[A320] Engine Stall Risk in IAE V2500-A5 Engines (SelectTwo, SCN22 Software)

Subject: Engine Stall Events and Mitigation Strategies for IAE V2500-A5 Engines (SelectTwo Configuration, SCN22 Software)

Summary:

This document addresses a series of engine stall incidents involving IAE V2500-A5 engines configured as "SelectTwo" and equipped with software version SCN22. These stalls occurred during descent at low altitudes and primarily affected engines with high compressor cycles. The document outlines the identified risk factors, mitigation strategies, and a permanent resolution.

Background:

• Between September and November 2018, eight engine stall events were reported, all resulting in In-Flight Shutdowns (IFSDs) with no engine relight due to low altitude.
• Extensive investigations yielded no conclusive hardware-related cause for the stalls.
  

Risk Factors:

• Events occurred at or below 5,000 feet altitude.
• Affected engines had High Pressure Compressors exceeding 10, 000 cycles since new/overhaul.
• "SelectTwo" configuration with SCN22 software was present.
• Packs or engine bleed valves were OFF (normally ON).
  

Investigation and Mitigation:

• Analysis revealed a potential for engine stall and IFSD during approach under the aforementioned conditions.
• SCN22 software closes the engine stability bleed valve (7A) in descent for performance improvement.
• This, combined with a closed aircraft bleed valve (failure or MMEL), could overload the High Pressure Compressor and trigger a stall.
  

Interim Mitigation:

• Airbus FOT 999-0094-18-00: Recommended using Nacelle Anti-ice (NAI) during descent below 10, 000 feet when MMEL applied to closed bleed or pack valves.
• This recommendation was incorporated into MMEL and Flight Crew Operating Manual (FCOM) updates.
• Operators have discretion to apply this recommendation fleet-wide or to affected aircraft only.
• Maintenance: Expediting maintenance on closed bleed or pack valves in affected aircraft (SCN22, HPC > 10, 000 cycles) was suggested to reduce reliance on NAI use.
  

Permanent Resolution:

• A new EEC software version, SCN23, modifies the logic of the 7A bleed valve closure, considering bleed consumer status and ensuring sufficient stall margin.
• This solution is available through IAE SB 73-0248 and Airbus SB 73-1138.
  

Conclusion:

While interim mitigation strategies are in place, implementing the permanent software update (SCN23) is crucial to address the root cause and ensure continued safe operation of these engines.

Note: This information is for general awareness only and should not be used for operational decision-making. Always refer to official regulatory sources and manufacturer documentation for complete and accurate directives.