Next-Gen Sensors May Help Avert Airline Disasters  

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Everyone on board a Scandinavian Airline System (SAS) jetliner died when it collided with a light aircraft and exploded at a Milan, Italy airport in 2001. The smaller plane had ended up on the runway where the SAS aircraft was taking off.

The following year, two planes collided in mid-air over �berlingen in the south of Germany on the edge of Lake Constance. One was a Russian passenger flight from Moscow to Barcelona, while the other was a cargo plane heading for Belgium from the Persian Gulf. Seventy-one persons died.

As air transport grows, takeoffs become more tightly spaced and more and more planes are circling airports as they wait for permission to land, the potential for disasters increases.

Last year alone, international air traffic grew by 5.9 percent. Parallel to this increase, the minimum distance between aircraft in the air in European airspace has decreased. The minimum vertical distance between aircraft has been halved from 600 meters to 300 for planes flying above 29,000 feet. The idea has been to increase airspace capacity by 20 percent

But what about safety up there?

In the wake of a number of disasters in the air in 2001 and 2002, the EU took up the problem and resolved that certain aspects of the industry should be studied in detail and evaluated in terms of safety. Several projects were launched under its 6th Framework Program.

One of these was the HASTEC project, which was to develop the next generation of pressure sensors for better aircraft altitude measurement.

"There is a need for aircraft sensors that are more accurate than current models, which are large and reliable, but expensive systems," says Sigurd Moe. "Among other things, they need to be more stable throughout their life-cycle. The problem with current sensors is that they need to be checked and calibrated regularly, and this is an expensive process since the aircraft needs to be grounded."

The problem is that mechanical tensions may develop in the connection with the sensor package itself. The scientists therefore had to produce a silicon based sensor structure in which such tensions would not transmit/propogate into the chip itself. The solution was a spiral silicon element in which the pressure-sensitive part was not affected even if the mounting stretches and drags the element.

As part of the EU funded 6th Framework Program, a new generation of pressure sensors has been developed for better aircraft altitude measurement to help avoid mid-air collisions.

Two Norwegian companies, working with British and Rumanian partners, have succeeded in improving current aircraft technology through the next generation of pressure sensors.

Moe of Norway's SINTEF ICT said: "There is a need for aircraft sensors that are more accurate than current models, which are large and reliable, but expensive systems. Among other things, they need to be more stable throughout their life-cycle. The problem with current sensors is that they need to be checked and calibrated regularly, and this is an expensive process since the aircraft needs to be grounded."

The technology is needed when two aircrafts that have been allocated the same flight corridor and need to maintain exactly the correct altitude during the whole flight if they are to avoid problems, explained Ole Henrik Gusland of partner company Memscap.

"This means that the altimeters must be correct even if the plane moves through warm and cold air strata, and such accuracy must be maintained throughout the lifetime of the aircraft. On the ground and in the air over Dubai, for example, temperatures can range from plus fifty to minus sixty degrees. Temperature differences of this magnitude are a great challenge for aircraft electronic systems. Airlines want to ground their craft as seldom as possible for calibration," said Gusland.

To manufacture these sensors, SINTEF produces silicon wafers with hundreds of chips on each wafer, several of which are laid on top of each other and glued together before being sawn into chips. Individual chips are then selected and integrated into a sensor package that has been developed by Memscap. The company produces, assembles and tests the sensor package itself.

The first prototype of the sensor has now been developed by the companies, which will undergo further testing and mounting. During the first six months of 2008 these new- technology sensors will be flight tested.