Mode S ELS Phased ApproachAt the time of the consultation and subsequent introduction of the Mode S Enhanced Surveillance (EHS) mandate, the CAA stated its intention to propose a further expansion of Mode S Elementary Surveillance (ELS) on aircraft operating in the remaining UK airspace from March 2008. This was the subject of a public consultation and Partial Regulatory Impact Assessment (RIA) process during 2006. Subsequent to the Partial RIA, it was decided to develop a phased approach to further implementation of Mode S ELS.
Phase 1 makes Mode S the technical means of compliance for the current transponder carriage rules. Based on the results of the public consultation that accompanied the 2006 Partial RIA, a Full RIA to, ‘AMEND THE AIR NAVIGATION ORDER 2005 FOR THE PURPOSE OF EXPANDING THE USE OF SSR MODE S TECHNOLOGY IN UK AIRSPACE' was submitted to the Secretary of State for Transport. This proposal was accepted and came in to force on 31 March 2008, for further details click here.
To register for the Mode S Phase 1 General Exemption please complete form DAP 1901. Please note, this exemption does NOT apply to IFR flight in Notified EHS airspace, currently the London TMA.
In Phase 2 the CAA proposes to extend the rules for carriage and operation of transponders, which as result of Phase 1 will be Mode S by default. The CAA conducted a public consultation on Phase 2 during a 17-week period between 1 February and 31 May 2008 and a total of 1,982 responses were received. Feedback from General Aviation stakeholders was also received at six consultation presentations. The CAA has now published its Synopsis of Comments Received and Summary of Responses Document to the Proposal for an Incremental Expansion of the Use of SSR Mode S Transponders in UK Airspace Consultation. For further details click here.
EuropeDetails of the Mode S carriage requirements for GA in Europe are available from the Eurocontrol General Aviation VFR Briefing Room.
Transponder Issues around Schiphol TMA 1The CAA has recently received a number of enquiries regarding transponder issues at Schiphol and potential implications for the UK. Please find below a synopsis of events.
1. The Schiphol CTR was enlarged to prevent unnecessary ACAS RAs in the final parallel approach area. 2. Prior to 12 March 2009, Class G airspace below Schiphol TMA 1 was excluded from the mandate to carry and operate a Mode S transponder above 1200 ft AMSL. However, since 12 March 2009, the mandate has included all motorized aircraft below the TMA and above 1200 ft AMSL. This raised the possibility of greater numbers of aircraft on the radar display.3. To prevent possible radar clutter, LVNL (the ANSP) developed an upgrade to their radar system. This upgrade reduced the size of the label of uncontrolled aircraft and changed its colour.4. This software upgrade was tested, and in October 2008, LVNL declared the ATC system ready for the introduction of the mandatory transponder carriage below the Schiphol TMA 1.5. On a 'good weather' weekend in late March there was a large amount of VFR traffic (presumably recreational) below the Schiphol TMA 1 and the software solution was found to be ineffective. The labels of the VFR traffic were overlapping each other and the labels of overflying IFR traffic became unreadable. It was also found that the label colour difference was not effective enough.6. There was a secondary problem that the labels of the IFR traffic which had been transferred to another sector (or to Schiphol TWR), but were still in the Area of Responsibility of the controller, also became smaller and changed colour because these were treated as uncontrolled traffic.7. In consequence, CAA-NL introduced an area around Schiphol below Schiphol TMA 1 in which no VFR traffic was allowed. They also introduced two areas around Hilversum and Lelystad where VFR traffic were not allowed to activate their transponder.8. A revised temporary measure was activated in May, which allowed the airspace below Schiphol TMA 1 to be accessed by VFR traffic below 1200ft with a deactivated transponder; providing a 300ft buffer to the base of the TMA. The airspace between 1200ft and 1500ft below the Schiphol TMA 1 can be used by commercial VFR traffic with prior permission from the LVNL Helpdesk. 9. LVNL and CAA-NL remain concerned about undetected infringements. There were 85 of in 2008. It is hoped that the buffer will prevent at least some of them. This measure remains under CAA-NL's close scrutiny.10. LVNL is now seeking a permanent technical solution but it is expected to be at least 6 months before it will be implemented.11. CAA-NL remain convinced of the necessity of mandatory transponder carriage and see it as a high priority to urge LVNL to implement a technical solution as soon as possible.
The issue at Schipol is a display issue rather than an SSR one and relates to the specific airspace design and controller tools. It is not the swamping of the radar system causing problems but the overlapping of large numbers of labels on the radar screen when GA are very active. This issue will not affect the UK, as NATS’ systems will be able to filter out responses from aircraft not in the controller’s area of interest. However, this filtering will not affect the ability of automated systems and safety nets to identify potential conflicts.
LPSTThe CAA has been encouraging the development of a portable Low Power SSR Transponder (LPST) for use on light and very light aircraft that may experience difficulty in installing higher power transponders. In support of this work the CAA has taken a leading role in developing and sponsoring various studies into the subject. Links to LPST reports can be found under the LPST Documents heading, in the Documents section.
Filser/Funkwerk TranspondersFor details of the Filser/Funkwerk transponders Airworthiness Directives click here.
ContactGeneral Mode S enquiries can be submitted to mode.s@caa.co.uk.
