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.
Controversy
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.
Issues debated
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.