Just how much power does the Unite union actually have in its dispute with British Airways?
A walk-out by BA cabin crew might be expected to bring the airline to its knees - simply because you can't run planes without them.
Passengers might be persuaded to go without hot towels or chicken chasseur, but the safety implications would be intolerable.
And it's certainly expensive. BA says the last strike in March - for a total of seven days - cost it £43m.
And that excludes the hard-to-quantify effects on future bookings - how many flights that would have been with BA have been made elsewhere?
So cost is a clear weapon in the union's arsenal. But BA is doing what it can to limit the union's access to ammunition, by minimising the effect on passengers.
In an interview on Friday, when BA unveiled a record annual loss of £531m, the airline's boss, Willie Walsh, said he hoped to fly 80% of passengers during the latest strike.
So the five-day walk out by cabin crew that began on Monday could only halt a fifth of journeys. How is this possible?
Well firstly, flights at Gatwick and London City are unaffected by the dispute.
BA is also "wet-leasing" up to eight extra planes - which come complete with their own crew and pilots.
Thousands more seats are being taken for BA passengers on more than 50 other airlines.
On top of that British Airways says thousands of staff have volunteered to work as cabin crew during the walkout.
So that all helps BA cope with the strikes - even if the measures are expensive and unsustainable on a permanent basis.
And then there's the cabin crew themselves. BA claims that on the first day of the March strikes, 57% of crew who were scheduled to work turned up.
By the last day, the airline maintains it was 73%.
Those figures include Gatwick and London City crews who aren't taking part in the industrial action, as well as non-union crews at Heathrow - but it still seems that at least some union cabin crew turned up for work, possibly despite voting for strike action.
And not only that, the number turning up increased as the strike went on.
The idea of losing pay and travel perks might have proved too big a disincentive.
The final way BA is managing to run so many flights with cabin crew on strike is by cutting services.
Cabin crew numbers have to be maintained at a minimum level for safety, but the airline admits that flights to and from Heathrow might have fewer crew on board than normal.
In economy class, for example, there could be no pre-ordered special meals, no child meals and no in-flight duty free.
Rather like hiring in extra aircraft, this is not a sustainable position if BA wants to maintain its reputation for service.
But it's hoping that during strike periods passengers will be more concerned about getting to their destinations.
And even though strikes are expensive, BA clearly feels the cost is worth bearing.
The changes to cabin crew agreements are worth £62.5m a year - so over time will comfortably pay for the extra costs of the strikes.
As long as there isn't lasting damage to the brand, that is.