It is revealing that the precision timing community refers to itself that way. Perhaps what we really need is an accurate timing community.
Real world concerns have been keeping me occupied lately, hence the lack of my relentless nattering. I am very pleased to see the conversation begin to turn to actual questions of actual civil timescales. It is about time some sense of reality was brought to the discussion. I will emphasize as always that we have literally centuries to reach any conclusions before making any changes to the current UTC standard. Ed Davies says: > The conclusion is that though, of course, there are lots of > things on an aircraft which need their own accurate timing > there is no pressing need for accurate synchonisation with > global standards and no big issues with multiple different > timescales - as far as the aircraft's internal systems are > concerned. I do believe that there are likely lots of systems and procedures on aircraft that require accurate timing. This paragraph, however, refers to various needs for precise timing. Undoubtedly the continued second by second health of modern aircraft requires a high level of precise synchronization between different subsystems. For many of those subsystems, it may be more important that they be synchronized with each other than the question of to what timescale they are synchronized. However, I doubt whether any complete inventory has been taken of the dependencies of aviation - or of any other technical or civil field - on *accurate* synchronization with time of day. One of the most embarrassing parts of the discussion to date has been the confusion of the precision timing community between periodic effects and secular effects. To say that any user community - especially one as important as aviation - has no pressing need for precise synchronization with global standards is NOT the same as saying that community has no pressing needs regarding what those global standards are. All it is, is a statement of the *level* of precision required for zeroing their clocks as well as a constraint on the schedule for do so. Aviation has many operational dependencies on time of day, not just on international time standards. It may be that many of those dependencies only care about time of day (the orientation of the Earth wrt the sun) to a precision of 1 second or 1 minute or 5 minutes or whatever. But precision is not the same thing as accuracy. Many of the operational time dependencies likely require that civil time continue - generally - to track time of day, rather than that clocks drift wrt the sun. Just because this drift might be small (for some purposes) for some number of decades following the abandonment of leap seconds, does not imply that a dependency on time of day does not exist. Rather, we would simply be setting an obscure trap for our children's children to solve. There is also the question of whether different airlines or different nations will choose the same operational procedures for setting the captain's clocks. If one airline or one nation makes the change to TI - a purely human generated standard - ALL airlines and ALL nations have to make the change. Our current civil time, since it is based by close approximation on mean time of day, requires only that nations (and their airlines, railways, shipping companies, phone companies, and on and on and on) adhere to a first principles definition of civil time. Leap seconds are not just a question of precision. We should understand the full implications of any proposed change to a standard as fundamental as civil time - before making the change. We aren't even close. Rob Seaman National Optical Astronomy Observatory
