Miles closer

An aircraft-mounted scanning system that could help to increase the number of planes arriving at busy airports without the need for new runways, is being developed in a European project involving Airbus.

Current international legislation stipulates that aircraft mustmaintain a safety distance of up to six miles from each other. This is to ensure that they are unaffected by the turbulence of planes travelling ahead of them.

But according to engineers working on the EU’s I-Wakeproject, although these swirls of air – known as wake vortices – are a hazard to be avoided at all costs, an across-the-board safety distance of six miles is overly cautious.

Dr. Thomas Peschel, one of the researchers involved in the project at Germany’s Fraunhofer Institute of Applied Optics and Precision Engineering, explained that by using sensors aboard aircraft to measure air vortices it should be possible to adjust safety distances according to circumstances, allowing airports to make better use of their capacity.

While radar is capable of measuring turbulence in wet conditions it is completely ineffective in dry weather, so the I-Wake team has developed a laser scanner which can determine whether the air is calm enough in dry conditions.

Peschel explained that in tests a small Cessna research aircraft equipped with a prototype system flew behind a large Airbus aircraft. The wake information provided by the system enabled the plane to travel safely within just over two miles of the Airbus, he said. ‘An aircraft equipped with the system is able to follow much closer than one that isn’t.’

While reducing the margin for error may sound like a recipe for disaster, air traffic management expert Dr Washington Ochieng of Imperial College confirmed that the current safety distances could be considered to be overly generous. ‘People are moving slowly towards flexible use of airspace – and this means trying to put more aircraft in the sky,’ he said.

The I-Wake system works by sending laser pulses into the air in front of the aircraft. The light is scattered on aerosol or dustparticles and registered by adetector.

Peschel explained that due to the Doppler effect, the wavelength of the incoming laser pulses shifts according to whether the airborne particles are moving towards or away from the beam.

From the difference relative to the incident wavelength, software is then able to calculate the strength of air turbulence within fractions of a second.

The prototype system was positioned behind the window of the Cessna’s cabin, but Peschel said that the final system will be positioned behind an optical window near the tip of the aircraft. Much of the development work will therefore focus on reducing the size of the system so that it can be accommodated in this crowded area.

Peschel said that while the system is between 5-10 years away from appearing on passenger planes, efforts to develop similar, but less effective, ground-based laser scanners are closer to commercialisation.

‘The difference with working from the ground is that you have a limited range of up to two or three miles, and for many airports the decline path starts long before that distance,’ he explained.