No. 2582-S-00
Revision 0 2013-05-24 Page 1/3
This document is available on the internet:
www.eurocopter.com/techpub
SAFETY INFORMATION NOTICE
SUBJECT: GENERAL
EC225/EC725 Main Gearbox Technical Investigation Update, Proposed
Improved Safety Measures and EC225 Roadmap for the complete
Return-to-Service
AIRCRAFT
CONCERNED
Version(s)
Civil Military
EC225 LP
EC725 AP
Introduction
In 2012 two EC225 helicopters made controlled water landings in the North Sea. In both incidents, the bevel gear
shaft which drives the MGB oil pumps cracked and ruptured after several further flying hours. This rupture resulted
in loss of oil pressure necessary for the MGB lubrication and along with an indicated failure of the emergency
lubrication system (EMLUB) resulted in a checklist action to land immediately.
Subsequent to the two events, protective measures were approved by EASA to permit those helicopters fitted with
similar shafts to continue flying. These measures have been implemented by a number of operators representing
approximately 50% of the affected fleet. Since the second event, in October 2012, approximately 100
EC225/EC725 and some Super Puma helicopters with similar shafts have continued to fly and these helicopters
have flown approximately 20 000 flight hours without any crack incident.
The aim of this Safety Information Notice is to update you with more detail on the technical investigation of the
EC225/EC725 Main Gear Box (MGB) events. In addition, we will present some new safety measures and provide a
roadmap to facilitate a common baseline for planning purposes. For some EC225/EC725 operators that are
currently flying, these new measures will simplify the operation and support of their aircraft. They will also lift some
restrictions for the operators’ aircraft which are equipped with the Health and Usage Monitoring System (HUMS).
The EUROCOPTER technical investigation has now determined the root causes of the crack initiation and the
characteristics of the subsequent crack propagation. Further safety measures are now being proposed by
EUROCOPTER in order to support the aircraft currently in flight and to allow the suspended fleet to safely return to
flight, starting in June/July 2013. These safety measures and their implementation are described below.
In the longer term, all affected shafts in the EC225/EC725 fleet will be replaced by new shafts. These new shafts
will have a modified design to eliminate any risk of crack initiation.
For the attention of
No. 2582-S-00
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Technical Investigation
The technical investigation has identified a combination of three root causes of crack initiation:
- Active corrosion in localised areas of the shaft;
- Reduced fatigue strength due to residual stresses inherent in the welding process; and
- Reduced fatigue strength due to stress “hot spots”.
As a result of identifying these root causes, we are able to propose:
- Additional Safety measures designed to significantly reduce the risk of crack initiation.
- New Safety measures, easier to apply than the current ones which in the unlikely event that a crack is initiated
provide warning and prevent failure.
For those operators not flying, our recommendation is that these measures should be implemented as part of a
return to service safety case. These new safety measures are detailed below.
New Safety Measures
A number of new safety measures are being discussed with the regulatory authorities. These include:
- Introduction of a shaft cleaning procedure which removes the presence of mud generated by the wear of the
splines and thus the localised humid environment on the shaft, thereby significantly reducing the possibility of
active corrosion and the likelihood of crack initiation.
- Replacement of one of the main gearbox oil jet pipes to provide permanent shaft cleaning and improved splines
lubrication.
- Introduction of an ultrasonic non-destructive inspection (NDI) as an alternative to the current eddy current
procedure. This NDI procedure, significantly faster to apply compared to the Eddy Current NDI ensures that crack
initiation should be identified before flight. The periodicity of this inspection procedure is under discussion with the
authorities and is expected to be set to permit approximately 8-10 hours flight between inspections.
- Certification of a HUMS based in-flight shaft monitoring system. When fitted, this system will consist of an
on-board cockpit amber warning to signal in-flight if vibration levels that indicate the presence of a crack. In the
event of a warning, the aircraft will continue to safely operate for sufficient flight time to permit the pilot to return to
base or perform a normal landing. Although subject to approval by the authorities, we anticipate that a flight time
of two (2) hours will be allowed following the initiation of an in-flight warning.
The shaft cleaning maintenance procedure is expected to be available in June 2013. This procedure will require
draining the MGB but does not require any new or special tools, skills, parts or consumables.
The replacement oil jet is currently being procured and is expected to be available from June 2013.
The process for performing the ultrasonic NDI inspection will be published beginning of June 2013. EUROCOPTER
training for your ultrasonic NDI inspectors will commence from 10th June. Planning is currently underway.
EUROCOPTER is studying how best to meet operator needs for additional qualified resources for these
inspections. The ultrasonic NDI inspection will require a standard ultrasonic test set and endoscope available at
your facilities, along with specific probes which EUROCOPTER will provide.
Certification of the HUMS based in-flight shaft monitoring system is expected by beginning of June 2013. Parts
ordering and aircraft modification can commence from June 2013, when the Service Bulletin is expected to be
issued.
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For aircraft equipped with HUMS, our aim is that the on-board shaft monitoring will in itself be sufficient to enable
the authorities to lift the flight restrictions over hostile terrain. For aircraft not equipped with HUMS, our aim is that
the ultrasonic NDI procedure will become an alternative to the current eddy current procedure. The classification of
which safety measures are mandatory and which are recommended is currently under discussion with the
authorities.
New Shaft Definition
In addition to these additional safety measures, the long term solution to prevent crack recurrence is to redesign
the shaft.
The redesigned shaft is expected to be certified in 2014. Production will commence in parallel with the certification
process. Production will be increased to a maximum rate to permit fleet retrofit to commence from the third quarter
of 2014. All newly delivered aircraft will be fitted with the new shafts.
The retrofit of the shafts in-service is expected to be conducted during the scheduled MGB overhaul, meaning that
the safety measures will be in-place until then. We are working hard to decrease the retrofit lead times and we will
inform you regularly on the improvements made.
Additional Information
Whilst not key contributors to the ditching root causes, the investigation unearthed some additional issues and
associated solutions:
- The emergency lubrication (EMLUB) system operated correctly but indicated failure due to a wiring problem. As a
first step the wiring on all aircraft has now been corrected. Further improvements are now planned to enhance the
effectiveness of the system. It will mainly consist of a glycol pump improvement and more precise periodic
maintenance. Detailed information on the EMLUB modifications will be published in an ALERT SERVICE
BULLETIN and a Safety Information Notice next week.
- The crash position indicator operated as designed, but it was not described in the Flight Manual. An update to the
Flight Manual has been implemented.
Way Ahead
The EUROCOPTER investigation methodology (root cause analysis) is currently being validated by the
airworthiness authorities and verified by an independent specialist, Shainin Engineering. At the same time the crack
propagation investigation is being independently assessed by the Georgia Technology Research Institute (GTRI).
Current discussions with the airworthiness authorities lead us to conclude that all approvals and validations should
be completed by June 2013. In this case EUROCOPTER estimates that the first helicopters will be ready to
return-to-service by the end of June/July 2013.
This Safety Information Notice will be updated in the first half of June, in order to describe in details the new
measures, and to allow you to better understand how the measures are linked and how they can be used.