Single Aisle CFM HMU delta-P valve seizure

1. Single Aisle CFM HMU delta-P valve seizure

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
Single Aisle CFM HMU delta-P valve seizure
Technical status, way forward and continued airworthiness
Nicolas CONSTANT
Engine Integration Certification and Continued Airworthiness
21st June 2012

2. Agenda

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
Agenda
• History of events
• Technical status and way forward
• Root-cause understanding to date
• Way forward towards root-cause
• Impact on airworthiness and mitigation actions
Risk analysis
On-going depairing at AFL / SDM / SBI ensures no unsafe condition
CFM plan to get all HMUs to below 10kfh within 24 months
EASA Proposed AD 12-035
Summary and recommendations
© AIRBUS Operations S.A.S. All rights reserved. Confidential and proprietary document.
21st June 2012

3. Background - HMU Fuel Metering System

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
21st June 2012
Background - HMU Fuel Metering System
• Through the Fuel Metering Valve (FMV) control system, the ECU orders the FMV
to rotate to modify the metered fuel flow to the fuel nozzles
• The Delta-P and by-pass valves ensure that the metered fuel flow is proportional
to the FMV area, by maintaining a constant pressure drop across the valve
• Failure of the Delta-P valve leads to failure of the FMV to regulate fuel flow, and
to engine shut-down
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4. Technical status - root-cause analysis

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
Technical status - root-cause analysis
• Water induced corrosion builds up on Hydro
Mechanical Unit (HMU) delta-p valve and
provides a rough surface for deposits from fuel
to build up and breach the clearance between the
rotating valve core and valve body
• Valve seizes and the delta p valve can no longer
regulate the pressure drop across Fuel Metering
Valve properly which results in loss of fuel flow
and engine rollback
© AIRBUS Operations S.A.S. All rights reserved. Confidential and proprietary document.
21st June 2012

5. Technical status – HMU delta-P valve investigations

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
21st June 2012
Technical status – HMU delta-P valve investigations
Valves received from 12 events
• All valves show sheared or bent drive pin which
is indicative of seized valve
• All valves show corrosion of the nitrided layer
induced by the presence of water
• All valves returned to lab have shown deposit
build up in addition to corrosion
• Lab analysis have evidenced Potassium,
Sodium, Sulphur and Copper in deposits
Event #4 - Aeroflot
Event #8 - Aeroflot
Event #7 -Rossiya
Consistent failure mode – Water induced corrosion
combined with fuel deposits causes valve to seize
© AIRBUS Operations S.A.S. All rights reserved. Confidential and proprietary document.

6. Technical status - fuel sampling results

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
21st June 2012
Technical status - fuel sampling results
• GosNIIGA fuel samples from AFL A/C VQ-BBB (event #11) and VP-BQS
Copper levels 3 orders of magnitude higher than normal
100X quantity of K found in right engine; Cadmium on fuel filter element
Gel-like compounds in deposits on filtering elements on right engine
Zinc levels 10X greater than normal
Increased electrical conductivity at 20°C
Extreme thermo-oxidative stability at 260°C
• GosNIIGA have proposed a mechanism for corrosion of the valve exacerbated by the
presence of Copper
• Presence of Copper in high concentration at temperatures of 150-160°C highly increases liberation
of water (H2O) & H2SO4 in higher concentration which in turn induce corrosion to metallic parts. It
also liberate fuel residues contributing to deposits
CFM and Airbus consider that the GosNIIGA reports (25-2012 CS GSM-AV and 31-2012
CS GSM-AV) provide indications of potential fuel contaminants having significant impact on
engine fuel system components
CFM and Airbus recommend that investigations into TS-1 fuel supply chains be launched
as a possible source of those contaminants
© AIRBUS Operations S.A.S. All rights reserved. Confidential and proprietary document.

7. Technical status – way forward

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
21st June 2012
Technical status – way forward
• Continue on corrosion mechanism understanding - launched
• Including evaluation of theory proposed by GosNIIGA and supported by fuel samples
• Fuel-wetted A/C and Engine hardware investigations - launched
• Compare hardware from event and non-event aircraft
• Testing with delta-P valve material and good TS-1 - launched
• Purpose is to determine if valve will corrode with good TS-1 sampled from AFL aircraft
• 5 valves in TS-1 fuel, 5 valves in Jet A fuel as a control
• Additional fuel sampling and analysis - launched
• TS-1 fuel to be sampled from Russian airports – other than SVO
• Jet A fuel to be sampled and analysed as a control
• TS-1 fuel supply chain investigations – not launched
• Potential HMU design changes – pending results of definitive root-cause
mechanism
© AIRBUS Operations S.A.S. All rights reserved. Confidential and proprietary document.

8. Continued airworthiness – initial risk analysis

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
21st June 2012
Continued airworthiness – initial risk analysis
• Initial risk analysis performed February 2012 on the basis of
• 6 failures at Aeroflot (AFL)
• 2 failures at Rossiya (SDM)
• 1 failure at S7 Airlines (SBI)
• Weibull model is used to determine which aircraft are at risk of
Dual In-Flight Shut-Down (Dual IFSD) on the basis of age of HMU
operating with TS-1 fuel
• It was determined that a number of aircraft fitted with 2 high-time
HMUs were above the EASA IR21 acceptable probability of 1 event
per 10^9 flying hour
• As a result, it was decided to request depairing of aircraft most at
risk at Aeroflot, Rossiya and S7 Airlines (all complete)
• Latest failure events in line with initial risk assessment
© AIRBUS Operations S.A.S. All rights reserved. Confidential and proprietary document.

9. Continued airworthiness - risk analysis ctd

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
21st June 2012
Continued airworthiness - risk analysis ctd
• The HMU flying hour of each HMU fitted to AFL, SDM and SBI aircraft is
now regularly monitored to ensure no aircraft is above the EASA
acceptable dual IFSD criteria – exemple for Aeroflot given below
© AIRBUS Operations S.A.S. All rights reserved. Confidential and proprietary document.

10. Continued airworthiness - mitigating actions

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
21st June 2012
Continued airworthiness - mitigating actions
• In the light of the current root-cause understanding, regular overhauling
of the HMU every 10000fh is the only means to avoid IFSDs
• Consequently, CFM have up-issued Cat 2 VSB CFM56-5A SB 73-0182
to i8 & CFM56-5B SB 73-0122 to i6 to request overhauling of HMU at
10000fh if operated for more than 50% time on TS-1 within any one year
period (irrespective of TS-1 adherence to spec)
• CFM have provided a consolidated plan to support airlines
operating with TS-1 fuel so that all HMUs are below 10000fh within
24 months
© AIRBUS Operations S.A.S. All rights reserved. Confidential and proprietary document.

11. Continued airworthiness - Airworthiness Directive PAD 12-035 content

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
21st June 2012
Continued airworthiness - Airworthiness Directive
PAD 12-035 content
• Requires airlines to determine if the HMU has been exposed to TS-1 for
more than 50% of fuel uploads in the preceding 12 months
• PAD is less restrictive than CFM VSBs: it request TS-1 usage assessment
over the last 12 months only - VSB requests assessment over any one year
period since last HMU overhaul.
• If so, airlines must remove the affected HMU from the engine for cleaning
and inspection, in accordance with CFM Service Bulletin (SB) CFM56-5B
73-0122 i8, or SB CFM56-5A 73-0182 i6, as applicable to engine type
• Compliance time:
© AIRBUS Operations S.A.S. All rights reserved. Confidential and proprietary document.

12. Summary

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
21st June 2012
Summary
• Airbus consider that, with the current root-cause understanding,
the actions in place are sufficient to assure Continued
Airworthiness for aircraft operated with mostly TS-1 fuel
• Adequate monitoring by CFM and Airbus of aircraft fitted with hightime HMUs, and proactively depairing when needed
• CFM plan for restoring all HMUs operated with TS-1 fuel below
10000fh within 24 months
• The Proposed EASA Engine AD 12-035 ensures the above plan is
adhered to by airlines operated with TS-1 fuel
• Technical activities towards definitive root-cause and fix are
launched, but this implies investigations into the TS-1 fuel supply
chain as a potential source of contamination; Airbus and CFM
recommend this be launched.
© AIRBUS Operations S.A.S. All rights reserved. Confidential and proprietary document.

13.

SA CFM HMU delta-P valve seizure - technical status, way forward and ctd airworthiness - EET12 - Ref. PR1208438 - Issue 1
21st June 2012
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