Aircraft deliveries will equate to around 7.2% of the installed fleet this year and the figure will continue to trend upwards through 2018, Flightglobal's Ascend consultancy predicts.
The rising ratio "drives increasing capacity growth and increases the risk of capacity surplus", said Ascend head of consultancy Rob Morris during a webinar yesterday.
He expects this figure to climb above 8% in the 2016-2018 timeframe. "Such levels could indicate global overcapacity based upon past history," he says.
Ascend is closely monitoring events in China and in the wider Asia-Pacific region "to read any negative implications there", says Morris.
He indicates "some risk" of supply exceeding demand in the single-aisle aircraft market but not until "the end of this decade".
Despite these movements, there also "many positive signs" within the aviation supply cycle, he notes.
During the past five years, around 50% of all aircraft deliveries have been used for fleet replacement. "This is ahead of the longer-run average from previous cycles, which is closer to 40%," says Morris.
But in 2015, year-to-date, the metric is actually below 20% and "close to the historical lows seen mid- or late-cycle".
Morris highlights a continued reduction in the average retirement age of aircraft, which he believes is driven by the manufacturers' "maintenance of production rates in the face of reduced demand in the last cycle".
He adds: "Although absolute retirement volumes are down – in themselves an indication of strength of demand over supply – age still continues to trend downwards."
Another encouraging sign is that average annual utilisation rates, in terms of hours flown, are at or near historical highs.
However, Morris notes, as the cycle dips this indicator "will turn down quickly" as airlines seek to constrain capacity – "so one to watch albeit as a lagging indicator for now".
Source: Cirium Dashboard
