On Tue, 11 Aug 2015 15:33:08 +0100, Basil Jet
wrote:

On 2015\08\10 21:12, Barry Salter wrote:
On 06/08/2015 00:44, Recliner wrote:

It arrives empty, presumably from Marylebone or Wembley, at the down
platform 3 at South Ruislip. I assume the Chiltern drivers all take turns
on this service after bringing in a peak train to Marylebone, so they
have
up-to-date route knowledge.

Runs empty from Wembley LMD to South Ruislip as 5V35, forms 2V35 to
Paddington, 2M30 back to West Ruislip, then 5H43 back to Marylebone,
though that's only part of the unit's diagram for the day.

The trains in question are only worked by Aylesbury drivers, and I
believe they need a Guard as well.

What use is a diversionary route that only a fraction of the drivers
have the route knowledge for?

More use than one that nobody has knowledge for.
How big in numerical figures is the "fraction" ? Are there also e.g.
freight drivers from somewhere else who could act as pilots if
necessary ?