Safety Pilot:

Passive safety

January 1, 2010

“Don’t just do something. Sit there!” That’s what my Mom used to say when bad things were about to happen without intelligent intervention. It applies to pilots, drivers, boaters, financial executives, and government regulators. Compared to machines, the homo sapiens’ conceit of being masters of the universe shows us to be consistently unreliable when it comes to repetitive tasks. We do excel, however, in thinking up ways to get out of mindless chores to refocus our short attention spans on really important stuff—such as whether to watch Dancing with the Stars or Seinfeld reruns.

But what about aviation safety advances that make a real difference without the uncertainty of human involvement? Passive safety devices require little or no input from pilots and are perhaps the unsung heroes in really moving the safety effort forward. An axiom of design that is often overlooked is to design the equipment around humans rather than forcing us to adapt. Changing long-term behavior across a population is extremely difficult and much of our equipment is designed for fairly capable people who are motivated to excel. The hard truth is that some of us are not the sharpest tools in the shed and even the best occasionally have a bad day. When it comes to flight critical equipment and operations, good automatic hardware consistently outperforms the sometimes mostly attentive, occasionally out-to-lunch human software.

A relatively recent option on many new aircraft and a fairly easy retrofit to older ones is aviation airbags. Airbags on cars save thousands of lives annually despite the occasional situations where an injury is exacerbated because someone didn’t follow even the simple instructions on their use, but the lifesaving potential is unquestioned.

The bags are brilliant in design: Buckle your seat belt and when the aircraft comes to a sudden unplanned stop, the bag deploys away from occupants to protect the body from the deadly second impact with the instrument panel. The clever thinking is that no instrument panels need to be torn apart or redesigned to hold the bag—one size pretty much fits all.

But my seat belt and shoulder harness will protect me, right? Not necessarily, especially if the attach points tear out, which they do once the design tolerance is exceeded. There’s too much detail to go into here but the concept makes a lot of sense for survivable accidents.

Other passive safety devices include automatic fuel tank switchers that keep the aircraft properly trimmed. Barring that, a timer that never forgets to remind the pilot to switch is an inexpensive fix to the fuel-starvation blues. We’ve previously discussed the benefits of low-fuel warning devices that automatically let the pilot know of impending silence.

I’ve written before about the excellent system where early model Piper Arrows automatically extended the landing gear if the pilot forgot. That arrangement doubtless saved hundreds, if not thousands, of gear-up landings. However, the legal system decided that pilots were unable to follow even the simplest instructions to override the system in those few circumstances where the automation might be inappropriate. Piper was forced to stop saving pilots from themselves.

Terrain Avoidance Warning Systems (TAWS) have prevented hundreds of accidents when pilots became disoriented relative to terrain. In newer versions the multifunction display turns red and an insistent voice shouts, “Terrain, pull up!” TAWS lets pilots know while there is still time to react, that a sudden stop is in the near future.

Collision avoidance warning systems are also a big help. The certified installations used by the airlines have prevented some big get-togethers aloft and the advisory versions used by many GA aircraft, although not 100 percent effective, identify a lot of traffic that pilots typically overlook.

Here’s a passive safety design that solved a problem in the go-around mode. Single-engine Cessnas built in the early 1970s offered 40-degree flap deflection. That allowed for a steep approach and short landing roll. The problem was that too many pilots forgot that climb rate was anemic to nonexistent if the flaps weren’t immediately retracted to 20 degrees in a go-around. Too many aircraft in too many trees dictated that flap travel be limited to 30 degrees. This limited landing performance somewhat, although it gave forgetful pilots a fighting chance to establish at least some climb instead of a mush into the obstacles.

Perhaps the granddaddy of all passive protection systems is on the Gulfstream V. The automatic emergency descent mode is activated when the cabin altitude climbs above 8,000 feet. The aircraft then rolls into a steep bank and the autothrottles are retarded to keep speed at MMO. There’s a rapid drop to a livable atmosphere of 15,000 feet where the G-V rolls wings level and stabilizes. No action is required on the part of the crew. The Payne Stewart Learjet 35 accident comes to mind when a pressurization system failed for undetermined reasons and the Lear flew for hours before running out of fuel and crashing.

Passive safety design is one of the best ways of saving us from ourselves because we don’t have to change at all. The hardware manages the problem—usually. Of course, a modicum of common sense and decision-making in any kind of flying, be it J–3 or G-V, allows the passive devices to stay that way.

Bruce Landsberg was named president of the AOPA Air Safety Foundation in 2009.