Commercial aircraft deliveries continue to rise at an unprecedented pace and the patterns of retirements have not materially changed since 2012, a pair of trends that appear to challenge theories that the falling price of jet fuel would prompt operators to rethink their buying and retirements strategies.

A report released by UK-based aerospace trade organization ADS Group shows a 10-percent increase in year-to-date deliveries compared with the same period last year and a 20 percent rise compared with January and February 2013. Meanwhile, a so-called white paper published on Monday by Dublin-based leasing company Avolon indicates the average retirement age has remained stable at roughly 25 years since its last report, published in September 2012.

The value of year-to-date deliveries for 2015 equates to £3 billion ($4.47 billion) for the UK’s aerospace industry alone, as deliveries of widebody aircraft rose nearly a quarter compared with last year’s figures, according to ADS. The group reported a further rise of 13 percent in order backlogs from February 2014 levels. The UK aerospace industry carries a nine-year backlog of what ADS calls work-in-hand, worth up to £175 billion ($261 billion) in orders, it added.

“Aerospace is a UK success story and the significant increase in deliveries this month is good news for companies across the country,” said ADS chief executive Paul Evertitt. “Industry expects to see a sustained increase in deliveries promoting new opportunities and growth at all levels of the supply chain.”

At the same time, Avolon sees a “low impact” on OEM deliveries from increased use of older aircraft due to cheaper oil, although updated analysis confirms average retirement age of most fleets continues to increase. The report concludes that operators will re-activate fewer than 200 incremental stored airliners (less than 1 percent of the global active fleet) in response to sustained lower fuel prices, and that the potential for deferred retirements linked to cheaper oil falls between 150 and 200 aircraft per year. The resulting effect on new deliveries equates to no more than 5 percent to 10 percent of production, which, it concluded, “OEMs are well-placed to manage.”

Other major findings that appear in the Avolon report include and estimate that, overall, almost 40 percent of the current stored fleet of 800 commercial jet aircraft will return to active service. It also cited estimates that nearly 85 percent of stored in-production aircraft will return to active flying, compared with only 30 percent of out-of-production types and less than 25 percent of stored aircraft older than 15 years of age.