Transcript Document

EC225 – UPDATE ON CURRENT SITUATION
HELICOPTER SAFETY STEERING GROUP (HSSG)
(Townhall Session – Aug 2013)
July 15
Agenda
• Status summary
• Recap of what happened
• Investigation findings and causes of failure
• Solutions to return to service
• Action by Regulators
• Assurance
• HSSG position and barrier model
• Forward outlook
HSSG
SUSPEND
FLYING
Suspension of
commercial
flights by UK &
Norway CAA in
North Sea
HSSG
INDEPENDENT
COUNSEL
January 2013
Eurocopter confirms
root cause for the
MGB shaft failure
2 sea landings
10/5/2012
22/10/2012
Launch of the investigation:
Eurocopter
& authorities (AAIB, EASA)
1st EC225
ready to return
Today to flight
EASA Certification
National Regulator
Approval
Shainin validation
GTRI Validation
Operators and
customers sign-off
SHAININ and GTRI verification with independent reports
First ground
and
flight test
campaign
Second ground
test campaign
Third ground
and flight test
campaign
Narrow down
hypothesis of
root cause for the
MGB shaft failure
Hypothesis of the
most probable
root cause for the
MGB shaft failure
Validation of
results and solutions
Reproduction of both crack
initiation scenarii on test
benches and in-flight
demonstration of the scenario
up to full rupture
Aircraft modifications and
maintenance training for
safety measures
EC225
Full
Return to
Service
SUMMARY
Investigation
• Eurocopter has thoroughly
investigated the shaft failures and is
confident that it has determined the
causes; the failure mechanism was
replicated on the test bench and in
the air.
• The investigation was independently
verified, including a review by a world
expert in fracture failures appointed
by HSSG.
• The AAIB investigation continues. An
update is expected late Q3.
• They are in constant liaison with
European and national regulators
• They do not regulate aviation
safety .
SUMMARY
Solution
• Safety proposals were endorsed by the
European Aviation Safety Agency (EASA)
and, for aircraft with safety measures in
place, the CAA has lifted the flying
restrictions over ‘hostile terrain’,
including the North Sea.
• The immediate solution uses the
existing shafts and multiple safety
barriers to enable the safe return to
service until a long term solution of a
newly designed shaft is ready.
• HSSG is confident that, with the
multiple safety barriers, the EC225
aircraft can now return to full service.
• The redesigned shaft will take 12-24
months to design, manufacture and fit
to the worldwide fleet.
SUMMARY
Communication
• After eight months of investigating,
testing, consulting and collaborating by
Eurocopter, helicopter operators, oiland-gas companies, regulators and
groups representing pilots, offshore
workers and others, the EC225 aircraft
can now return safely to full service.
• The helicopter operators are
implementing the safety measures now.
• The first aircraft will be ready to fly in a
few weeks. Timeframes for
reintroduction differ between
operators.
• Collectively, industry leadership must
now engage the workforce to restore
confidence in flying before people
board the aircraft.
INVESTIGATION - WHAT HAPPENED?
Investigation
•
•
•
•
•
The main gearbox (MGB) shafts
failed in the region of the welded
joint between the bevel gear and
the lower shaft driving the MGB
lube oil pumps
The lower shaft parted, causing
loss of drive to the lube pumps.
The aircraft could continue to fly
but had to land immediately.
The cause of failure was cracking
due to a combination of factors.
After cracks formed, they grew
around the circumference until the
shaft failed after a further 20 flying
hours.
Initial cracks formed in the weld
area, though the exact initiation
points differed.
EC225 Main Gearbox (MGB)
The vital function of the rotor system wasn’t
affected. The aircraft could keep flying for a
period, but gearbox lubrication was lost
EMERGENCY LUBRICATION SYSTEM
Other Issues
• There is an emergency lubrication (EMLUB) system fitted to the EC225 to
provide lubrication and cooling of the gearbox in the event that oil is lost.
• In both incidents the EMLUB suffered false warning alarms indicating
failure and the pilots landed immediately.
• On both occasions the EMLUB was working.
• The system indication faults have already been rectified by Eurocopter.
• During the investigation, other EMLUB defects were uncovered that
could compromise system performance. These will be rectified before
the aircraft returns to service.
• The solution to restore the full performance is:• New glycol pump with optimized flow rate
• PCB card exchange
• Change of pressure switches (optimized thresholds)
• Improved maintenance procedure with specific tools
Investigation
•
A thorough and exhaustive
investigation was carried out.
•
Many causes of failure were
considered and each had to be
looked into and ruled in or out by
engineering and testing.
•
No single cause emerged. The
failures were traced to a
combination of multiple factors.
•
The complexity and depth of the
investigation is why it took so long
to complete and to confirm the true
causes.
ROOT-CAUSE ANALYSIS
A shaft failure root cause analysis, with 149 possible
root causes, had been systematically analyzed.
The cause of crack initiation has been found, it
requires the combination of three factors:
1.
Active corrosion in localized areas submitted to
fatigue loads:
•
non conventional corrosion, acting
permanently because:
moisture remains trapped (unlike usual
corrosion) stress and temperature
2.
Plus the effect of residual stress due to the
manufacturing process.
3.
Plus the effect of stress “hot spots” due to shaft
geometry.
Many
branches to
look into
Methodology and results were challenged and
reviewed by the airworthiness authorities, Georgia
Tech Research Institute and Shainin Engineering and
HSSG independent expert.
10
Investigation – Cause of Corrosion
• The gear shaft is hollow and ventilated by air
laden with water vapour. The gearbox is hot
with the rotors turning but cools when shut
down.
Hollow shaft is open to
atmosphere
• As the shaft cools, water vapour condenses on
the metal surface as droplets – like
condensation on a shower door or dew on a
car windscreen.
• The shaft rotates at 2400 rpm, causing strong
centrifugal force. Oil sprayed into the lower
shaft by jets is carried to the weld area and
splines by this force. Water is denser than oil.
Centrifugal force throws the water out against
the inside of the shaft where it becomes
trapped under the paste.
• Water at the weld hole is believed to have
arisen during manufacture as the parts were
handled.
Oil is sprayed into the
shaft by jets
Solutions
• Immediate solution
•
Involves using the existing gear shafts
with additional safety measures.
Section through
existing shaft
• Long term solution
•
•
New gear shafts installed.
12 – 18 months to implement.
• Why not wait for the new shafts?
•
The existing shafts are safe with the
extra safety measures.
• Why is the new shaft necessary?
•
The new stronger shaft will remove the
need for the additional safety measures
required by the regulators.
Section through
new shaft
Reduced hot spots
and moisture
traps
Increased fatigue
strength
SAFETY BARRIERS - PREVENTION
Immediate Solution
• Eliminate moisture traps, prevent
active corrosion:
• Clean shaft and remove paste
• Remove and replace weld
hole plug.
Part with a small
amount of paste.
Failed part with large
amount of paste.
• Modify oil jets to spray oil further up
inside the shaft
• Improves lubrication of gear splines, reduces
wear and formation of metal dust
• Keeps weld zone clean preventing moisture
traps / corrosion
Orientation of the new
oil jets
SAFETY BARRIERS - DETECTION
Immediate Solution
• Inspect shafts regularly using ultrasonics
• Ensures early detection of small cracks preflight.
• Every 8 -11.5 flight hours
• Modify on-board health and usage
monitoring system (HUMS) to monitor shaft
vibration
• Detect cracks in flight in time to allow safe
landing.
• “MOD 45” HUMS channel is monitored
continuously and displayed in-cockpit.
• In the event of a MOD 45 alarm, the pilot
must land within 2 hours.
• After detection, pilot reduces power to slow
the crack growth rate to further increase
the safety margin.
Swiss Cheese Barrier Model
Gearbox shaft rupture
Loss of drive to oil pumps
Land immediately
(ditch if over sea)
Maintenance
cleaning to remove
residue.
Replace one of the
main gearbox oil jets
to improve
lubrication
of splines.
Ultrasonic inspection
of the weld and ledge
areas at regular
intervals
“In-flight MOD45”
HUMS monitoring
Swiss Cheese Barrier Model
Gearbox shaft rupture
Loss of drive to oil pumps
Land immediately
(ditch if over sea)
Maintenance
cleaning to remove
residue.
Replace one of the
main gearbox oil jets
to improve
lubrication
of splines.
Ultrasonic inspection
of the weld and ledge
areas at regular
intervals
“In-flight MOD45”
HUMS monitoring
REGULATORY APPROVAL
Action by the Regulators
European Aviation Safety Agency (EASA)
• EASA is the independent regulatory body responsible for the certification and
airworthiness of aircraft through Europe.
• EASA has reviewed Eurocopter’s technical findings and has validated the
proposed solutions. On 16th July, it issued an Airworthiness Directive (AD)
detailing the set of modifications and inspections required to ensure a safe
return to service for the EC225.
Civil Aviation Authority (CAA)
• The CAA is the UK regulatory body that authorises flying of civil aircraft
(including helicopters for offshore operations) in the UK.
• Following EASA’s AD, the CAA revised its Operational Directive (OD) to lift the
restrictions on flights as long as the additional safety measures mandated by
EASA were implemented in full.
• Subject to the implementation of the additional safety measures, on 16th July,
the CAA revised the restrictions.
INDEPENDENT VERIFICATION
Shainin Engineering
Expertise:
Engineering consultancy for aviation, aerospace, defence.
Retained by: Eurocopter
Scope:
Independent review of root cause analysis, findings and conclusions.
Outcome:
Confirmed that the Eurocopter investigation findings related to the crack initiation and
propagation are correct, and detailed enough to determine corrective actions.
Georgia Tech Research Institute (GTRI)
Expertise:
Highly-regarded applied research and development organization
Retained by: Helicopter operators Bond Offshore, Bristow Group, CHC Helicopter
Scope:
Validated Eurocopter’s crack propagation rate test results and the effectiveness of the
proposed crack detection methods.
Outcome:
GTRI calculations have verified the results and confirmed the suitability of the in-flight
HUMS monitoring. GTRI have delivered their final report to operators and EC.
Professor Michael Burdekin, OBE, FREng, FRS
Expertise:
International expert in strength of materials, fatigue failures and cracking
Retained by: Step Change in Safety - Helicopter Safety Steering Group
Scope:
Independent counsel on structural integrity and fracture mechanics modelling
Outcome:
the investigation, root causes findings and safety barriers solutions were soundly based
and noted the thoroughness and professionalism of Eurocopter
HSSG CONCLUSION
HSSG Supports the Safety of the EC225 Return to service
• HSSG has closely monitored the Eurocopter investigations and engaged
independent experts to ensure that the results and proposed solution
are valid and robust.
• In a special meeting of the HSSG on 17th July, the HSSG discussed the
safety measures for the interim solution to resume flying.
• Based on its understanding of the Eurocopter investigation, the actions
of the regulators, and on the independent verification, HSSG is confident
the conclusions are sound, that the multiple safety barriers are suitable
and sufficient to prevent a gearbox shaft failure, and that the EC 225 is
safe to fly.
• The focus of the HSSG is now to ensure that the oil and gas community
who will be using this aircraft are fully informed and understand why the
regulators have determined that the aircraft is safe to fly.
• HSSG has produced a communications plan, with key events, information
packs and so on, to spread the understanding.
ANY
QUESTIONS?