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Although
most of us think of airplanes as glistening specks in the sky,
they actually spend more time on the ground than they do flying.
While on terra firma, their tires play an important role in
ensuring the safe and timely operations our customers count
on us to provide. Since we get lots of questions about aircraft
tires, which are a good deal different from those on your automobile,
I’d like to tell you something about them in this month’s
column. |
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Aircraft
tires, which are still made by hand, are huge! Those on
the largest airplane in our fleet, the MD-11, range up
to 54 inches in diameter, which is more than twice the
size of a tire on a Ford Taurus. They are inflated with
nitrogen, which maintains a more even pressure than standard
air, and, when mounted on a wheel, can weigh 850 pounds
and carry as much as 210 pounds of pressure per square
inch. |
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| Crandall |
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American
maintains an inventory of about 5,000 wheel-and-tire assemblies
to support the 640 jetliners that operate our more than 800,000
flights a year. With between six and twelve tires on each
airplane, that’s more than five million tire landings
a year. A set of tire treads lasts for about 200 landings,
on average, which means that we do more than 25,000 tire changes
a year – or about 70 each day. Every tire is inspected
before every flight and when worn to a specified tread limit,
we change it.
To
support all this activity, we get about 25,000 new and newly
retreaded tires each year. Radial tires similar to those in
common use on automobiles are available for jetliners, but
they are expensive , cannot easily be retreaded, and provide
no safety advantage over the traditional bias-ply tires that
American and most other carriers use. Since the treads on
airplane tires wear much faster than the sidewalls, retreading
is a common practice. Our tires thus spend most of their productive
life as retreads, and since recapping produces a lot less
waste than discarding and replacing perfectly sound tire casings,
using bias-ply tires makes environmental as well as economic
sense.
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Although the greatest wear on tires occurs during
taxi, especially when the aircraft is turning, many passengers
think that touchdown is the toughest time for tires. That
impression is fostered by the puffs of smoke you see when the
rubber comes in contact with cement as a tire's speed goes from
zero to landing rates as high as 170 mph in a split second.
Working with our tire suppliers, we've looked at ways to "spin
up" a tire before landing to eliminate that result, but a workable
solution remains elusive, principally due to the weight it would
add.
How an airplane tire is used determines
how often it can be retreaded. Tires on the four-wheel
main gears of our DC-10s and 767s scrub off more rubber during
turns than those on the two tire main gears of our Super 80s
and 727s, for example. On average, main-gear tires can
handle from five to nine retreads, and nose-gear tires can be
recapped from three to 15 times.
Ensuring that every tire is in tip-top shape
and that we have spares in all the appropriate places is a job
of an aircraft-engineering team at our principal maintenance
base in Tulsa, Oklahoma, the many people who inspect tires,
and the line mechanics who change them at airports around the
world. They all do a first-rate job, which means you can
sit back and enjoy your flight with full confidence that the
tires are in great shape for another smooth landing.
Mr.
Crandall is former chairman of American Airlines Inc. and this
article originally appeared in the March 1997 issue of American
Way. This article used with permission of American Way. |
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