鈥淲HEN did you ever see an airline saying its planes are safer?鈥� asks NASA
engineer Lisa Jones. Switch on your TV, or open your newspaper and you鈥檒l see
plenty of ads from automobile manufacturers trying to outsell each other on
crumple zones, passenger air bags and side-impact bars. 鈥淲e think aviation can
do the same,鈥� she says.
It would be a timely move. Predicted increases in air traffic mean that there
could be an average of one major air accident a week in 20 years鈥� time. But that
doesn鈥檛 mean people have to die. Four out of five accidents happen during
take-off or landing, when speeds are low enough for passengers to survive the
crash. In Britain鈥檚 most serious recent air crash, at Kegworth, Leicestershire,
in 1989, there were 47 fatalities, but 79 people survived. The same year, at
Sioux City, Iowa, a similar proportion survived the 350-kilometre-per-hour
crash-landing of a DC-10. If some can get out alive, shouldn鈥檛 everyone be able
to walk away?
It鈥檚 a question the US Army has been addressing for years, with impressive
results. Military aircrew are now walking away from crashes which, 20 years ago,
would have killed them. Their cockpits are toughened, shock-absorbing cells,
protected by underfloor foam that absorbs the impact of a crash-landing. Their
seats are designed to deform, absorbing the shocks that might otherwise inflict
fatal spinal injuries. And the Army is testing in-flight air bags and novel seat
harnesses which inflate to protect their occupants.
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In principle, aircraft manufacturers could already be building some of these
innovations into the planes that take us on holiday. But no one is forcing them
to do so, nor is there any hint that regulations governing commercial aircraft
are about to change.
Despite this, Jones and her colleagues are hoping to bring some pressure to
bear. They are working on a NASA programme to come up with more 鈥渃rashworthy鈥�
designs for airliners. It is part of a $500 million process, kick-started
by Al Gore when he was US Vice President, aimed at persuading regulators,
airlines and plane makers to rethink the design of commercial aircraft. Many of
the programme鈥檚 lessons have come from a NASA-commissioned study, completed in
February last year by crash consultancy Simula Technologies in Phoenix, Arizona.
Simula analysed a number of survivable commercial airliner accidents to see what
lessons could be learned. Jones reckons that many of its suggestions could be
applied to existing aircraft. These include strengthened, shock-absorbing seats,
three-point harness seat belts and strengthened overhead lockers.
But it is not always enough to make a few selective alterations. The Boeing
737 that crashed at Kegworth was fitted with strengthened seats. Unfortunately,
nothing had been done to reinforce the floor, with the result that many of these
seats simply ripped from the floor in the impact, and piled their occupants into
a fatal crush at the front of the cabin. The most crucial and pressing need in
aircraft safety is the most fundamental one: changing the way the aircraft is
built. 鈥淎 good seat in a bad airplane is no better than a bad seat,鈥� Jones
says.
The first step towards a crash-proof design involves creating a structure
that absorbs the force of the initial impact. Some researchers believe
commercial airliners fall at this first hurdle. Gary Frings, an engineer
evaluating crashworthiness concepts at the Federal Aviation Administration鈥檚
Technical Center at Atlantic City, New Jersey, says they pass on too much of the
energy of the impact to the people inside. 鈥淎ircraft are too rigid鈥攊t
would be better if they collapsed more in an impact to absorb more energy,鈥� he
says. Clive Chirwa, editor of the International Journal of Crashworthiness,
agrees. He thinks the need for changes in the design of a commercial airframe is
obvious. 鈥淚t must be designed to crumple,鈥� he says.
Not everyone sees it that way. Europe鈥檚 giant plane maker, Airbus, says that
its fuselages already do crumple, and Gil Wittlin, of the Californian
crashworthiness consultancy Dynamic Research, doesn鈥檛 think there鈥檚 much that
can be done to improve fuselage designs. Simula chairman Stanley Desjardins
agrees. 鈥淐urrent fuselage structures are very efficient right now,鈥� he says.
Nevertheless, the US Army is investigating new concepts in fuselage design.
Karen Jackson鈥檚 team at the Army Research Laboratory in Hampton, Virginia, is
working on a fuselage designed to make a 36 km/h vertical impact entirely
survivable for those inside. This, Jackson says, is a realistic impact velocity
observed in actual crashes. The fuselage is made of carbon composite, and its
underbelly deforms so that foam packed under the cabin floor can absorb the
energy of crash-landing. This cushions the floor and upper section of the
fuselage, so they keep their shape, protecting the passengers inside. Jackson
has successfully tested a scale model of the new fuselage, and this month a
joint NASA-US Army programme will crash test a full-scale model of a section of
this design by swinging it like a pendulum from a 75-metre-high gantry at NASA鈥檚
Impact Dynamics Research Facility at Langley, Virginia.
Plane makers are likely to argue that abandoning metal fuselages and learning
how to use composite material instead would be too expensive. But some
crash-proofing specialists say the industry should take the principles of
crashworthy fuselages and apply them in metal. Aluminium is ductile, and if used
in the right way should be reasonably good at absorbing energy. Chirwa advocates
abandoning the traditional angled sections of aluminium used to build an
aircraft fuselage鈥檚 circular and longitudinal frames and replacing them with
aluminium tubing. This, he says, would provide an equal strength-to-weight ratio
while absorbing more energy in an impact.
When the underbelly deforms, the cargo hold could provide the crumple zone.
Parts of the hold鈥攚hich is often near-empty鈥攃ould be packed with
shock-absorbing foam, as the US Army has done with its crash-proof fuselage.
Belly-to-floor collapsible struts could also absorb some of the impact.
As well as the underfloor hold area, airliner fuselages have another feature
that could be used to advantage: a tendency to break in certain places. The
fracture zones often lie between the nose and the wing, aft of the wing, and
just in front of the tail. Some crash-proofing designers propose making a virtue
of this. Ed Fasanella, who is working with Jackson at Langley, says that the
break points could be designed to absorb extra energy, and to provide escape
points for passengers. Jones agrees, and advocates removing several rows of
seats either side of the break points and replacing them with galleys and
toilets. This would ensure that passengers were at a safe distance from the
opening at an impact.
Once these changes to the fuselage design have been made, attention can turn
to the interior. First on the crash-proofer鈥檚 agenda is the passenger seat.
Donat Desmond, a survivor of the Kegworth crash, is now 4 centimetres shorter
than when he boarded the plane. Although this was a crash-landing at relatively
low velocity, close to normal landing speeds, passengers in the worst affected
parts of the aircraft were crushed by forces up to 28 times their weight. Some
suffered broken femurs or spinal injuries. Desmond鈥檚 spine was compressed as a
result of being pressed down into the tough metal seat frame during impact. The
forces, and lack of shock absorption, pushed some seats through the cabin
floor.
More than a decade later, seats, cabins and floors identical to those in the
Kegworth crash are still rolling off plane makers鈥� production lines. Yet seat
designs like those now used by the military could soften impact forces in future
crashes, and potentially save lives. Military helicopters are now fitted with
energy-absorbing 鈥渟troke seats鈥�, designed by Desjardins. 鈥淭here have been a few
severe crashes with the new seats where occupants got bruised a bit but
otherwise survived,鈥� Desjardins says. 鈥淚n some cases the aircraft were destroyed
but the seats and the pilots remained intact.鈥� He believes the same technology
could be used to make energy-absorbing floor anchorages for passenger
aircraft. As well as reducing spinal injuries, this could dampen the forward
motion of the seat and prevent the crushing of passengers towards the front of
the plane.
Some other innovations are less straightforward. Seat belts can make the
difference between life and death, but how do you put secure, three-point
harnesses鈥攍ike those used in cars鈥攊n a standard airliner? No one can
agree on where to fix the shoulder strap. Anchor it to the seat back and you
need a completely new seat design to take the force of a crash. An alternative
is to fix it to the cabin roof, but some fear that this could produce a cat鈥檚
cradle of webbing that would block emergency exits and hamper rescuers after an
accident. Another popular suggestion for improving crash survivability is
turning the seats round. All the Royal Air Force鈥檚 VC-10 transports are fitted
with rearward-facing seats, but in commercial aircraft this too would mean
redesigning the seats to take the load they would experience in a crash. This
measure is still under review.
There are other improvements that would heighten crash survivability,
however. Overhead lockers often burst open on impact and send their contents
hurtling through the cabin. Strengthening the lockers would prevent this. Fire
is another killer. Simula estimates that one-fifth of passengers that die in
crashes are killed by fire, not the impact. This fire is usually fed by spilt
fuel. While the toughened fuel tanks fitted to military aircraft might not suit
airliners, because they restrict the amount of fuel that can be carried, Jones
says that valves that automatically shut off fuel flow if the wings break off
could be fitted even to existing planes.
Jones hopes to mount a dramatic demonstration of the power of crashworthy
design sometime in 2004. Her plan is to acquire a small airliner and crash-proof
just one section of it, leaving the remainder unchanged. Then she鈥檒l simulate a
crash-landing by swinging it from the Langley gantry. Jones is confident this
demonstration will show the worth of installing crash-proofing measures in
existing aircraft.
But she is well aware that the plane makers are unlikely to take up her
suggestions, not least because鈥攑aradoxically鈥攑eople might sue them
if they did. 鈥淥ne of the responses we get from airlines and aircraft
manufacturers is that if they retrofit a safety feature like a better seat, then
someone injured or bereaved in an earlier accident can make a liability claim,鈥�
she says. The fact that the seats had to be changed looks like an admission that
there was something wrong with their predecessors.
As a result, aircraft manufacturers tend to do the minimum that鈥檚 required
under official regulations. Replacing the current lap belt with three-point
belts is 鈥渁n issue for the airworthiness authorities鈥�, according to Airbus
spokesman David Vailypilai. Preventing passengers placing heavy objects in the
overhead lockers is 鈥渦p to the airlines鈥�.
The plane makers are focussing on different concerns. 鈥淲e are trying to make
something that is not only safe but which also makes operational and commercial
sense,鈥� says Vailypilai. 鈥淲e put all of our efforts into making sure our
aircraft don鈥檛 crash.鈥� Airbus鈥檚 policy is that extra safety considerations ought
to be left to the regulators.
Boeing has a similar approach. 鈥淚t comes down to deciding whether prevention
is better than crash-proofing,鈥� says spokeswoman Liz Verdier. 鈥淲e are working on
ways to mitigate approach and landing accidents鈥攎ost of our efforts tend
to be in preventing the occurrence in the first place.鈥�
That seems to leave changing the safety regulations as the best hope for
improving crashworthiness. But the Federal Aviation Administration, the official
regulatory authority for US aviation鈥攁nd therefore the de facto regulator
for much of the flying world鈥攊s almost powerless to demand sweeping
changes. Even relatively minor safety changes to aircraft require an
international treaty agreed with the FAA鈥檚 European counterparts. Negotiating
its terms is an extremely lengthy process. 鈥淲e are trying to make the
manufacturers aware of new ways of building airplanes, but these things will not
happen overnight鈥攖his will take years,鈥� says Frings. US legislation also
requires the FAA to conduct a cost-benefit analysis before demanding changes
which could affect airline economics. 鈥淲e don鈥檛 want to regulate people right
out of business,鈥� Frings says. Some safety campaigners believe the FAA gives too
much weight to these commercial concerns. 鈥淭hey have the power to make changes
aboard every aircraft flying in and out of the USA鈥攊f they want to use
it,鈥� says Gail Dunham, president of the National Air Disaster
Alliance/Foundation, a group representing air-crash survivors and victims鈥�
relatives.
Pressure from the accident investigation boards might make a difference to
the situation. Or there might just be another way. With airlines often in bitter
competition with each other, flying demonstrably safer planes might offer a
commercial edge. If just one airline were willing to step out and invest in the
new technology of passenger safety, everything could change very quickly. In the
coming era of weekly crashes, there should be plenty of people who prefer to fly
the safer skies.
