Future Air Navigation Systems

Today, London Heathrow became the fifth European Airport to introduce Airport Collaborative Decision Making (A-CDM). Having conducted successful trials throughout April and May of this year the airport has today joined Munich, Brussels, Frankfurt and Paris Charles de Gaulle in becoming fully A-CDM operational.

Efficiency is increased when airports are linked to the rest of the air traffic management system. Benefits include: greater adherence to slot times, more efficient aircraft turn-round and pre-departure sequences, accurate predictions of landing time for arriving flights, improved planning for outbound flights, reduced airport and en-route delays, enhanced decision making capabilities, reduced fuel burn and CO2 emissions.

Charles de Gaulle and Brussels airports are both integrated into the network and report impressive environmental savings:

Paris CDG has seen a 7% reduction in taxi times which relates to a daily saving of 14.5 tonnes of fuel.

Brussels however, has reduced taxi-out and taxi-in times by 25% and 15% respectively since introducing A-CDM, saving airlines 7,200 tonnes of fuel annually.

Lufthansa's e-taxi trial at Frankfurt.

High levels of competition and the increasing price of oil have further highlighted the importance of operational efficiency within the aviation industry.

Improving efficiency allows operating margins to be increased, a factor which is especially important to low cost carriers. The improvements also allow airlines to remain competitive or even gain a competitive advantage. Reduced fuel burn also allows environmental concerns to be addressed.

The price of oil is driven by changes in global supply and demand, along with political, geographic and economic factors. This means that things like political instability in oil producing regions, growing demand from BRIC economies, increasing investment demand and natural disasters all affect the price of oil, and therefore airline operating costs. More recently, events such as the Arab Spring, Iranian missile tests and record low temperatures in Europe have all caused oil prices to increase.

Ground Operations

In 2010 the average taxi time and holding point delay at Heathrow was over 22 minutes. With a fuel burn of around 500kg per hour at idle, an A320 sized aircraft will consume over 180kg of fuel before it has even taken off. This is both an expensive and inefficient way to get the aircraft to the runway. Alternatives include:

Single Engine Taxi: Pretty self-explanatory really,  jet engines are notoriously inefficient at low speeds, some airline have SOPs allowing aircraft to be taxied under the power of one engine in an attempt to save fuel. Single engine taxi procedures can be adopted on both taxi-out and taxi-in; however criticism has arisen over the technique as if an engine is not started in time prior to takeoff delays will be caused, which will most likely affect other aircraft when operating at busy airports. On top of this, engine life is thought to be reduced by this technique due to the reduction in warm-up time between engine start and the application of high power settings for takeoff.                                                               

Towing: Again, fairly self-explanatory. Virgin began trials of this technique in 2006 at both Gatwick and Heathrow airports. This involved aircraft being towed to a "starting grid" close to the runway where the engines were then started prior to takeoff. Unfortunately the trial hasn't really lead to anything, maybe due to worries over the undesigned cyclic loading which repetitive towing of a fully loaded aircraft subjects the nose gear. The benefits however are clear. Virgin claim that their aircraft consume 1.5 tonnes of fuel just getting to the runway; towing would deliver fuel savings and therefore reduce emissions. The local area would also see benefits due to a reduction in noise and an improvement in local air quality.

Taxibot: A cooperative venture between Airbus and Israel Aerospace Industry (IAI)that is set to eliminate the problem of excessive stress on the aircraft nose gear! The device uses a load alleviation system and is set to see its introduction into commercial service during 2012. The project is revolutionary, allowing pilots to control the Taxibot tug via a cockpit-operated drive system. Eventually it is expected that there will be 2 designs of Taxibot, one for single aisle and another for widebody aircraft; each will incorporate a diesel engine to provide power to electrically driven wheels.    

http://www.airbus.com/presscentre/pressreleases/press-release-detail/detail/taxibot-set-to-usher-in-a-new-era-of-airport-taxiing/

http://www.ricardo.com/en-GB/News--Media/Press-releases/News-releases1/2011/IAI-awards-Ricardo-contract-to-support-next-phase-of-TaxiBot-development/

http://blog.seattlepi.com/aerospace/2009/11/23/taxibot-could-cut-aircraft-emissions-save-fuel/

http://www.greenaironline.com/news.php?viewStory=522

   4. Electric Taxi: This concept consists of electric motors which are located in either the main land gear or nose gear. The electric motors are powered by the APU and allow the aircraft to taxi without the use of their main engines. Lufthansa undertook feasibility trials of the technology in December 2011. An A320 aircraft was taken out of service and modified to incorporate the e-taxi technology.

Beyond the fuel savings, advantages include reduced noise and emmisions, benefitting the local population.

Here’s a video demonstrating the concept:

This is surely the future?

http://www.lufthansa-technik.com/applications/portal/lhtportal/lhtportal.portal?requestednode=395&_pageLabel=Template7_8&_nfpb=true&webcacheURL=TV_I/Media-Relations-new/Press-Releases/E_Taxi_Demonstration_EN.xml

http://www.dlr.de/dlr/presse/en/desktopdefault.aspx/tabid-10172/213_read-2646/

Before you read: GNSS = Global Navigation Satellite System

So far, the GNSS constellations available to the aviation industry have not offered the necessary accuracy for precision critical applications such as an RNP approaches.

Using the American Global Position System (GPS) constellation as an example:

The satellites transmit 2 services, the first a coarse acquisition code, the second a precision positioning service. As civilians we can only intercept the coarse acquisition code (the PPS is encoded for use by military users only). Therefore, the accuracy we can achieve isn't accurate enough for a precision aviation application.

Until GALILAO (the high-precision civilian GNSS built in partnership by the European Commission and European Space Agency (ESA)) is operational (estimated 2015) a method is needed to improve the accuracy of the existing GPS and GLONASS signals (Russian built GNSS). This improvement has been achieved through EGNOS (European Geostationary Navigation Overlay Service) a joint European Space Agency/Eurocontrol venture. EGNOS consists of 3 geostationary satellites and a network of ground stations. The ground stations monitor the accuracy of the GNSS signal and transmit corrective data to the geostationary satellites who in turn broadcast it to aircraft - this corrective data allows atmospheric bending to be accounted for.

This might be a bit off topic, but while looking at safety nets I came across Runway Overrun Protection Systems (ROPS).  Runway excursion is of serious concern to the aviation industry at the moment because occurrences are increasing at a rate greater than the rate of global fleet expansion. Put simply, runway excursion is an incident where an aircraft unintentionally leaves the runway and can occur during takeoff or landing phases of flight – ICAO defines runway excursion as “A veer off or overrun off the runway surface”.   

ROPS shows the position at which the aircraft will stop along the runway (in wet or dry conditions) on the aircraft's nav display. The point will move along the length of the runway depending on the systems evaluation of aircraft approach profile, aircraft breaking capability and landing distance available (LDA). If ROPS predicts a runway overrun occurrence a visual warning is given to the pilot, along with a repeated aural alert: “RUNWAY TOO SHORT”. Research has shown that when pilots are presented with a non-standard situation, their instant reaction is to revert to a pre-programmed response. In the event of runway overrun it has been found that pilots have often reduced reverse thrust to idle upon reaching 80kts, a standard procedure, rather than reacting to the non-standard situation in front of them. For this reason, the ROPS system gives the aural cue “KEEP MAX REVERSE” if the aircraft is at risk of runway overrun and is approaching 80kts.

Airbus has made their ROPS system commercially available to other aircraft manufacturers in an attempt to combat the number of global runway excursion incidents.  

http://aviationknowledge.wikidot.com/aviation:runway-excursions

http://www.mexico.icao.int/summit/2011/THU/SAFETY2011-Airbus-Bill-Bozin.pdf

*Warning - Acronym Rich*

When researching the future of ATM it became apparent that the planned increase in European capacity is expected to be supported by an improvement of safety nets. The impacts of aviation accidents are very high, therefore the Chicago convention dictates that ‘states are required to provide a safe air traffic service within their airspace'.

“Safety nets help prevent imminent or actual hazardous situations from developing into major incidents or even accidents” (Eurocontrol)

Safety Nets can be split into two categories: Ground based and Airborne.

Ground Based safety nets use surveillance data to provide a conflict alert up to two minutes before impact. Controllers are expected to assess the situation and react to the alert. Ground safety nets have been evolving since their first use over 30 years ago and will continue to become more accurate with the introduction of more accurate surveillance data (e.g. WAM, ADS-B).

STCA (Short Term Conflict Alert) aims to eliminate occurrences of loss of separation by alerting controllers of an imminent infringement of separation minima. STCA has been mandatory in ECAC (European Civil Aviation Conference) surveillance areas since 2008 and has already provided benefits; in 2007 there were 3 category B incidents at Maastricht Upper Area Control Centre, following 8 in each of the 3 years previous – Eurocontrol attributes this to the introduction of STCA.

APW (Area Proximity Warning) provides an alert when an unauthorised aircraft penetrates (or has the potential to penetrate) the controlled airspace volume.

MSAW (Minimum Safe Altitude Warning) provides an alert when an aircraft is threatened by CFIT (Controlled Flight Into Terrain). This is based upon the proximity of the aircraft (as determined from surveillance data) to known terrain.

APM (Approach Path Monitor) is very similar to MSAW but is specialised for the approach phase of flight. APW, MSAW and APM are required where the relevant dangers exist (e.g. mountainous regions) within ECAC surveillance areas by December 2013 (Except for France and the Netherland which are exempt).

Airborne safety nets take the form of onboard alerts and resolution advisories, which pilots are expected to follow in order to avoid the hazardous situation. Onboard systems provide the alerts based upon derivations from various data sources and often have warning times shorter than those offered by ground based systems (up to 40 seconds).

ACAS (Airborne Collision Avoidance System) (also known as Traffic Collision Avoidance System) is used as the final line of defence in the event of a loss of separation. The system interrogates mode C or S transponders of nearby aircraft and gives traffic advisories/avoidance advisories should a conflict be detected. Eurocontrol estimate that ACAS reduces the risk of mid-air collision by a factor of around 5.

(E)GPWS (Enhanced/Ground Proximity Warning System) reduces occurrences of CFIT by providing an alert when sink rate, ground proximity, glide slope deviation, incorrect landing configuration, loss of altitude on takeoff/go around or a predicted terrain hazard is detected. Primary input data is provided by the radio altimeter, which warns of approaching  terrain. EGPWS uses an accurate three-dimensional map to plot the location of the aircraft in relation to surrounding mapped terrain.

Ground based MSAW and APM systems compliment the onboard (E)GPWS system, providing a level of redundancy. Likewise, STCA and APW systems have their airborne equivalent – TCAS, also providing a backup. Future airborne safety nets may include High Energy Approach Monitoring Systems (HEAMS) and Runway Overrun Protection Systems (ROPS). Furthermore, SESAR is working towards displaying ACAS resolution advisories on controller workstations via RA downlink. Beyond 2020 STCA and ACAS will need to be adapted to accommodate new separation modes – compatibility between the two systems would also be beneficial.

The future ATM (Air Traffic Management) system will aim to provide a tenfold increase in safety, a 10% reduction in fuel burn, a 10% reduction in emissions, a 50% reduction in ATM costs and an increase in capacity by a factor of 3.

The future air traffic management system will adopt a performance based approach to achieve the European Commission objectives of the SESAR programme. These goals are expected to be achieved through:

A transition from airspace to trajectory based operations. TBO will require a new approach to airspace design and planning.Traditionally, Air Traffic Management (ATM) has grown within the constraints of an airspace based paradigm and as such end-to-end trajectory was given little consideration. This airspace-centric view leads to trajectories effectively being bent to fit within defined volumes of sky. Trajectory based operations should more easily facilitate: user preferred routings, user preferred time of arrival, 4D trajectories and the sharing of this trajectory information with all relevant stakeholders via SWIM (System Wide Information Management). Should trajectory intervention be required (e.g for weather or deconfliction) the downstream effects can be more easily considered. Overall, uncertainty will be removed, leading to a capacity increase.

Collaborative planning. In future, ATM decisions should be made collaboratively, with all stakeholders (such as airline operations centres (AOC), airport operations and pilots) being consulted. Collaborative decision making will be supported by SWIM which will allow the power of shared decisions to be fully exploited; ensuring that the priorities of the AOC and airport are considered during all stages of flight. Factors such as fleet management priorities and fuel consumption figures can be shared to provide benefits to system users. Collaborative planning and decision making will increase flexibility and efficiency, allowing capacity to be managed responsively. In future flights will be managed from gate to gate, with increasing levels of automation.

Integrated airport operations. When airports are linked to the rest of the ATM system efficiency gains can be achieved. Airport operations will benefit directly through greater adherence to slot times due to efficiencies found in aircraft turn-round and pre-departure sequence. A-CDM (Airport Collaborative Decision Making) is a key enabler in the integration of the airport with the rest of the network – Charles de Gaulle and Brussels airports are both integrated into the network and report impressive environmental savings. Paris CDG has seen a 7% reduction in taxi times which relates to a daily saving of 14.5 tonnes of fuel. Brussels however, has reduced taxi-out and taxi-in times by 25% and 15% respectively since introducing A-CDM, saving airlines 7,200 tonnes of fuel annually.

Air traffic controllers in the Frankfurt region have embarked upon trials of Wide Area Multilateration (WAM) technology, a system intended to improve aircraft tracking.

A number of ground stations are strung across the surveillance region. These antennas intercept the SSR replies transmitted by aircraft operating within the airspace and send the time of signal arrival to a central server (this requires the synchronisation of very accurate internal clocks at the ground stations). The server can then calculate the aircraft's position very accurately from the time difference of arrival (TDOA) of the signal at the multiple ground stations. The aircraft position is located upon a mathematically calculated hyperboloid. At Frankfurt a region of 128 x 80nm is served by around 12 ground stations.

WAM systems can calculate an aircraft's position to within 50m, less than the wingspan of a modern jet transport aircraft. This is much more accurate than traditional radar positioning.

WAM updates every second, whereas radar updates every 4 - 12 seconds (typically 5 seconds). WAM will therefore give controllers a greater degree of confidence in congested airspace, theoretically allowing them control aircraft with closer separations.

The system takes advantages of existing aircraft avionics, meaning that there is no need to modify aircraft - the system is technologically mature and can be implemented immediately. Furthermore, WAM ground stations can be easily upgraded to receive ADS-B transmissions as more aircraft become equipped.

The system boasts low life cycle costs and can provide seamless coverage of the desired surveillance region (filling in the gaps where mountainous terrain or other such obstructions create blind spots).

Other current WAM applications include:

- A trial in London where 6 ground stations will serve a region covering Heathrow, Gatwick, Stansted and Luton.

- The installation of multilateration units in the North Sea, where small, lightweight, low powered stations will be located on offshore drilling platforms.

Although WAM provides many benefits, it is likely that radar will remain a fundamental surveillance tool.

On the 8th of February 2012 Swiss International Airlines undertook trials of a new technology promising an enhanced level of situational awareness in the cockpit. The Airbus A330-300 aircraft tested the ADS-B In (Automatic Dependent Surveillance-Broadcast) system on a flight from Zurich to Montreal. The system shows a real time display of surrounding traffic on the aircraft's nav display (it also has the capability to be displayed on class 2 & 3 Electronic Fight Bags). The ATSAW (Airboune Traffic Situational Awareness) system was certified by EASA (European Aviation Safety Agency) and is expected to be capable of providing traffic information for all stages of flight.

By using the ADS-B Out signal transmitted by surrounding aircraft the onboard Honeywell traffic computer can display this information to the pilot by synthesising the traffic situation onto the aircraft's nav display.

Operations over the North Atlantic are likely to see the most immediate benefits. Currently, controllers do not have a radar image of the traffic situation in this airspace, meaning that requests for new flight levels are often denied due to the controllers requirement to procedurally maintain separation. The technology tested in February will allow pilots to safely identify an opportunity to climb or descend through traffic (while still requiring an appropriate clearance from ATC). Under these circumstances flights can be operated at their optimum cruising level, increasing efficiency and therefore reducing fuel burn and emissions. It will also more readily allow avoidance of turbulent flight levels.

Eurocontrol see's potential benefits for situational awareness at airports and for visual separation on approach. Greater situational awareness will increase safety in all stages of flight.

These trials were part of Eurocontrol's CASCADE programmes ATSAW pioneer project.

On the 12th of February 2012, an airbus A320 test aircraft successfully completed the world’s first flight using 4D trajectory techniques. The 4D trajectory concept includes the conventional 3D aspects of lateral and vertical navigation, along with the fourth dimension, time. This means that at a given position, a merging point for example, the aircraft should be at the correct lateral position, be at the correct altitude and should have reached this position at a specified time. The current target for 4D RTA (required time of arrival) at a desired position is +/- 30 seconds. February’s flight actually achieved an accuracy far greater than this.  

“Starting from Toulouse, the test aircraft flew through the Eurocontrol Maastricht Upper Area Control Centre (MUAC) airspace where the airborne and ground systems agreed on a first time constraint at a merging point close to Copenhagen airport. The flight then continued into Danish airspace to demonstrate an optimised descent to Copenhagen. After reaching the first merging point, the aircraft climbed to a cruise level from which it negotiated a second time constraint at a merging point close to Stockholm Arlanda Airport. The flight then descended into Swedish airspace in a fully optimised way to the second merging point and landed at Arlanda.” (Thales, 2012)

The initial 4D (I-4D ) technology employed by the flight is expected to eventually lead to full 4D operations. The test demonstrated the ability for successful interaction between an aircrafts FMS (Flight Management System) and ground systems using datalink. It also showed the systems capability to successfully achieve time targets set by controllers. If trials continue to be successful 4D trajectories could be used commercially in Europe as early as 2018.

Single Event Effects

Single Event Effects (SEE) refer to the harmful impact and interaction of charged particles with microelectronics, such as microprocessors or semiconductor memory. These occurrences can cause upsets in logic processes or burnout of components, both very significant events when considering an aviation application.  

The threat of SEE will increase as the density of processor chips onboard aircraft continues to rise. Communications satellites are also at risk, with the flight safety foundation estimating that if spares were not held it may take up to 5 years to replace affected satellites.

The Airline Space Weather Workshop (attended by participants from the U.S Air Force, American Airlines, United Airlines, Continental Airlines, British Airways, Qantas, Lufthhansa and U.K Met Office) in 2004, determined that future aircraft are likely to require permanent sensors to monitor crew and avionic risk levels.

http://www.swpc.noaa.gov/NOAAscales/NOAAscales.pdf

FANS technologies, can make aircraft more susceptible to space weather (by allowing accurate polar navigation for example) but it can also attenuate its effects. If HF radio communication is degraded or not available due to space weather aircraft may use satellite communications (if equipped). If operating in polar regions aircraft having difficulty with HF communication will be required to re-route, following a track below 82 degrees north in order to facilitate the use of SATCOM or similar system. 

In October 2003 the FAA issued their first solar radiation alert.

“Satellite measurements indicate high levels of ionizing radiation coming from the sun. This may lead to excessive radiation doses to air travellers and should be preceded by appropriate ATC clearances” (FAA, 2003)

The above alert lead to instances of flights from the U.S to Europe being conducted at lower than normal altitudes. This was as a result of the perceived threat to passengers and crew posed by solar radiation.

Solar weather can also have other impacts upon the safe conduct of flights, including disruption of HF communications, navigation system errors and radiation hazards to avionics.

But what is it that causes these solar threats?

The Sun has an activity cycle of roughly 11 years, with the last solar maxima being experienced in 2001. At some points on the sun its magnetic field becomes twisted, becomes entangled and eventually breaks, at which time there is a release of an enormous amount of energy – these events are known as solar flares. Solar flares can project ultraviolet and X-rays towards the earth where they interact with the ionosphere.

The video shows the last major solar flare event just 3 days ago on the 6th of March.

Sometimes stellar mass is released in the form of plasma, this is known as a coronal mass ejection (CME). It is the interaction of this plasma and our atmosphere that causes the aurora borealis (northern lights) and the aurora australis (southern lights).  

Juha-Pekka Luntama, of the European Space Agency refers to space weather as:

“conditions on the sun and in the solar wind, magnetosphere, ionosphere and thermosphere that can influence the performance and the reliability of space-borne and ground-based technological systems and endanger human life or health”

The problems occur when conditions allow this plasma to enter the magnetosphere. Under these circumstances the plasma of the CME creates Geomagnetically Induced Currents (GIC’s). When GIC’S occur in power networks they can damage transformers and cause widespread power loss.

The above attempt to do a 'back of an envelope list of the potential benefits of FANS technologies' escalated...

Benefits of FANS

- The economic health of the system is directly related to its efficiency. FANS will increase efficiency.

- GNSS (Global Navigation Satellite System) will allow a percentage of the existing ground infrastructure to be retired.

- Surveillance will be extended through ADS (Automatic Dependent Surveillance).

- Navigational accuracy will be improved through GNSS, leading to reduced separations and increased capacity.

- A direct exchange of information will be enabled between an aircraft FMS and the ground. This allows intelligent processing which improves the detection and resolution of conflicts. This also allows the automatic generation and transmission of conflict free clearances. This is made possible through the use of ground based processors, which will allow an increase in traffic.

- Flexibility will be introduced, allowing rapid adaption to changing traffic requirement.

- Airlines will benefit as operating costs are reduced through the implementation of more efficient flight profiles. Lower airline costs will act as a vehicle for lower fares, making flying more affordable; this will increase both social and economic mobility.

- Airlines can seek competitive advantage through greater efficiency and lower operating costs.

- Nations providing air navigation infrastructure will benefit through reduced costs, as portions of the ground equipment strung across the globe can be dismantled.

- GA will gain access to remote areas where reliable navigation is currently out of reach. GA aircraft will also find busy airports more accessible.

- Environmental pressures will be eased with shorter routes leading to a lower fuel burn per flight and therefore reduced emissions. Airlines may also decide to reduce contingency fuel, further reducing fuel burn.

 - Noise will be reduced by up to 30%. Optimised profile descents will replace the current step down method, reducing noise, fuel burn, emissions and delays, while increasing airport capacity.  Departure routes can be adapted to avoid highly populated or noise sensitive areas, further reducing the effects of noise through control of the noise footprint.

- Technological trickledown .

- Ground – air information exchange will see improvements, allowing data links to become more direct and efficient, further improving ATM services.

- Communication will be improved through improvements in the handling and transfer of data. Channel congestion will be reduced allowing communication capacity to be increased. Communication errors will be reduced, leading to an increase in safety.  Portions of ground based communication equipment (e.g. certain HF equipment) can be phased out.

- Reduced separations over oceanic areas will increase capacity.

- FANS will allow preferred routings/flexible tracks/user preferred trajectory.

- More timely response to altitude change requests.

- There will be a greater availability of diversion airfields, due to GNSS landing capabilities. Ground based approach aids will not be required.

- DARPS, Dynamic Air Route Planning System.

- Waypoint insertion errors will be reduced, leading to an increase in safety. Previously, the accuracy of the whole system has relied on the accuracy of the position reported by the pilot.

- Traditional forms of CNS (communication, navigation and surveillance) have proved hard to implement in many regions of the world. Often due to the remote, inhospitable or unstable nature of the region. FANS will allow accurate navigation anywhere in the world, without the need for extensive ground infrastructure.

- Elimination of the need for altitude loss when crossing tracks.

- 4D navigation can be achieved with autothrottle ensuring the RTA (required time of arrival) +/- 30 seconds.

- User charges for use of the FANS infrastructure may be reduced. ANSPS (Air Navigation Service Providers) charge for traditional services and due to the improved handling efficiency of FANS/CPDLC services may offer a reduced rate.

- Excessive levels of congestion can be eliminated through improved flow management. A smooth flow in and out of terminal areas can be achieved using real time flow management strategies.

- Efficient approach streams can be achieved when operating configurations of parallel or converging runways, increasing airport capacity. Furthermore, single runway IMC capacity is expected to increase to single runway VMC capacity levels.  Safety will also be increased, with conflict reduced between approaching and departing traffic at adjacent airports.

- Safety will be increased further through reduced pilot and controller workload.

- FANS will allow the industry to grow safely, allowing traffic increases to be met in a controlled and orderly manner.

- Regions in which control has previously been procedural will see the introduction of positive control.