Welcome - MALMS FAQs |
No, MALMS has been designed so that NO tools are required for operation. This removes the possibility of equipment being dropped / left on the runway.
What level of computer skills are required to operate the system?
MALMS assumes no computer skills and can be used by staff at all levels. Selection from simple option lists given on the back-lit touch screen ensures intuitive operation. For example only 5 simple actions are required to start data collection:
It is so easy and quick!
Do you have to drive differently to measure toed services?
No - operators just follow the lights irrespective of the beam toe. The positioning of the sensor arrays allows for the difference in beam direction.
Why not use a PC for data collection?
The MALMS data logger has been designed to combine maximum robustness with easy of use. Industrial grade electronics, waterproof / military connectors and solid state disk drive are housed within a metal enclosure to provide maximum reliability under all operating conditions. The easy to use menu driven back-lit touch screen continues to be preferred by users since it does not require any computer skills and can be used successfully used by virtually any operator. (Where cost is the most important factor a laptop PC based option is available, please consult TMS).
Why do you recommend a trailer?
The MALMS trailer ensures that sensors are mounted in the best measurement position without any vehicle adaption - this enables the optimum accuracy to be maintained with any vehicle. (If it is required to have a vehicle mounted system please consult TMS).
Does the sensor array have to be so large?
The size and shape of the Light Sensor Array is designed to give high accuracy even when the driver deviates from the optimum course. To ensure best accuracy the sensor array has been designed to ensure that measurements are taken when the sensors are a significant distance from the light source - typically the minimum measurement distance is 4m - which defies the smallest size of the array.
Furthermore, MALMS automatically corrects for deviations of up to +/- 0.25m from runway axis, which lowers level of concentration required by driver. However, this requires an array that is larger than the theoretical size.
Why is minimum measurement distance important?
The accuracy of the Average Beam Intensity measurement is based on 3 key factors:
1) Although accuracy of light level is determined significantly by the quality of the light meter (including its photopic response characteristics) the basic laws of physics define that measurement should be taken a significant distance from the light source to obtain accurate results - the ICAO design manual specifies that measurements should be taken at a distance of 100 x the size of the light source.
2) Since Cd = (Lux) x (Distance)² the calculation of Intensity is dependant on the accuracy of the distance figure. In a mobile system the biggest source of error is likely to be the accuracy with which the location of the light source can be determined and this factor becomes less significant the larger the measurement distance.
3) Similarly errors in determining the position of each measurement in the defined beam area become less significant the longer the measurement distance.
Analysis undertaken during the UK CAA Research Project showed that measurement distances less than 2m (which can be achieved with small sensor arrays) would produce significant errors. MALMS has a minimum measurement distance for runway services in excess of 4m, which computer simulation showed to be a good compromise between the size of the sensor array and measurement accuracy.
Can a few data points give a good average?
Obviously the number of data points will affect accuracy - at the limit a single point reading taken in the specified beam area can have a variation of +/- 50% compared to the average calculated by the specified ICAO method (assuming the max / min ratio of 3:1 specified in ICAO Annex 14). At the other extreme a high number of points can have an equally high error if they are taken in the wrong place. Therefore, a high number of data points is no guarantee of accuracy.
MALMS calculates data for each 1º grid point (within the specified main beam area) that sensors have tracked through. MALMS does not give results for grid points when the sensors have not actually tracked through the point or close to it. From these readings the Average Intensity is calculated by simple averaging as specified by ICAO. Since MALMS typically covers 85% of the grid points for inset runway fittings, the resultant value is close to that obtained by conventional goniometer measurements covering all grid points.
The MALMS process places much emphasis on accurately determining where each sensor was for each set of measurement data. Data from different sensors at different distances (remember those furthest away are likely to have the smallest positioning errors) may relate to the same point in the beam. MALMS calculates an intensity reading for each 1º grid point from all available readings. Since even with the large MALMS sensor array, the sensors do not track exactly through each grid point data will be extrapolated as required.
Why have multiple sensor arrays?
MALMS has one array of sensors to measure light (the Light Array) and another (the Position Array) to locate each light source and determine the offset of the measurement system when over the light.
MALMS works to the ICAO specified measurement method and calculates Average Intensity from measurements taken in the Main Beam area - trigonometry then defines the position that the Light Array should be mounted relative to the light source. For services (such as TDZ) where the beam is displaced from the axis of the runway (TDZ are either toed towards or away from the runway centre line) the Light Array must also be displaced. Since the position array is designed to measure offset relative to the ideal position it should be positioned over the axis of the light source even if the beam is toed. Therefore, the two sensor arrays have to move relative to each other as the system is configured for different beam characteristics.
Does Trailer / Vehicle Bounce affect accuracy?
The MALMS trailer has been specifically designed to provide a stable platform for the sensor arrays when measuring both inset and elevated AGL services. However, any vehicle or trailer will bounce if the surface is bad - especially where there are drains / gullies on the runway edge.
The MALMS measurement technique, using multiple readings with a minimum measurement distance in excess of 4m, minimises the impact of any bounce. At these distances, a movement of 75mm (a really extreme bounce) equates to less than 1 degree difference in location within the beam. Therefore, for MALMS bounce has only a minor impact on accuracy. In comparison, a system that measures nearer to the light source will find bounce a significant factor. A system with a small array must measure close to the light - at 1.2m only 20mm of bounce equates to 1º.
Why do you not show results as you go?
MALMS calculates beam intensity by averaging points on the 1º grid within the main beam area as specified by ICAO. The intensity for each grid point is itself calculated from measurements taken from different sensors (at different distances, minimum 4m) as they move through the beam.
However, MALMS does not assume the course of the vehicle (and hence the sensors) through the beam - it calculates it. From this course information it calculates the position of each sensor in the beam for every reading. To do this it uses sophisticated analysis software that may replay the data several times for each light source in order to get the most accurate data.
This "post-processing" is undertaken following data collection in order to allow the Data Logger to collect data from the sensors at maximum speed.
What happens if the maximum speed is exceeded?
The factor that limits operation is the speed at which measurement data can be transmitted over the network that connects the sensors to the Data Logger. This is limited by the speed of the network the ability of the Data Logger to read and store it. Each sensor node has its own microprocessor to control the measurement cycle, provide automatic range changing / diagnostics and network interface. This does not have any practical limitations.
The maximum speed at which all available data is logged is 80kph - above this speed some data may be lost but at all practical operational speeds this will only be a small percentage of that required for maximum accuracy and accuracy will only be marginally reduced.
What data quality checks does MALMS have?
MALMS is designed to ensure that only good accurate data is collected and the location of the data is correctly identified. The quality of the data is checked at least 3 times during the MALMS process - on completion of the survey run; during the post-processing and finally when it is read into the database.
This multi stage data verification both identifies any possible quality problems at the earliest stage and prevents results being allocated to the wrong location.
How quickly can you exit the runway?
At any speed at any time - the robust mechanical design enables the system to safely clear the runway in extreme situations.
Can you restart anywhere?
In theory data collection can be resumed part way along an inspection course. However, this has been disabled since it reduces the effectiveness of the integral data quality checks - with the speed of MALMS it is easier to repeat a survey run than to find the correct place to restart.
