The London mayor’s recent decision to endorse the Thames Estuary’s Isle of Grain as the site for a new major hub airport has already raised concerns about threats to local birds, but perhaps it is threats from the birds that deserve the most attention.

The airport’s projected flight paths would take aircraft over a large coastal wetland of salt-marshes and mud-flats that are home to hundreds of thousands of wading birds and waterfowl. The area, under a major migratory route, also provides a vital feeding stop for 350,000 wintering birds each year.

This high bird population concerns conservationists because birds have a record of striking aircraft at high speeds. Bird strikes are especially common around airports because it is only at departure and landing that aircraft venture below their bird-free cruising altitudes.

Bird strikes

In 2009, a US Airways flight famously ditched in the Hudson River after striking a flock of geese during its takeoff from LaGuardia. Nobody died in that “miraculous” landing but many other flights have been less fortunate over the years.

Bird strikes are most dangerous when the birds are sucked into an aircraft’s engines. As a result, the engines are designed to be bird-resilient, which is no mean feat. Protective grilles, which seem intuitive, are an engineering dead-end, as any grille strong and dense enough to withstand birds at high speeds would occlude the turbines and pose a risk of being smashed into the blades.

Greg L

So, instead, the manufacturers design the engine interiors to be incredibly strong, with each blade of a modern engine representing the vanguard of materials science. Even so, before it can enter service, each new engine design must demonstrate its bird resilience in a series of standardised regulatory tests. Engineers mount it on a test frame, rev it up to high speed, and shoot dead birds into it from a gigantic air cannon. The birds – spread across three sizes: “small,” “medium” and “large” – are fired at hundreds of miles per hour to simulate the speed a plane would be travelling at takeoff.

The battle for the skies

But tests are never perfect and all designs have limitations, as can be seen by the accident record. This means that there is an onus on airport operators to keep the presence of nearby birds to an absolute minimum.

They do this by making the area as inhospitable to birds as possible. Many drain ponds, cut down woodland, and replace natural grass with artificial grass. Some use elaborate ruses to keep birds away from runways, ranging from plastic (or real) hawks and rubber snakes, to distress calls played over loudspeakers. Others go as far as shooting birds directly. Should the Isle of Grain airport be approved, its operators will be at war.

JohnArmagh

The success of such efforts is invariably limited. Natural selection has yet to endow birds with an aversion to airports, and most become inured even to sophisticated attempts at intimidation. Scarecrows are claimed as nesting places; loudspeakers double as popular perches. Any new airport on the Thames Estuary will undoubtedly have “bird issues” of some degree, however extensive its “bird management” strategy, and all the available evidence suggests that those issues could be substantial, perhaps even deal-breakers.

Tried and tested?

In 2003, the government was considering a similar project on the Cliffe Marshes, which also lie on the Thames Estuary, just to the west of the Isle of Grain. It commissioned a report on the bird-strike risks of the proposed site, the results of which were not encouraging.

The report found that the proposed airport would carry bird-strike risks that were greater than most, if not all, major airports in the UK. “Even with world-class management and mitigation measures in place,” it concluded, “it is not considered possible to reduce the risk to a level similar to that experienced at other UK airports”. When the government eventually abandoned the proposal it cited the bird-strike report in its reasoning.

The Isle of Grain is not identical to the Cliffe Marshes in relation to its avian population, and the area will undoubtedly have its own specificities when the government conducts a new report to assess its bird risks. Yet the close proximity of the two sites, which arguably overlap in some places, suggests that the numbers and findings of any new investigation are likely to be similar to those of the 2003 report, and many experts expect the broad conclusions will be the same.

We shouldn’t be too surprised if another airport proposal built on solid economic logic is eventually brought low by intractable avian hurdles.