However, the NTSB stopped short of calling for the FAA to require air bags. Instead, it called for more study of air bags, while calling for the FAA to take action on something that the NTSB has long considered a fundamental part of occupant protection: shoulder harnesses.
The NTSB's first study of the crashworthiness of general aviation aircraft was adopted in 1972. It focused on the pilot's role in reducing impact forces during a planned emergency landing. Pilots are able to have some effect on crash forces by keeping the airplane under control, being precise with airspeeds, selecting what terrain and objects to hit when there are options, and sacrificing aircraft structure to absorb energy.
In 1980, a safety study documented past accidents, regulatory developments and crashworthiness research. The Safety Board issued recommendations to the FAA that included making shoulder harnesses mandatory. It also called for sharp objects to be removed from instrument panels. Another study adopted in 1980 resulted in the NTSB asking the FAA to require improvements in fuel systems for the prevention of postcrash fires. In 1983, the Safety Board began a three-year follow-up study of general aviation crash worthiness. It issued more than two dozen recommendations to the FAA to improve crash survivability, one of which was to require the use of shoulder harnesses for all takeoffs and landings. In response, the FAA ordered installation of shoulder harnesses for all seats in newly manufactured small airplanes beginning on December 12, 1986. On June 4, 1993, it was reported that properly used shoulder harnesses reduced major injuries by 88%, and fatalities by 20% over lap belts alone. It urged owners of older aircraft to obtain approved shoulder-harness kits. Now, the NTSB says it's time for the FAA to mandate that shoulder harnesses be installed on all general aviation airplanes that aren't currently equipped with such restraints in accordance with the FAA's Advisory Circular. Here are three accidents in which the NTSB found that use of shoulder harnesses would have made a difference.
The single-engine Cessna was taking off from Phillips Flying Ranch Airport, Rockwall, Texas, for a flight to Terrell, Texas. The flight instructor had scheduled a night instructional flight with a student at Terrell. When the airplane failed to arrive, a search was initiated. The wreckage was found about 100 yards southeast of runway 13 at Rockwall. The airplane had come to rest inverted. The pilot was fatally injured. A fuel-tank vent tube was blocked with mud, consistent with the mud nest of an insect. In addition, examination of the carburetor revealed that the accelerator-pump expansion spring was rusted and broken into two pieces. Rust chips were found at the bottom of the carburetor bowl. An autopsy concluded that the pilot's death was due to blunt-force injuries of the head and neck. Investigators learned that the pilot had a history of right-shoulder pain that was intermittently treated with prescription medications.
The occupant space in the cabin area wasn't compromised by the crash. Recovery personnel reported that although the pilot had been using his seat belt, the shoulder harness wasn't being used at the time of the accident. Friends of the pilot told investigators that the pilot's shoulder problem made it painful for him to use the shoulder harness.
The NTSB determined that the probable cause of this accident was the pilot's failure to maintain aircraft control following a loss of engine power due to contamination in the carburetor. Contributing to the severity of the accident was the pilot's failure to utilize his shoulder harness.
The single-engine airplane had been flying from Houston Executive Airport, Brookshire, Texas, to Hicks Airfield, Fort Worth, Texas, a distance of 233 nm. The pilot told investigators that as he was flying through Fort Worth Meacham International Airport's airspace, the engine momentarily skipped, then quit. The pilot declared an emergency with Meacham tower, and was cleared to land. He maneuvered for runway 16, and tried three times to restart the engine. When it wouldn't start, he committed to an engine-out landing. However, he realized that he wouldn't make it to the airport, and elected to perform a gear-up forced landing on a highway entrance ramp. During the crash, the pilot's head struck the instrument panel and he was seriously injured. The airplane wasn't equipped with shoulder harnesses.
Examination revealed that the fuel-metering unit was partially separated from the engine, and the throttle-control cable was disconnected. The mixture-actuating arm was fractured into two pieces. The mixture-control cable was attached to one of the pieces by hardware not approved for the purpose.
The NTSB determined that the probable cause of this accident was failure of the operator to ensure that the metering unit's throttle arm and throttle cable were secured using manufacturer-approved hardware. A contributing factor to the pilot's injuries was the lack of shoulder restraints.
The instructor and student took off from McGregor, Texas, in the single-engine aircraft for a scheduled instructional flight. They had filed IFR, climbed to VFR on top, and cancelled their IFR flight plan. They maneuvered for about 20 minutes, then went to another airport to practice landings and takeoffs. On the return trip, they picked up an IFR clearance and received vectors for the VOR approach to runway 17. Because the wind was from the north, they requested a circling approach to runway 35. They broke out of the overcast at about 1,300 feet AGL. While maneuvering to join the left downwind for runway 35, the pilot ran the checklist, turned on the electric boost pump, then switched from the right to the left fuel tank. The instructor told investigators that he observed normal fuel pressure and fuel flow. The instructor reported to investigators, "Immediately after I looked away from the gauges, the engine began sputtering and acting like it was going to die. At this point, I put my hands on the controls and went full power with the throttle, while telling [the pilot] to switch back to the right tank." The engine then sounded as if it was going to regain power, but then quit again. The instructor took the controls. Realizing they weren't going to make it to the runway, the instructor landed in a field. The airplane was substantially damaged.
Both the instructor and pilot received minor injuries, and were able to get out unassisted. Fuel was found in both tanks. The airplane wasn't equipped with shoulder harnesses. The instructor told investigators, "I hit my chin on the dash of the aircraft when we hit the ground. The dash of the aircraft had some padding in it, so the injury was a lot less severe than it could have been. It made my gums bleed a little and my jaw hurt for a few days. Shoulder harnesses would have prevented me from hitting my chin on the dash."
The NTSB determined that the probable cause of this accident was a loss of engine power for undetermined reasons. Contributing to the severity of injuries was the airplane's lack of shoulder harnesses.
Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, NY 10602-0831.