When a 270 request cannot be processed because the information source's system is down/inaccessible, is a 271 (version 5010 or 5010A1) response with ST, BHT, HL*1**20*0 and 2000A/AAA with AAA03=42, and SE considered a compliant response?
Are additional loops required?
This is expressly addressed in the TR3. If the Information Source's system is down/inaccessible, the compliant response requires returning 2100A AAA. 2100 AAA03 Code 42 – Unable to Respond at Current Time states "Use this code to indicate that Information Source Identified in Loop 2100A is unable to process the transaction at the current time. This indicates that there is a problem within the Information Source's system."
Use of 2000A AAA is intended for entities other than the information source (such as a clearinghouse) and would not be appropriate for the reason stated in the Request Description. 2000A AAA03 Code 42 Unable to Respond at Current Time states: "Use this code to indicate that the entity identified in either ISA08 or GS03 is unable to process the transaction at the current time. This indicates that there is a problem within the systems of the entity identified in either ISA08 or GS03 and is not related to any problem with the Information Source Identified in Loop 2100A."
Use of 2100A AAA requires ST, BHT, 2000A HL, 2100A NM1, 2100A AAA and SE segments (as well as ISA/GS/GE/IEA).