Assessment of Training Aircraft Crew Exposure to Electromagnetic Fields Caused by Radio Navigation Devices

: The paper depicts research concerning the value of the electric component of the electromagnetic (EM) energy determined by the NHT3DL meter by Microrad with the 01E measuring probe during a number of ﬂights made by Aero AT-3 R100, Cessna C172, and Tecnam P2006T ﬁxed wing aircrafts and a Robinson R44 Raven helicopter. The point of reference for the recorded measurement was the normative limits of the electromagnetic ﬁeld (EMF), which can inﬂuence a pilot in the course of a ﬂight. Selected studies of the maximum value recorded by the meter was E = 10.66 V/m when landing at an airﬁeld equipped with the VHF (Very High Frequency) omnidirectional radio range (VOR) approach system. Particular attention has been paid to changes in electric ﬁeld intensity during the operation and their effects on the type of radio navigation systems as well as communication with the airﬁeld control tower. The obtained results were validated in the Statistica 13.3 software for the purpose of a detailed stochastic analysis of the tested values. Results obtained are subject to the mandatory requirements of Directive 2013/35/EU as well as to the relevant regulations in Poland.


Introduction
The influence of (electromagnetic) EM energy on human organisms is the topic of research in many research centers around the world. There are no clear criteria for assessing its effects. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) describes guidelines providing protection against adverse health effects related to exposure to non-ionizing radiation [1,2]. Preventing undesirable effects on the human organism and the environment is the main goal of protection against ionizing and non-ionizing radiation. The electromagnetic field energy is present in the world around us, but we should focus on its tolerable level. The level of the exposure threshold is necessary for the negative health effects to be present. The limits of the electromagnetic field (EMF) take into account the presence of direct and indirect health effects. They refer to exposure regardless of its duration and include the effects of both short-term and long-term exposure [3,4].
In general, measurements of the electromagnetic field of radio navigation equipment are carried out in function checks of newly installed systems or for diagnostic purposes. In such instances, airplanes with measuring equipment or ground measuring systems are used [5][6][7].
In the literature, studies on the quantitative determination of air crew exposure to the energy of electromagnetic fields are rare. It is also difficult to find studies dealing with passenger exposure. The ICNIRP commission undertakes extensive research in a similar field, however, it is usually only related to the effects of EM field energy on ground handling staff [8,9]. Novak (2012) used a Piper PA-34-220T airplane equipped with on-board instrumentation together with ground instrumentation for the comparative aerial measurements of and landing, the airplane is temporarily within the range of the beam electromagnetic field being radiated from ground-based navigation guidance devices. This section introduces and briefly describes the most important and most commonly used radio navigation equipment in airplanes [23][24][25].

VHF Omnidirectional Radio Range (VOR)
The VOR works at the frequency band range from 108 MHz to 118 MHz to ensure the aircraft can receive direction to the ground station location. In order to obtain the demodulation of the signal of a VOR transmitter station, the VOR receiver in an aircraft provides course information relative to the transmitter station. The aircraft position can be derived by triangulating two or more stations. VOR stations provide a relative course to the ground stations. The VOR functions continuously at carrier frequencies with the code identification applied to four letters in Morse code, transmitted on a modulation tone of 1.02 kHz.

Instrument Landing Systems
The Instrument Landing System (ILS) constitutes a navigation aid to help landing when visibility is poor, according to Instrument Flying Rules (IFR). The ILS is based upon a radio navigation system (RNS) that guides the aircraft down a slope to the touchdown area on the runway. Multiple radio transmissions that enable an exact approach to landing with an ILS are applied here.

Localizer
A localizer constitutes one of the radio transmissions. It is used to oversupply horizontal guidance to the center line of the runway. The localizer transmission is of a Very High Frequency (VHF) broadcast in the lower range of the VOR frequencies band, from 108 MHz to 111.95 MHz on odd frequencies only. Two modulated signals are generated from a horizontally polarized antenna group beyond the far end of the approach runway. They set up an enlarging field that is of 21/2 • width (about 1500 feet), 5 miles from the runway. The field tapers are situated near the landing threshold. The left side of the access area is filled with a VHF carrier wave modulated with a 90 Hz signal. The right side of the given approach includes a 150 MHz modulated signal.

Glideslope
A selected glideslope broadcast holds vertical guidance of the aircraft down the right slope to the touch down point. RF signals help to direct the aircraft precisely to the touchdown point, located at the beginning of the runway. The inclination of the radio signals is approximately 3 degrees, that is, the slope of a typical air traffic airplane approach path. The transmitting glideslope antenna is established off to the side of the approach runway approximately 1000 feet from the threshold. As it approaches the runway and the field narrows, it transmits a wedge-like pattern. The polarization of the glideslope antenna is horizontal. The transmitting frequency band range constitutes the UHF from 329.3 MHz to 335.0 MHz.

Compass Locator
Additional radionavigation aid are marker beacons, outer, middle and inner. The outer marker beacon is typically 4-7 miles from the runway threshold, which provides additional information to the pilot about the distance from the touchdown point. A middle marker beacon is located on the center navigation light approximately 3500 feet from the runway threshold. However, before the pilot uses the information provided by the marker beacons, the compass locator helps to intercept the approach navigation aid system. The function of an external marker compass locator is performed by an NDB beacon with a transmitting power of 25 W and a range of approx. 15 miles. It transmits omnidirectional Low Frequency (LF) from 190 Hz to 535 Hz radio waves.

Marker Beacons
Marker beacons broadcast signals that point at the localization of the aircraft along the glidepath to the runway. As mentioned above, an outer marker beacon transmitter is situated 4-7 miles from the threshold. It spreads a 75 MHz carrier wave modulated with a 400 Hz audio tone in a set of dashes. This transmission corresponds to a very narrow and directed straight up. A middle marker beacon is placed roughly 3500 feet from the runway and transmits at 75 MHz. Its transmission is modulated with a 1300 Hz tone that constitutes a series of dots and dashes due to be distinguished from the all dash tone of the outer marker. An inner marker beacon is eventually used and the modulated signal is transmitted only in a series of dots with a frequency of 3000 Hz. It is located at the Missed Approach Point (MAP), which is the land-or-go-around point of the access close to the runway threshold.
2.2.5. Distance Measuring Equipment (DME) DME is utilized to estimate distance between the aircraft and the runway threshold and works on the query-response timing principle. The airborne transceiver sends 2 pairs of radio pulses. The ground station receives and identifies them and sends a response while handling approximately 100 on-board devices. DME radiometers operate in the frequency range of 960-1215 MHz with a 1 MHz channel spacing; the duplex spacing of the query-response channel is 63 MHz 25. Table 1 contains data on the frequency and power emitted by ground-based radio navigation equipment.

. Receivers and Instruments
The localizer, glide path, and eventually the marker beacon and DME receivers are actuated by the one control unit, which is, as expected, located in a separate avionics bay. In cases of light aircrafts, where the available space is narrow, the receiver units are placed underneath the pilot's seats. There are a large number of different varieties of ILS indexes in operational use. One of them is the cross pointer indicator, used both in the traditional version as a device built into the plane's dashboard and in the glass cockpit version (visual indicator on the display screen).

Aerials
Localizer aerials are typically based in the vertical stabilizer. Similar aerials can feed two localizer receivers; the aerial system and receivers are generally applied for VOR as well. When a third localizer receiver is installed, its aerial is generally placed in the nose section, mostly within the radome given for weather radar. The glidepath receiver antenna is usually placed on the nose of the aircraft to obtain the best possible receiving conditions. Marker beacon aerials are usually mounted on the bottom surface of the aircraft fuselage. They are usually flush mounted type. Figure 1 shows a schematic of the radio navigation equipment system near the airport landing runway. well. When a third localizer receiver is installed, its aerial is generally placed in the nose section, mostly within the radome given for weather radar. The glidepath receiver antenna is usually placed on the nose of the aircraft to obtain the best possible receiving conditions. Marker beacon aerials are usually mounted on the bottom surface of the aircraft fuselage. They are usually flush mounted type. Figure 1 shows a schematic of the radio navigation equipment system near the airport landing runway.

The Test Airplanes
Measurements of the electric component (E) of EMF were carried out in four different aircraft: an Aero AT-3 R100, a Cessna C172, a Tecnam P2006T, and a Robinson R44 Raven helicopter. The measurements were carried out in accordance with the PN-T-06580-3: 2002 standard [26], which defines the methods of measuring and assessing EMF at workplaces with frequencies from 0 Hz to 300 GHz. The airplanes presented are used every day for flight training in the Center of Aviation of the State School of Higher Education in Chełm, Poland.
The AT3 R100 is the smallest aircraft used for the tests. Its origin is connected with an amateur design, Pottier P220, which was a popular homebuilt aircraft. Although the AT3 resembles the P220, it is a completely new design, with major structural and conceptual changes that were necessary to comply with certification regulations. As mentioned, it is a small airplane (wingspan 7.60 m) with two side-by-side seats. The airplane is certified for VFR (Visibility Flight Rules) flights, however it is equipped with most of the IFR instruments for primary training in IR flights. Therefore, some of the avionics are placed in unusual locations, for example under the seats.
The Cessna 172 and the Robinson R44 Raven are widely used general aviation aircrafts. They are very popular as training aircrafts and are equipped with full IFR avionics.
The Tecnam P2006T aircraft is a twin engine type with retractable landing gear. It is powered by a pair of Rotax piston engines and is certified for IR flights, being equipped with the IFR instruments.

The Test Airplanes
Measurements of the electric component (E) of EMF were carried out in four different aircraft: an Aero AT-3 R100, a Cessna C172, a Tecnam P2006T, and a Robinson R44 Raven helicopter. The measurements were carried out in accordance with the PN-T-06580-3: 2002 standard [26], which defines the methods of measuring and assessing EMF at workplaces with frequencies from 0 Hz to 300 GHz. The airplanes presented are used every day for flight training in the Center of Aviation of the State School of Higher Education in Chełm, Poland.
The AT3 R100 is the smallest aircraft used for the tests. Its origin is connected with an amateur design, Pottier P220, which was a popular homebuilt aircraft. Although the AT3 resembles the P220, it is a completely new design, with major structural and conceptual changes that were necessary to comply with certification regulations. As mentioned, it is a small airplane (wingspan 7.60 m) with two side-by-side seats. The airplane is certified for VFR (Visibility Flight Rules) flights, however it is equipped with most of the IFR instruments for primary training in IR flights. Therefore, some of the avionics are placed in unusual locations, for example under the seats.
The Cessna 172 and the Robinson R44 Raven are widely used general aviation aircrafts. They are very popular as training aircrafts and are equipped with full IFR avionics.
The Tecnam P2006T aircraft is a twin engine type with retractable landing gear. It is powered by a pair of Rotax piston engines and is certified for IR flights, being equipped with the IFR instruments.
All the four aircrafts used in the test flights are of metal construction.

The Device for the Test of Electromagnetic Fields
The E tests were carried out with the NHT3DL meter by Microrad, with the 01E measuring probe ( Figure 2). The device is used for measurements and tests of electromagnetic fields in a wide range of frequencies present in the general environment as well as in the working environment in accordance with the international standards as described in [27]. The measurement of the electrical and magnetic components of the electromagnetic field takes place in the three directions X. Y. and Z for the peak impulse value (PEAK) and the effective value (RMS), which determines the maximum value in time. In terms of high frequency, the effective value (RMS) is most often adopted in standards and legal acts [28]. The E tests were carried out with the NHT3DL meter by Microrad, with the 01E meas-uring probe ( Figure 2). The device is used for measurements and tests of electromagnetic fields in a wide range of frequencies present in the general environment as well as in the working environment in accordance with the international standards as described in [27]. The measurement of the electrical and magnetic components of the electromagnetic field takes place in the three directions X. Y. and Z for the peak impulse value (PEAK) and the effective value (RMS), which determines the maximum value in time. In terms of high frequency, the effective value (RMS) is most often adopted in standards and legal acts [28]. The obtained values are saved to the device memory using an SD card. The meter, with a built-in temperature and humidity sensor, is located in the housing. Figure 2 shows the measuring device with the probe. The device enables the measurement of fields emitted by such groups of objects as industrial devices, medical devices, transformer stations, high-voltage lines, railways, the defense industry, radio transmitters, wireless telecommunication systems (base stations, mobile phone, broadcasting equipment, satellite, communication equipment). A measuring probe marked as 01E was used.
The 01E probe is commonly used to detect both CW (Continuous Wave) and modulated signals in the frequency ranges from 100 kHz to 6.5 GHz, which in turn allow applications in the industrial, scientific, medical, telecommunications, and power plants sectors. The high sensitivity of the 01E probe makes it capable of measuring human exposure to electric fields in both public and environmental conditions [29].
The technical parameters of the probe are presented in Table 2.  The obtained values are saved to the device memory using an SD card. The meter, with a built-in temperature and humidity sensor, is located in the housing. Figure 2 shows the measuring device with the probe. The device enables the measurement of fields emitted by such groups of objects as industrial devices, medical devices, transformer stations, high-voltage lines, railways, the defense industry, radio transmitters, wireless telecommunication systems (base stations, mobile phone, broadcasting equipment, satellite, communication equipment). A measuring probe marked as 01E was used.
The 01E probe is commonly used to detect both CW (Continuous Wave) and modulated signals in the frequency ranges from 100 kHz to 6.5 GHz, which in turn allow applications in the industrial, scientific, medical, telecommunications, and power plants sectors. The high sensitivity of the 01E probe makes it capable of measuring human exposure to electric fields in both public and environmental conditions [29].
The technical parameters of the probe are presented in Table 2. The measurements of EM energy took place from the moment the crew started taxiing until they stopped after landing.

The Flight Test Campaign
As already mentioned, the measurements were carried out under real conditions during flights of the training aircrafts mentioned above. As the aim of the work was to investigate the influence of individual radio and navigation devices on the strength of the electromagnetic field in the plane, the measurements were started at the beginning of the landing approach, during IFR flights.
In order to analyze the electric field strength, measurements were made on various flights that lasted from 1 h to 4.6 h. A total of 12 flights were made, 3 flights on each plane. As part of the flight test campaign, measurements were carried out during the procedural approach to landing using the ILS system. Moreover, the measurements were carried out during en-route flights with the use of VOR and GPS radio navigation aids, as well as during navigation exercises in the controlled zone of the Depułtycze Królewskie airport. The flights were carried out both during the day and at night, in various weather conditions, but the use of radio navigation devices was the same, regardless of the conditions.

Results and Discussion
This section presents the results of selected E measurements by means of the NHT3DL meter with the E01 measuring probe. The obtained RMS values to which the regulations refer were analyzed. Operating temperature 0-50 °C Size 327 × 60 Ø (mm) Weight 120 g The measurements of EM energy took place from the moment the crew started taxiing until they stopped after landing.

The Flight Test Campaign
As already mentioned, the measurements were carried out under real conditions during flights of the training aircrafts mentioned above. As the aim of the work was to investigate the influence of individual radio and navigation devices on the strength of the electromagnetic field in the plane, the measurements were started at the beginning of the landing approach, during IFR flights.
In order to analyze the electric field strength, measurements were made on various flights that lasted from 1 h to 4.6 h. A total of 12 flights were made, 3 flights on each plane. As part of the flight test campaign, measurements were carried out during the procedural approach to landing using the ILS system. Moreover, the measurements were carried out during en-route flights with the use of VOR and GPS radio navigation aids, as well as during navigation exercises in the controlled zone of the Depułtycze Królewskie airport. The flights were carried out both during the day and at night, in various weather conditions, but the use of radio navigation devices was the same, regardless of the conditions.

Results and Discussion
This section presents the results of selected E measurements by means of the NHT3DL meter with the E01 measuring probe. The obtained RMS values to which the regulations refer were analyzed.         The maximum values of the electric field strength where E = 4.59 V/m were observed during the approach to landing for the flight marked as AT3 no. 1. At this point, the aircraft was on the VOR approach path. Comparing the results for the flight marked as AT3, flights no. 4 and no. 5 were training flights without approach to landing at Lublin airport, where ILS and VOR navigation devices are installed. The highest values of electric field strength were present during radio correspondence with Depultycze Krolewskie airfield tower, where E = 0.73-1.09 V/m. The next aircraft analysis was the Cessna C172 ( Figures  6-8). Selected flights took place with an approach to landing at Lublin airport (VOR, ILS). The maximum values of the electric field strength where E = 4.59 V/m were observed during the approach to landing for the flight marked as AT3 no. 1. At this point, the aircraft was on the VOR approach path. Comparing the results for the flight marked as AT3, flights no. 4 and no. 5 were training flights without approach to landing at Lublin airport, where ILS and VOR navigation devices are installed. The highest values of electric field strength were present during radio correspondence with Depultycze Krolewskie airfield tower, where E = 0.73-1.09 V/m. The next aircraft analysis was the Cessna C172 (Figures 6-8). Selected flights took place with an approach to landing at Lublin airport (VOR, ILS). For flight no. 1 with the Cessna 172, the maximum values to which the pilot and the passenger were exposed were E = 9.75 V/m. On the basis of the analysis, it was noticed that the maximum values of E = 8-9.75 V/m occurred during landing phase with the VOR system.   For flight no. 1 with the Cessna 172, the maximum values to which the pilot and the passenger were exposed were E = 9.75 V/m. On the basis of the analysis, it was noticed that the maximum values of E = 8-9.75 V/m occurred during landing phase with the VOR system.        For the second training flight in the Tecnam P2006T aircraft, the highest values recorded showed that E = 1.25 V/m during correspondence with the airport. The analyzed flights (Figures 11 and 12) took place in a circuit pattern without ILS and VOR systems. The tests for the Robinson R44 are described in Figures 12-14. For the second training flight in the Tecnam P2006T aircraft, the highest values recorded showed that E = 1.25 V/m during correspondence with the airport. The analyzed flights (Figures 11 and 12) took place in a circuit pattern without ILS and VOR systems. The tests for the Robinson R44 are described in Figures 12-14. For the Tecnam P2006T flight no. 1, the highest values of E = 2.0 V/m were read at the VOR approach path.
For the second training flight in the Tecnam P2006T aircraft, the highest values recorded showed that E = 1.25 V/m during correspondence with the airport. The analyzed flights (Figures 11 and 12) took place in a circuit pattern without ILS and VOR systems. For the Robinson R44 helicopter flight no. 1, the highest values of the electric component, where E = 3.22 V/m, were read for the correspondence with the airport via radio.  The tests for the Robinson R44 are described in Figures 12-14. For the Robinson R44 helicopter flight no. 1, the highest values of the electric component, where E = 3.22 V/m, were read for the correspondence with the airport via radio.   In order to observe the regularities in the studied electromagnetic field phenomena resulting from the large number of samples obtained by measurements, a statistical analysis was performed. The statistical analysis implemented values of the electric field intensity measurement by the NHT3DL meter into the Statistica 13.3 software. The values of the analyzed variables are determined by the mean value, median, standard deviation (SD), and range of variation. The researchers assumed an error of inference which equals 5%, and the level of significance was p < 0.05. The characteristics of electric field for selected flights are depicted in Table 3. The average electric fields value for the analyzed airplanes ranges from 0.147-0.624 V/m. The parameters of the tested quality is very high, in the range of 0.013 V/m-10.87 V/m. In order to verify this hypothesis, the differences between the indicated airplanes tests obtained with the NHT3DL meter are presented in Figure 15. In order to observe the regularities in the studied electromagnetic field phenomena resulting from the large number of samples obtained by measurements, a statistical analysis was performed. The statistical analysis implemented values of the electric field intensity measurement by the NHT3DL meter into the Statistica 13.3 software. The values of the analyzed variables are determined by the mean value, median, standard deviation (SD), and range of variation. The researchers assumed an error of inference which equals 5%, and the level of significance was p < 0.05. The characteristics of electric field for selected flights are depicted in Table 3. The average electric fields value for the analyzed airplanes ranges from 0.147-0.624 V/m. The parameters of the tested quality is very high, in the range of 0.013 V/m-10.87 V/m. In order to verify this hypothesis, the differences between the indicated airplanes tests obtained with the NHT3DL meter are presented in Figure 15.  It can be observed that values exceeding the electric field limit occur in selected Cessna 172 and Robinson R44 flights. Figure 16 presents a frame-moustache graph with marked averages and standard deviation. From Figure 16, it can be observed that there are differences in the mean of the electric component of electromagnetic fields between different types of airplanes. In order to establish whether there are statistically significant differences between the electric fields for particular types of testing airplanes, the Student's t-test (Table 4) was carried out. It can be observed that values exceeding the electric field limit occur in selected Cessna 172 and Robinson R44 flights. Figure 16 presents a frame-moustache graph with marked averages and standard deviation.  It can be observed that values exceeding the electric field limit occur in selected Cessna 172 and Robinson R44 flights. Figure 16 presents a frame-moustache graph with marked averages and standard deviation. From Figure 16, it can be observed that there are differences in the mean of the electric component of electromagnetic fields between different types of airplanes. In order to establish whether there are statistically significant differences between the electric fields for particular types of testing airplanes, the Student's t-test (Table 4) was carried out. From Figure 16, it can be observed that there are differences in the mean of the electric component of electromagnetic fields between different types of airplanes. In order to establish whether there are statistically significant differences between the electric fields for particular types of testing airplanes, the Student's t-test (Table 4) was carried out.

Conclusions
Measurements of the electromagnetic field in training airplanes were carried out using the Microcard NHT3DL electromagnetic field meter with the 01E probe, during flights, on the landing approach supported by radio navigation systems. During the measurements, the meter was placed between the front seats of the pilots. The obtained measurement results were subjected to statistical analysis. It was concluded as follows: The use of the VOR system during the approach phase of the Aero AT-3 R100 aircraft also resulted in a high recorded maximum value of E = 4.59 V/m.

•
The short-range, radio-assisted navigation system (ILS) generated increased values of the electric field. The range of 2.5-5.45 V/m for the Cessna C172 aircraft should be specified here, however, the values allowed in the regulation were not exceeded here. • Larger field interactions and higher field strengths in the VOR beacon system compared to the ILS system can be correlated with the purpose of the system, in particular with the power of transmitting devices. It went up to 200 W in the case of VOR and up to 50 W in the short-range ILS guidance system.  Therefore, a representative group of instructor pilots should be tested to identify trends. This will be the subject of our team's future research work. Another interesting topic is the study of exposure to electromagnetic energy in electric powered trainer airplanes. This is especially important in the era of the global development of the aviation industry and the regional development of aviation infrastructure.