Re: Is the 747-100 really "too" old ?

Date:         19 Feb 97 02:46:19 
From:         "gears" <>
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>Are planes designed to "expire" after so many cycles ? What happens to
>maintenance schedules and certification process once a plane acheives
>its expected lifetime ?

Airplanes are designed to expire, so to say, after so many cycles/hours.
The metal used in its design is subject to vibration, pressurization,
extreme temperture changes, all which cause the metal to expand and
contract each time the aircraft flies.  The expansion and contraction of
this metal causes it to fatigue after so many revolutions.  The manufacture
decided the aircraft's life expectancy based on mathimatical formulas when
the aircraft was first designed.  When the time period for the aircraft was
up, instead of grounding the aircaft and shipping it off to some desert,
the manufactures extended the life span by adding aging aircraft
inspections, these inspections being more detailed and intense than the
standard maintenance inspections the aircraft was subject to during its
initial life term.  Most of the additional inspections are attached to the
aircraft when it goes through the heavy  "c" or "d" check maintenance
inspection.  Some can be done during lesser checks such as "a" checks or
"b" checks.  The additional inspections are also regulated by either cycles
or hours.

The 747-100 aircraft, like other aging aircraft such as the DC-10, 737,
727, and so forth, are under this  type of certification program.  If a
discrepancy is found during this inspection, repairs can be made through
engineering orders and standard maintenance practices to bring the aircraft
back into service.

Additionally, throughout the aircraft's life, many service bulletins have
been made available to increase the durability of specific areas, and
airworthiness directives have been issued to mandate that certain areas of
the aircraft be improved so it can continue to fly.  All the inspections,
service bulletins, and ad's are kepted in the aircraft's records and
reviewed by Production Control, Maintenance Records and Reliability, and
Quality Assurance to ensure that all the required maintenance has been or
is scheduled to be performed.  Each type of aircraft has its own Time
Limits manual which outlines what areas need to be looked at and when, this
includes airframe, powerplant, emergency equipment, and components.

Basically, each type of aircraft is set up to receive maintenance visits at
a predetermined time.  When it gets to its life expectancy, it continues to
fly, and continues on its maintenance schedule, with more inspections
attached to it.  The heavy C checks come around approx. each year and the
heavy D checks come around aproximatley every 6-10 years, depending on the
type of aircraft and and cycle and hours interval it' s maintenance
schedule is set upon.

Hope this helps