Another Ancient Military Plane Grounded

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."

Originally Posted by Jay Honeck

My comments are related to the fact that these planes are old and past
due for replacement.

With that "logic" can we safely say your 30+year old Cherokee is old and past due for replacement?

You have obviously never served in the military, and don't have a clue to the various missions of each branch, much less the capabilities of their respective aircraft.

With that "logic" can we safely say your 30+year old Cherokee is old
and past due for replacement?

You have obviously never served in the military, and don't have a clue
to the various missions of each branch, much less the capabilities of
their respective aircraft.

Clearly your contention is that the grounding of the P-3s and F-15s
was unnecessary. On what do you base this assessment?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

rotor&wing wrote in
:

You have obviously never served in the military, and don't have a
clue to the various missions of each branch, much less the
capabilities of their respective aircraft.

I see, you know for a fact that he doesn't have a DD-214?

--

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

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.

I don't understand. Overdesign doesn't necessarily mean greater longevity;
by definition, over design means that there is too much of something to
meet the requirements. If the spec is zero fatigue failures in X years,
then overdesign gives the same x years and there is waste. Were the planes
designed for 50 years, 25 years?

(Paul Tomblin) wrote in
:

In a previous article, "Steven P. McNicoll"
said:
"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.

Maybe that's where they make McPlanes?



Maybe he worked for Ronald McDonald. :-)

--
Marty Shapiro
Silicon Rallye Inc.

(remove SPAMNOT to email me)

On Dec 20, 7:26*pm, wrote:

----------- snip F-15 grounding story -------------

conspiracy mode on

The USAF has made it clear they'd like a lot more F-22s... If for some
reason
a big % of their front-line fighters (F-15) couldn't fly, might that
be used for leverage with
Congress to approve funding for more 5th gen fighters? I'm just
sayin'...

If the USAF wasn't so hell-bent on having the latest tech in their
planes, I'm sure Boeing & Lockheed Martin
could sell them more brandy-new Eagles and Falcons. Probably for a
good price too.

conspiracy mode off

As far as bang for the buck, the old platforms still flying like the
C-5, P-3, B-52, KC-135 are still getting the job done, but at a huge
cost to maintain. How many times have the H model Stratoforts been
essentially rebuilt and updated? Same with the KC fuelers (new
engines) That ain't cheap, and the 52s are still fuel pigs because of
their old engines. Witness the C-5 RERP project which is hanging
modern CF6-80 engines and upgrading the flight deck to glass. Way over
budget, and the original plans to convert all the Galaxys has been
pared down to just the C-5Bs due to corrosion issues and program cost.
I've read many accounts of airborne engine/prop failures in the P-3
fleet, but as that plane descended from the L188 Electra from the 50's
it doesn't surprise me. Old airframes flying in a corrosive
environment just means that much more maintenance. The KC-XXX contract
is supposed to be decided in February/March next year and that's way
overdue.

If the USAF wasn't so hell-bent on having the latest tech in their
planes, I'm sure Boeing & Lockheed Martin
could sell them more brandy-new Eagles and Falcons. Probably for a
good price too.

In the "olden days" (like, the 1950s-60s) up throught Robert McNamara,
the USAF always had a "range" of fighters to do different jobs. Since
(I presume) the assembly line for Falcons/Vipers could be re-started
fairly easily, you'd think the Air Force would want a few dozen
squadrons of F-16s, and two squadrons of F-22s, rather than (for
example) just eight squadons of F-22s...

Given the current status of our Air Force -- essentially impotent in
the War on Terror, and shrinking fast -- this would seem the most
logical path for them to take. At the rate they're going, in ten
years we'll have a single squadron of fighters on each coast and one
on the Gulf of Mexico, a hand-full of bombers and tankers -- and
that's about it. Everything else will be Air National Guard.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:
If the USAF wasn't so hell-bent on having the latest tech in their
planes, I'm sure Boeing & Lockheed Martin
could sell them more brandy-new Eagles and Falcons. Probably for a
good price too.

In the "olden days" (like, the 1950s-60s) up throught Robert McNamara,
the USAF always had a "range" of fighters to do different jobs. Since
(I presume) the assembly line for Falcons/Vipers could be re-started
fairly easily, you'd think the Air Force would want a few dozen
squadrons of F-16s, and two squadrons of F-22s, rather than (for
example) just eight squadons of F-22s...

The services always seem to want a clean sheet design for new aircraft,
which generally raises the cost substantially.

No one seems to want to take a usefull old design and just improve
it where the technology has advanced, such as in engines, avionics,
and materials.

Though to be fair the Air Force is doing that with the C-130 and
the Army with the CH-47.

Given the current status of our Air Force -- essentially impotent in
the War on Terror, and shrinking fast -- this would seem the most
logical path for them to take. At the rate they're going, in ten
years we'll have a single squadron of fighters on each coast and one
on the Gulf of Mexico, a hand-full of bombers and tankers -- and
that's about it. Everything else will be Air National Guard.

Which is probably as it should be as there is no Soviet Union with
waves of bombers poised to attack the US for fighters to defend against
nor a Soviet Union with US bombers flying 24/7 poised to attack in
retribution.

Plus in an era of ICBM's and cruise missles, the days of massive
fighter dog fights and protection of bombers are essentially over.

The current requirement is mostly for transport of the Army and
ground support for the Army.

It doesn't take supersonic bombers or Mach 3 fighters to do that.

--
Jim Pennino

Remove .spam.sux to reply.

On Dec 21, 1:05 pm, wrote:
Jay Honeck wrote:
If the USAF wasn't so hell-bent on having the latest tech in their
planes, I'm sure Boeing & Lockheed Martin
could sell them more brandy-new Eagles and Falcons. Probably for a
good price too.
In the "olden days" (like, the 1950s-60s) up throught Robert McNamara,
the USAF always had a "range" of fighters to do different jobs. Since
(I presume) the assembly line for Falcons/Vipers could be re-started
fairly easily, you'd think the Air Force would want a few dozen
squadrons of F-16s, and two squadrons of F-22s, rather than (for
example) just eight squadons of F-22s...

The services always seem to want a clean sheet design for new aircraft,
which generally raises the cost substantially.

No one seems to want to take a usefull old design and just improve
it where the technology has advanced, such as in engines, avionics,
and materials.

Though to be fair the Air Force is doing that with the C-130 and
the Army with the CH-47.

Given the current status of our Air Force -- essentially impotent in
the War on Terror, and shrinking fast -- this would seem the most
logical path for them to take. At the rate they're going, in ten
years we'll have a single squadron of fighters on each coast and one
on the Gulf of Mexico, a hand-full of bombers and tankers -- and
that's about it. Everything else will be Air National Guard.

Which is probably as it should be as there is no Soviet Union with
waves of bombers poised to attack the US for fighters to defend against
nor a Soviet Union with US bombers flying 24/7 poised to attack in
retribution.

Plus in an era of ICBM's and cruise missles, the days of massive
fighter dog fights and protection of bombers are essentially over.

The current requirement is mostly for transport of the Army and
ground support for the Army.

It doesn't take supersonic bombers or Mach 3 fighters to do that.

--
Jim Pennino

Remove .spam.sux to reply.

Mao charlie will soon be the next boogie man..don't close those Lock-
Boe-Northrop factories yet...JG