Why the rush to store the world's airliner fleet could add unexpected costs to airports' maintenance bills

We've seen the photos. We've marvelled at their perfect alignment – an almost biologically ordered arrangement of aluminium on “tarmac”. But the rush to store the redundant aircraft of the COVID-19 pandemic may churn up some challenging infrastructure issues when the time comes to bring these airliners out from hibernation.

Some of you might recall the annual cry of our roads "melting" at the height of the summer, maybe even vehicles getting stuck on the highway. To tell you the truth, it isn't as wild an assessment as you may think. The majority of our roads are constructed from asphalt - a mixture of stone and bitumen still often incorrectly referred to as "tarmac". Bitumen itself is a product from the refinement of crude oil and its softening point is not that high - somewhere in the mid fifties degrees centigrade.

On a hot summer's day, it is not a surprise then that our road surfacing begins to deform or move. The effects are more pronounced the heavier and more concentrated the loads that are applied during this period. Although elevated temperatures accelerate the deformation of asphalt, this behaviour is still exhibited at lower temperatures but over a longer period. It does so because asphalt (or more specifically bitumen) is a viscoelastic material. In other words, over time it does not respond linearly to an applied stress.

Why is this important? Much of the stored COVID-19 fleet is being parked in corners of airports that never see a stationary aircraft for more than a passing moment - taxiways, aprons, secondary runways - and many of these are what we term flexible pavements, or those constructed of asphalt. An A380 or 747 is not a light aircraft and they are often parked with fuel in the tanks to act as ballast. I hope the picture is now becoming clearer. The longer the aircraft are stored in unsuitable places, the higher the likelihood that repairs to flexible pavements will be needed. As the summer rolls in, the effects will become more pronounced. There is a reason why stands, runway holding points and the first 1000ft of many asphalt runways are predominantly concrete!

In the meantime, a temporary solution is to spread the load. Park aircraft on suitably sized road plates, as the authorities at Schiphol have done, and follow the guidance from Airports Council International.

https://aci.aero/wp-content/uploads/2020/04/200403-Airlfield-Ops-Advisory-Bulletin-FINAL.pdf