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Threshold Inspection & Application Training europe bv
Ir. Franc J.M. Buijsen
Level 3, UT, ET, MT, RT
www.tiat.nl
Development of an in service NDT
inspection procedure
�How are inspections issued:
–Based on calculations
–Based on criticality
–Based on tests
–Based on service experience
–Based on service experience
�Procedures will end up in:
–NDT manual (NDTM)
–Service Bulletin (SB)
–(Component) Maintenance Manual
Threshold inspection & application Training europe bv
Example: Fokker 50 mid-life inspections
�Because of criticality a one time
inspection is issued on certain frames
for corrosion.
This inspection is know as a mid life
�This inspection is know as a mid life
inspection
�Components involved
–(Cross frames, engine frames, brace struts,
flap track support frames)
Threshold inspection & application Training europe bv
�Engine frames (fwd, aft and A-frame)
�Steel cross frames
�Lower and upper brace struts
�Flap track support frames
Initial inspection
�Procedure nr.
•Part 2, 71-20-01, engine frames
•Part 2, 71-20-02, brace struts
•Part 2, 55-10-01, steel cross frames, hinge support frame
•Part 2, 57-53-01, flap track side support frames
Threshold inspection & application Training europe bv
For 71-20-01 the inspection required removal of the
engine frames
This was a “big” logistical problem for the customers, so an on
wing procedure was developed
Pra
ctic
al c
once
rns fo
r th
e N
DT
per
sonnel
per
form
ing thes
e in
spec
tions
�Positioning of the tube head (16 kg)
�Measuring distance
Calculating exposure time
�Calculating exposure time
�Selecting thickness (kV setting)
�Selecting the correct IQI
�Operator fatigue
Threshold inspection & application Training europe bv
On aircraft situation
A-frame
(looking up)
Side-view rear frame
Threshold inspection & application Training europe bv
Side-view rear frame
Initial inspection results
�After some time first corrosion was found an investigation was
started on the whole process
�This investigation revealed some interesting results
–Fokker 27 revealed no corrosion problems
–Corrosion protection fluid had changed being the reason for the corrosion
–When developing the procedure as a mid life inspection it was not realized
that engines can be changed very easily from aircraft to aircraft or even left
and right on the same aircraft
and right on the same aircraft
–The inspection was called out at aircraft serial number
–All radiographic inspections were registered to the aircraft
�At the time some engines were notinspected and some
engines may have been inspected several times
–Solutions:
–a SB (SBF50-71-045) was issued to re-inspect all engine frames based on
serial number (forward-, aft-and A-frame)
–Because of corrosion findings inspection has been changed into a repetitive
inspection for the engine frames
Threshold inspection & application Training europe bv
A second inspection issue
�At the end of 2004 first findings of weld defects
–During corrosion inspection weld defects were found in one
weekend on three different engine frames at the same
maintenance facility
�Research is started to investigate cause
–Cause: production defects caused by welding robot
–Cause: production defects caused by welding robot
–Defects should have been found during production
inspection
Threshold inspection & application Training europe bv
Magnetic indication of weld defect
Res
ult: SB
F50-7
1-0
48
�Measurement of the weld defect
–Paper test
Threshold inspection & application Training europe bv
SB
F50-7
1-0
49
�One time X-ray inspection of welds that were
out of lim
it–2-5 mm 2 weeks
–>5 mm no further flight
Threshold inspection & application Training europe bv
Concl
usi
on
�Fokker 50 engine frames have ended up with two
unexpected problems found during in-service
inspection which altered the inspection philosophy
–Corrosion
•Due to improper corrosion protection (engineering)
–Weld defects
•Due to welding process (manufacturing)
•Due to poor quality control (inspection)
�Inspection was called out as a mid-life inspection
(critical component) which was incorrect because
engines are interchangeable (maintenance planning)
Threshold inspection & application Training europe bv