Is it possible to have different frequent flyer numbers for different flights on the same reservation?

Summary: This is technically possible, but in practice you may struggle to find an agent with the expertise and motivation to help you achieve it. Depending on your exact itinerary, a self-service work-around may be possible. As always with all things involving multiple airline IT systems, your mileage may vary.

First, some background. The details of your booking are stored in a PNR; there is a huge library of special codes that will alter how the airlines work with the booking. For loyalty purposes, the relevant ones (at least for amadeus, which is what I work with) are:

• FQTV, the account to be used for collecting miles
• FQTS, the account to be used for determining extra benefits conferred by status in the loyalty programme
• FQTR, the loyalty programme from which points were redeemed for travel

In principle, these could vary at the level of each individual flight. In practice, when booking through an airline's website you'll simply be prompted for a single frequent flyer number, with the following effects:

• It will apply to all flights on the PNR
• It will apply for both mileage earning and determining status
• Once set, it is rare for the website to offer a way to change it (but see option 3 below)

(Sometimes you can't even specify the number yourself, if it's auto-associated with your booking: this typically happens when you redeem miles for a flight. If you were hoping to enjoy the benefits of status from another airline - obviously earning on redemptions is unlikely to be possible - then you'd also benefit from the tricks below.)

However, this is a limitation of the websites rather than the underlying legacy systems - aviation IT development moves at a glacial pace, feature development is prioritised for what will improve things for typical customers, and this kind of issue is simply too niche to get attention. So you'll probably want to introduce a human into the process. There are a number of options:

1. Don't book through the website

Instead, use a travel agent, whether online or bricks-and-mortar, who knows their way around PNRs and can make the original booking with appropriate frequent flyer numbers associated to each flight. (There are some OTAs who specialise in loyalty programme maximisation like this, and will be familiar with what to do. Others may not be.)

2. Request changes to an existing booking

Here, you are looking for help from someone from the airline itself. This could be a call centre agent, check-in agent, or lounge agent. Again, expertise, policies and technical access will vary, depending on the precise airlines involved. You'll have more luck if you're a high-ranking elite member of the loyalty programme calling your dedicated support line a month in advance, than if you ask a busy third-party check-in agent on the day of departure.

3. Make changes as you travel

The idea here is to make changes at the booking level, but only after each flight has posted to the relevant loyalty programme. This will therefore depend on your itinerary; the OP mentions four flights, so if flights 1 and 2 are on the same day, it's likely that the account set for the second one will also credit the first one.

For a more typical out-and-back with a good few days in between, though, this is something I have successfully done. The changes can be made by a check-in or lounge agent, and are simpler than trying to specify flight by flight (and hence more likely to succeed!). But in the case of bookings on Oneworld airlines such as JAL, you can self-serve using the Finnair website. This will let you open a booking (using PNR and surname) and alter 'the' frequent flyer number. I have even managed to use this to get credit for a flight on BA when the original booking was with KLM, but they rebooked me after a cancellation! (I am uncertain whether this trick relies on the marketing airline using amadeus rather than sabre; comments welcome).

One concern is if the airline in question doesn't process loyalty transactions until all travel is complete, whether through IT limitations or because policy requires all flights to be taken before any credit is given (to discourage dropped final legs). If so, then presumably all flights will be assigned to the most recently set loyalty programme.

4. Claim after travel is complete

A final option is to not set a frequent flyer programme with any part of the booking, and instead make retroactive mileage claims for just the legs relevant to each programme. The problem here is that, again, online tools will probably only let you claim for an entire PNR, and when getting in touch with customer services, you'll need to be very clear that you only want to claim for a subset of the flights.

In addition, this approach means you won't be able to benefit from some status benefits. For instance, if you get free seat selection in advance of travel, this will need you to enter a suitable account. You could probably still get lounge access by showing a status card, but beware of the lounge agent 'helping' by adding the account to the booking!

Final remarks

In general, the situtation you want to avoid is having the whole booking processed by one frequent flyer programme. Getting flights 'uncredited' - even if they were ineligible for mileage earning - is much harder. But until you do so, the second programme will consider the booking already spent (to prevent double-dipping flights for earning in two programmes at once). Even a well-meaning agent might misunderstand your request or lack the technical know-how to set things up correctly, leaving the whole booking with a single number associated.

So don't bank on a clever split like this to, for instance, reach your mileage target for the year; try to arrange for the most likely outcome to be that the more lucrative flights get credited to the best programme; and treat it as a bonus if you manage to extract some miles from the other legs.