NavList:

Starting with aircraft navigational errors, on one flight before I retired my co-pilot was from another company on secondment. En route over Northern Canada he insisted on cross checking our triple IRS position with every NDB that came into range, which was his company's procedure. I asked him what he would propose to do if the positions differed. Before he could answer, the NDB he had just tuned showed a forty mile error. There would have been a lot of violations and form filling if I had followed his initial suggestion in MNPS airspace. It is, surely, difficult to have hard and fast rules on how to cross check navigation and how to react if errors become apparent but awareness of the possibility of the cross check itself being in error is also necessary. In the current wrong airport/runway dialogue, what do you do if you can see the correct numbers (say 09R) on the threshold but your ILS shows full fly left? You could be at the wrong airport, but before you firewall the thrust levers, check that you have tuned the correct ILS.

In a marine setting, I wonder how the solo competitors in the (astro only) 2018 Golden Globe non-stop round the world race will use their "ellipse error proportions" knowledge. I hope that if they are avoiding an isolated reef they ignore the math and assume that they are at the nearest edge of such ellipse to the reef, plus their planned offing.

Bill Ritchie

PS - that NDB had been decommissioned and simultaneously recommissioned elsewhere that very day with the same frequency and callsign. I hadn't registered that fact when I scanned the hundreds of NOTAMs pre-flight as I didn't intend to use it.