I am taking a flight purchased from United for Seattle (SEA) to Casablanca (CMN). Some segments are operated by other carriers but in United’s name. The ticket says:

United 4688 Operated by trans states airlines dba united express


United 8647 Operated by Air Canada Rouge

Whose luggage rules apply for the carry-on bag and the "personal item"? Unfortunately, the dimensions vary significantly between their various sets of rules.

Carry-on bag:

  • United: 22" x 14" x 9"
  • Air Canada: 21.5" x 15.5" x 9" | 55cm x 40cm x 23cm

Personal item:

  • United: 17: x 10" x 9"
  • Air Canada: 17" x 13" x 6" | 43cm x 33cm x 16cm
  • 1
    In my experience these size restrictions are not enforced strictly by "traditional" carriers such as United and Air Canada. If your carryon is 22 x 15.5 x 9, they'll almost certainly take it; the same with a personal item measuring 17 x 13 x 9."
    – phoog
    Commented Oct 13, 2017 at 20:55
  • I revoke my close vote, sorry, carry on is different.
    – user4188
    Commented Oct 14, 2017 at 7:31

2 Answers 2


Tripadvisor briefly mentions carry on in their AIR TRAVEL - Baggage Rules for Multi-Airline Schedules - Which Allowance? article:

Your hand baggage (carry on) allowance is determined by each airline operating the flights, and when code shares are involved it's the operating carrier. If you are traveling on multiple airlines on the same itinerary your hand baggage must comply with the strictest of the rules set by the airlines concerned.

This makes sense. If the gate dragon decides to put your 115L backpack in the sizer to force you to gate check, they won't have the time to analyze the finer points of your booking. Also, some airlines actually have reasons for their carry on rules.

But common sense apparently doesn't apply for passengers whose ultimate ticketed origin or destination is a U.S. point (and Canada):

For passengers whose ultimate ticketed origin or destination is a U.S. point, U.S. and foreign carriers must apply the baggage allowances and fees that apply at the beginning of a passenger's itinerary throughout his or her entire itinerary. In the case of code-share flights that form part of an itinerary whose ultimate ticketed origin or destination is a U.S. point, U.S. and foreign carriers must apply the baggage allowances and fees of the marketing carrier throughout the itinerary to the extent that they differ from those of any operating carrier.

This is 14 CFR § 399.87 so it's binding, Canada has a copy of it. While there's a lot of confusion whether it applies to carry on or not, apparently it does! Here's the official FAQ on it:

  1. Does section 399.87 apply to carry-on baggage policies? Does section 399.87 apply to bags other than a passenger’s first and/or second checked bags?

Section 399.87 applies to all baggage allowances and fees, including carry-on baggage policies and policies related to checked items beyond the first and second checked bags.

  • So in conclusion it seems that, for any US/Canada starting/terminating itinerary, if an operating carrier must force you to gate-check due to physical size capacity limit, at least they cannot impose a fee beyond that promised by the marketing carrier. But if your goal is to avoid a gate check, abide by the size policy of the operating carrier. Is my understanding correct? Commented Oct 14, 2017 at 14:40
  • 1
    That is certainly advisable. I have no idea what happens if someone shows up for a connecting Air Canada flight with a nine inch thick personal item which United let on and waves the transportation.gov FAQ (" including carry-on baggage policies ") at the gate dragon. Legally you might be right but is there a time to resolve this?
    – user4188
    Commented Oct 14, 2017 at 14:43
  • :-) Got it, practicalities versus legalities. Thanks for all the info. Commented Oct 14, 2017 at 14:50
  • 1
    As far as I can remember, Air Canada never enforced their sizers (United did). There was that time when AC decided to enforce carry on weight rules even for business passengers (!) but that happened at check in so I do not think even during those crazy days you would have had any issues. And, of course, after a few months, they decided they have better things to do than badger their best customers with pesky rules. So the real practical solution is not to give a beaver's ass about AC's rules... but of course, past performance is not indicative of future results.
    – user4188
    Commented Oct 14, 2017 at 16:55
  • That last sentence must be a Canadian idiom. ;-) I've learned so much from your posts today. Commented Oct 14, 2017 at 17:00

Which airline’s carry-on size limits apply

You must comply with the rules of the operating carrier. This is always the case with carry-on baggage dimensions and weight. This is due to physical differences in the aircraft. No ticket type can change the bin size ;). And safety due to seat pitch and anything else the airline determines.

Meaning, your carry-on must meet the smallest dimensions of any carrier on the itinerary. If not, the bag simply may not fit. There is no amount of bureaucratic word salad that can change basic geometry.

Note, realistically, those dimensions are effectively the same and it is highly unlikely any staff will notice unless that extra .5" UA allows prevents the AC bin from closing. If that happens, sorry, you can be Oscar Munoz, CEO of UA, and they'd still make you check the bag.

The only time baggage allowances can vary is in total allowances of checked baggage and then it depends on a number of factors such as program status and most significant carrier.

  • Correct, and if it changes, the operating carrier of the first leg applies to the complete flight (but not the return flight - there again the first operating carrier counts). Basically where you drop your bags off.
    – Aganju
    Commented Oct 14, 2017 at 1:53
  • @Aganju The Answer and Comment seem good, but can you cite some authoritative reference? Commented Oct 14, 2017 at 4:16
  • This answer is completely wrong. It's the Most Significant Carrier.
    – user4188
    Commented Oct 14, 2017 at 7:25
  • @chx We’re only looking at carry on bags here, so IATA’s MSC rule wouldn’t apply to those. And since we have a flight probbly originating from a US point, DoT regulation § 399.87 would probably apply, not MSC.
    – Calchas
    Commented Oct 14, 2017 at 7:30
  • @Aganju This question and answer are confined only to carry on bags. In the case of checked bags for tickets originating in the US, the first marketing carrier’s rules apply for the whole ticket. (But in practice you just get the most generous allowance from any one leg throughout the whole ticket.)
    – Calchas
    Commented Oct 14, 2017 at 7:32

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