Fatigue-Induced Crack an Aircraft Fire Extinguisher Outlet Discharge System: A Maintenance Case Study of an Airbus A330-900

Gunawan Sakti; Laila Bungas Sarwani; Hadi Prayitno; Roil Bilad

doi:10.2478/fas-2025-0009

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Fatigue-Induced Crack an Aircraft Fire Extinguisher Outlet Discharge System: A Maintenance Case Study of an Airbus A330-900

Fatigue of Aircraft Structures

AHEAD OF PRINT

By: Gunawan Sakti , Laila Bungas Sarwani , Hadi Prayitno and Roil Bilad

Open Access

|Jul 2026

Figures & Tables

Structured analysis workflow illustrating the sequential process of system evaluation.

Airbus A330-900 engine fire extinguisher system and outlet discharge location in the engine nacelle area, showing the installation zone and observed crack location.

Close-up visual observation of the crack on the outlet discharge component.

S–N curve with operational region highlighted.

Comparison between the observed crack (A) on the outlet discharge component and the simplified edge-crack model (B) used to estimate the stress intensity factor. The crack was located at the fillet/shoulder transition region and exhibited an approximate visible length of 5 mm.

Crack-growth curve obtained from MATLAB-based Paris Law simulation under elevated cyclic loading conditions.

Schematic of crack initiation and propagation mechanism.

Post-maintenance functional test sequence of the fire extinguisher system: (a) cropped excerpt of the approved task card used as the maintenance reference; (b) verification process performed on the aircraft; and (c) normal cockpit fire panel indication confirming system serviceability.

ACTION

RESULT

1. On the ENG/FIRE control panel 255VU:

–
push and hold the TEST pushbutton switch.

On the ENG/FIRE control panel 255VU:
- –
  on the ENG1/FIRE and ENG2/FIRE pushbutton switches, the FIRE legends come on.
- –
  on the ENG1 and ENG2/AGENT 1 and AGENT 2 pushbutton switches, the SQUIB and DISCH lo legends come on.
On the ENG MASTER control panel 125VU:
- –
  on the ENG1 and ENG2 FIRE/FAULT annunciators, the FIRE legends come on.
After some seconds:
- –
  the continuous repetitive chime operates.
On the CAPT and F/O glareshield panels 411VU and 412VU:
- –
  the MASTER WARN lights flash.
On the EWD:
- –
  the ENG1 FIRE and ENG2 FIRE warnings come into view with related corrective action.
On the SD:
- –
  the ENGINE page automatically comes into view.

2. On the ENG/FIRE control panel 255VU:

–
release the TEST pushbutton switch.

–
all the annunciator lights go off.
–
the continuous repetitive chime stops.
–
on the EWD, the warnings go out of view.
–
on the SD, the ENGINE page goes out of view.

Safety factor estimation results_

Parameter	Estimated Value
Allowable Stress	120 MPa
Operational Stress	95 MPa
Safety Factor (SF)	1.2
Condition	Critical / Near Limit

Methodological parameters and assumptions_

Parameter	Extracted Value / Description	Methodological Role
Aircraft type, Maintenance event	Airbus A330-900, C-Check C03	Case object, Inspection context
Component analyzed	Outlet discharge Engine fire extinguisher system	Defective component, Safety-critical aircraft system
Inspection focus	Distribution piping and outlet discharge	Data collection scope
Crack length	< 5 mm	Main observed defect size
Defect location	Engine nacelle, Zone 420	Operational environment
Operational exposure	5,642 FC and 10,834 FH	Fatigue evaluation reference
Data sources	Inspection records, visual observations, AMM & task cards	Primary evidence-based, Maintenance procedure reference
Analysis type	Qualitative and semi-quantitative engineering analysis	Analytical approach
Fatigue method	Simplified Basquin-type relation	Fatigue life estimation
Crack growth method	Paris Law-based simulation	Crack propagation estimation
Representative stress amplitude	95 MPa	Localized cyclic loading assumption
Paris Law constants	C =2.5 × 10⁻¹¹, m = 3.2, Y = 1.12	Crack growth simulation parameter
Safety evaluation	Safety factor analysis	Structural margin assessment
Risk evaluation	FMEA	System-level risk assessment
RPN equation basis	Severity × Occurrence × Detection	Failure prioritization metric

FMEA results with RPN values_

Component	Failure Mode	Cause	Effect	S	O	D	RPN	Mitigation
Outlet Discharge	Crack	Fatigue, vibration, thermal	Leakage	9	6	5	270	Replacement
Distribution Piping	Blockage	Debris	Flow restriction	7	4	4	112	Cleaning
Extinguisher Bottle	Pressure loss	Seal failure	System failure	10	3	3	90	Inspection

References

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Articles in this issue

DOI: https://doi.org/10.2478/fas-2025-0009 | Journal eISSN: 2300-7591

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Language: English

Submitted on: May 9, 2026

Accepted on: Jun 16, 2026

Published on: Jul 9, 2026

Published by: ŁUKASIEWICZ RESEARCH NETWORK – INSTITUTE OF AVIATION

In partnership with: Paradigm Publishing Services

Keywords:

Aircraft fatigue,

fire extinguisher system,

outlet discharge crack,

Paris Law,

failure mode and effects analysis,

Airbus A330-900

Related subjects:

Engineering,

Introductions and overviews,

Engineering, other

© 2026 Gunawan Sakti, Laila Bungas Sarwani, Hadi Prayitno, Roil Bilad, published by ŁUKASIEWICZ RESEARCH NETWORK – INSTITUTE OF AVIATION
This work is licensed under the Creative Commons Attribution 4.0 License.

AHEAD OF PRINT

Fatigue-Induced Crack an Aircraft Fire Extinguisher Outlet Discharge System: A Maintenance Case Study of an Airbus A330-900

Figures & Tables

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5a.

Fig. 5b.

Fig. 6.

Fig. 7.

Safety factor estimation results_

Methodological parameters and assumptions_

FMEA results with RPN values_

Paradigm

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