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Output Number
IR19990022
Approval Date
Published Date Time
Recommendation type
Interim recommendation
Mode
Aviation
Date released

The Bureau of Air Safety Investigation recommends that the Civil
Aviation Safety Authority initiate appropriate action to ensure
that Australian operators of Boeing 737 aircraft immediately
inspect all main landing gear actuator beam arm assemblies for
evidence of cracking.



As a result of investigation into this occurrence, the Bureau
simultaneously issues the following interim recommendatiAons:



IR990019



The Bureau of Air Safety Investigation recommends that Boeing
Commercial Airplane Group alert Boeing 737 operators to this safety
deficiency and implement an appropriate inspection program.



IR990020



The Bureau of Air Safety Investigation recommends that Boeing
Commercial Airplane Group review the effectiveness of Service
Bulletin 737-32A1224.



IR990021



The Bureau of Air Safety Investigation recommends that the Federal
Aviation Administration note the above safety deficiency and
interim recommendations and take appropriate action as considered
necessary to ensure the integrity of Boeing 737 main landing gear
actuator beam arm assemblies.



IR990023



The Bureau of Air Safety Investigation recommends that Australian
operators of Boeing 737 note the above safety deficiency and
interim recommendations and take appropriate action as considered
necessary to ensure the integrity of Boeing 737 main landing gear
actuator beam arm assemblies.

Organisation Response
Date Received
Organisation
Civil Aviation Safety Authority
Response Text

I refer to your interim recommendation IR990022 in regard to the
Actuator Beam Arm failure on B737 VH-CZL on 12th Mar 1999. The
incident resulted in substantial secondary damage to the wing
structure and flight control cables, and it was this damage, rather
than the undercarriage failure, which was of major concern (the
undercarriage is designed to fail safe).



CASA has investigated the incident, and found that this failure was
previously covered by inspections mandated by AD/B737/57. Those
inspections ceased after a modified actuator beam arm was
installed, as nominated by the AD as closing action. VH-CZL had a
modified actuator arm beam, and inspections for cracking were
therefore not required.



The significance of the secondary damage suffered by VH-CZL was
such that CASA decided to reintroduce initial and repetitive
inspections by reissue of AD/B737/57 Amendment 1. This amended AD
was issued on 29 March 1999 and requires visual and ultrasonic
inspections even if the actuator arm had been replaced. Boeing was
advised of the action and requested to advise us when suitable
terminating action is developed.



The US FAA was also advised of our action. The FAA has subsequently
issued AD 99-10-12 effective 27 May 99 to perform almost identical
work as required by the CASA AD. The FAA AD was issued as a final
form without industry consultation.



The action initiated is considered adequate to correct the unsafe
condition revealed by the incident involving VH-CZL. This action
will be reviewed when further information is received from Boeing
or the FAA.



Receipt of IR990022 enabled urgent corrective action to be
initiated by CASA, and subsequently by Boeing and the FAA.
Expeditious issue of IR990022 by BASI is therefore much
appreciated.