Re: [LEAPSECS] PT Barnum was right

From: Poul-Henning Kamp <>
Date: Thu, 06 Jul 2006 18:43:13 +0000

In message <>, John Cowan writes:
>Rob Seaman scripsit:
>> Most troubling would be if two moving platforms are depending on GPS
>> units with differing delays, e.g., two airplanes following neighboring
>> flight paths. How far does an airplane move in 2 seconds? What is
>> the minimum separation required by the FAA?
>Jetliners travel at about 550 mi/hr, or 246 m/s. Required horizontal
>separation depends on circumstances, but is rarely less than 3 miles =
>4828 m. So if the discrepancy is 2 s, there is a safety factor of
>about an order of magnitude. Good enough.

The ban on hand-held GPS for primary means of navigation is partly
because of the worries about the slowness of updates.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk_at_FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Received on Thu Jul 06 2006 - 11:43:49 PDT

This archive was generated by hypermail 2.3.0 : Sat Sep 04 2010 - 09:44:55 PDT