Ir. Franc J.M. Buijsen - NDT

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)


�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


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


On aircraft situation

A-frame

(looking up)

Side-view rear frame


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


Some corrosion examples

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


Magnetic indication of weld defect

Typic

al w

eld d

efec

t


Res

ult: SB

F50-7

1-0

48

�Measurement of the weld defect

–Paper test


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


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)


Ir. Franc J.M. Buijsen - NDT

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