Are you being a good neighbour?

Are you being a good neighbour?
Managing the impact of aircraft noise in your neighbourhood.

Recently, I became involved in a project to the update the SID’s and STAR’s of an International Airport. The procedures being revised were created in the 1970’s and are based on the navigation technology available at that time. Navigation technology used in that era required the protection of significantly more airspace to allow for wider aircraft instrumentation and ground facility signal inaccuracy.

One example of an airway allowing for this increased inaccuracy is that of an airway utilizing NDB (non-directional beacon) ground stations for position fixing. (I hear many asking, ‘ NBD in this era of RNAV/GPS overlays?’) The NDB airway incorporated a wide cone of protected airspace due to the systemic uncertainty of actual position information. Imagine for a moment an ice-cream cone laid on its side, the NDB will be at the point of the cone and as you move away from the bottom of the cone/NDB, the volume of protected airspace increases according to increased likelihood of positional error.

The airway’s wide footprint had the added effect of diluting the noise footprint of the traffic on a single route. If 10 aircraft are following the same airway, and the airway is 10 miles wide, this meant that the possibility of two aircraft following the exact same track over the ground was remote.

The increased precision of the navigational instruments and the availability of GPS has been a major improvement in both the cockpit and from an air traffic management point of view.

Airspace planners have welcomed the increased predictability of the tracks to be flown. Regulators have used the evidence produced from historical track monitoring and increased positional reliability to justify reducing lateral track separation standards in congested airspace in order to increase airspace capacity in the vicinity of busy airports. This is evident in the reduction of RNAV performance criteria from Required Navigational Performance (RNP) 5 to RNP 1 in many Terminal Control Areas. Airline operators have also welcomed the increased predictability these precision tracks provide, as they are now able to forecast fuel burn more accurately. Pilots are able to fly the same track profile almost every time.

This increased precision has had some unexpected, adverse effects on the population surrounding the airport. Where the arriving or departing aircraft would have previously be dispersed in a swathe 5 nautical miles (NM) wide, the aircraft are now concentrated in a corridor 1 NM wide. Initially you may think... “We have just provided a measure of noise relief for 80% of the previously affected area”. While this may be true, you have also increased the traffic footprint of the 1 NM corridor by 400%!

While the benefits of incorporating the latest RNAV technology are abundantly evident to those in the aviation industry, it is important to remember many

people do not understand why an aircraft must fly at low altitudes over an area more than 10 miles from an airport.

The response of the local community to the presence of an international airport in the local area is generally positive. Some of the obvious benefits offered by the presence of an airport are:

Economic activity

Prestige of having an airport close by Ease of travel for business and leisure

Incoming tourist travellers

The majority of complaints from neighbouring communities relating to an airport’s activity are directly attributable to aircraft noise and the disturbance this causes.

Most airports have a quiet hours movement policy. These noise restrictions along with the reduced noise footprint of modern engines has had a dramatic impact on reducing the actual noise created by flying activities. The perceived disruption is another issue.

There are a number of activities an airport is able to engage in that will reduce the negative feelings toward the aircraft operations. These engagement activities do not have to compromise the airport’s operation. The engagement will involve the building of a relationship between the airport and the surrounding community.

Most people are generally more receptive and acceptant of disruptive activities if they understand what, and why, it is happening.

Noise is a by-product of any industrious activity. Think for a moment about the sound of pounding nails while building a house or the laughter of children in a playground. If your neighbours feel like they are being treated with respect and have had their concerns genuinely heard and acted upon, the relationship between the airport and the neighbouring community will begin to flourish.

If you would like to discuss this issue with me just drop me a line and I will respond to you as soon as I can. 

How Precise is GPS Timing?

Just how precise is GPS



A recent global interruption in January 2016 of the GPS system has highlighted how many systems and industries are reliant on the precise timing provided by the GNSS system.  The GNSS system is the Global Navigation Satellite System.  This system covers all satellite based Position, Navigation and Time keeping satellites of which GPS (USA) is but one.  Other systems include GLONASS (Russia), BEIDOU (China), GALILEO (European Union), and a couple of regional constellations operated by Japan and India.

Although many of us use the GNSS/GPS information regularly in our daily lives, most of us have little idea of how dependent we are on the system.

The GNSS/GPS signals continuously provide 3 functions: Position, Navigation and Time. (PNT)

The position and navigation elements are obvious to those of us who are in any way technologically aware, but the timing aspect is less well understood.

Most wireless networks involving data exchange or data transfer require precise timing for system synchronization.  This precision of timing is measured in micro-seconds.  In some cases the level of precision required is measured in nano-seconds.

These periods of time, the micro and nano second, are rarely used so I needed to be able to relate them in a more common form.  Here is a comparison.


1)   The old saying for getting something done quickly is to have it done “in a heartbeat”.  For most people the average resting heart rate is between 60 and 80 beats per minute.  If we use 60 beats per minute, it takes one second between heartbeats.

2)   Another saying is “in the blink of an eye”.  Research has shown that it takes between 300 and 500 milliseconds to blink.  A millisecond is one one thousandth of a second.  So again assuming 330 milliseconds for a blink it will take 1/3 of one second to blink.

3)   A microsecond is one one millionth of a second.  Numerically that looks like this, 0.000001 of a second.  According to Wikipedia,  “one microsecond is to one second as one second is to 11.574 days.”

4)   A nanosecond is one one billionth of a second.  Again it looks like this, 0.000000001 of a second.  Wikipedia describes it as “one nanosecond is to one second as one second is to 31.71 years.   Rear Admiral Grace Hopper of the US Navy provides an excellent visual description of the nanosecond in this YouTube clip:


The recent event that disrupted the GPS network was caused by a 13 microsecond error in the system.  This error was enough to raise alarms and render some systems unusable for 12 hours.  These affected systems included radio broadcasts, internet service, communications systems and aviation ground navigation systems. 


This raises the question, “How reliant are we on the GNSS/GPS system?” and “How vulnerable is that system?”


Article 6

Over the last few weeks we have had a look at the GPS system and considered some of its outstanding applications.  Coupled with this broad list of capabilities, the extent of GPS integration through out our society has been equally impressive.

The ubiquitous presence of GPS technology and high levels of availability have created a sense of confidence in the system that is a little concerning.

As we considered in a previous article, the GPS system itself is no longer owned and operated by a single military power reserving the ability to withdraw the signals without warning. New commercial off the shelf GNSS/GPS receivers now have multi constellation capability, allowing the user to switch between the GPS, GLONASS, BEIDOU or GALILEO network of satellites at will. 

This system redundancy, along with assurances from the United States that the GPS service will not be denied without warning, has relieved a serious concern within safety critical industries, such as aviation. With justifiable confidence in the integrity of the signal and the removal of the Selective Availability function, aviation authorities have started to develop instrument approaches into airports where previously there was no viable instrument approach available.  These new instrument approaches have saved air operators a lot of time and money by improving their ability to operate in bad weather.

The major Air Traffic Control system upgrade currently underway in the United States (Next Gen) is heavily reliant on GPS.


So, the availability of the GNSS signal issues has been resolved with assurances of continuous broadcast and multiple system redundancy. 


This brings us to the signal itself. 


Dr. Charles Curry, of Chronos Technology, compared the power level of the GPS signal arriving at your hand held receiver as to that of the power a 20 watt light bulb generates 20,000 kilometers away.

The satellites that produce the GPS signals are in orbit 20,000 kilometers above the earth.  That is a long way for the GPS signal to travel even without any obstacles.  Now consider that the signal must pass through the ionosphere.  The ionosphere shields the earth from much of the solar radiation generated by our Sun.  The absorption of this solar energy stimulates electromagnetic activity that has a direct impact on radio waves.  Short wave radio operators regularly bounce their radio signals off the ionosphere in order to increase their effective range.


As the GPS signal is this weak, it is easily subject to radio interference.  The interference can completely ‘block’ the signal, or just distort it sufficiently as to corrupt the position or time information.  Most GPS receivers will be able to alert you to the fact that the signal information has been compromised and therefore unreliable. 


Naturally occurring interference primarily happens during a period of increased solar activity.  This increase in the Sun’s electro magnetic activity agitates the ionosphere causing it to interfere with most radio signals.  It is during these solar events you generally get the most spectacular displays of the Aurora Borealis.  This atmospheric interference is generally widespread, and usually notified through the various space agencies such as NASA and the European Space Agency.


Man made interference is a more localized event involving electronic devices either designed specifically to disrupt the GPS signals or electronics that have malfunctioned and are broadcasting on frequencies not intended.


Interference can happen as a result of frequency harmonics.  This is where a broadcast is being made on a frequency that is a mathematic multiple of the GPS frequency.  If for instance the GPS frequency is 8 wavelengths, but a powerful transmitter was broadcasting in the area on frequency of 4 wavelengths, the wave patterns intersect and the more powerful frequency will over power the weaker one.


Powerful transmitters in adjacent frequency bands to the GPS spectrum can ‘splash over’ and cause interference as well. 


The most common cause of man-made interference is created by the use of Personal Privacy Devices (PPDs).   PPDs are readily available on the Internet and illegal to operate in most countries. These devices are common and causing an increasing number of problems for GPS signal sensitive operations.

PPDs are used by individuals hoping to defeat GPS tracking hardware fixed to commercial vehicles or in an effort to avoid other forms of position monitoring.


Newark Airport in New Jersey, suffered major losses of GPS integrity with its Ground Based Augmentation System (GBAS) as a result of interference.  The source of the interference was eventually traced to a van driver passing the GBAS building at the same time twice a day, while on the interstate highway adjacent to the airport.  It took the airport and FAA three months to catch the driver.  The driver had no idea that his jammer was affecting other GPS receivers.  The driver was given a fine of $35,000 for using the device.  There are numerous cases of jammers affecting Ports, Railways, and cellular telephone service.  The city of Seoul, South Korea has been subjected to massive GPS jamming by the North Koreans on more than one occasion.  These events have caused major disruption to electronic services reliant on GPS signals.  


Criminals also use these devices to help them steal high value vehicles by defeating the GPS trackers fitted to the car.


These devices simply broadcast on the GPS frequency at a higher power level then the true GPS signal thereby ‘drowning’ out the genuine signal.


The other systems we have identified as being dependent on the GPS signals are also at risk of jamming by the same devices, either intentionally or not.


Direct-Track Consulting has been involved in extensive field trials testing commercial products designed to detect and locate the source of GPS signal interference.  The results have been excellent and provide a quick and effective method of detecting and finding the source of localized GPS interference (jamming). 


If you suspect that your GPS signal may be suffering unexplained failures and require assistance in securing the integrity of your GPS reliant system contact me for a no cost initial consultation.


Article 5

In the previous articles we have discussed the broader aspects of the GNSS/GPS system and how it affects us in a rather general way.  I would like to spend a few minutes considering how the GPS system impacts and affects you personally.

Most of us are aware of the handheld Garmin or TOM TOM GPS receivers in your car or that you take on holiday.  They are exactly what they say they are, GPS receivers.

Those of us with smart-phones, are aware of the integrated phone tracking location service, that is GPS based.

As I contemplate how to illustrate the wide variety of GPS applications within the scope of this short article I realize that doing so is going to be quite difficult.  

As I quoted in the first of these articles,  “There is no area of commerce in the UK that is not reliant on GPS.”[1]

Each sector on the following list is only the tip of the network where GPS is employed.


·      Aviation,

·      Banks,

·      Cellular Telephone network,

·      Electric Power Grids,

·      Stock Market trading,

·      Cargo tracking,

·      Railway signaling,

·      Maritime Navigation,

·      Automatic Highway tolls,

·      Geo Surveying

·      Surveillance


You will quickly see the obvious relationship between GPS and other transportation roles such as Aviation, Cargo Tracking, Maritime Navigation and so on, however the relationship to Banks and the Stock Market may not be as obvious. 

If you remember, the GPS signal provides Position, Navigation and Time information.

The Financial industry relies very heavily on the synchronized timing signals generated by the GPS system in order to execute computerized trades across the world.  Every financial trade must have a synchronized date/time stamp to provide proof of when the trade took place.  In the era of computerized high-speed trades, a few milliseconds can be the difference between a major profit, or a catastrophic loss. 

This level of precision is essential for the international financial markets to continue to function.  If the clocks are out of sync the computerized trading stops.

The same requirements of precise timing are also relevant to the cellular telephone networks and radio/television transmission. 

If a radio transmitter is broadcasting on the same frequency but from 2 different sites, the signals must be perfectly synchronized or the result will be carrier wave interference and the frequency will be blocked with an unpleasant squeal.  This is caused as both signals run over and interfere with the other.

For the Cellular telephone networks to work effectively each cell mast must be synchronized with all of the other masts within the network. 

As you drive along the highway, hands-free of course, the signal from your phone is ‘handed’ from one tower to the next giving you a continuous connection to your other party.  If these these signals are not synchronized, each mast will be acting independently and there will be no continuity of signal reception.  The absence of continuity will make an uninterrupted call impossible.  Think about that the next time you are in the car and your phone call lasts 50 miles.

In the last installment of this series we will look at some of the vulnerabilities of the GPS system.


[1] Dr. David Last

Article 4

How powerful is that signal coming from the GPS satellite?


The GNSS/GPS system is a constellation of satellites orbiting the earth at an altitude of approximately 20,000 kilometers,  (12,000 miles) providing PNT signals 24 hours a day. 

Previously we looked at who actually owns and controls the various GNSS/GPS satellite constellations.  The United States are the owners of GPS, the Russians have GLONASS, the Chinese BEIDOU, the European Union own the GALILEO system while Japan and India control their own regional systems.  Eventually there will by approximately 150 satellites in orbit, providing PNT (Position, Navigation and Time) signals to the earth. 

These satellites are designed to have a significant life expectancy.  In addition to producing the PNT signals 24 hours a day, the satellite must have sufficient internal power to perform self-maintenance functions as well as number of other tasks.

The satellites generally have small batteries and solar panels are the only external source of power for the electronics on board.

Those of you with an electronics background know that in order to produce a powerful signal you need to have a powerful transmitter. And with a powerful transmitter you need a sizable power source.

This fact has forced the engineers who developed the GPS system to strike a balance between power and functionality.  In order to manage the satellite power requirements the designers had to reduce the demand for power to run all of the satellite’s systems.

One of the ways to reduce the power requirement on board the satellite was to reduce the power of the signal produced by the GPS transmitter.  It is a simple trade-off, more signal power shorter satellite lifespan, less power equals a longer lifespan.  Therefore the strength of the GPS signal, is comparatively, very weak.

Professor Charles Curry, of Chronos Technology, compares the power of the GPS signal, generated and reaching your handheld GPS unit, to the power output of a 20-watt light bulb shining at a range of 20,000 kilometers.  This power level is microscopic in the radio spectrum.

Even using specialist radio reception equipment to “hear” the GPS signal in its raw form is very difficult.  It would be like trying to hear a whisper in a rock concert. 

The raw GPS signal strength is below the noise floor of random space noise.  Random space noise is the radio energy produced by our Sun and other stars.  To our naked ears the space noise would sound like static, or the constant hiss of white noise to our ears.

In order for the GPS receivers on earth to “hear” the signals from the GPS satellites, the scientists have coded the GPS signal.  Your hand-held receiver is designed to look for this specific code pattern amongst the noise and when it finds it, the receiver locks onto the signal.  

Once the signal is identified and verified the receiver can work out its position using the geometry of triangulation.  You need at least 3 signals from different satellites to work out your position in 3 dimensions.  Latitude, longitude, and altitude.  A signal from a fourth satellite allows precise time measurement, the fourth dimension. 

In the Aviation community increased capacity of airports and airspace is now being measured in 4 dimensions.  It is no longer just where but also when.

Next time, what services are dependent on the GPS PNT signals?

Who owns the GNSS/GPS system?

Third Post:

Who owns the GNSS/GPS system?


The first operational navigation system using information derived from a constellation of satellites was the Global Positioning System developed and owned by the United States Government/Military.  The system is reported to have become fully operational in 1995. 


The first GPS receivers available for civilian use were very crude by today’s standards.  The accuracy levels were in the 100’s of meters as opposed to the 10’s of meters available today.  The level of accuracy available to civilian GPS units improved in May of 2000 when the US Military turned off the ‘Selective Availability’.  Selective Availability is a system installed on the GPS satellites to deliberately degrade the accuracy of the GPS signal.  This functionality was designed in order to deny any potential enemy precise position information that could be used against the US.


The complete unilateral control the US Military had over the GPS system caused concern among other nations and industries.  The fear was that if you became reliant on the GPS signal for safety critical operations or for operations competing with the US national interest, the GPS signals could be denied at the flip of a switch by a foreign Military Power.


This discomfort encouraged a number of nations and one group of nations to develop their own versions of GPS.  The Russians have developed and have deployed their own Global system called GLONASS.  The Chinese have developed their own Global system called Beidou, The Japanese and Indians have their own regional systems covering their specific geographical areas.  These various systems are all controlled by the Military of their governments.


The only Global system owned and operated entirely by civilian authorities is the European Union’s Galileo system.  The Galileo system is in the deployment stages with 4 satellites in orbit at the time of writing.


Many older GPS receivers are capable of receiving signals from one (GPS) constellation only.  Newer GNSS receivers are multi constellation capable and this has increased system flexibility and integrity.  

The assurances from the US that they will not switch off the GPS signals has encouraged a dramatically increased use of, and dependence on, GPS technology over the last 15 years.


Next: How powerful is that GPS signal?

Second Post

In my first article we briefly discussed the level of integration the GPS system has in our society.  3.5 Billion GNSS receiver units with a forecast of 7 Billion in use by 2019.  On top of that was the dramatic statement by Dr. David Last that “there is no area of commerce in the UK that is not reliant on GPS”.


The GPS signal provides the framework from which your hand held receiver determines, with surprising accuracy, your position on the earth in three dimensions.  The GPS receiver can also workout your direction of travel and the speed at which you are moving relative to the surrounding geography.

These functions are the most regularly used and most widely understood.  The GPS signal is also given the acronym PNT.  P for Position, we understand that, N for Navigation, again generally understood and the last one is T for Time. 


The Time portion of the signal is not widely understood and warrants some discussion. 


It is reported that in excess of 90% of all 3.5 Billion GPS receivers are employed in a time keeping role as opposed to the Position and Navigation applications. The size of a common GPS receiver is half the size of the fingernail on your pinky finger, and costs around 2 US dollars to buy.  Granted there are some units that cost over 30,000 dollars, but they have the most expensive atomic clocks in them, however the vast majority of receivers do not.


Why is precision time keeping so important, and what industries are so reliant on precise time?


If you have a network of electronic sensors or switches that rely on opening and closing at the same or at coordinated times, each sensor must have a clock built into it so the sensor knows when to act. Now imagine a network of 50 sensors acting together to supply electricity from the wind farm in Scotland to your bedside light in London.  Each sensor must know what the exact time is and when to act.   All of the sensors must have a common time so the flow of electricity is not interrupted causing the circuits to trip and cause a blackout.  These clocks are coordinated to millisecond precision.  If the master clock is in Scotland and the secondary clock is in London, there will be some delay as it takes time for the electronic signals to travel between the two.  This delay is unacceptable as it can cause disruptions, therefore each sensor must have it’s own synchronized clock.  With all of these clocks spread around the country it is inevitable that one or more will drift, even slightly, out of time.  The best way to synchronize the clocks is by using the precise time signal broadcast from the GPS satellites.


Industries that rely on precise timing are the electric distribution companies, the financial services sector (time stamping currency trades), television and radio services, mobile phone networks and safety sensitive transportation applications (Aviation) to name a few.


In the next article we will look at who owns GNSS satellites.   


First Post

This is the first in a series of posts detailing the work Direct-Track has been involved with during the last few months.  We have been involved with work on assessing and identifying the vulnerabilities related to the GNSS/GPS system. 

For clarification there are a number of satellite constellations either in service or in the development stages.  These different systems are owned and operated by different nations or groups.  They all have their own unique identification and capabilities, but for the purposes of this article I am going to refer to the whole of the GNSS system as GPS. 

A huge number of us are active users of the signals produced from the GNSS satellite constellations supporting the GPS system, and a large percentage of us are unaware of the level of reliance we have on the system.  It is estimated that there were 3.6 Billion, yes that is Billion, GPS devices in use at the end of 2014.  That is 1 device for every 2 people on earth.  It is estimated that by 2019 there will be 7 Billion devices reliant on GPS signals.

The level of integration of GPS technology and functionality is shocking.  Dr. David Last, a world renowned expert on radio navigation and the impact of GNSS usage, states that “There is no area of commerce in the UK that is not reliant on GPS.”

Think about that for a second,  “ area of commerce…”.  The definition of commerce as described in the Collins English dictionary is “…the activity embracing all forms of the purchase and sale of goods and services.”

That includes banking, on-line purchases, mobile phone networks, delivery and cargo shipping services, electricity grids, radio and television services… anything to do with business.  Not just finding your way to the nearest restaurant you like via your handheld GPS unit.  We are all directly reliant, in one form or another, on the continued integrity of the signals received on earth from the GPS satellites.

In the next article we will look at how the GPS signals are used in various industries.

Procedural Control Instruction

Recently Direct-Track Consulting was involved in the development and delivery of a specialized course of instruction for Ab-Initio ATC students in Procedural Control.

Procedural Control is a form of control relying on the protection of an aircraft in flight based solely on position information given via voice communication.  With no other aids such as radar or ADS-B to assist the controller in establishing the aircraft’s position.

This skill is considered an ancient form of Air Traffic Control but in many of the worlds remote locations this method of separating aircraft is all that is available. 

The courses Direct-Track delivered were for the En-Route as well as Approach Sectors. 

Remote tower feasibility

Direct-Track Consulting has been selected to provide operational expertise in the developing of a plan to establish a remote Visual Control Room at Dubai International Airport to act as a contingency facility.

The Remote Tower concept has been gaining credibility with the recent certification of the remote operation at Ornskoldsvik airport in Sweden.  

The technological advances in communications and visual sensors have led a number of jurisdictions into considering the options provided in these capabilities.

While some facilities have established remote operations on a portion of the airport, ie for areas of poor sight lines, Budapest has pushed back the boundary by actively working to provide the Aerodrome Control service in its entirety from a remote location.  The Control tower in Budapest is a relic from the Soviet Bloc era and is in need of complete replacement.  The option being considered is the complete operation of a busy, parallel runway airport from remote site.  Direct-Track provided support and first hand knowledge of the issues associated to remote operations.

Dual Diagonal Approaches

Direct-Track was selected to provide operational expertise in the development of the Safety Case associated with the Dual Diagonal (DD) Approach concept at Dubai International Airport.

The Dual Diagonal concept is based on straight in approaches to parallel runways laterally separated by only 386 meters.  This configuration has caused problems for the airport as it wants to increase runway arrival capacity by allowing landings on both runways simultaneously. Current ICAO wake turbulence rules dictate that the two runways at Dubai must be considered as a single runway for wake turbulence application.  This restriction limits the use of the right hand runway as irrespective of the type of aircraft single runway wake turbulence spacing is to be applied.

The geometry of the runways has the threshold of the right hand runway inset by over 1000 meters.  This factor has been taken into account and by projecting the descent profile back from the runways, the profile of the aircraft on the right hand runway is always above the descent profile of the aircraft on the left.  Using this fact and the accepted logic of wake always descending, the case is being made that less than ICAO spacing is appropriate as the flight paths will never cross and therefore wake transference will not be a factor.

Specialist wake vortex analysis is being carried out using LIDAR technology to support the assumptions.