Are aircraft maintenance requirements adeqate ?

[JF Mezei]

Southwest has, for a long time, been known for efficient aircraft
utilisation, doing a lot of relatively short hops and short turn arounds.

In the last few days, there have been a number of stories about WN
having problems, notably a 1.5m long hole opening in the roof of a
737-300. (15 years old).


Is maintenance frequency dictated on flight cycles, or some hybrid
cycles and age ?

In other words, is it possible that Boeing got its 737-300 certicated
with a maintenance protocol which did not take into account the type of
use that airlines such as Southwest would be making ?

Since WN is one of the first airlines to make such efficient use of
aircraft, it would be one of the first with older aircraft exhibiting
problems that wouldn't happen with legacy carriers whose planes would
have fewer cycles per year of age.

Since the trend is for all airlines to increase aircraft utilisation
rates, is it possible that all narrowbodies would see their maintenance
protocols adjusted to reflect a higher number of cycles per year ?
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[matt weber]

On Mon, 04 Apr 2011 16:08:32 -0400, JF Mezei

Post by JF Mezei
Southwest has, for a long time, been known for efficient aircraft
utilisation, doing a lot of relatively short hops and short turn arounds.
In the last few days, there have been a number of stories about WN
having problems, notably a 1.5m long hole opening in the roof of a
737-300. (15 years old).
Is maintenance frequency dictated on flight cycles, or some hybrid
cycles and age ?

Maintenance is drive by both hours, and cycles, and for some items it
is whichever happens first

Post by JF Mezei
In other words, is it possible that Boeing got its 737-300 certicated
with a maintenance protocol which did not take into account the type of
use that airlines such as Southwest would be making ?
Since WN is one of the first airlines to make such efficient use of
aircraft, it would be one of the first with older aircraft exhibiting
problems that wouldn't happen with legacy carriers whose planes would
have fewer cycles per year of age.

The Aircraft involved wasn't especially old, built in 1996. My
thumbnail says about 50,000 hours and 36,000 cycles. I would be very
suprised if there were not a number -300's with more hours and/or more
cycles. Southwest apparently does have a program where at some point
in the life of the aircraft, they will replace the aluminum 'skin'
panels.

Post by JF Mezei
Since the trend is for all airlines to increase aircraft utilisation
rates, is it possible that all narrowbodies would see their maintenance
protocols adjusted to reflect a higher number of cycles per year ?

Probably not, since a good part of the maintenance is already driven
by cycles. The question is will the FAA reduce the number of cycles
between certain maintenance events.

The FAA is likely to mandate eddy current or other inspections at
shorter invervals, and in places not previously subject to inspection
as the immediate consequence of this event.So look for an AD
(Airworthyness Directive) mandating the changes in frequency and
locations of inspections as the primary outcome.
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[jbaloun]

On Apr 4, 1:08 pm, JF Mezei <***@vaxination.ca> wrote:

snip

Post by JF Mezei
In other words, is it possible that Boeing got its 737-300 certicated
....the type of
use that airlines such as Southwest would be making ?

... number of cycles per year ?

Post by JF Mezei
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One example of higher cycle rate is the Aloha Airline case.

http://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243

I think the Aloha Airline type of usage is a higher rate than the
Southwest usage. Boeing was aware of the Aloha conditions and was
advising them on steps to take. I recall that Aloha was a little slow
on either inspections or repairs and the failure happened.

As for the upper aft fuselage that opened on the Southwest 737, the
upper fuselage between the vertical stab. and the wing is exposed to
worst case tension conditions due to the combination of pressurization
and the higher tension loads due to pull-up maneuvers. (all part of
the complex dynamics of flight load cycles). All primary structure
should include fatigue resistant details, and even more so when the
load conditions are known to be highest in tension. This case was
unexpected because all analysis indicated that it should be good for
the normal lifetime. So either there is an unexpected effect happening
on these 737s or it may trace back to a deviation during
manufacturing.

When I heard the report I imagined a case where Boeing (or
subcontractor) hired a new person to drive rivets and they were not
doing it right but they passed inspection and a few planes got into
service with some sort of damage enough to shorten the life. Hopefully
the investigation can determine the root cause. Also apparently the
cracks were below the surface and hard to detect.
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