 |
What is Mode S?
|
|
|
|
|
Mode S is a Secondary Surveillance Radar technique that permits selective interrogation of aircraft by means of a unique 24-bit aircraft address, thus avoiding the risk of confusion or mis-identification due to overlapping signals. Mode S has been standardised by ICAO for many years. It employs ground-based interrogators and airborne transponders and operates in the same radio frequencies (1030/1090 MHz) as conventional SSR systems with which it is backwards compatible.
|
|
|
|
| |
Why do we need Mode S in Europe?
|
|
|
|
|
Mode S is being deployed because the current SSR systems have reached the limit of their operational capability. This takes the form of exceeded maximum number of targets, RF pollution, lost targets, identity errors and Mode A code shortage. Mode S is therefore a necessary SSR replacement in airspace subject to high levels of traffic density and will form part of the basis of the Surveillance infrastructure for much of the first quarter of the 21st Century.
|
|
|
|
| |
What are the sources of Radio Frequency (RF) Pollution that affect SSR?
|
|
|
|
There are five sources of RF pollution:
- Acquisition Squitter
- Extended Squitter
- ACAS transactions
- Self-generated Second Time Around Replies
- Replies from other Radar Interrogations (Traditional Fruit)
|
|
|
|
| |
What is the fundamental concept of Mode S ELS?
|
|
|
|
|
The fundamental concept of Mode S ELS is the assignment to each aircraft of a unique ICAO 24-bit address by the State Registration Authority. Mode S ELS uses this unique 24-bit aircraft address for selective interrogation and to acquire downlinked Aircraft Identification (commonly referred to as Flight ID). Among other attributes associated with Mode S ELS is the ability to acquire altitude in 25 foot increments.
|
|
|
|
| |
What are the benefits of Mode S ELS?
|
|
|
|
The benefits of Mode S ELS are:
- Selective addressing of aircraft in order to overcome garbling, fruiting and over-interrogation (which together constitute RF congestion).
- Automatic acquisition of Aircraft Identification (Flight ID), which enhances radar identification and has the capability to relieve the shortage of Mode A codes.
- Backwards compatibility with Mode A/C.
|
|
|
|
| |
What is Mode S EHS?
|
|
|
|
|
Mode S EHS consists of Mode S ELS supplemented by the extraction of downlink aircraft parameters (DAPs) for use in the ground air traffic management (ATM) systems. Some parameters are for display to the controller, known as controller access parameters (CAPs) and others are for ATM system function enhancements, known as system access parameters (SAPs).
|
|
|
|
| |
What are the benefits of Mode S EHS?
|
|
|
|
|
Mode S EHS is the first stage in making use of air derived data in the form of downlink aircraft parameters, either directly to the controller or to air traffic management systems. EHS permits improved situation awareness and eases R/T congestion, thus enhancing safety and also capacity, as proven in studies, simulations and cost benefit assessments. It will help to reduce the increasing amount of level busts and improve the performance of other safety net tools.
|
|
|
|
| |
What are the Mode S (EHS) mandates?
|
|
|
|
The requirements of Mode S EHS apply to IFR flights as GAT by fixed wing aircraft in the designated airspace notified (currently) by Germany, France and the United Kingdom when the aircraft has a maximum take-off mass greater than 5,700 kg or a maximum cruising true airspeed in excess of 250 kt.
The mandates take effect for civil registered aircraft from 31 March 2005 in Germany and the United Kingdom, and with effect from 31 March 2007 in France for aircraft considered to be EHS capable.
Transition arrangements permit operators to retrofit aircraft until 31 March 2007 upon application to the Mode S Exemption Coordination Cell (ECC) and, exceptionally until 31 March 2009, for up to 10% of an EHS capable fleet when operators provide proof of being faced with disproportionate installation costs. This latter exceptional exemption also permits a delay in compliance with Mode S ELS until 31 March 2009.
See also other circumstances that permit exemption from the EHS requirements in the answer to the following question:
|
|
|
|
| |
What exemptions are applicable to the Mode S EHS airborne equipment requirements?
|
|
|
|
In addition to the time scales permitted for aircraft retrofits, answered in the previous question, operators may apply to the Mode S Exemption Coordination Cell (ECC) for EHS exemptions in the following circumstances:
- When the aircraft is not capable of providing the required DAPs.
- When it is intended to withdraw an aircraft from service by 31 December 2007
- When flights are conducted for the purpose of flight testing, delivery and for transit into and out of maintenance bases.
- When only occasional access to Mode S EHS designated airspace is required. ‘Occasional’ being an average total flying time of 30 hours annually per airframe.
|
|
|
|
| |
Why do we need to downlink Aircraft Identification (Flight ID)?
|
|
|
|
|
The reporting of Aircraft Identification (commonly referred to as Flight ID) is an ICAO requirement for Mode S, level 2 and above, transponders. It permits direct radar identification by a controller and has the capability to relieve the shortage of Mode A codes. Correct setting of Aircraft Identification is also essential for the correlation of radar tracks with flight plan data in the air traffic management and airport operator ground systems.
|
|
|
|
| |
Where can I find the 24-bit aircraft addresses allocated to each country?
|
|
|
|
|
The allocation of 24-bit aircraft addresses, formerly known as Mode S addresses, is described in the ICAO convention, Chapter 9 of Annex 10, Volume III. Alternatively, contact your State aircraft registration authority.
|
|
|
|
| |
Why are we required to fit Mode S whilst ADS-B is expected just around the corner?
|
|
|
|
|
Although ADS-B can be used as a replacement for secondary surveillance radar in remote low traffic density airspace, such as that in much of Australia or Alaska, it is not expected that ADS-B will be used as a sole surveillance means in high density traffic areas like the core area of Europe. The Mode S transponder extended squitter is also an enabler for ADS-B operation.
|
|
|
|
| |
Why are we required to fit Mode S while we do not receive any apparent benefits?
|
|
|
|
|
For safety reasons, collision avoidance and additional information to ATC. In essence, there is a need to upgrade ATM to enable all airspace users to continue to operate, to the maximum extent, without new constraints having to be imposed due to a lack of ATC surveillance capacity and integrity.
|
|
|
|
| |
Are there any DAP exemptions with regard to Mode S EHS?
|
|
|
|
An aircraft is considered to be either EHS capable, or EHS non-capable.
To be categorised as EHS capable, the aircraft must be able to provide the DAPs that are explained in the Information Paper – Categorisation of Mode S EHS Capable/EHS Non-Capable Aircraft.
Operators of EHS non-capable aircraft registering with the ECC will be granted an exemption but are strongly encouraged to supply any of the listed DAPs that are feasible and therefore benefit from the Mode S services that are available. Transmitted DAPs are to comply with the requirements of JAA NPA 21-12a (or the latest issue).
|
|
|
|
| |
What is the determining factor in deciding whether an aircraft is EHS capable or not?
|
|
|
|
|
It is whether the list of required downlink parameters are readily available on the aircraft. See paragraph 3.3 of the Information Paper, ‘Mode S Enhanced Surveillance-Assessment of Aircraft capability’.
|
|
|
|
| |
What is the situation concerning new production aircraft that are not EHS Compliant?
|
|
|
|
According to the Mode S EHS mandates, fixed wing aircraft, having a maximum take-off mass greater than 5,700kg or a maximum cruising true airspeed in excess of 250 kt, with a first CoA issued on or after 31 March 2005, should be EHS compliant for IFR/GAT flights in Mode S EHS designated airspace. However, the regulatory authorities have relaxed the requirement, in such cases, providing an application for exemption is made and the aircraft becomes EHS compliant by 31 March 2007 at the latest.
If the aircraft is not EHS capable and of a type existing prior to 31 March 2005, an open exemption will be granted upon application in the same manner and subject to the same conditions granted to older non-EHS capable aircraft.
If the aircraft has a new type certificate, together with a first CoA issued, on or after 31 March 2005, it will be granted an EHS exemption, upon application to the Exemption Coordination Cell, until 30 March 2007. After this date, the aircraft must be EHS compliant in order to continue operating in Mode S EHS designated airspace.
Full details are contained in the Information Paper – ‘Mode S Enhanced Surveillance Requirements for new Build Aircraft.
|
|
|
|
| |
Regarding the Mode S EHS MMEL / MEL, how does the pilot know if one or more DAP parameters is not functioning properly?
|
|
|
|
There are no flight deck indications to inform the pilot that the transponder is not sending one or more DAP’s, or the accuracy of the downlinked information. The pilot may be aware, indirectly, due to the failure of sensors which provide information to the transponder, such as the Flight Management System or Air Data System.
The Air Traffic Controller may also report lost, missing or incorrect DAP’s, which should be recorded in the aircraft’s techical fault log – to be corrected within the time stated in the MMEL. Alternatively, lost or missing DAP’s may be discovered during the periodic maintenance check (see JAA NPA 20-12a para 12 and JAA Temporay Guidance Leaflet No. 13 para 12).
|
|
|
|
| |
Regarding the Mode S EHS MMEL / MEL, what is the meaning of: “DAP required or not required for the intended route"?
|
|
|
|
The Mode S Enhanced Surveillance (EHS) DAPs will be required, by aircraft operating in French, German and United Kingdom airspace from March 2007. If an aircraft is starting from an country whose airspace does not require Mode S EHS and flying to another country, whose airspace also does not require Mode S EHS, then the aircraft may fly with Mode S Elementary Surveillance capability only – or with one or more DAP’s failed. This assumes, of course, that the fligt plan does not cause the aircraft to fly over airspace in which Mode S EHS is required.
|
|
|
|
| |
If one or more parameters of either ELS or EHS are inoperative, is it necessary to note this in the ICAO flight plan? If there is a requirement, where is this specified?
|
|
|
|
None of the applicable TGLs, AMCs or AICs state that inoperative parameters are to be entered in the FPL. However, in the case of a known transponder or airborne equipment anomaly where an Airworthiness Directive (AD) has been issued by EASA, the AD might identify a requirement to enter specific text in item 18. For example, in the case of unavailable selected altitude data, an entry such as "/Mode S EHS/NO SEL ALT/" might be specified in the AD.
An EASA MMEL study group is currently reviewing this issue (Feb 2009), in conjuction with the FAA.
|
|
|
|
| |
I am a private pilot. Am I affected by Mode S requirements?
|
|
|
|
|
Yes, if you intend to fly in Mode S designated airspace and where the carriage and operation of an SSR transponder (Mode A/C) is already mandatory. See the answers to earlier Mode S mandate questions.
|
|
|
|
| |
Is my Mode S transponder, fitted for ACAS, sufficient for European Mode S implementation?
|
|
|
|
|
Not necessarily. The transponder must include the Aircraft Identification Feature, support Surveillance Identifier codes and have RA reporting capability. Consult the latest EASA/JAA documentation.
|
|
|
|
| |
How is Aircraft Identification correctly set in the aircraft?
|
|
|
|
|
The setting of onboard Aircraft Identification must correspond to the aircraft identification entered in item 7 of the flight plan, or, if no flight plan has been filed, the aircraft registration. Full details and examples are contained in the Specimen Aeronautical Information Circular – ICAO 24-Bit Aircraft Addresses and Aircraft Identification Reporting, which may be accessed at :
|
|
|
|
| |
How should the transponder operate when the aircraft is on the ground?
|
|
|
|
|
When switched-on, on the ground, the transponder will respond only to selective addressing. This is important at aerodromes where Advanced Surface Movement Guidance and Control Systems (A-SMGCS), based on Mode S multilateration, are being used. Flight crew should make themselves aware of any detailed on-the-ground Mode S transponder operating instructions promulgated by such aerodromes. See also www.eurocontrol.int/airports/, click-on A-SMGCS
|
|
|
|
| |
Could the use of 250 kt and 5700 kg MTOM as discriminants for carriage requirements be clarified?
|
|
|
|
|
Aircraft with a maximum cruising true airspeed that does not exceed 250 kt and with a maximum take-off mass at or below 5700 kg are not subject to the Enhanced Surveillance Mode S airborne equipment requirements. Those discriminants have been chosen to match the criteria already used by ICAO and the ACAS implementation programme. Mode S equipped aircraft with a maximum cruising TAS in excess of 250 kt must also have antenna diversity according to ICAO Annex 10. Aircraft with a MTOM greater than 5700 kg, or, having more than 19 passenger seats are also required to carry and operate ACAS equipment (transition arrangements apply until 30 March 2006).
|
|
|
|
| |
What airspace will be affected by Mode S requirements for VFR flights?
|
|
|
|
|
The airspace affected will be declared in the national AIPs. The Mode S implementing States, however, have made it clear by, the issue of AICs, which parts of the airspace they intend to designate for the carriage and operation of Mode S ELS airborne equipment. Generally speaking, the airspace where an SSR transponder is already mandatory will become subject to Mode S. A final implementation date of 31 March 2008 has been coordinated between the participating States. This date, which may in some situations be subject to a transition phase, takes account of the ICAO Annex 6 requirements for ‘all aeroplanes to carry and operate an SSR transponder’, and, also when the density and complexity of the airspace is likely to justify it.
|
|
|
|
| |
Flying IFR includes GA operations at night, Could you clarify?
|
|
|
|
|
Eurocontrol documentation and Specimen AICs clearly distinguish between VFR flights and IFR as General Air Traffic (GAT). Flights by General Aviation aircraft are not regulated uniformly throughout the European States. For example, a night flight might be classed as IFR in one State and VFR in another. Thus, the (revised) 31 March 2007 date applies, day or night, as published by the participating States for IFR/GAT flights in accordance with the rules and provisions of ICAO.
|
|
|
|
| |
Will ATC disregard our (GA) radar returns, as now?
|
|
|
|
|
Some sectors do some don’t according to their responsibilities in a specific piece of airspace. At lower altitudes the situation changes and both civil and military controllers, particularly those working control zones and the ‘open FIR’ take careful note of all radar returns that might compromise separation criteria.
|
|
|
|
| |
Why are Surveillance Identifier (SI) codes required?
|
|
|
|
|
An Identifier Code (IC) is the means by which an aircraft’s Mode S transponder identifies a particular interrogating station and, subsequently, can selectively respond to it. Initially, there were only 15 Interrogator Identifier (II) Codes available for this purpose, however, amendment change 73 to ICAO Annex 10 resulted in an additional 63 codes being made available in the form of Surveillance Identifier (SI) Codes. Due to the number of Mode S stations that will be operational in Europe, it is essential for aircraft to be equipped with Mode S transponders that support both II and SI code functionality.
|
|
|
|
| |
Why are some Mode S stations “clustered”?
|
|
|
|
|
See first the answer to the previous question. If a number of Mode S ground stations are sited in close proximity, it can be more efficient and effective (in reducing RF pollution), to “cluster” these stations (so that from the aircraft transponders’ perspective, they act as one interrogator) rather than allocate a number of individual II/SI codes.
|
|
|
|
| |
What are the benefits of SSR Mode S for controllers?
|
|
|
|
Due to its selective method of interrogating targets, SSR Mode S presents controllers with a much improved radar environment. RF pollution (eg. replies from other radar interrogations and ACAS transactions) is greatly reduced, tracks are not lost due to target saturation and overlapping tracks (eg. aircraft in holding stacks) are more readily discernable.
EHS presents controllers with a continuous display of magnetic heading, indicated air speed/Mach no., vertical rate and selected altitude for each compliant aircraft, thereby reducing considerably the number of air/ground R/T exchanges and providing verification that instructions have been complied with.
|
|
|
|
| |
Can an aircraft be identified using the downlinked Aircraft Identity feature?
|
|
|
|
|
Direct recognition of the aircraft identification of a Mode S equipped aircraft in a radar label provides verification of radar identity for the purpose of providing a radar service. This is in accordance with ICAO SARPs. However, within the ATM system, automatic correlation of the downlinked aircraft identification with the aircraft identification entered in the ICAO flight plan is needed to confirm the identity of flights.
|
|
|
|
| |
Will a Mode A code need to be allocated to an aircraft flying within declared Mode S airspace?
|
|
|
|
[Note: Declared Mode S airspace is defined as airspace volumes/sectors within which a Mode S Elementary Surveillance service is operational].
Yes, Mode S equipped aircraft identified by direct recognition of the aircraft identification feature in the radar label with Mode S will be assigned with either the Mode S conspicuity code (Mode A “1000”), or a discrete Mode A code. For flight plan/aircraft correlation purposes, two methods are currently available for use:
- Correlation Method - Use of Mode A Conspicuity Code
Under this method, correlation between the flight plan and the aircraft radar return is established and maintained based on a match between the downlinked Mode S aircraft identification and the aircraft identification in the flight plan. Unless a discrete Mode A code needs to be assigned for other reasons, the Mode S conspicuity code (Mode A “1000”) may be assigned by the correlating ATSU.
- Alternative Correlation Method - Use of Mode A Code and Mode S in Combination
Correlation may be effected, in accordance with current procedures, by assigning a discrete Mode A code (from the ORCAM Allocation Table). The Mode S capability of the flight will be systematically detected and correlation maintained by the Mode S protocol. Within Mode S airspace, when correlation has been achieved, the discrete Mode A code used for this purpose can be released at an early stage.
Note: The majority of ANSPs favour this alternative correlation option, at least in the early stage of Mode S operational introduction, but have set the 'Use of Mode A Conspicuity Code method' as the ultimate goal.
|
|
|
|
| |
|
|
