Optimized tire performance is directly
related to the use and care the tire is given. While the single most important
action for obtaining optimum tire performance is a program of regular tire
inflation maintenance, user (pilot) actions and the condition of the airport
surfaces are also important. The following information is to help bring an
awareness of these important factors which can further your tire investment.
Unnecessary tire damage and excessive wear
can be prevented by proper handling of the aircraft during taxiing.
Most of the gross weight of any aircraft
is borne by the main landing gear which may consist of two, four, eight, or
more tires. The tires are designed and inflated to absorb the shock of landing
and will normally deflect about three times more than a passenger car or truck
tire. The greater deflection allows the tire to carry the heavy loads. It also
causes more working of the tread, produces a scuffing action along the outer
edges of the tread and results in more rapid wear.
If an aircraft tire strikes a chuckhole,
stone, or some foreign object lying on the runway, taxi strip or ramp, there
is more possibility of it being cut, snagged or bruised because of the high
operational deflection. If one of the main landing gear wheels, when making a
turn, drops off the edge of the paved surface, this may result in severe
sidewall or shoulder damage. The same type of damage may also occur when the
tire rolls back up over the edge of the pavement.
With dual main landing gear wheels, it is
important that they equally share the weight carried by that landing gear
As airports grow in size, and taxi runs
become longer, chances for tire damage and wear increase. Internal tire heat
buildup also can be of concern. Speed, length of rolling and stops are
all-important in influencing heat buildup. A taxi speed of 40 mph for 35,000
feet is demonstrated during the TSO certification of a tire. For either speeds
or taxi distances greater than these limits, a 5-10 minute pause is
recommended before takeoff.
For less foreign object damage in taxiing,
all personnel should make sure that ramps, parking areas, taxi strips, runways
and other paved surfaces are regularly cleaned and cleared of all objects that
might cause tire damage.
BY USING BRAKES
Increased airport traffic and longer taxi
runs are subjecting tires to more abrasion from turning and pivoting while
Severe use of brakes under pivoting
conditions can wear flat spots on tires and cause them to become out of
balance, making premature retreading or replacement necessary. Pivoting on
surfaces with heavy texture or a step condition can locally tear the tread
from the casing. This tear may not show as a separation until later in the
tire's service life.
Careful pivoting of an aircraft also helps
prolong tire tread life. When an aircraft is turned by locking one wheel (or
wheels), the tire is scrubbed, with great force, against the pavement. A small
rock or debris that would ordinarily cause no damage can virtually be screwed
into the tire. This scuffing and grinding action takes off tread rubber and
places a very severe strain on the sidewalls and bead areas of the tire at the
same time. Making wide radius turns will reduce tread rubber removal and
OF AIRPORT FIELD
Regardless of preventive maintenance and
the care taken by pilot and ground crew, tire damage is almost certain to
result if runways, taxi strips, ramps and other paved field areas are in bad
condition, strewn with debris or poorly maintained.
Chuckholes, pavement cracks or step-offs
in the pavement can all cause tire damage. In cold climates, especially during
winter, all pavement breaks should be repaired immediately.
Accumulated debris on paved areas,
including hangar floors, is especially hazardous. Stones and other foreign
material should be kept swept off all paved areas. Special attention should be
paid to make sure that tools, bolts, screws, rivets and other repair materials
are not left lying on an aircraft so that when it is moved, they fall to the
floor. If a tire rolls over such material it can result in punctures, cuts or
complete failure of the tire and tube.
Chemicals and hydrocarbons such as jet
fuel, hydraulic fluids, grease, cleaning agents, etc., can damage aircraft
tires by softening or deteriorating the rubber surface. During aircraft
maintenance, tires should be covered to protect them from accidental spills.
Keep runway surfaces clean so that tires are not parked in surface puddles.
Immediately upon contact with a hydrocarbon substance, wash the contaminated
area first with denatured alcohol then with a soap and water solution. If the
rubber feels soft or spongy when probed, remove the tire from service.
Nylon aircraft tires will develop flat
spots under static load. The degree of this flat‑spotting will vary
temperature of the tire when the aircraft is first parked,
pressure in the tire,
load being applied to the tire while the aircraft is parked,
length of time the tire is subject to a combination of the above
type of construction (under similar conditions, a radial tire will develop
less flat spotting than will a bias tire).
On a practical level, aircraft maintenance
personnel cannot influence all of these variables. To minimize the condition,
inflation pressures should be kept at their specified operating levels and
loads held to a minimum during the static load period.
Under normal conditions, a flat spot will
disappear by the end of the taxi run. In the unusual case where deep
flat‑spotting has occurred, additional taxiing is recommended prior to
An aircraft that is to remain idle for a
period longer than three days should either be moved every 72 hours or blocked
up so that no weight is on the tires. Aircraft in storage (out of service for
more than 14 days) should be blocked up so that there is no weight on the
Cross-cutting of runways is common at many
major airports around the world. It improves drainage, reduces the danger of
standing water and thus, decreases the risk of hydroplaning. However, the
sharp‑edged ridges of concrete that result can cause chevron-type
cutting of the tire tread ribs, particularly on the high-pressure tires used
on jet aircraft.
Chevron cutting occurs during aircraft
touchdown at "spin-up." As the tire begins to accept aircraft loads,
it deforms slightly in these cross-grooves. At the same time rapid
acceleration is occurring. The forces required to accelerate the tire to
ground speed cause a tearing action which forms the chevron.
These cuts are at right angles to the ribs
and rarely penetrate to the fabric tread reinforcement ply or protector ply,
Refer to the section on "Tire Serviceability Criteria" for handling
This condition results when, on a wet
runway, the tire's tread is progressively lifted off the runway surface. A
wave of water builds up in front of a rolling tire, allowing the tire to ride
on the water and lose contact with the runway surface. Loss of traction,
steering ability and braking action occurs. This action is usually referred to
as "dynamic hydroplaning." Its occurrence is a function of water
depth and aircraft speeds.
The same phenomenon can result when a thin
film of water on the runway mixes with the contaminants present or if the
surface texture of the runway is smooth. This is called, 'viscous
hydroplaning." Generally the irregular condition of the runway surface is
sufficient to break up this film.
Today, most airport runways are designed
to minimize water buildup. Cross grooving is one example. In addition, tires
have circumferential grooves which help to dissipate water.
An aircraft tire experiencing hydroplaning
(usually viscous hydroplaning) may form an area of reverted rubber or skid
burn in the tread. This area will be oval in shape similar to a flat spot. If
the reinforcing ply or protector ply is not exposed, the tire can remain in
similar reverted rubber tread condition can occur if the tire slides on ice
for any distance.
Tire removal criteria should be based on
operational and tire condition factors. To be considered are: runway cross
grooving, tire footprint area (number and remaining depth of grooves), and
level of runway flooding. When operational and tire condition factors are
conducive to hydroplaning, removal criteria should be advanced to 232"
(1.5mm) remaining skid.
Tire performance can be improved by using
slow taxi speeds and by letting the aircraft roll during landing and by
avoiding hard braking. Whenever possible, make large radius turns which
minimize tire scrubbing.