The Most Significant Carrier Rule of IATA

When a journey uses flights from several airlines, which airline's baggage allowance applies? The answer often comes from the "most significant carrier" (MSC) rule. The 2015 version of this article explained the idea in general terms. This update shows how airlines describe it on their own pages today. IATA's passenger baggage page does not name the rule. It says that each airline's conditions of carriage always apply and that allowances vary by airline and route.

What airlines say

• Etihad: an allowance can differ on flights operated by a partner airline, and the ticket shows the allowance for each part of the trip. For trips that start or end in the United States, the first airline you fly with decides the rules for the whole trip, either its own baggage policy or that of the most significant carrier, usually the airline operating the longest part of the journey. Etihad cites the US Department of Transportation's regulations for this.
• Aeroflot: when a trip includes carriers other than Aeroflot, including codeshare flights, the allowance follows the rules of the route's most significant carrier. If separate tickets were bought for separate flights, the allowance on each ticket applies to its own flight.

A worked example

Etihad gives this case: you fly with Airline X from the United States to Abu Dhabi and then with Etihad to another destination. Airline X's rules decide your baggage allowance for the whole trip.

How to find your allowance

1. Look at the baggage allowance on your ticket or confirmation. A trip booked on a single ticket shows one allowance for each part.
2. For a trip with separate tickets, each ticket has its own allowance, and a connecting flight with a lower allowance can mean an extra charge.
3. If the trip mixes airlines, ask the airline that issued the ticket, or the airline operating the longest part, which allowance applies.
4. Read the airline's conditions of carriage if the rule is unclear.

Piece or weight

IATA notes that routes within, to or from the United States and Canada commonly use the piece concept, which counts bags rather than total weight. A common size limit for a piece is 158 cm (length plus width plus height), and many regions cap a single bag at 32 kg.