Airbus Hydraulics Reliability

Failure modes and possible causes

No air from compressor

• Frequent dirt on ducts
• Low reservoirs
• Fan or compressor blades minor damaged

Fire in fuel or oil system

• Losses in pressurized air to pneumatic system
• No fuel or damage to fuel supply system

Debris impacts

• Environmental strikes (e.g. bird impacts)
• Damages to engine (e.g. bird strikes)

Damage to fuel supply system

• No fuel or not pressurized
• No combustion
• Cavitation

Undergo scheduled maintenance

• Mechanical link failure
• Shafts, bearings or gears damaged

No hydraulic pressure from engine driven hydraulic pumps

• No fuel or damage to fuel supply system (Green, Yellow)
• Debris impacts (e.g. bird strikes)

Electronics valve control

• Environmental control in airports

Redundancy in Reservoirs failure failure electronics not Wear, pressurized, Supply Mechanical misalignments cavitation pressuriz failure Bleed of the spool Maintenance, ed air to valve checks after Wrong pneumati abnormal Overpressure, reservoirs c system operations Sealings failure wear, pressure (too temperatures high or too low) Fuel or oil Fire losses Frequent inspections, No fuel or Low or no maintenance damage to fuel Supply pressurization in No combustion APU ed air to reservoirs, if Safety (manual?) pneumati together with No air intake opening of air c system dual engine intake failure Damages to Undergo Mechanical shafts, bearings scheduled link failure or gears maintenance Pneumatic Loss of system Cavitation pressure Supply misfunctioning working Frequent Reservo Misfunctioning fluid to inspections, ir ng or loss of hydraulic maintenance Loss of Leakages connected system working fluid hydraulic system Damages

1. Mechanical shafts, bearings or gears
2. Pressurized blades or pistons or engine compression
3. Hydraulic rotating parts driven mechanism connected to pump failure
4. Loss of maintenance
5. Leakages
6. No electric power
7. Damage to electric system, power cables
8. Winding or damage to electric motor
9. Pressurized failure
10. Damage to mechanical shafts, bearings or pump hydraulic link failure
11. Undergo up to 21 MPa
12. Damage to blades or compression mechanism rotating parts failure
13. Loss of working fluid
14. Loss of gas pressure
15. No energy

1. Periodical reservoir or oscillations in storage inspections
2. Spring damage
3. The connected check after absorb gas dispersion
4. Diaphragm hydraulic abnormal pressure in the fluid damage system, operationsulator oscillations enhancement
5. Periodical loss of leakages inspections, working fluid compressibility effects
6. Not mechanical or RAT not safety (manual?) deployment control failures working deployment
7. Reduced or damages to careful choice of debris impact null blades position operativity
8. Emergen damages tocy mechanical shafts, bearings pressuriz link failure or gears RAT ation of hydraulic
9. No periodical inspections, maintenance of hydraulic blades or system pressurization
10. (Blue) Compression mechanism (depending on failure what volumetric pump is used)
11. Damages to hydraulic blades or motor failure pistons or rotating parts
12. Damages to no hydraulic transfer periodical hydraulic blades or power pressure

1. 63 inspections
2. pump failure pistons or transfer between maintenance
3. rotating parts PTU hydraulic check after systems Damages to abnormal Mechanical (Green, shafts, bearings 7 3 4 84 operations link failure Yellow) or gears Less Loss of hydraulic Leakages 5 3 4 60 working fluid power transfer
4. Working Loss of Less Check after Ducts Leakages 7 4 3 84 fluid working fluid hydraulic abnormal 10 displace power operations;
5. Loss of ment transfer to 7 3 5 105 scheduled pressure users maintenance
6. Links failure 8 1 1 8 Check after Fatigue, overload; Mechanical overload scheduled 8 2 3 48 failure No actuation Conversi maintenance on of No power Actuato Damages to Periodical 8 3 2 48 pressure supply r prior hydraulic inspections, into system
7. Reduced power maintenance; Less effective motion 6 4 3 72 components supply check after actuation or abnormal reduced
8. Loss of Leakages 6 4 4 48 operations excursion working fluid
9. Valve control Electronics Redundancy in 9 1 6 54 failure failure electronics
10. Wear, Control Mechanical Wrong Control misalignments

9 2 6 108 Maintenance,rudder failure control inputvalve of the spool checks afteractuation to actuators abnormalOverpressure, operationsSealings failure wear, 9 3 4 108temperatures Reduced orAllow FrequentMechanical Wear, not allowedHinge rudder 9 3 4 108 inspections,failure misalignments ruddermotion maintenancemotion

As expected, there are not dramatically high Risk Priority Numbers. The highest isrelated to a not very controllable event as debris impact. The second highest valueregards the electric motor and is quite influenced by possible low detectability of theissue, so it can be reduced by inspections and maintenance, as reported in the FMECA,but also by developing some damage detection system or some redundancies inelectric power supply. On the opposite side the lowest RPN are associated to theaccumulators, as expected from the brief discussion in the first chapter.

11Minimal Cut Sets definition (and Fault Tree Analysis)In Fig.7 the Fault Tree Analysis of the system is reported.

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The Minimal Cut Sets and their progressive derivation are listed below.

• X1 X1 X1
• X2 X2 X2
• E1 X3, X5 X3, X5
• X3, X6 X3, X6
• X1 X3, X7 X3, X7
• X2 X3, X8 X3, X8
• E2 X4, X5 X4, X5
• E3, E4, E5 X4, X6 X4, X6
• X1 X4, X7 X4, X7
• X2 X4, X8 X4, X8
• X3, X5 X5, X7 X5, X7
• X3, X6 X5, X8 X5, X8
• X3, X7 X6, X7 X6, X7
• X3, X8 X6, X8 X6, X8
• X4, X5 X9, E4, E5 X9, X14, E5
• X4, X6 X10, E4, E5 X10, X14, E5
• X4, X7 X11, E4, E5 X11, X14, E5
• X4, X8 X12, X13, E4, E5 X12, X13, X14, E5
• X5, X7 X12, X3, E4, E5 X12, X3, X14, E5
• X5, X8 X9, X15, E5
• X6, X7 X10, X15, E5
• X6, X8 X11, X15, E5
• E3, E4, E5 X12, X13, X15, E5
• X12, X3, X15, E5
• E3: X9, X16, E5 X9 X10, X16, E5 X10 X11, X16, E5 X11 X12, X13, X16, E5 X12, X13 X12, X3, X16, E5 X12, X3 X9, X17, X18, E5
• E4: X10, X17, X18, E5 X14 X11, X17, X18, E5 X15 X12, X13, X17, X18, E5 X16 X12, X3, X17, X18, E5 X17, X18
• E5: X19 X20 X21 X12, X22, X5 X12, X22, X23 12

Final MCS: X1 (…continues) (…continues) X2 X9, X15, X20 X12, X13, X14, X22, X5 X3, X5 X10, X15, X20 X12, X3, X14, X22, X5 X3, X6 X11, X15, X20 X9, X15, X12, X22, X5 X3,

X7 X12, X13, X15, X20 X10, X15, X12, X22, X5X3, X8 X12, X3, X15, X20 X11, X15, X12, X22, X5X4, X5 X9, X16, X20 X12, X13, X15, X22, X5X4, X6 X10, X16, X20 X12, X3, X15, X22, X5X4, X7 X11, X16, X20 X9, X16, X12, X22, X5X4, X8 X12, X13, X16, X20 X10, X16, X12, X22, X5X5, X7 X12, X3, X16, X20 X11, X16, X12, X22, X5X5, X8 X9, X17, X18, X20 X12, X13, X16, X22, X5X6, X7 X10, X17, X18, X20 X12, X3, X16, X22, X5X6, X8 X11, X17, X18, X20 X9, X17, X18, X12, X22, X5X9, X14, X19 X12, X13, X17, X18, X20 X10, X17, X18, X12, X22, X5X10, X14, X19 X12, X3, X17, X18, X20 X11, X17, X18, X12, X22, X5X11, X14, X19 X9, X14, X21 X12, X13, X17, X18, X22, X5X12, X13, X14, X19 X10, X14, X21 X12, X3, X17, X18, X22, X5X12, X3, X14, X19 X11, X14, X21 X9, X14, X12, X22, X23X9, X15, X19 X12, X13, X14, X21 X10, X14, X12, X22, X23X10, X15, X19 X12, X3, X14, X21 X11, X14, X12, X22, X23X11, X15, X19 X9, X15, X21 X12, X13, X14, X22, X23X12, X13, X15, X19 X10, X15, X21 X12, X3, X14, X22, X23X12, X3, X15, X19 X11, X15, X21 X9, X15, X21 Il testo formattato con i tag html sarà:

X7 X12, X13, X15, X20 X10, X15, X12, X22, X5X3, X8 X12, X3, X15, X20 X11, X15, X12, X22, X5X4, X5 X9, X16, X20 X12, X13, X15, X22, X5X4, X6 X10, X16, X20 X12, X3, X15, X22, X5X4, X7 X11, X16, X20 X9, X16, X12, X22, X5X4, X8 X12, X13, X16, X20 X10, X16, X12, X22, X5X5, X7 X12, X3, X16, X20 X11, X16, X12, X22, X5X5, X8 X9, X17, X18, X20 X12, X13, X16, X22, X5X6, X7 X10, X17, X18, X20 X12, X3, X16, X22, X5X6, X8 X11, X17, X18, X20 X9, X17, X18, X12, X22, X5X9, X14, X19 X12, X13, X17, X18, X20 X10, X17, X18, X12, X22, X5X10, X14, X19 X12, X3, X17, X18, X20 X11, X17, X18, X12, X22, X5X11, X14, X19 X9, X14, X21 X12, X13, X17, X18, X22, X5X12, X13, X14, X19 X10, X14, X21 X12, X3, X17, X18, X22, X5X12, X3, X14, X19 X11, X14, X21 X9, X14, X12, X22, X23X9, X15, X19 X12, X13, X14, X21 X10, X14, X12, X22, X23X10, X15, X19 X12, X3, X14, X21 X11, X14, X12, X22, X23X11, X15, X19 X9, X15, X21 X12, X13, X14, X22, X23X12, X13, X15, X19 X10, X15, X21 X12, X3, X14, X22, X23X12, X3, X15, X19 X11, X15, X21 X9, X15, X21

X15, X12, X22, X23X9, X16, X19 X12, X13, X15, X21 X10, X15, X12, X22, X23X10, X16, X19 X12, X3, X15, X21 X11, X15, X12, X22, X23X11, X16, X19 X9, X16, X21 X12, X13, X15, X22, X23X12, X13, X16, X19 X10, X16, X21 X12, X3, X15, X22, X23X12, X3, X16, X19 X11, X16, X21 X9, X16, X12, X22, X23X9, X17, X18, X19 X12, X13, X16, X21 X10, X16, X12, X22, X23X10, X17, X18, X19 X12, X3, X16, X21 X11, X16, X12, X22, X23X11, X17, X18, X19 X9, X17, X18, X21 X12, X13, X16, X22, X23X12, X13, X17, X18, X19 X10, X17, X18, X21 X12, X3, X16, X22, X23X12, X3, X17, X18, X19 X11, X17, X18, X21 X9, X17, X18, X12, X22, X23X9, X14, X20 X12, X13, X17, X18, X21 X10, X17, X18, X12, X22, X23X10, X14, X20 X12, X3, X17, X18, X21 X11, X17, X18, X12, X22, X23X11, X14, X20 X9, X14, X12, X22, X5 X12, X13, X17, X18, X22, X23X12, X13, X14, X20 X10, X14, X12, X22, X5 X12, X3, X17, X18, X22, X23X12, X3, X14, X20 X11, X14, X12, X22, X5(continues…) (continues…)In this analysis Minimal Cut Sets from first to sixth

1. order were identified, as reported in Tab.2.
2. 13MCS order Number of MCS detected1 22 123 274 295 366 8

Tab.2 Minimal Cut Sets orders

The most "dangerous" are the two first order MCS, related to hinges and rudder control valve, so a reliability improvement can be achieved by increasing the reliability of these two components. All second order MCS are related to the pneumatic system, so further reliability improvements can come from a reduction of the importance of the pneumatic system for our purposes, adding a parallel device, for example grantingre