In the aftermath of the Air France Airbus 330 airliner crash in to the Atlantic, questions are once again being raised about the safety of flying by onboard computer systems.
Aviation safety expert and journalist David Learmount of Flight Global argues that the debate in the aviation industry is not about the safety of flying by wire, but more about how much control should stay with the pilot, at what point the computers should intervene, and what the manual control interface should be like?
Despite the fact that no new large airliner will ever again be designed with a flight control system that is purely mechanical or hydraulic, control by digital “fly-by-wire” remains an issue with which some of the media still struggle when reporting on aviation issues.
In its early days in the 1990s, that used to be true also of pilots’ perceptions of FBW, but that has reduced now to a peripheral level among those with no direct experience of it.
The same could be said of one of the most obvious FBW-enabled components: the side-stick or mini-stick flight control. Airbus has embraced it completely, but Boeing has chosen not to. That visible symbol has always tended to be the lightning conductor for disagreement where it existed.
But now that FBW is mature, and the industry has refined and deployed it to best advantage, it is easier to argue that the controversy was mainly in people’s heads and never had any real substance.
So what of the future for control systems? No manufacturer now disputes the principle that digital FBW systems are optimal for all but the smallest and simplest aircraft. Two big airframers have chosen different – but equally valid – FBW system architecture.
They also show varying approaches to pilot/aircraft interface and to what aircraft responses the system’s normal flight law should deliver to the pilots. Finally, they differ a little over where flight envelope protection intervenes, and a lot over whether it can be overridden.
But the outcome of all of these is that the aeroplanes are much the same to fly manually as they would have been with conventional controls, despite the behind-the-scenes electronic trickery that the pilot is effectively employing to control the aircraft.
Autopilot/flight management system
The bottom line is that, when the pilots of modern airliners are managing them using the autopilot/flight management system – which is what happens for 99% of every trip – there is absolutely no difference, from the flightcrew perspective, between an FBW aircraft and one which is conventionally controlled.
In 1993, Flight International wrote: “Before the dramatic air transport avionics changes in all the major manufacturers’ types between 1981 and 1991, there had been no conceptual change in aircraft man/machine-interface design since the 1940s and, arguably, since well before that. Improvement in pre-1980s cockpits consisted of the gradual application of ergonomics – which is important, but not fundamental – and increasing sophistication in electro-mechanical instruments.”
We went on: “Formerly, pilots had faced no conceptual change in flying or flight management technique at any stage between primary trainer and airliner cockpit.” It was these conceptual changes, rather than the actual flying characteristics of the aircraft, which were – and remain – the main issue, because the differences in line pilots’ day-to-day tasks in the new machines (compared with the traditional) was wrought far more by the advance of systems automation, advanced avionics and sophisticated flight management systems than by FBW or flight envelope protection.
Today, most new business jets and some latest regional airliners are – or soon will be – rolling off production lines with FBW flight control systems, so it is clear the concept of having the pilots’ manual control inputs vetted and – in some circumstances – modified by a flight control computer system is not at issue.
Issues still debated are: how much control should stay with the pilot, at what point the computers should intervene, and what the manual control interface should be like.
For the future, aircraft manufacturers don’t talk about fundamental changes in control philosophy or technology, but about taking full advantage of the system they have to improve reactive technology, such as load alleviation and lessening structural stresses.
Advances in control technology, says Thales, will all come in the form of improved man-machine interface, with empathic, intelligent systems that work with the pilot to manage the total mission. The pilot? Yes, one pilot. If customers accept the concept, of course. Why do you need two when the system will be the co-pilot to the captain?
Pictures from Rex Features.