Safety in Aviation Metal Fatigue
Monday, September 22, 2014
Saturday, September 13, 2014
Post #5 Aircraft Mishaps due to NDI results negatively and possitively
In effort in providing
examples why NDT/NDI is critical in the aviation maintenance process,
the following are a couple of examples from the National Transportation Board that are a primary reason why it’s import for the inspections but to follow proper procedures in recording periodic maintenance or conduct modifications.
This first accident was caused due to failure of not recording data of implementing
Manufacture modifications and NDI/NDT technician’s failure to conduct inspections.
On May 18, 2011, about 1727 Pacific daylight time,
a modified Boeing 707, registration N707AR, operating as Omega Aerial Refueling
Services (Omega) flight 70 crashed on takeoff from runway 21 at Point Mugu
Naval Air Station, California (KNTD). The airplane collided with a marsh area
to the left side beyond the departure end of the runway and was substantially
damaged by postimpact fire. The three flight crew members sustained minor
injuries. The flight was conducted under the provisions of a contract between
Omega and the US Naval Air Systems Command (NAVAIR) to provide aerial refueling
of Navy F/A-18s in offshore warning area airspace. According to the Federal
Aviation Administration (FAA), Omega, and the US Navy, the airplane was
operating as a nonmilitary public aircraft under the provisions of 49 United
States Code Sections 40102 and 40125.
Shortly
after liftoff, when the airplane was about 20 feet above the runway and about
7,000 feet down the runway, all three crewmembers heard a loud noise and
observed the thrust lever for the No. 2 (left inboard) engine rapidly retard to
the aft limit of the throttle quadrant. The captain stated that he applied full
right rudder and near full right aileron to maintain directional control and
level the wings, but the airplane continued to drift to the left. The captain
reported that he perceived the airplane would not continue to climb and decided
to "put it back on the ground."Injuries to Persons Impact Information section his
brief for more information the three crew members sustained minor injuries.
Damage to Aircraft The airplane sustained substantial damage due to impact
forces and was partially consumed by post fire.
Figure 1. Diagram of a Boeing 707 engine nacelle strut, showing the fracture area on the midspar fitting
.
Service Bulletins and
Airworthiness Directives
To address
the midspar cracking issue, a series of Boeing service bulletins (SB) and FAA
airworthiness directives (AD) were published between 1975 and 1993, beginning
with Boeing SB 707-3183 (dated June 27, 1975). Subsequently revised and updated
(revision 1, dated May 13, 1977), SB 707-3183 called for an initial inspection
of inboard and outboard midspar fittings on the No. 2 and No. 3 engines,
followed by repetitive close visual inspections at varying flight cycles
(depending on airplane configuration) and eventual replacement of the fittings
with an improved design that incorporated larger radii of 1.0 inch in critical
areas. Replacing the fittings was a terminating action for the repetitive
inspections. The bulletin also included instructions to enlarge the pylon
access cover over the fitting for better access (for both inspection and
cleaning). Revision 2 of SB 707 3183 (dated January 28, 1988) incorporated SB
707-3377 (dated November 21, 1979), which gave instructions for the
installation of nacelle droop stripes to facilitate visual detection of broken
nacelle support structures, such as midspar or overwing fittings, by indicating
a misalignment between the nacelle strut skin and the fairing skin. The FAA
required the actions recommended in SB 707-3183 and its revisions via ADs 77
09-03, 88 24-10, 92-19-15[4], and 93 11-02.
Omega
records indicated that the company conducted the first visual inspection in
1996, shortly after the conversion. Omega observed that the AD list for the
airplane indicated that AD 93-11-02 was completed, but inspections per the
Boeing SB were entered into the maintenance program and continued until 2003,
when a records review found that, in 1983, a previous owner/operator had marked
the compliance status of the AD in effect at the time (77 09-03) with
"C" (meaning complete)[5]. This status reconfirmed to Omega that the
records showed the fittings had been replaced and inspections were no longer
necessary, and Omega deleted the inspection requirement from its maintenance
plan.[6] Following the accident involving Omega
flight 70, an examination of the No. 2 and 3 nacelle struts confirmed that both
the inboard and outboard midspar fittings were of the older design and had not
been replaced with the improved design in accordance with the AD. The
examination also noted that droop stripes had been installed on the accident
airplane nacelles, as required by the AD.
Tests and Research
Metallurgy
The Nos. 1 and 2 engine pylon
fitting components were brought to the NTSB Materials Laboratory for
examination. Metallurgical examination revealed that the No. 1 pylon-to-engine
bolts, the No. 1 engine pylon-to-wing fittings, and the No. 2 engine pylon-to-wing
fittings all failed in an overload event with the exception of the upper and
lower tangs of the inboard midspar fitting on the No 2. pylon, which failed due
to fatigue.
The upper tang of the No. 2
pylon inboard midspar fitting failed in the reduced section between the lug
where the drag support fitting was normally attached and the chromium-coated
radius, with the fatigue initiating at its upper inboard corner and occupying
approximately 15 percent of the fracture surface. Corrosion product covered the
fatigue fracture surface, consistent with it being exposed to the atmosphere
for a significant time. Chemical cleaning of the fatigue fracture surface
revealed that mechanical damage had obliterated any fatigue fracture features
that may have been generated in the upper inboard corner and the corrosion
product had obliterated any fine fatigue features, such as striations, leaving
only vestiges of crack arrest marks. The lack of striations prevented a
striation count analysis. The cleaning procedure also revealed surface fissures
on the fatigue fracture surface that were oriented parallel to arc-shaped crack
arrest marks and are consistent with high stress, low cycle fatigue
propagation.
Chromium electroplated coating
had been applied to the upper tang radii, and machining marks in the coating
adjacent to the fracture face indicated that a machining operation had been
performed after the electroplating. It is probable that the machining operation
was intended to remove any excess coating that might have interfered with the
fit of the lug in the drag support fitting. The examination noted that
machining marks would have intersected with the inner edge of the fracture face
at the inboard upper corner and may have been the fatigue initiator, but
mechanical damage in the corner prevented a determination.
The lower tang of the No. 2
pylon inboard midspar fitting failed in the inboard chromium plated radius with
the fatigue initiating at multiple locations in the upper portion of the
inboard edge and occupying approximately 1 percent of the fracture face.
The plated radii in the No. 2
pylon midspar fittings were measured at a nominal 0.38 inch, identifying them
as the older style fittings that should have been replaced in accordance with
the effective AD. The new midspar fittings have radii of 1.0 inch. (2013, January 2).
Reference
NTSB. (2013, January 2).
Omega Aerial Refueling Services flight crashed on takeoff. Retrieved from
http://www.ntsb.gov/investigations/fulltext/AAB1301.html
The next example are images of stress and heat fractures or broken of due to fatigue cracking with in a aircraft engine.
Figure 1. This is a good compression blade that will be loaded into a compression fan blade ring assembly. |
Fig 3. This is an example of figure 2. debris as tiny as it was, now shows secondary impact into this compression ring set of blades. |
Fig 4. As the compression and combustion mix as you can see this would be results in seeing a flame blow out. |
Saturday, September 6, 2014
Post #4 NDI and Fire Invesigation
In the past 14 years there have
been an increase in-flight fires some of which resulted in crashes(Wood &
Sweginnis, 2006) . A fire accident usually can be broken down using
the “Swiss cheese model method” meaning a chain of events leading up to an incident
or accident crash. Fires in some cases is due to the better understanding of
the in flight process. Other reasons involve aging or overload electrical
systems and poor choices of insulating materials. The inability of the flight
crew to identify the source of the fire (in so cases) do anything about it has
also contributed (Wood & Sweginnis, 2006) .
In avoiding an aircraft fire or a Fire Crash Investigation
(FCI) it is critical again in the NDI field to detect stress areas in the metal
prior to flight or to search for the clues that lead to the cause of the fire whether
in flight or post crash fire. This is why according to manufacture
specifications under certain conditions over the aircrafts life time, regardless
of platform, need to follow protocol and or periodic maintenance scheduling in
finding a stress build up in the aircraft structure.
In an investigation in looking for
clues is what FCI calls Slipstream effect. Since pretty much all aircraft use Aluminum, the point at which sagging and bending occur is at 850
degrees F. Might see this on a post crash fire and think in-flight fire. At 1175
degrees F the alloy will melt completely and molten metal may slipstream into
tiny droplets that might impinge on structure. Gravity droplets at the crash
scene will be larger.
Below is a chart of various metals
and their melting points, notice Aluminum is close to the bottom of the chart along with other common materials mostly used in current aircraft.
Here
are some illustrations found by NDI proving the exact area in the metal, (aluminum) that could
very well lead to or did cause fires due to over stressed areas. These images
are what NDI technicians’ are looking for after the part is manufactured before installed into service, and
while in service in figures 1 and 2.
Figure 3. The highlighted
area in yellow using Ultrasound method, being a very weak section in the weld
on a hydraulic actuator. Hydraulic oils being the heat source, is compressing
into this area therefore generating friction and heat. If this weld is weak enough or corroded enough,
its springs a leak. The temperature at which this oil comes out and (where) it
comes out could determine if a fire could start in-flight or on the ground.
Fig.4. Using Liquid Pentrant shown under black light exposing
the indication (cracked/weakened) area.
As heat is placed on an area of
metal, the metal will start to expand therefore now losing its strength. How fast it loses its strength is determined by
the source by which is originating (heat). Eutectic Melting is the lowest melting
temperature of any alloy metals in the chart above, under a
high stressed load the metal is subject to this point a phenomena accrues
called the “Broomstraw Effect” within the grains of the metal becomes pronounced
and delimitation happens between the layers/grains then one would see in a “green
stick” fracture Fig. 5. This is considered highly indicative of in-flight fire,
the assumption being that the heat occurred in flight and the stress occurred at
impact. This can also occur if the part
is under high stress as it is normally used in the aircraft and then
heated. Thus a “broom straw” fracture is
not a 100% guarantee of in flight fire.
The eutectic melting temperature of aluminum alloy is approximately 890
degree F (Wood & Sweginnis, 2006)
Figure 5.
Fig.6
Fig 6. Is an illustration as the dripping heat source impacts the structured air frame part, the heat expands and alters the metal properties and weakens the metal thus effecting its purpose used in the aircraft. NDI found this part using Ultrasound. However Eddy Current, Magnetic, or X-ray methods could expose this defect. Question is the area, size, what type of defect is being sought will determine the method used and go from their.
The breakdown of questions in the chain of fires / excess heat as follows; in methods and questions that are apart of the investigation that NDI/NDT will be considered in
Ignition
i) Ignition source must raise the temp of the combustible
vapors or mist
ii) Sparks from aluminum may not ignite jet fuel
iii) Must have sustained ignition to continue the fire
e) Solids
i) Materials may char or burn decomposing into other
compounds, some hazardous
ii) All substances will be affected by heat and may have
varying flash points and
potential for flashover
f) Aluminum alloys in aircraft
i) Prolonged heat causes structure weakening
(1) High heat / short time
(2) Low temp / long time
ii) Eutectic melting: Lowest melting point creating a “broom
straw” effect if metal is
highly stressed. Stress along metal “grain marks.” Might be
an indication of in-flight
fire as the heat weakened the metal and the impact caused
the stress. Takes about
890 degrees (warning–if the part is under a high load then
it might be an in-flight
issue).
iii) Slipstream
effect: Sagging and bending occur at 850 degrees. Might see this on a
post crash fire and think in-flight fire. At 1175 degrees
the alloy will melt completely
and molten metal may slipstream into tiny droplets that
might impinge on structure.
Gravity droplets at the crash scene will be larger.
vi) Other clues to
check
(1) Crumpled parts
(a) Check inside for fire evidence maybe in-flight or high
intensity ground fire
(2) Buried parts show fire damage that maybe occurred
in-flight
(3) Mud and soot should be on top of soot–maybe
(4) Molten metal-ground fire-puddle or pool in-flight will
have a pattern
(5) Rivet holes if failed in-flight then should be
clean–maybe
(6) Consistent fire damage. In-flight should show adjacent
parts with same fire
pattern. Equipment by fire-then other parts should show
pattern. (Lawin, 2014) .
References
Wood, H., & Sweginnis, R. (2006). Aircraft accident
investigation. Casper, Wy: Endeavor Books.
Lawin, R. (2014). Air detective tip 14. In R. Lawin (Ed.), SFTY
330 Aircraft Accident Investigation 0911Retrieved from
https://erau.blackboard.com/bbcswebdav/pid-15077989-dt-content-rid-29820714_4/institution/Worldwide_Online/SFTY_UG_Courses/SFTY_330/Air_Detective_Tips/AirDetectiveTip14_0911.pdf
Saturday, August 30, 2014
Post #3 Safety in NDI Link on Space Shuddle
I'd like to invite you in reading a little bit in how NDT helped in the investigation of the Space Shuddle Crash in 2003
click on the ink below:
http://erau.summon.serialssolutions.com/2.0.0/link/0/eLvHCXMwVd1BCgIxDAXQIi5dCYpLLzDQNm2TrsXBA8wFmiZdDt5_ZQqCeIn_eYv8zDNgoOaHJM9QWm6Wf2ItXVLT1GuR_7n80y-k1rM76H5x2_rcHq_l-wxgeWcTL1WSWKXnTIIxGQEljBBZI3asWaFqQJp_vbtZkZnmbnkjmAWbQShc3dE8rTd3Z0oqEX2LgEmriaN4RZOEAiKH8QHqmi3w
click on the ink below:
http://erau.summon.serialssolutions.com/2.0.0/link/0/eLvHCXMwVd1BCgIxDAXQIi5dCYpLLzDQNm2TrsXBA8wFmiZdDt5_ZQqCeIn_eYv8zDNgoOaHJM9QWm6Wf2ItXVLT1GuR_7n80y-k1rM76H5x2_rcHq_l-wxgeWcTL1WSWKXnTIIxGQEljBBZI3asWaFqQJp_vbtZkZnmbnkjmAWbQShc3dE8rTd3Z0oqEX2LgEmriaN4RZOEAiKH8QHqmi3w
Post # 2 Safety in NDI Operations and Maintenance
Safety in NDI
Chapter 21: Operations and Maintenance
In Aircraft Structure Repair
maintenance environment, more specific, Intermediate Level capacity, there is a
very close similarity between civilian and military maintenance production.
Military often uses the Federal Aviation Administration (FAA) guide lines as a
model, but will modify procedures as it fits the operations of the military routine
or non routine maintenance procedures.
The first step in receiving a part
for repair is to determine the damage and assess if it is repairable or not.
Assuming that it is, then the determination of what different repairs or
modification this component requires. If the component is requiring a
modification, usually that requirement is coming from the Fleet Engineer
Support Team of the aircraft company.
Same goes for the (FAA) guidelines such as the pilot compiling with
Airworthiness Directives and Service Bulletins and using out sourcing for the
maintenance.
As part of the maintenance process for
aviation components, also applies to the aircraft support equipment. The military
calls is it Government Support Equipment (GSE). These parts also pass through NDI
for inspections in order to reduce costs for purchasing new end item support or
bench equipment in effort in maintaining a smooth maintenance production flow.
If there are any modifications to
be made, either Intermediate or Depot Level maintenance may perform engine or
airframe structure modifications, weight and balance repairs. When the required
maintenance is completed, new records are entered into the aircraft life record
as the same as FAA requests the same. In
the military, it’s a requirement, not a request.
Depot Level maintenance, usually if
the aircraft itself or aircraft platform components make it to this level, it
is accompanied with its acceptance records like the Accident/Incident files plus
Service Difficulty report records, usually a the aircraft is reached its
maximum flight hours or (high time), and is scheduled to be dismantled down to
just the airframe, and all major and structural
components are inspected, serviced, NDI’d if needed ( most aircraft structural components
are NDI’d/ approved for serviceability) then reassembled, and reinstalled back
on the aircraft.
In all removal of either aircraft
or GSE components, in most cycles will require some or all of its parts to undergo
a NDI inspection for continued serviceability. NDI is the number one safety entity
in the process of proper serviceability. In the event of an aircraft accident,
parts
Air Detective Tip 13 for Aircraft
Accident Investigations
Tip 13: Paper Trail Checklist is a
detailed record accountability of the same check list as a military aircraft
changes ownership/ custody from one command squadron to another including
Intermediate and Depot Level Maintenance squadrons go through the same process.
To name a few examples are as follows:
Record and Document Checklist
1. Aircraft and Maintenance
a. Logbooks and maintenance records
b. Aircraft flight manual (AFM) and
master manual for revisions check
c. Weight and Balance documents to
include cargo manifests
d. Fueling documentation to include
location and quality, inspection of last fueling
location
e. Air Worthiness Directives (AD's)
and Commercial Service bulletins
f. Maintenance and service
inspections and repairs
g. Service Difficulty Reports
h. Cockpit and Flight Data
Recorders (do not disturb or open)
2. Operations
a. Mission and historical profile
information of flight
b. Maintenance procedures
c. Crew assignments
d. Briefing records
3. Personnel
a. Crew logbooks
b. Training and check ride
documents
c. Flight personnel packages that
is legally obtainable and relative to mishap
4. Weather
a. All METAR, NEXRADS, TAFS or
other reports available to mishap area weather
b. Witness reports of local area
c. Tower special reports
(Lawin, 2014)
Reference
Lawin, R. (2014). Air detective tip 13. In Retrieved from https://erau.blackboard.com/bbcswebdav/pid-15077977-dt-content-rid-29793014_4/institution/Worldwide_Online/SFTY_UG_Courses/SFTY_330/Air_Detective_Tips/AirDetectiveTip13_0911.pdf
Sunday, August 24, 2014
Post #1 Safety in NDI- What is NDI/NDT?
Welcome to NDI. Many people do not know about NDI or even
what NDI is. It is a crucial part of an inspection process for aircraft or for
any metal that is going to be under large amounts for stress loads. What dose
NDI stand for? Non Destructive Inspection, meaning that an assembly of many
components is left intact and we are able to inspect inside the metal or
internally without disassembly of the part. Case in point, take a land mover
Detroit diesel engine. It is very large and extremely heavy. To pull an engine
of this size and the costs associated with it are very costly. In order to save
steps and prevent wasted time diagnosing problems they call in an x-ray team.
Suppose this engine is suspected to have a cracked cylinder. An x-ray is performed on the area and an
x-ray film is produced with the image area of interest. The film does confirm
not only wear the suspected in the area but also reviled other areas that need
attention and the engine being repair.
There are six main techniques used
and there are: Eddy Current, Ultrasound, Magnetic Particle, Liquid Pentrant,
Visual, and x-ray. I’ll explain each later.
NDI has been around NDT has
been practiced for decades. Over the years, technological advances spurred
rapid developments in techniques and instrumentation. It is impossible to
identify exactly when this science began; however, we know that it has been
evolving for centuries. For example, blacksmiths used a sonic technique
(listening to a ring of different metals) to shape them as desired (Zuuk,2011).
The roots of modern NDT began
prior to the 1920s, but awareness of different methods truly came in the 1920s.
During this era there was an awareness of some of the magnetic particle tests
(MT) and X-radiography (RT) [in the medical field (Zuuk,2011).
Reference
Zuuk. (2011, Janurary 01). History of non-destructive testing. Retrieved from http://www.zuukinspection.com/ndtnde/history-of-non-destructive-testing/ Sunday, August 17, 2014
Safety in NDI and its uses
Hi all,
This a test to see if I have this blog down right. Le me know OK?
This a test to see if I have this blog down right. Le me know OK?
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