The meaning of optimum in planning

So what is an optimum plan? I hear the word optimum all the time, and in my experience it often is used to describe a situation which is complex and needs improving, but those who use it are often not sure how. So how to take this and make more meaningful?

Optimum means the best. So what is best? Does it mean the most efficient, perhaps the most complex? Hang on doesn’t that imply length and costly? Maybe effective and practical are better descriptions? Well this can be formed if we have an objective, as this allows us to direct the plan giving us the practical approach, and to evaluate it giving us the effectiveness. Note that there may be several objectives, but best not to have too big a shopping list as some may be in conflict and dilute the plan e.g. a plan that gives maximum flexibility will not be the most efficient in terms of its use of resources. Resources are all the things required to enable the plan e.g. the sub-band available for planning. Also a resource is the effort to create the plan as well as that available to enact it. We also need to consider other practical aspects, such as constraints. These may be straightforward, e.g. the limitations of receiver technology and how we represent it. Constraints may also exist in the form of assumptions that arise due to poor definition of the problem e.g. lack of data describing service area. Assumptions can also be constraints in that are too general or invalid, or there may be limited resources available to do the optimization. Assumptions are also needed to say something about the future. In general it is very hard to predict the future, so an optimum plan will have to make assumptions. If the plan is not forgiving of change, then that is a danger. The best plans are perhaps those that are based upon simple and manageable criteria (i.e. SMART), and are subject to periodic review to ensure that they are appropriate throughout the lifetime of the plan.

It is therefore paramount that optimum is not confused with ideal; perhaps a better phrase is a practical plan that is effective delivering a tangible benefit compared to the situation of today. So optimum is perhaps a word that is best avoided, as it can be interpreted in so many ways and lead to unrealistic expectations. Effective and practical are terms that seem to be more balanced and meaningful…

Revisiting aeronautical communications safeguarding

In my post on Safeguarding aeronautical communications from windfarms, I said that I would try and understand more on significant work and report back, because the official guidance was quite limited and it It was clear to me from my own projects that work had been done but frustratingly nothing published.

The Aviation Management Board Meeting held at MOD, Eskmeals on Thursday, 18 July 2013 gave a hint of the work in progress. The public minutes from the meeting contain a reference regarding work done:

“NATS was funding this £1.8m research programme over two years. It has five aims: to build on earlier work; to develop scientifically credible evidence on detrimental effects; to determine operational impacts; to develop guidance material; and for NATS to develop software tools to assess wind farm applications. QinetiQ and Pipehawk were the main contractors and the work would be undertaken at the Shooters Bottom and Red Tile sites. The research was due to start in August and run until the end of September 2013. The software would be developed by January 2015. The guidance document would need to be timed to fit in with CAA’s CAP schedule.”

So nothing tangible yet, although it turns out that NATS have published some of the trial data in an FAQ in relation to a windfarm planning application, but it is a little obscure as it only seems to appear on the Preston Council planning portal rather than being more prominent on NATS website. The FAQ confirms a little on the nature of issues and notes whilst measurements have been done, notably at Shooter Bottom Farm 2009 and Goonhilly in 2007, that there are no concrete criteria, and more work needs to be done.

Since this post was created in 2014 the FAQ link to Preston City Council planning portal in respect of AGA impact no longer functions, so I attach a copy of the FAQ from my archives. This cites a NATS internal report from December 2009 concerning Shooters Bottom Farm Field Trial which yielded an RCS of 48.6 dBm² in the back scatter region and 54.9 dBm² in the forward scatter region at VHF for a turbine of hub height 65 m and tip height 100 m.

Finally in 2019 CAP670 was updated in a more comprehensive way and now contains “Appendix A to GEN 02: Methodology for the Prediction of Wind Turbine Interference Impact on Aeronautical Radio Station Infrastructure”, which is what I presume is the culmination of this work that was due in 2015. This section includes specific methods and planning figures that can be used in make safeguarding assessments. The RCS planning figure for a large industrial turbine is 41 dBm² at VHF in the back scatter region and 51 dBm² in the forward scatter region. These figures are significantly lower than the Shooters Bottom trial, so presumably reflect other data perhaps of a more statistical nature.