1. The Fundamental Mathematical Formula of Ticket Reissues
When a passenger changes a travel date, routing, or cabin class, the original ticket coupon must be exchanged for a new electronic ticket number. The financial settlement requires an exact multi-step calculation known as Additional Collection (Add-Collect).
The universal formula for determining the passenger's payment is:
2. Historical Pricing vs. Current Pricing (The Flown Coupon Rule)
One of the primary causes of massive Agency Debit Memos (ADMs) is applying current day fares to an itinerary where the passenger has already flown the outbound sector.
Under IATA Resolution 722 and ATPCO Category 31, if coupon 1 is in 'F' (Flown) status, the agent must lock the fare calculation using the historical currency exchange rate (BSR - Banker's Settlement Rate) and historical tariff active on the exact date the original ticket was issued. Only the un-flown sectors may be recalculated according to the specific Cat 31 combinability conditions.
3. Handling Residual Values: When the New Fare is Lower
When a passenger switches to a cheaper flight or lower booking class, the calculation yields a negative fare differential. Depending on the airline's ATPCO Cat 31 rules, this residual value is handled in one of three ways:
1. Non-refundable forfeiture: The difference is forfeited by the passenger and the new ticket is issued at equal value with zero refund.
2. EMD for Future Travel: The airline allows the residual balance to be issued on an EMD-S (Electronic Miscellaneous Document - Standalone) valid for 12 months.
3. Refundable balance: The residual is returned to the original form of payment through ARC/BSP refund accounting.
