7.3 Mileage System & Fare Basis Codes

Mileage System & Fare Basis Codes

When pricing international air itineraries, passengers frequently travel via intermediate connecting cities rather than non-stop routes. To establish fair pricing for circuitous routings while granting passengers flexibility, IATA developed the Mileage System. In parallel, every ticketed flight segment is bound by a Fare Basis Code that encodes the rules, restrictions, and service class of the purchase.

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Fundamentals of the IATA Mileage System

The IATA Mileage System evaluates whether a passenger's chosen routing stays within acceptable distance limits relative to the direct non-stop fare. Two fundamental mileage metrics form the core of this evaluation:

1. Ticketed Point Mileage (TPM): The actual, official point-to-point distance in statute miles between two ticketed cities, as published in the IATA Air Distances Manual.
2. Maximum Permitted Mileage (MPM): The maximum distance allowed between origin and destination for a specific fare component. The MPM is established by IATA by adding a standard 20% distance allowance to the direct non-stop distance.

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TPM vs. MPM: Distance Comparison and Fare Validation

To validate a fare component, the tariff engine calculates the sum of all TPMs for the flown segments and compares it against the published MPM for the origin-destination pair.

$\text{Total TPM} = \text{TPM}_1 + \text{TPM}_2 + \dots + \text{TPM}_n$

• If Total TPM $\le$ MPM: The passenger is flying within the permitted mileage. The base fare requires no mileage surcharge.
• If Total TPM $>$ MPM: The passenger has exceeded the permitted mileage. The itinerary must be checked for Extra Mileage Allowance (EMA) or assessed an Excess Mileage Surcharge (EMS).

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Extra Mileage Allowance (EMA) Deductions

Certain geographic connecting hubs (e.g., routing via Singapore SIN, Dubai DXB, or Tokyo TYO) involve circuitous mileage that airlines actively encourage. To prevent penalizing passengers for transiting these hubs, IATA grants an Extra Mileage Allowance (EMA).

• Mechanism: EMA is a specific mileage deduction subtracted from the Total TPM before performing the MPM comparison.
• Formula: $\text{Net TPM} = \text{Total TPM} - \text{EMA}$
• Rule: EMA is non-cumulative; if multiple EMA routes apply, only the single highest applicable EMA deduction may be claimed.

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Excess Mileage Surcharge (EMS) Tiers and Formula

When the Net TPM exceeds the MPM, the excess ratio determines the Excess Mileage Surcharge (EMS) percentage applied to the base NUC fare.

$\text{Mileage Ratio} = \frac{\text{Net TPM}}{\text{MPM}}$

Official IATA EMS Surcharge Scale

Key Rule: The EMS percentage is applied to the Base NUC fare, not to taxes or Q-surcharges.

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Worked Numerical Example: EMS Calculation

Scenario: A passenger flies London (LHR) → Dubai (DXB) → Bangkok (BKK) → Singapore (SIN).

• Sum of Segment TPMs (Total TPM): 7,420 miles
• Applicable EMA (via DXB): 400 miles
• Published MPM for LHR-SIN: 6,500 miles
• Base NUC Fare for LHR-SIN: 1,200.00 NUC

Step-by-Step Calculation:

1. Calculate Net TPM: $7,420 - 400 = 7,020\text{ miles}$
2. Calculate Mileage Ratio: $\frac{7,020}{6,500} = 1.0800$
3. Determine EMS Tier: $1.0800$ falls into the range $1.0501 - 1.1000$, triggering a 10M (10%) surcharge.
4. Apply Surcharge to Base NUC: $1,200.00 \times 1.10 = \mathbf{1,320.00\text{ NUC}}$

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Deconstructing Fare Basis Codes

A Fare Basis Code is an alpha-numeric code (up to 8 characters) assigned to an airline ticket segment. It acts as a shorthand summary of ticket rules.

Syntax Example:  YHW3M      ->  Y | H | W | 3M
                 QLXAP14    ->  Q | L | X | AP14

Read a fare basis code left to right: the prime (class) code first, then any seasonality, day-of-week, fare-type and restriction elements appended by the filing carrier. Airlines file their own conventions, so the pattern below is the reliable exam knowledge, not a universal template.

Elements of a Fare Basis Code

1. Prime Code (1st Character): Indicates the primary booking class / cabin tier.
   • F, A, P: First Class family
   • J, C, D, I, Z: Business Class family
   • W, E, T: Premium Economy family
   • Y, B, M, H, K, L, Q, V, S, N, O, G: Economy Class family
2. Seasonality Code: Indicates travel period.
   • H: High season / Peak period
   • L: Low season / Off-peak
   • K: Shoulder season
3. Day-of-Week Code:
   • W: Weekend travel (Friday–Sunday)
   • X: Midweek travel (Monday–Thursday)
4. Fare Type / Flexibility Identifier:
   • EE: Excursion Fare (discounted fare with stay restrictions)
   • AP: Advance Purchase restriction (e.g., AP14 = 14-day advance purchase required)
5. Minimum / Maximum Stay Restrictions:
   • 3M / 6M: Maximum stay allowed is 3 months or 6 months.
   • 3D / 7D: Minimum stay required is 3 days or 7 days.

Worked decode — QLXAP14: Q = a discounted Economy prime code; L = low/off-peak season; X = midweek (Monday-Thursday) travel only; AP14 = 14-day advance purchase required. A client asking on the Thursday before departure to fly on a Saturday fails this fare on two counts at once — the advance-purchase rule and the day-of-week rule.