Pilots working for Aer Lingus are going on strike and working to rule in their pursuit of a pay claim.

The flight crew will walk out from 5am to 1pm on Saturday 29 June, aiming to disrupt the start of of the school holiday exodus for many families. More than 100 flights will be grounded.

In addition the pilots will begin an indefinite “strict work to rule” at one minute past midnight on Wednesday 26 June. More than 100 additional flight cancellations have ensued.

Millions of passengers are booked to fly on the Irish airline over the summer – including from the UK via Dublin to North America.

Aer Lingus says it told the union that “industrial action at this time of year would cause very significant disruption and have a devastating impact on customers and their families going into the summer holiday season”.

In addition to the effects of the strike, the airline has decided to cancel up to one in five flights during the first week of the work to rule as it seeks to minimise the risk of flights being grounded on the day.

Direct Aer Lingus UK services from Manchester across the Atlantic, and the Aer Lingus Regional operation – which is provided by a separate carrier, Emerald Airlines – are unaffected.

These are the key questions and answers.

What is the dispute about?

In a ballot in pursuit of better pay, pilots voted 99 per cent in favour of over industrial action on an 89 per cent turnout.

Captain Mark Tighe, president of Ialpa, says: “Our pay claim is for 24 per cent, which equates to inflation since our last pay rise in 2019. Aer Lingus have increased their profits by 400 per cent to €255m [£216m] last year.

“Our pay claim is entirely affordable, and Aer Lingus management need to quickly change position if they want to avoid this dispute escalating.

“We are in this position because management have failed to provide us with a meaningful offer on pay that accounts for inflation and the sacrifices made by pilots to save Aer Lingus during the pandemic.”

He accuses Aer Lingus management of insisting pilots “sell their working conditions in exchange for any increase in pay”.

Captain Tighe says: “We are absolutely not prepared to do that, especially when Aer Lingus is making enormous profits.”

The airline says it hoped to “continue to engage in meaningful direct discussions on productivity and flexibility proposals to enable increased pay” but Ialpa refused it.

“Profitability levels in Aer Lingus are the lowest in the IAG group with operating margin significantly lower than pre-Covid levels, making continued investment in the business by IAG challenging,” the airline says.

“Investment of such profits in paying exorbitant increases to already very well-paid pilots is simplistic in the extreme.

“Ialpa demanded an unsustainable level of increase in pilot pay that was not supported by any increases in productivity or flexibility. Our pilots are highly regarded colleagues, and they are rightfully well paid for the work that they do.

“Aer Lingus pilots are more than fairly compensated compared to the market.

The airline also says the union’s “failure to engage in the various independent processes in a responsible manner jeopardises our growth plans including our plans to fly to more destinations”. And it is criticising Ialpa for announcing the action at just one week’s notice, as required by law – rather than 15 days, which would give it more time to prepare for disruption.

What effect will the strike have?

More than 50 outbound Aer Lingus flights are scheduled to depart from Dublin between 5am and 1pm on Saturday 29 June. All are likely to be grounded, along with the inbound flights.

They include transatlantic departures to New York JFK, Washington Dulles and San Francisco.

Aer Lingus says it will inform passengers booked on 29 June about their options on Saturday 22 June.

The strike was called later than the work to rule. Ialpa’s Captain Tighe said: “We have been forced to escalate this dispute following a campaign of antagonism by Aer Lingus management directed toward our members.

“Aer Lingus has not sought any meetings since the notice of work-to-rule was served earlier this week. The company has made no effort to negotiate a settlement to avert action commencing on Wednesday,” he said.

Captain Tighe added: “The scale of next week’s anticipated flight cancellations, as described by Aer Lingus, illustrates the extent to which the company relies on the flexibility and goodwill of pilots.”

What does a “strict work to rule” mean?

Pilots will refuse any flexibility with their work. The Irish Airline Pilots’ Association (Ialpa) says the action will result in its members:

In a perfect world, the Aer Lingus operation would continue absolutely as normal. But aviation is a very dynamic industry and much can go wrong with the best-laid plans – including, for example:

Normally in any airline there is a degree of flexibility and goodwill among staff to adapt the operation in order to get people where they need to be. If that is removed by the pilots, disruption can swiftly ensue.

What sort of problems could arise?

Fridays in summer are extremely busy for air-traffic control across Europe, with pressure added by the closure of a large slice of airspace in eastern Europe. “Slot delays” of an hour or more are not unusual. Airlines will typically shuffle their fleets and crews to minimise the disruption for everyone, but Ialpa indicates this will not be possible.

Across the Atlantic – an extremely important market for Aer Lingus from Dublin and Shannon – summer storms are common. An unexpected delay at, say, Chicago, could mean that the pilots go beyond the normal basic flight duty period. The captain is allowed to extend the flight duty period by two hours “in the event of unforeseen circumstances” at his or her discretion – which will often mean the difference between completing a flight or leaving passengers stranded. The indication from the Irish pilots’ union is that this would not be granted.

A scenario in which bad weather or a mechanical problem meant a long delay on the ground in the US could mean passengers stranded overnight, with the aircraft being stuck at an American airport rather than back in Dublin ready for its next mission.

What is the effect of the work to rule so far?

Ahead of the first week of the action, Aer Lingus said it would cancel between 10 and 20 per cent of flights.

On 26, 27, 28 and 30 June, 26 flights (13 round trips) are grounded. Most of them are links from Dublin and Cork to the UK and Continental Europe. Four round-trips from Dublin to New York JFK are also grounded.

Aer Lingus says it “will alert customers directly through the contact details provided upon booking to alert them if their flight is cancelled”.

The airline says: “If we have been able to rebook you on another flight, we will send you an email confirming this and your new itinerary. Please be advised that teams in Aer Lingus are doing their best to accommodate customers whose flights have been cancelled. However, as we are in peak summer, there is limited capacity.

“If the new flight is not suitable you can still choose to rebook, request a voucher, or avail of a refund to your original form of payment.

“If your booking was made with a travel agent, or through another airline, you will have to contact them to manage your options.“

If my flight is disrupted, what are my rights?

You could decide not to travel and request a refund voucher for future travel – but there is no point in doing so because you are entitled for a full cash refund.

The airline says you can “change your flight online” and that if the new one is cheaper – which frankly is extremely unlikely – any fare difference will be refunded.

But the vast majority of passengers will want to fly as close to their orignal plans as possible.

As an EU airline, Aer Lingus must comply with European air passengers’ rights rules. These stipulate a duty of care in the event of delays and cancellatioons.

Regardless of the cause of disruption, the airline must get passengers to their destination as soon as possible. For European destinations, that could mean Aer Lingus buying you a ticket on Ryanair.

In the event of a transatlantic cancellation, Aer Lingus could have to buy seats on Air Canada, American Airlines, Delta, JetBlue, United or WestJet. Given that so many flights are very heavily booked, though, it may take time to find spare seats.

For overnight delays, Aer Lingus must provide hotels and meals.

In addition, passengers are likely to be entitled to cash compensation of between €250 (£220) and €600 (£520).

How badly will UK passengers be affected?

During the school summer holidays in Northern Ireland, many families travel south to Dublin to fly to Mediterranean destinations. They are entitled to be found alternative flights if seats are available.

The Aer Lingus Manchester-North America operation is unaffected, as are Aer Lingus Regional flights from various UK airports to Dublin. But those regional flights often carry passengers who are heading for the US and Canada – using the excellent pre-clearance facility for US Customs and Border Protection, which means you arrive in an American airport as a domestic passenger.

Someone with a booking from, say, Birmingham via Dublin to Boston, could insist on being rebooked on Air France, KLM or another airline if seats are available.