Being asked to "verify direct XXX"

On Sat, 16 Apr 2005 04:29:32 GMT, Paul Folbrecht
wrote:

My two-part question is 1) Should I be concerned at all by being asked
such a question by ATC?

Perhaps. It may just be controller confusion (can't remember if you
were cleared direct or not). However, there is a very good chance
your groundtrack is not matching up with 'direct ABC VOR', so the
controller is either prompting you to get back on course or wants to
make sure that you are indeed going to ABC VOR.

Does your GPS have an HSI display? It makes holding the course much
easier.

And 2) Just _what_ is the IFR "heading tolerance", anyway??

I don't think there is one (other than as defined by the PTS during
your IR checkride). The only way a controller knows if you are off
heading is if your ground track changes. Given the sample/update rate
of radar displays, I would think most short term heading deviations go
unnoticed.

***Question for the controllers on the newsgroup: How often does your
radar display update? Every 15 seconds? 30?

Realistically, an occasional heading excursion of 10degrees should not
matter (grabbing a chart), but I do think 25 is excessive (even if
only temporary). If you are in IMC and drifting that far off heading,
you need to work on your scan and control, or limit the activities
that cause the distraction (grabbing maps, lunch, etc).

-Nathan