Airlines warned of more disruption in ash crisis

The impact of ash on aircraft air conditioning systems could be serious, warned aviation lecturer Stephen Wright of Leeds University.

Planes will be "hoovering up" the additional ash and this could lead to unscheduled or emergency landings, Mr Wright added.

He went on: "Sometimes dirt levels are so high that air conditioning 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."

He said low concentrations of ash were deemed low risk by the UK Civil Aviation Authority as they had minimal effect on airline engines. But air-conditioning cooling systems filtered all dirt out, so there would be a cumulative build-up even when low levels of ash were present.

Mr Wright said: "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.

"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."

Plane passenger watchdog the Air Transport Users Council yesterday called on airlines to make it easier for passengers to claim their money back after the ash-cloud crisis.