June 4, 2010

expert reaction to Easyjet’s ash radar

Easyjet have announced plans to test equipment to detect ash in the air during flights, allowing them to avoid potentially dangerous ash clouds.

Dr Colin Brown, Director of Engineering at the Institution of Mechanical Engineers, said:

“Whilst we welcome the chance to gather data and help us understand how the ash is distributed this should not be seen as a silver bullet that will allow unlimited flying.

“It should be remembered that it is not the pilot who directs the plane but the air traffic control staff, and thus evasive action may well be slower and less effective in order to maintain that control.

“The ash clouds in question are in densities of around 1 part per billion and it stretches the imagination that infra-red spectroscopy could detect plumes at 100km distance through absorption – let alone radiation – as is needed here. Indeed, even at 100km, planes travelling at 800kph would enter the cloud within minutes. It seems more likely that data could be gathered over a distance of metres and hence fractions of a second before the cloud is upon the plane.”

Dr Thurai Rahulan, Lecturer in Aeronautics at the University of Salford, said:

“Forward Looking Infra Red (FLIR) devices have been used in military and police aircraft since the nineties. Since they generate an image based primarily (but not exclusively) on temperature differences, hot ash particles and rocks can be detected during ejection transients.

“The international standard atmosphere temperature variation is linear with + 15 deg C at sea level to -55 deg C at 11km altitude. My guess is that the heavier stones/rocks will fall back whilst still hot whereas the light particles in suspension will cool down quickly to ambient temperature. However, the dissipation of the remnant pocket of heat energy might be slow giving time for it to be detected by an infrared scanner.

“Police units are normally tuned to maximise contrast (standard or reverse video) between + 15 deg C (tarmac and countryside) and + 40 deg C (human body and cooling engines).

“It is best not to make too many promises until results from flight tests are compared with through-ash flight measurements by instrumented aircraft.

“The drawbacks are redesign of the packaging within the radar dome (radome) to accommodate the FLIR system and warning indicators on the pilot display panel, the power draw, financial costs (purchase & maintenance) and certification issues.

“In addition to the trip fuel, aircraft are required to carry additional quantities for diversions, contingencies and emergencies. But bad weather already creates mass diversions occasionally and hence the radar is unlikely to lead to a chaotic situation following diversion due to volcanic ash.”