Geophysical Centre in Dourbes

In order to account for the influence of the aircraft itself or of its payload on the compass, a compass calibration is made on a compass calibration pad. This happens for new aircrafts or when needed (change affecting avionics, special payload…)

A certified compass calibration pad is a dedicated area inside the airport premises, which is suitable for performing aircraft compass swings. Swings involve rotating the whole aircraft to known magnetic azimuths and, for each orientation, observing the compass deviations.

Left: results of magnetic survey show this site is not suitable to establish a calibration pad. Right: results of DI measurements show this calibration pad is valid for class 1 certification

Deviations of the compass due to magnetic interference are noted and result into a compass correction card, which shows appropriate adjustments according to the desired heading.

We offer certification, including the following assistance for new calibration pads:

• Site validation: selected site must be convenient for aircraft accessibility and must be suitable for the largest aircraft likely to be certified, but magnetic cleanliness must also be addressed (for instance nearby infrastructure, underground cables, pipes, gutter or reinforced concrete may have a significant effect).

• Materials validation: materials chosen for the construction must of course have a very low magnetic signature. We propose to validate the selection of materials by performing measurements on samples in our lab

• Cleanliness validation: after construction, we measure the magnetic cleanliness all over the calibration pad.

• Certification : basically, magnetic declination is measured at N points of a grid covering the compass rose. After correction of daily variation of the magnetic declination, min and max values are extracted. MaxDev is defined as the half of the difference between those two values. Based on MaxDev value, we deliver a class 1 (<0.1°) or class 2 (<0.25°) certification.