J ersey Airport 27 ILS Localiser
Introduction:
The ILS Localiser and Glide Path serving Runway 27 is now out of service.
The foundation for this decision to withdraw this from service is based upon the knowledge that due to the number and the frequency of the failures of the Localiser 27 with the characteristics of the known faults.
This decision has not been taken lightly and we have explored all the available scenarios, in conjunction with the Manufacturer, to keep the Localiser in service. The conclusion is that it must remain out of service until Array replacement – May 2007.
Fault History:
The first failure occurred in January 2004, when service was lost until it was repaired under warranty.
A second failure occurred at the re-commissioning Flight Inspection in May 2005, and was rectified during that inspection.
From the second failure there has been a period of stability up until December of last year; since then we have experienced four failures; all due to faults on the Antenna Array.
Each time we have been successful in restoring the Localiser to service but it was becoming increasingly apparent that the Antenna Array was succumbing to damage from its location and the environmental conditions.
Environmental Conditions:
The Localiser 27 is situated at the Western end of the runway overlooking St.Ouen’s bay, located in a very harsh environment and consequently suffers from the following:-
• Exposure to paraffin vapour and jet blast from departing aircraft due to its close proximity to the runway; this is possibly the closest Localiser to it's runway in the world
• Exposure to salt laden air coming from off the sea
• Exposure to Westerly winds, that due to the cliff/gabion wall, are in excess of
120Knots when the airfield wind speed is only 65Knots
• The Array is near to it's operational limits for wind speed
It is due to these environmental conditions that components on the Array are suffering mechanical fatigue, and it is this fatigue that is giving cause to the mechanical and electrical faults which we are now experiencing as antenna failures.
Recognising the severity of the above and the risk of total failure, a decision was taken in February of this year to request Thales ATM; the supplier & manufacturer of the Instrument Landing System; to investigate the possible replacement of the legacy Antenna Array with a current-production version.
It was also specified that the replacement Array must be robust enough to operate in the environmental conditions, carry a full two year warranty and a minimum support package of ten years; the current expected lifecycle of the ILS.
Another consideration was for the Antenna Array to be replaced by the second week of May in order to align it with the Annual Flight Inspection thereby lessening the costs to Jersey Airport.
A Thales ATM representative visited Jersey at the beginning of March to carry out a survey. Whilst carrying out the survey the representative also performed electrical checks, and eventually confirmed that the Array was in need of replacement.
It was also agreed that Jersey would carry out a tranche of investigatory work, and that the Localiser should be rigorously monitored.
It was during this last tranche of work that more faults have been identified which ultimately have brought us to the decision that the Localiser must be removed from service.
Current Status:
Thales ATM have now confirmed that a full size Log Periodic array is available and can be installed immediately prior to the May Flight Inspection (10th May). This provided that the Localiser plinth can be extended by some 1.8 metres to the North; this has now been confirmed as being achievable within the required timeframe.
It should be noted that our situation has now been elevated to emergency status within the Thales ATM organisation with the Managing Director, Mr.Paul Khan giving it priority rights for production etc.
Brief History of Existing Antenna Array:
Although the Instrument Landing System (ILS) was replaced in April/May 2003 the
Localiser Antenna Array was not.
The Airport Management at the time made a commercial decision not to replace the Antenna Array based on the knowledge that the existing Array was only three years old (having only been replaced in March 2000), and the benefit to the Airport would be a reduction in the cost of the replacement ILS by £70,000.00.
It was also noted that the replacement of the Array in 2000 had cost the Airport in the region of £65,000.00 and had been in service for only three years of expected twelve year lifecycle.
Historically, several previous Antenna Arrays at this site have suffered shortened lifecycles also, due to the aforementioned reasons.
Since the time of the replacement ILS, the Antenna Array has become a legacy item; having now been withdrawn from production and support is now virtually non- existent due to the availability of spare parts and very limited engineering expertise.
Costs
The planned programme is still being developed as further details emerge.
A budgetary quotation has been received from Thales ATM of £73,000 for their aspects of the work to this must be added the plinth extension (ROM costing of £10,000) and additional flight check costs of £5,000. There will be some additional costs for mobilisation etc. In total costs are likely to exceed £90,000 but not £100,000.
Impact of the loss of 27 ILS on Airport operations:
The impact upon our operations is totally weather dependent.
If the wind dictates the use of runway 09 then there is no impact at all however when runway 27 is in use then the visibility minima will increase whilst the ILS for runway 27 is out of service. Runway 27 is the dominant runway, from a prevailing wind situation, accounting for approximately 65% of the time.
The next best navigational aid available to a pilot is the DVOR/DME at St Martin. Using this navigational aid the minima below which a pilot of a commercial aircraft should not make an approach increase from a horizontal visibility of 550 metres to 900 metres and the height at which he must be able to see the runway increases from 200 feet to some 400 feet. Each operating company has their own limits for operations which depend upon may factors including aircraft type, aircraft equipment fit, training etc. The preceding figures are thus only approximate.
The amount of time for which the visibilities are below these various minima vary very significantly from year to year and season by season.
The horizontal visibility is well recorded - for the last two years of records the visibility was less than 1000 metres during operational hours in April and June for 41 hours and 15 hours.
The vertical visibility is more subjective and will be the more demanding. We have records of the cloud base height but as the clouds are frequently broken it can be the case that a pilot may be able to land with a broken cloud base of 300 feet but not with one of 600 feet; it depends upon where the breaks in the cloud are.
From a qualitative perspective the impact of the loss of ILS is very significant. The slightest hint of fog, with a 27 runway in use, will make all the commercial operators give serious thought to canceling a flight.
Jeremy Snowdon
Chief Electronics Association
29 March 2007
gov.je