UPDATE 2-British Airways, pilots' union agree preliminary pay deal to end dispute

(Adds union confirmation)

Nov 22 (Reuters) - British Airways and its pilots' union BALPA have reached a preliminary agreement to end the pay dispute that resulted in the first walkout by pilots in the airline's history, the union said on Friday.

The agreement came after the two sides held talks under the auspices of the ACAS arbitration service.

BALPA said in a statement: "We can confirm that BALPA, BA and ACAS have put together a new pay and conditions proposal and, subject to final checks, BALPA expects it will shortly be consulting its 4,000 BA members on them."

A BA spokeswoman said "We welcome this positive step."

As part of the agreement, BA agreed to insert an inflation protection clause to its previous pay offer of an 11.5% rise over three years, the Financial Times reported.

The airline also offered improvements to working conditions, rostering and flight bonuses, the paper added.

British Airways pilots went on strike for 48 hours in September, grounding 1,700 flights.

BA, part of International Consolidated Airlines Group , said in September that the strikes had cost it 137 million euros ($151 million). (Reporting by Alistair Smout in London and Rama Venkat in Bengaluru; editing by Jonathan Oatis and Louise Heavens)