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May 12, 2016 By R Warning COURSE PREVIEW ► Theory    ► Earth magnetism Compasses Compass errors Practice    Compass swing site Compass swing Alternative methods May 12, 2016 By R Warning Permanent Magnetism ► Certain materials can be magnetized, By putting them in a magnetic field After removing the field remnant magnetism will be kept S N May 12, 2016 By R Warning Electro Magnetism ► Around a conductor that conducts electrical current a magnetic field is also generated May 12, 2016 By R Warning Earth magnetism The earth can be seen as a giant magnet The magnetic poles however not align exactly with the geographic poles The exact place of the magnetic poles is not constant, but varies in time May 12, 2016 By R Warning Magnetic Variation True North Magnetic north May 12, 2016 Variation By R Warning Magnetic variation is the angle at a certain point on earth between the magnetic north and the true north Due to the fact that the place of the magnetic north is not fixed, the variation changes In Holland about one degree every six years The variation is not a function of the geographical position, But can vary due to changes in the earths rock formations Lines of equal variation around the globe are so called isogonics lines May 12, 2016 By R Warning Variation must always be added to the magnetic heading to get the true heading! T North M North Variation is positive if the true north is to the right (east) of the magnetic north Else it is negative May 12, 2016 By R Warning + variation Inclination (magnetic dip) The direction of the magnetic force at a certain point on earth is not always exactly horizontal Only at the equator At the poles they are nearly vertical The angle of force line with the horizontal is called the inclination or dip angle A magnetic compass uses only the horizontal component of the earths magnetic field But the inclination tends to tilt a magnetic compass May 12, 2016 By R Warning Inclination Inclination card May 12, 2016 By R Warning 10 0° May 12, 2016 90° 180° By R Warning 270° 30 360° The compass swing location A compass swing must be carried out on an approved site! ► An approved site should be accessible and level ► Free from magnetic fields (except earths magnetic field.) ► Should be at least 46 meters away from steel framed buildings and 91 meters from buildings containing electrical power generation ► Large enough to swing the aircrafts it’s intended for There are two compass swing site classifications ► Class with a permit able deviation of ±10’ ► Class with a permit able deviation of ±25’ Periodic re-survey ► A class site must be re-surveyed every years ► A class site every years (??) The surveying party must work with the standards of the Admiralty Compass Observatory (ACO) and must be recognized by the CAA (Source: CAA UK leaflet 8-1 compass base surveying) May 12, 2016 By R Warning 31 Swing site’s at Schiphol There is only one compass swing site at Amsterdam! This is the fairway near the Martinair hangar’s The site near the old Fokker buildings is not surveyed and contains a lot of iron in the ground May 12, 2016 By R Warning 32 The Compass swing A compass swing contains two parts The correction swing Where the compass is calibrated and the A, B and C errors are adjusted The calibration swing, where the remaining deviations are noted and written on the deviation table that is mounted in the aircraft Note that with a Fokker 100 with IRS systems, the IRS may be used as reference Else a approved prismatic landing compass mounted on a tripod should be used as a reference Keep in mind that, when standing in front of the aircraft with a reference compass, the reading is 180° with respect to the aircrafts heading When reading the reference compass make sure there is sufficient distance between the compass and the aircraft Take also care not to wear any iron tools, watches, radio’s etc Be also aware that the reference compass comes also with a deviation card! May 12, 2016 By R Warning 33 Tail Window stile 030 Prism To read the reference compass, position the compass so that the window style and the vertical stabilizer line up with the compasses lubber line Make sure the reference compass is adjusted horizontally before reading May 12, 2016 By R Warning 34 Preparing the compass swing Before a compass swing is undertaken make sure the following preconditions are met: ► Authorization of the airport authorities ► Towing facilities ► Daylight! Make sure you have the following equipment with you ► A stairs to leave and enter the aircraft in the field (if there is no air stair on F100) ► Special adjustment tool for the standby compass ► Flat screw driver for “A” fault adjustment stby compass and compensator adjustment ► Wrench to loosen and tighten the locking nuts on the AHRS compensator unit ► Voltmeter to measure the compensation voltages on the compensator ► Two Porto phones to communicate between outside and inside of aircraft ► Master compass and tripod or pylorus and bracket and course list ► Correction form, deviation form and deviation cards May 12, 2016 By R Warning 35 Start at North The Readout of the master compass The readout on the aircraft compass Adjusted readings May 12, 2016 By R Warning 36 Example calculation May 12, 2016 By R Warning 37 The calibration swing After the correction swing is performed, a calibration swing should be made The calibration swing is to verify the correct adjustment of the compass and to make a deviation list and deviation cards, to make the crew aware of the remaining deviation errors We are making a full 360 degrees swing with 30 degrees interval On every interval we note the deviation of the standby compass and the two AHRS systems and the standby compass in emergency power condition For the standby compass the maximal deviation may be 10 degrees but between successive (30°) steps the difference in deviation may be 4° maximum! The maximum deviation for the AHRS may be 2°! After the calibration swing a deviation form should be filled in for tech records and deviation cards should be made for in the cockpit May 12, 2016 By R Warning 38 The pylorus method With a normal compass swing a master compass is used as reference As an alternative a pylorus can also be used if the compass swing site is approved for this method A pylorus is an instrument with witch we can very precisely measure a angle between two points In our case the longitudinal axis of the aircraft and a known point at some distance away The angle between this known point and the aircraft heading is predetermined for all compass headings used during the compass swing By measuring the angle with the aircraft longitudinal axis, and comparing this with the predetermined value, we can calculate the deviation May 12, 2016 By R Warning 39 Before we start using the pylorus, we have to align the instrument with the aircrafts longitudinal axis This is done by putting the instrument on a known spot (cockpit side window), Level the instrument and then point the instrument exactly to the wing tip and adjust the bottom reference ring of the pylorus to 240.25° (F50) as given on the job card Now the zero should be exactly in line with the aircrafts longitudinal axis After this we can shoot for every 30° heading a suitable target from the target list By subtracting the value given on the target list , With the actual readout on the pylorus scale, the datum heading can be calculated Subtract the readout heading from the datum and you get the deviation May 12, 2016 By R Warning Fixed distance 32cm 40 330 N Value on target list Actual value α α May 12, 2016 By R Warning 41 Focus Fine adjust Deviation scale Clamps to fix pylorus to aircraft window structure Horizontal adjustment longitudinal axis adjustment ring longitudinal axis adjustment ring Fixing Bolt May 12, 2016 By R Warning 42 Leveling bubble May 12, 2016 By R Warning 43 The End May 12, 2016 By R Warning 44 [...]... 91 meters from buildings containing electrical power generation ► Large enough to swing the aircrafts it’s intended for There are two compass swing site classifications ► Class 1 with a permit able deviation of ±10’ ► Class 2 with a permit able deviation of ±25’ Periodic re-survey ► A class 1 site must be re-surveyed every 5 years ► A class 2 site every 2 years (??) The surveying party must work with... the correct heading Then, as the aircraft nose approaches north again the compass lags In the Netherlands this error is 2,5° with a 1 ° bank and 25 ° with a 10 ° bank May 12, 2016 By R Warning 18 Acceleration error A second way to tilt the compass card out of the horizontal plane is to accelerate or decelerate the airplane With the card mounted with its CG below the pivot, acceleration causes the card...Intensity The strength off the earth magnetic field is not constant on all places on earth The strength of the magnetic field is measured in oersed In the Netherlands the earths magnetic field is about 0.471 oersted May 12, 2016 By R Warning 11 Compasses May 12, 2016 By R Warning 12 Aircraft compasses There are tree kinds... After successful adjustment of the compass system, the voltages should be measured and written down on a sticker on the remote compensator unit This way a remote compensator unit or flux valve can be replaced without the need to do a new compass swing Only the voltages should be taken over from the old compensator unit Inside the remote compensator unit is also a circuit that transforms the tree wire... remaining deviations are noted and written on the deviation table that is mounted in the aircraft Note that with a Fokker 100 with IRS systems, the IRS may be used as reference Else a approved prismatic landing compass mounted on a tripod should be used as a reference Keep in mind that, when standing in front of the aircraft with a reference compass, the reading is 180° with respect to the aircrafts heading... Daylight! Make sure you have the following equipment with you ► A stairs to leave and enter the aircraft in the field (if there is no air stair on F100) ► Special adjustment tool for the standby compass ► Flat screw driver for “A” fault adjustment stby compass and compensator adjustment ► Wrench to loosen and tighten the locking nuts on the AHRS compensator unit ► Voltmeter to measure the compensation voltages