Flash, Quickly Demagnetized

The call came shortly before closing time. The mission: to get a grounded commercial aircraft ready to go again as quickly as possible. The problem: magnetism after a lightning strike. The start of another "lightning operation" for the emergency specialists from Maurer Magnetic in Grüningen, Switzerland.

According to the US Aviation Authority, every aircraft in the fleet is struck by lightning at least once a year. Most lightning strikes, over 95%, occur when flying through clouds at an altitude between 1,500 and 4,500 m. A plane can easily cope with lightning strikes, and yet lightning strikes can cost the operator of the plane dearly. An inspection is required to uncover and remedy possible damage. And that can take a while. For short-haul aircraft that cover up to eight routes a day, every minute of an unplanned stay on the ground is a significant cost factor. So also in the present case. The flash had entered the frame of the cockpit window. Only a small black area on the outside was evidence of the impact,but the standby compass then showed a deviation of 110 °. The suspicion: increased magnetism in ferromagnetic components in the vicinity of the compass. Time for the experts.

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Degaussing specialists eliminate increased magnetism

Immediately after the call to Maurer Magnetic AG was received, a degaussing specialist set off. A portable demagnetizer of the type DM 200-PC as well as a selection of flexible cable coils. These make it possible to demagnetize a wide variety of components, including large ones, directly on site. "Our emergency vehicle is always ready to go, which is why we can leave for any European airport within a day," said operations manager Christian Spiess, commenting on the flexibility of the mobile emergency command from Maurer Magnetic.

Time is money, so everything had to be lightning fast. During the journey, the employee sent the names, dimensions and weights of the equipment carried, as well as copies of his passport and vehicle documents, to the airport security staff. The fastest possible access to the hangar was a prerequisite for ensuring that problems were solved just as quickly. After a smooth check of people and equipment, the next step was to troubleshoot the aircraft.

Previously, airline maintenance technicians had made various attempts to deal with the problem with the existing demagnetizers. As it turned out, without success. The shape of the magnetism on the cockpit was a widely scattering magnetic field. A magnetic compass served as an indicator in order to be able to optimally assess the position of this special situation. The interference field with peak values ​​of 10 Gauss led to the compass being rejected. After the measurement results were determined, the demagnetization was started directly.

Special coil helps

A patented special coil is used to generate the alternating magnetic field. With the help of a crane, this was guided piece by piece along the magnetized frame of the cockpit window. Standing on a gangway, the Maurer Magnetic employee coordinated the positioning of the 20 kg cable spool. Only 30 demagnetizing pulses were required to thoroughly demagnetize all nine cockpit windows. The performance of the mobile demagnetizer from Maurer Magnetic can be continuously adapted to the current situation. The magnetized stainless steel frames were treated with the field strength permitted by the aircraft manufacturer for demagnetizing parts in the vicinity of the standby compass. The compass was previously removed in accordance with regulations so that it does not also undergo demagnetization.

“Demagnetization with the Maurer Degaussing pulse demagnetizer is very safe. The coil is completely electrically insulated and does not transmit any electrical fields or eddy currents, as they occur with iron-loaded coils. The device controls the demagnetization electronically. Our process leaves no residual magnetism. Due to the large volume field and the high cycle rate, our demagnetization is also more effective and efficient than previous approaches,”explains Managing Director Albert Maurer about the patented Maurer Degaussing process.

Hidden "magnetic stoves" are ticking time bombs

About an hour later: final test on the apron. The cockpit windows were completely free of magnetism, the compass needle no longer showed any errors and could be adjusted manually without any problems. “It is important to completely eliminate all local areas of magnetism in an assembly. If residual magnetism remains, the component can be re-magnetized,”explains Albert Maurer, explaining the risk of incomplete demagnetization. According to the expert, hidden 'magnetic sources' are ticking time bombs. Shocks and vibrations, such as those that occur during landing, are often sufficient to re-magnetize components. But not in the present case. Preparations began almost at the same time as the demagnetizing specialist left,to get the aircraft ready for further traffic. (ud)