Consumer champion Which? is calling for a major overhaul of aviation complaint handling.

All airlines should be made to sign up to a single dispute resolution service with “real teeth” that makes binding decisions within a reasonable timeframe.

The majority of the largest airlines flying from the UK are signed up to one of two UK schemes, Aviation ADR or CEDR.

While both have been authorised to handle escalated passenger complaints since 2016. neither is mandatory.

Ryanair quit complaints arbitration scheme ADR after being made to pay more than £3.6 million in handling fees and compensation last year, claimed Which?.

Aviation ADR received more than 14,000 Ryanair complaints in the first 11 months of 2018 and the airline was told to pay out more than £2.6 million to passengers in compensation between October 2018 and the end of March this year, according to the most recent complaints data.

Ryanair also had to pay at least £75 for each complaint Aviation ADR handled – suggesting a bill for more than £1 million in fees alone during 2018.

But after Ryanair cut ties with the arbitration scheme at the end of November last year, only 553 passengers in total pursued claims with the Civil Aviation Authority in the following four months.

This suggests a huge saving in fees and compensation for Ryanair, which cannot be compelled to pay out even if the aviation regulator finds in a passenger’s favour, Which? said.

At April of this year, 466 of these claims were unresolved and official figures do not reveal if anyone had received compensation.

Even when Ryanair was with Aviation ADR, passengers complained of waiting as long as a year to receive any money – despite a pledge that claims would be processed within 90 days.

One passenger, Kasia Nieduzak, told Which? Travel she made a complaint to Aviation ADR after her flight was cancelled in September 2017. She received a ruling from the arbitrator in July 2018 and finally received her compensation in November 2018 – but only after a 14-month battle that involved around 170 phone calls and sending 45 emails.

Which? wants the aviation sector to have a single mandatory resolution scheme which handles complaints swiftly and has “real teeth”.

Which? Travel editor Rory Boland said: “The broken aviation complaints system favours the interests of airlines over passengers – allowing them to wriggle out of paying compensation and putting many people off claiming at all.

“The uphill struggle that many have faced trying to claim the compensation they are owed has left thousands of holidaymakers significantly out of pocket for delayed and cancelled flights.

“It demonstrates why all airlines must be made to sign up to a single resolution scheme with real power to ensure passengers are treated fairly and money is paid out where it’s due.”

Airlines are now allowed to choose who handles their complaints. British Airways has chosen CEDR. Tui, Easyjet, Virgin Atlantic, Wizz Air and many small airlines have opted for Aviation ADR. Other airlines have chosen not to have an official arbitrator at all.

Ryanair cut ties with Aviation ADR after the arbitrator said it would rule in favour of passengers claiming compensation for delays and cancellations caused by the airline’s own staff striking.

This means complaints against Ryanair and Jet2 among others are handled by the CAA by default.

Ryanair said:Our policy is to pay all valid claims within an industry-leading ten days of receipt and while regrettably, we fell short on this occasion [with Kasia], this is certainly not representative.”

There was no reason for any of its customers to complain to Aviation ADR after it left the scheme, as they were all told to contact the CAA or the appropriate European authorities.

The airline admitted that not all of the passengers who were owed compensation from 2018 had been paid. It said that Aviation ADR had not yet issued payment instructions for the last few passengers affected but that when it did they would be paid within ten days.

Aviation ADR said the passenger’s complaint took longer than normal because of an initial miscommunication between the passenger and Ryanair.

It added: “Following the formal determination being issued it took some time for Ryanair to pay the compensation to the passenger.

“We consistently chased for confirmation that the payment had been made but as you will appreciate we are not a regulator so could do no more than chase.”