When is the strike taking place?
Both the airline and pilots had said they hoped to reach a resolution and avoid a strike.
But after negotiations broke down, members of the SAS Pilot group walked out on April 26th in all three countries. The group represents almost all (95 percent) of the airline's pilots in Scandinavia, 1,500 people in total.
It's unclear exactly how long the strike will last, so passengers with flights booked in late April and early May should follow updates on the situation.
Why are the pilots striking?
The strike comes after unsuccessful negotiations on a collective bargaining agreement between the pilot group and the airline. Salary increases are the biggest sticking point but other issues relate to working hours and scheduling.
The SAS Pilot group has said that their salary requests are in line with the market rate, while one SAS negotiator called their requests "unreasonable and extreme".
IN DEPTH: Why are strikes so rare in Sweden?
How do I know if my flight is affected?
Not all flights are cancelled or delayed. Flights operated by SAS partners are unaffected, but that leaves around 70 percent of scheduled flights, including most domestic, European and all long-haul flights.
SAS has cancelled 673 flights on Friday, affecting more than 72,000 passengers. It said another 100,000 passengers could be affected over the weekend.
SAS has published a list of flights which are guaranteed to operate despite the strike, which you can find here. You can also search your flight number (which you can find by logging into SAS or by checking your flight confirmation email) to see your flight's status.
If your flight has not been guaranteed, it's a good idea to keep checking the SAS website to check the status of your flight. The airline has said it aims to keep customers informed via text message.
If my flight is affected, what are my options?
SAS has offered free re-booking to some passengers.
In order to apply for the free re-booking, you need to meet a few conditions. Your flight needs to be with SAS and booked directly with the airline, booked for April 26th-29th with the booking made before April 24th. The flight number must begin with 117 and it must be one which hasn't been guaranteed (see the list above). If you meet these conditions but booked via a travel agent, you should contact them about re-booking.
If you re-book, the flight must take place between May 6th and September 30th, 2019. You can read more here.
If you decide not to re-book and see how things turn out, you'll have a few different options if a strike does take place.
Under EU law, you should receive food and drink plus monetary compensation for delays over a certain time, and compensation or free re-booking if your flight is cancelled. But passengers' entitlement to these benefits depends on whether the delay or cancellation is due to "extraordinary circumstances", defined as events that couldn't have been avoided even if the airline took all reasonable measures. Occasionally, strikes are deemed to be "extraordinary circumstances".