Automation is supposed to relieve an aircraft pilot's workload and reduce errors. The reality can unfortunately be very different sometimes. When the pilot and the aircraft do not interact as foreseen, automation technology can be the cause of disturbing instability, which has resulted in catastrophic failures. Tools and techniques developed by the EU-funded ARISTOTEL project are already being used by industry, and should reduce the risk of such accidents.
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Aircraft and rotorcraft pilot couplings (A/RPCs) are uncontrollable oscillations (or swaying) of the aircraft, and are caused by a gap between the pilot’s understanding of the vehicle’s dynamics and the actual motion taking place, or by the pilot’s unintentional actions to take control.
It is extremely difficult to recognise and analyse an A/RPC event. This is due not only to the difficulty of reconstructing what happened from an accident scene, but also because potential witnesses tend to be unaware of these events, even when they are highly trained.
Despite decades of preventative measures, A/RPCs persist and are in fact increasing in modern aircraft.
‘Dynamic and complex’
“Today's aircraft are more dynamic but at the same time more complex than their predecessors,” says ARISTOTEL project coordinator Dr Marilena Bos-Pavel from Delft University of Technology in the Netherlands. “This complexity combined with a high pilot workload can cause A/RPC problems. The high time delays introduced by the automation is a leading cause of such problems.”
The project team compiled a database of A/RPC events from across the world and soon discovered that most incidents involve helicopters. The next step was to build helicopter models to capture real rotorcraft behaviour. Simulators were also used to examine biodynamic effects from, for example, muscle tension in a stressful situation.
Much of the research focused on the seconds before and after an A/RPC. The team introduced a time delay to the controls in one of the simulators and then monitored the pilot’s behaviour as he or she became aware of the delay and then sought to compensate for it. The observations led to greater understanding of events in these critical minutes.
Better and safer designs
The ARISTOTEL research has resulted in a far greater understanding of what can cause A/RPC events. By developing innovative design guidelines, as well as methods and training protocols for enhancing A/RPC prediction and prevention, the project should help to speed up the development, testing and certification of helicopters and increase their safety.
“Previously, there were no design guidelines for testing A/RPC in helicopter simulators. But as a direct result of our work, this is no longer the case,” says Bos-Pavel.
These guidelines will help designers to assess, early in the design process, the flying qualities, biodynamic effects and susceptibility of new aircraft to adverse A/RPC events. Crucially, they should lead to safer designs.
Despite only finishing in September 2013, the research carried out under ARISTOTEL has already been integrated into the design process by the aerospace industry to improve flight safety – a real testament to the project’s success.
And with the EU having set the goal of reducing aircraft and rotorcraft accidents by 80% by 2020, these promising results have come just at the right time.