More trouble ahead from volcanic ash?

Aviation lecturer Stephen Wright believes the impact of ash on airplane air-conditioning systems could be serious and will build over the next few weeks as planes begin to 'hoover up' the additional ash in the atmosphere.

Air-conditioning systems provide fresh air to pressurise the cabin as well as the warming the internal temperature of the plane. Once clogged with dirt, they can overheat, forcing the pilot to shut the system down and make an unscheduled or emergency landing. Overheating of the system can be serious, as on many planes the air-conditioning units are sited underneath the central fuel tank.

"As planes taxi round airports, the air-conditioning systems suck up dirt which then clogs up the heat exchangers," says Stephen Wright, who worked in the aviation industry before joining the University's Faculty of Engineering. "Sometimes dirt levels are so high, systems are having to be changed after just three to four months, whereas they're expected to last around 18 months. The planes will now be sucking up ash as well which will put these systems under very high stress."

Low concentrations of ash are deemed low risk by the UK Civil Aviation Authority as they have minimal effect on airplane engines. But air conditioning cooling systems filter all dirt out, so there will be a cumulative build up even when low levels of ash are present.

"Once the air-con unit is clogged up, it is less effective and so tries to work harder to maintain pressure and temperature -- and so begins to overheat," says Wright. "The systems have built-in safety controls, so they're unlikely to catch fire. However, overheating will mean pilots have to shut down the affected system, and as this provides fresh air to the cabin, the loss will normally result in either an unscheduled or emergency landing.

"At the very least, the air industry will be looking at much higher maintenance on these systems to keep them working, at a time when the grounding of planes has put them under severe financial pressure."