AS is a long standing BA partner and, as of 31st March 2021, a full member of oneworld. You can book AS flights using your Avios through BA: prior to AS joining oneworld this was only possible on the phone through your local service centre, but it is now possible to book online with some caveats, specifically that at this time (August 2022) it's not possible to retrieve the AS PNR via ba.com - the chat function on alaskaair.com is staffed by helpful and responsive agents though who can get your AS PNR issued quickly. You can book flights up to 330 days in advance.

It has been reported that flights operated by Skywest "Skywest operating as Alaska Airlines" for flights like SEA-SLO are not possible to book with Avios. The system may initially allow agents to grab inventory but then will send back an error message when going further even with the telephone booking.

Avios Cost
The cost should be in line with the normal BA reward price banding. To get an idea of what your flight may cost check the distance with the BAEC flight calculator or using gcmap, and then have a look at the avios banding here.

Note that all AS flights (just like any other non-BA flights) are priced at the peak avios rates. Also note that from 2 February 2016, redemption rates for travel on American Airlines, Alaska Airlines, and TAM will start at 7,500 Avios rather than 4,500 Avios, effectively pricing Distance Band 1 flights as Band 2.

If the flight includes a number of stops under the same flight number then the avios charge is for a non-stop flight from the departure point to the destination. For example, for Seattle to Juneau AS65 the service makes three stops enroute. However, the avios rate charged is as if it were non-stop Seattle to Juneau flight (7,500 avios) and not the avios total for four segments.

Taxes, Fees, and Charges
As with other non-BA reward bookings you need to pay the taxes, fees, and charges. You should be able to predict what this will be by having a look at the taxes, fees, and charges on the AS website or on itamatrix.

BA policy is to charge Ł15/US$25 for offline award tickets but there has been consistent and sustained reports for years of agents waiving fees. As recently as 1/2017, there have been confirmatory reports that the telephone fee has been consistently waived. When initially calling the call center let your first sentence be, "Can you help me with an Alaska booking that I cannot complete online." The agents have all proactively waived fees in every circumstance. If they do not, HUCA (hang up and call again - or ask supervisor to waive)

Can I Check Reward Availability Online?
You can attempt to make a booking on ba.com and this should at least show Alaska mainline routes. You can also check AA website and the AS website. If AS reward flights show as available on aa.com, then they should be bookable with BA using avios. Check MileSAAver availability not AAnytime availability. AA may be better to check as this should show partner reward availability.

Checked Bags?
AS charges for checked bags on all economy fares, however oneworld ruby & sapphire members are entitled to 2 free bags and emerald members to 3 free bags. Note that oneworld elite baggage allowance is only applied to the passenger with the elite status: 1 GCH and 3 blue members on the same booking only provides 3 bags free, not 12. See the baggage information here. Note that you can only add bags at OLCI, at the airport, or on the phone no earlier than 24 hrs before the flight. Baggage fees are also waived for Alaska Credit Card holders and up to 6 companions on the same booking.

Redemptions in First include 2 checked bags per passenger as the base entitlement.

oneworld Benefits?
AS joined oneworld on 31st March 2021: priority check-in, priority boarding, baggage allowance* and lounge access for passengers with status all apply per the normal oneworld/AS policies. Alaska's table is here.
(* see the Checked Bags question above for an important detail)

Does the 24 hour Cooling Off Period Apply?
Yes it does. However, you must cancel by phone - it is not possible to do it online. Miles are refunded immediately into your Avios account, taxes (if returned) just take a few days to be credited.

Can I Amend the Booking?
Yes, subject to fees and reward availability on the flight you want to move to. You need to do it on the phone. Fees (both the offline fee and change fee) are shown here.
Because of the fee structure of BA Avios - it is often beneficial to book two one ways instead of one roundtrip if you are unsure about either your departure or return dates.

Can I Cancel the Booking?
Yes you may subject to the usual fees here Fees (both the offline fee and change fee) are shown here. If the taxes, fees, and charges you paid were less than the cancellation fee due then you simply forfeit the taxes and fees paid and that serves as your effective cancellation fee. If taxes, fees, and charges you paid were more than the cancellation fee then you would pay the cancellation fee USD55 but get back your taxes in full as well as your miles. (Rather they debit USD55 from your taxes and fees and return to you the balance remaining to your form of payment.)

Can I SDC Same Day Confirm on an AS Avios Ticket?
Yes, AS Avios tickets are eligible for AS same day confirmed change benefits as detailed on the AS website. If AS agent tells you differently HUCA. But AS website should allow you to do this regardless.

Are AS Avios tickets upgradeable with cash?
Yes, AS Avios tickets can be upgraded by paying a fee at 24hr check in, "U" inventory allowance, space available. Please note upgraded U fare class tickets are not eligible for lounge access.

Do AS Elite Benefits apply to AS Avios tickets?
Yes, if you are AS MVP Gold for instance your AS Avios ticket is eligible for Complimentary Upgrades and as long as your AS FFN is in the reservation, you will be automatically added to the AS complimentary upgrade list (AS in 12/05/16 changed policy to allow complimentary upgrades to apply to award tickets - including Avios awards) Gold Guest Upgrades, however, have never been allowed to be applied to AS Avios tickets.

Can I book Virgin America flights now using avios?
As of 25 April 2018, Virgin America no longer exists as far as reservations systems are concerned. Former VX flights are now AS flights and can be booked with Avios.