Turning now to practical issues, fitting a mode S transponder in many aircraft and gliders is a challenge:
* For aircraft with limited or no electrical power and all gliders, the situation is virtuallyimpossible. Since 1989 the CAA has been saying that “industry is developing low power, lowcost transponders” but of course that is not true. Mode S transponders use a lot more power than ordinary A/C transponders and recent trials of de-rated Mode S transponders suggest that they do not perform adequately but still consume substantial power. With batteries only it would be possible to operate a Mode S transponder for short periods but this will not work for continuous operation.
* In many aircraft and gliders, space and weight constraints make fitting impossible because transponders need instrument panel space with a substantial distance behind. For example, they need a lot more room than a modern radio.
* The practical issue of cost is important because for many, the cost of a transponder installation will be a high proportion of the value of the aircraft. Proportionality is an important factor in regulations.
Aircraft owners may choose to fit Mode S where they can but many will choose not to do so for these and a whole variety of other considerations and they should not be restricted more than is necessary to achieve the required level of safety.
Links:
What the LAA Thinks of the Consultation
Practical Issues
Why Mode S Transponders and Not A or A/C
Transition and Exemption Arrangements
Deadline 31st May 2008
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