NASA is planning to drop-test a surplus Marine Corps CH-46 helicopter on Aug. 28 with the goal of gleaning new data on rotorcraft crashworthiness and seat belt design. The hulk will be rigged with 40 cameras, numerous sensors and 13 crash dummies.

The test is part of NASA's Rotary Wing Project. During the test, onboard computers will record more than 350 data channels. The helicopter will be swung like a pendulum, and then the connecting cables will be released allowing it to fly freely into a dirt pile at 30 mph, simulating a severe, but survivable crash.

New civil helicopters have been required to be equipped with energy-attenuating crew and passenger seats and multipoint restraint systems since the mid-1990s. That standard requires seat structures to be able to withstand vertical loads of 30 G's (a G is equal to the force of gravity) at a rate of 30 feet per second during dynamic testing: they fire a seat down a test sled and/or drop it with a hapless crash dummy attached.

The level of structural deformation/integrity coupled to the measured loads on the dummy determine if a particular design passes or fails. All this is very expensive, and historically seating manufacturers have been able to achieve this standard largely by focusing on seat structure as opposed to seat comfort. This is why the seats in most new utility-class helicopters feel like bricks.

Over the years seat manufacturers have attempted to mitigate the discomfort by using ergonomic seat backs and pans, with somewhat mixed success.

Helicopters, by their nature, minimize airframe weight and that means the focus on crashworthiness must be placed elsewhere. In a crash, the goal is to minimize the transfer of mechanical energy from the helicopter to the occupants.

This can be done several ways: Designing the helicopter with a high-inertia rotor system, that allows it to autorotate at slower speeds — and therefore impact at lower velocities — is perhaps the most critical. Numerous studies have shown that helicopters with low-inertia rotor systems crash at much higher vertical velocities and require seats with considerably better load attenuation to minimize injury.

Other methods to improve crash survivability include equipping the helicopter with skids that can absorb crash loads, as opposed to retractable wheeled gear, or building energy attenuating features into the floor of the helicopter, the seats and the restraints.

In all helicopters — but particularly in those outfitted for EMS — it also is critical that portable items are properly secured away from the strike zones of the occupants. Balancing this with the need for ready access in flight is the reason why designing a good medical interior is often such a vexing problem.

The NASA study promises to shed more light on occupant survivability and one day could lead to helicopter interiors that are not only safer, but also more comfortable.