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News & Tips ............................................................................................... 16
MayJune 1999
Vol. 47 No. 3
AVIATION MECHANICS BULLETIN
Copyright � 1999 FLIGHT SAFETY FOUNDATION INC. ISSN 0005-2140
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Foundation buys all rights to published manuscripts. Payment is made to authors upon
publication. Contact the Publications Department for more information. Managing Aircraft-tire
Wear and Damage Requires
Adherence to Removal Limits
Aircraft tire/wheel-assembly failures
involve various operational and main-
tenance factors, but detectable dam-
age to one or more tires sometimes is
the underlying cause. Such failures
occur infrequently; nevertheless, cor-
rectly maintaining tire components
whether in a new tire or a retreaded
tire helps ensure that tire/wheel
assemblies will perform reliably un-
der high static loads and dynamic
loads. The airframe manufacturers
procedures typically specify limits for
wear and damage.
Airlines typically establish tire-
maintenance procedures that
anticipate the use of products from
different tire manufacturers. The
procedures are written to comply
with applicable regulations and safe
practices developed by airframe,
wheel and tire manufacturers. When-
ever the safety of a tire is in question,
the tire should be removed from ser-
vice and should be sent to a certified
repair-and-retread station for further
inspection and disposition.
For most tire anomalies, a consensus
based on experience and testing in the
aviation industry guides an appropri-
ate response or a range of appropriate
responses. Separation of plies and
FSF Editorial Staff 2
FLIGHT SAFETY FOUNDATION AVIATION MECHANICS BULLETIN MAYJUNE 1999
tread or tire bulges, for example,
require immediate removal of the tire
from service. Nevertheless, differences
in perception or in the evaluation
criteria applied by flight crews and
maintenance crews sometimes gener-
ate questions about airworthiness, as
shown in the following incident report.
The report to the U.K. Confidential
Human Factors Incident Reporting
Program (CHIRP) in 1998 said, Dur-
ing completion of the exterior inspec-
tion prior to departure, I noticed that
the right nose-wheel tire [of a Boeing
777] was bald with several cuts down
to and, in one case, through the tire
cords. An inspection of the technical
log shows that the [extended-range
twin-engine operations (ETOPS) pre-
departure check], transit [predeparture
check] and ramp check had been
signed off as satisfactory. A verbal
question to the ground engineer as to
the serviceability of the nose wheel
received the response, Oh, thats OK
for lots more landings. Only when I
entered a defect in the tech log to
the effect of Please confirm service-
ability of right nose wheel [was] a
wheel change called for. It was then
apparent that nose wheels were out
of stock and that one needed to be
obtained from an outside contractor.
A two-hour delay resulted. I am sure
that commercial pressure played a
strong part in the attempt to dispatch
the aircraft in this state. But two peo-
ple had to sign the relevant checks and
inspections in the tech log, and I am
sure that at least one of the signatories
was signing for someone elses work.
(CHIRP note: This incident was inves-
tigated by the airline and the tire was,
in fact, serviceable, with two millime-
ters [(mm); 0.079 inch] of tread re-
maining over more than 75 percent of
the tire. The cuts referred to by the
reporter were ozone-induced cracks
and were acceptable. The airline has
since issued [tire-tread] depth gauges
to be used on this [aircraft] type).
1
The report shows that some anoma-
lies in tire/wheel assemblies are ac-
ceptable conditions and are not
cause for removal of the tire from
service. Maintenance technicians
must communicate clearly the ap-
proved tire-maintenance procedures
and the applicable wear limits or
damage limits in a given situation.
For example, spiral wrap the rein-
forcing cords wound into the tread of
some retreaded tires to reduce chev-
ron cutting and tread chunking
typically begins to show as a tire
wears, but the appearance of these
cords does not compromise safety.
(See Limits for Tire Damage Also
Involve Common Principles on page
9 for a discussion of chevron cutting
and tread chunking.)
Deviations from approved tire-
maintenance practices including as-
sessment of wear and damage have
potentially serious consequences. Sep-
aration of tires and tire treads from tire/
wheel assemblies has been cited as a FLIGHT SAFETY FOUNDATION AVIATION MECHANICS BULLETIN MAYJUNE 1999
3
causal factor in some accidents and
incidents. Typically, the reports do not
say whether the underlying damage or
wear could have been detected prior
to the event.
2
Nevertheless, one typi-
cal consequence with adverse safety
implications has been tire-tread delam-
ination on takeoff, with various de-
grees of foreign-object damage to
aircraft engines, control surfaces and
other components.
The accident and incident reporting
system (ADREP) maintained by the
International Civil Aviation Organi-
zation (ICAO) contained the follow-
ing events involving various types of
damage that originated in one or more
tires:
The report for a March 1992 in-
cident involving a tire failure on
a Boeing 737-400 during take-
off from Milan, Italy, said, On
takeoff, just after V
1
, the pilot felt
a slight bump. The crew were
unaware of any damage until the
[air traffic] controller advised
them of debris on the runway and
a passenger reported damage to
the right wing. The pilot rea-
soned that the right main gear
had suffered tire damage and
diverted to [London Stansted
Airport, England]. A tendency to
roll to the right dictated a 30-
degree flap landing, but a safe
landing was made. The tread of
the right outboard main-wheel
tire had separated completely,
although the tire remained in-
flated throughout the landing.
Half of the right gear-leg door
had been torn off, and the in-
board flap assembly was dented.
A falsework [access] panel on
the wing undersurface was also
damaged, and the inboard
ground spoiler had a 10-inch
[25-centimeter (cm)] hole in the
trailing edge. The tire, which was
on its second retread, failed af-
ter 236 landings. Examination of
the tire tread indicated a number
of cuts consistent with the tire
having run over a foreign object.
It was not possible to establish
where or when the tire had suf-
fered the damage, which led to
the tread failure, although it was
likely to have been within the last
one or two departures.
The report of a June 1990 inci-
dent involving a tire failure on a
McDonnell Douglas DC-9-50
during takeoff from Atlanta,
Georgia, U.S., said, During
takeoff, the no. 4 tire blew. The
aircraft returned and landed safe-
ly. Damage to the [tire] inner
liner consistent with underinfla-
tion was found. The maintenance
program for the operator re-
quired tire pressure to be checked
with a gauge during layover in-
spections. The inspection was
done the previous day. Recap
records revealed that the tire was
recapped and delivered to the 4
FLIGHT SAFETY FOUNDATION AVIATION MECHANICS BULLETIN MAYJUNE 1999
operator with a pinhole in the lin-
er which allowed a s