By Marilyn Adams, USA TODAY
Like airline food and airport security, the cabin air in jetliners
is something we love to hate.
It's so dry it can make throats itch and eyes
water. It's so low in oxygen that it can induce headaches or dizziness
or it can make us tired.
Airplane maker Boeing
(BA) heard all those gripes and is promising to do something about
them. After much research, it set out to build a more comfortable cabin
air system for its 787 Dreamliner, the new long-range, midsize jet
scheduled to begin service in 2008.
Boeing says cabin air in the 787, which will seat
about 300, will contain more oxygen, more humidity and fewer pollutants
than on current jetliners. As a result, it should make passengers feel
better during and after their flights.
Where air comes from now
On airplanes flying today, cabin air comes from a
very unlikely place: the inside of the jet engine.
This so-called bleed air is diverted to the
inside of the plane before it mixes with fuel and combusts. It is so hot
and under so much pressure that it must be vented into the airplane
through ducts made of titanium, one of the strongest metals.
Before the air enters the cabin, it is cooled
and, in most cases, filtered through high-efficiency particulate air
(HEPA) filters that remove most dust, pollen, bacteria and viruses.
About 75% of the U.S. commercial fleet is equipped with HEPA filters for
But about 25% of the fleet — the oldest planes —
are not, and the Federal Aviation Administration has not required
airlines to retrofit those planes.
The FAA says studies to date have found that
airplane cabin air, even without HEPA filters, is at least as clean as
the air in most homes and offices. Nonetheless, the FAA is continuing to
fund research at universities on cabin air pollutants, filters and other
In existing planes, cabin air is compressed to
the pressure that exists at 8,000 feet above sea level. Airplanes
pressurize only to that high altitude because they're built from
numerous aluminum pieces held together by rivets and other fasteners.
Higher air pressure pushing against the inside
walls of the metal fuselage would increase wear and tear on the plane
and hasten metal fatigue, which leads to costly repairs for airlines.
The high heat of engine air — up to 530 degrees
Fahrenheit right after takeoff, when the engines are working hardest —
makes it extremely dry. The only humidity in a plane comes from the
breath of the occupants.
And because metal planes are susceptible to
corrosion, which requires costly repairs, airlines keep cabin humidity
very low — at about 4% — to keep costs down. Siphoning off engine-bleed
air also reduces the available engine power, increasing fuel
How the 787 will be different
The 787's cabin air system will be fundamentally
Cabin air will be vented directly from the
outside through dedicated inlets on each side of the plane's belly and
won't pass through the engines, says Mike Sinnett, the 787 project
The 787 system will be driven by electricity
generated by the engines. An electrical system makes it easier to
humidify the cabin air because it's not starting with the hot, dry air
from the jet engines, says physicist Hans Weber of consulting firm Tecop
International in San Diego.
With the 787 fuselage made of composite material,
it's possible to increase the humidity without corroding the airplane
over time. On the 787, the manmade composite material is formed and
baked into large barrels that are linked together to form the fuselage.
The composite material doesn't corrode as aluminum does. As a result,
the 787 cabin air system will allow 15% humidity, a more comfortable
level than the current 4%.
The 787 crew will be able to program the cabin
air system for optimal humidity based on the number of passengers
aboard, Sinnett says.
The cabin air will be compressed to resemble an
altitude of 6,000 feet above sea level, instead of 8,000 feet,
increasing the air pressure and oxygen inside the cabin.
As a result of its lower simulated cabin
altitude, the 787's air will have 8% more oxygen for absorption into the
blood. In studies, only 15% of passengers breathing 787-type air
reported throat irritation, vs. 30% of passengers breathing traditional
Put simply, "The lower you go, the better people
feel," Sinnett says.
"The impact is more pronounced the longer the
Boeing-sponsored studies have found volatile
organic gases build up inside the tight confines of a plane, making some
passengers feel ill. Sources include hand wipes, cologne and vinyl
As a result, Boeing has designed the 787 with not
only the HEPA filters now in widespread use, but also a second filtering
system that removes as many of the bad gases as possible.
Airlines wild about it
The plane is wildly popular so far, with about
400 now on order. But most of the industry fixation with the 787 is
related to economics.
The new jet will be lighter, faster and more
fuel-efficient than its predecessors or competitors, which should save
John Greenlee, flight planning director at
Houston-based Continental Airlines, says the favorable economics of
operating the plane were the top considerations in ordering 20 787s.
But the innovative ventilation system was also a
factor, he says, because it will help differentiate Continental from
"On flights of eight, 10 or more hours, we think
people will arrive feeling fresher," Greenlee says.
Aerospace consultant Richard Aboulafia of the
Teal Group in Fairfax, Va., says other airlines are likely to view the
improved ventilation as Continental does: a secondary but important
consideration in buying the plane.
"If the economics are good, comfort can help with
marketing and buzz," he says.