Another Ancient Military Plane Grounded

More metal fatigue. Our military might as well be a chapter of the
Antique Aircraft Association in Blakesburg, Iowa...
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Washington, USA - "Structural fatigue"
(WAPA) - The US Navy decided to ground 39 of its 161 P-3C Orion
reconnaissance planes, because according to data resulting from
examinations they show signs of "Structural fatigue on the lower
section of the wing". The aircraft will now undergo maintenance
interventions, which are expected to take from 18 to 24 months.

The P-3C Orion is a maritime patrol aircraft, produced in its first
model in the late 1950s by the Lockheed Martin Corporation, which
played an important role in the Cold War and are presently employed
among other in reconnaissance operations in the Iraq conflict. These
four-engine turboprops are expected to be gradually replaced by
Boeing's P-8A Poseidons, but the Navy counts to continue using the
P-3s until 2019. Therefore careful and periodical maintenance
activities will be needed.

Another model of aircraft of the US armed forces to have recently
showed signs of fatigue has been the F-15 jet fighter (see AVIONEWS).
(Avionews)
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How long can our guys be expected to hold the line with these ancient
airplanes?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

In a previous article, Jay Honeck said:
Another model of aircraft of the US armed forces to have recently
showed signs of fatigue has been the F-15 jet fighter (see AVIONEWS).
(Avionews)
************************************************* ************************************************** ******
How long can our guys be expected to hold the line with these ancient
airplanes?

Well, when each generation seems to cost 10 times as much as the previous
generation, I question how long until the Air Force consists of one
multi-role fighter bomber, one attack aircraft, one tanker, an AWACS, and
85 B-52s.


--
Paul Tomblin http://blog.xcski.com/
Violence is the last resort of the incompetent.
The competent, of course, make it their *first* resort.

Paul Tomblin wrote:
In a previous article, Jay Honeck said:
Another model of aircraft of the US armed forces to have recently
showed signs of fatigue has been the F-15 jet fighter (see AVIONEWS).
(Avionews)
************************************************** ************************************************** *****
How long can our guys be expected to hold the line with these ancient
airplanes?

Well, when each generation seems to cost 10 times as much as the previous
generation, I question how long until the Air Force consists of one
multi-role fighter bomber, one attack aircraft, one tanker, an AWACS, and
85 B-52s.




A far as "bang for the buck" the B-52 is the best airplane
the Air Force ever purchased

A far as "bang for the buck" the B-52 is the best airplane
the Air Force ever purchased

Agreed. Boeing must've built the BUFF hell-bent for strength, since
I've never heard about *any* fatigue issues in the fleet.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

On 18-Dec-2007, Jay Honeck wrote:

Agreed. Boeing must've built the BUFF hell-bent for strength, since
I've never heard about *any* fatigue issues in the fleet.
--
Jay Honeck

I once saw a drawing showing with shading of all the skin and structure that
has been replaced on the B-52 fleet over the years, and as I recall it
involved most of the exterior. Very little of the skin is original, if
memory serves me correctly. I think they replaced panels and structure
before fatigue became an issue.
On this topic, did ya'll know the entire USAF F-15 fleet is grounded with
the exception of the F-15Es? There was a recent crash of a Missouri ANG
Eagle in which the nose section snapped off in flight just behind the
cockpit. The pilot ejected safely. They've since identified other cracks
in the fuselage longerons of the crashed aircraft. They've found similar
fatigue cracks in eight other Eagles during four separate fleet-wide
inspections, and thet've decided not to lift the grounding order until
they are sure they've identified all of the potential areas for fatigue
cracks.
Scott Wilson

This article was just posted on a Google military aviation group. I thought
some of ya'll might like to read it.
Scott Wilson

Robins team believes last snag cleared in F-15 groundings
19-12-2007
By Gene Rector -
ROBINS AIR FORCE BASE --
After a tedious, highly detailed process much like crime scene
investigation, Robins Air Force Base engineers believe they have cleared the
last technical hurdle affecting the nation's F-15 fleet. Older models of the
supersonic fighter have been grounded three times - the latest happening
Dec. 4 - following the Nov. 2 crash of a Missouri Air National Guard F-15C.
The last two stand downs have affected only the F-15 A through D models,
about 450 aircraft. The newer, heavier and more robust F-15Es - 224 aircraft
- were returned to flight Nov. 11.
The investigation has focused on upper cockpit longerons near the canopy
area. To this point, cracks have been found in eight aircraft - all F-15Cs.
Officials zeroed in on that area after eye witnesses to the crash said the
jet appeared to separate immediately behind the cockpit during normal
training maneuvers. The pilot ejected with only minor injuries. Col. Stephen
Niemantsverdriet, 880th Aircraft Sustainment Group commander at Robins, said
cracks have been found in both the right and left upper cockpit longerons of
the eight aircraft. He said 97 percent of the fleet has been inspected.
Longerons are metal rails that run horizontally and hold the fuselage
together.
The Warner Robins Air Logistics Center at Robins is the worldwide manager of
the Air Force's F-15 fleet, providing resupply, periodic overhaul and
engineering oversight for the premier, but aging air superiority weapon
system. The F-15 first entered the Air Force inventory in 1975. The latest
model - the F-15E - joined the force beginning in the late 1980s. The fleet
averages 25 years of service. Robins engineers have issued eight inspection
orders to flying units since early November -the latest at midnight Dec. 15
- identifying areas to be inspected and the techniques to be used. "Based on
our review and interaction with Boeing and the accident board, we believe we
have captured and mitigated all the risks," Niemantsverdriet indicated.
"We're just at the point of getting the airplanes flying again, although
that decision will be made by Air Combat Command and other using command."
McDonnell-Douglas, the original manufacturer of the F-15, was purchased by
Boeing some years ago. A thinning of the longeron at a key stress point -
possibly due to a manufacturing defect - may be the root cause of the mishap
and the cracks found in the eight aircraft. "More than likely it is a
manufacturing issue and we have pulled all the Boeing material discrepancy
reports," the group commander said. "So far, we have not been able to
isolate it to a particular production run or series. The cracks show up in
aircraft as old as 1978 and as new as 1985."
Recurring checks had not called for a review of the area in the past. "It
was a 25,000 to 100,000-hour part," the colonel stressed. "So it was not
included in our depot and phase inspections. It was designed to
significantly outlast the aircraft." However, the Robins team has learned
that a number of factors create additional stress on the component - a
splice joint in the two-piece longeron with different material thicknesses
coming together, reduced width proceeding from the joint, angle variations
and changes in the canopy sill. "So a large amount of activity occurs in
that single spot," Niemantsverdriet acknowledged. "It's like a creek that
narrows down, making the water flow faster."
The inspections call for a thorough review for cracks in the longeron and a
check for prescribed thickness. "We're looking at a good portion of the
longeron - about 30 inches - and we're checking thickness at about 90
different locations. For an aircraft to be released to fly, there must be no
cracks and the thickness must meet production tolerances," he said. If
thickness issues crop up on crack-free aircraft, Boeing - at the request of
Robins - will conduct fatigue life analysis to see if the aircraft can be
returned to flight. Replacement longerons will be manufactured at Robins.
Niemantsverdriet said a production order has been placed for 15 with an
anticipated 120-day lead time. "We believe we can accelerate that," he said,
"although one of the limiting factors will be availability of material." The
Robins commander had high praise for his engineering team, the
non-destructive inspection lab on base and technicians on the center's
maintenance line who have assisted with validating and verifying inspection
orders before they were released to the flying units. "My hat's off to our
engineering team and the people who have given us a very significant amount
of support," the colonel stressed. The team may be able to enjoy Christmas
if nothing else emerges. "We pushed extremely hard over the weekend to issue
what we believe will be the last (inspection order)," Niemantsverdriet
pointed out. "They deserve kudos for all the hours they have put in that
have brought us to where we are today. They've done a great job."

On Tue, 18 Dec 2007 16:14:02 -0500, WolfRat wrote:

Paul Tomblin wrote:
In a previous article, Jay Honeck said:
Another model of aircraft of the US armed forces to have recently
showed signs of fatigue has been the F-15 jet fighter (see AVIONEWS).
(Avionews)
************************************************** ************************************************** *****
How long can our guys be expected to hold the line with these ancient
airplanes?

Well, when each generation seems to cost 10 times as much as the previous
generation, I question how long until the Air Force consists of one
multi-role fighter bomber, one attack aircraft, one tanker, an AWACS, and
85 B-52s.




A far as "bang for the buck" the B-52 is the best airplane
the Air Force ever purchased


WolfRat

Only when they had air supremacy which the fighters gave them )

Big John

On Dec 18, 1:14 pm, WolfRat wrote:


A far as "bang for the buck" the B-52 is the best airplane
the Air Force ever purchased

A friend of mine who's an aerospace engineer (used to work for
McDonald Douglas) told me that the older design often has stronger
structure than newer ones. He said in the old days the engineers had
very few tools and models for stress analysis of complex structure,
and they often overdesigned and resulted in planes that're much
stronger than the certification calls for. These days with advanced
computer model, if the certification calls for say max 3.8G and the
design goal is 15% above the certification limit, the engineers can
come up with a structure that'll break very close 4.4G, nothing more
and nothing less. The benefit of this is lighter weight and better
fuel efficiency, but it also means
the structure is not as overbuilt as older planes.

On Wed, 19 Dec 2007 00:13:24 -0800 (PST), M wrote:

On Dec 18, 1:14 pm, WolfRat wrote:


A far as "bang for the buck" the B-52 is the best airplane
the Air Force ever purchased

A friend of mine who's an aerospace engineer (used to work for
McDonald Douglas) told me that the older design often has stronger
structure than newer ones. He said in the old days the engineers had
very few tools and models for stress analysis of complex structure,
and they often overdesigned and resulted in planes that're much
stronger than the certification calls for. These days with advanced
computer model, if the certification calls for say max 3.8G and the
design goal is 15% above the certification limit, the engineers can
come up with a structure that'll break very close 4.4G, nothing more
and nothing less. The benefit of this is lighter weight and better
fuel efficiency, but it also means
the structure is not as overbuilt as older planes.

**********************************************
M

Your correct. In earlier days they used a slide rule to design and
built the birds very strong so they wouldn't fail in test phase and
when released to Squadrons.

Now with design computers they build new birds as light as possible to
meet design specs. They then fly bird in test phase and anything that
breaks they beef up. Result is the best performing bird they can
design.

This is just a laymans description but all should understand it
whether they are a Aeronautical Engineer or not )

Big John

"M" wrote in message
...

A friend of mine who's an aerospace engineer (used to work for
McDonald Douglas) told me that the older design often has stronger
structure than newer ones.


Well, he could have worked for Donald Douglas, and he could have worked for
McDonnell Douglas, but I think it unlikely he worked for McDonald Douglas.