Perhaps a timely question seeing as the wx atm is somewhat ordinary down sth here.
The 50ks viz is a little odd but I assume a typo there:-)
A pilot is or the word "committed" as you mention refers to when he/she can no longer land at their intended destination with the req'd fuel res intact. The time avail & the time to divert to an alt is when the above figure applies. If yr in a hold as you mention then you simply work out how long you can hold for b4 you need to bug out to yr Alt & land with those reserves, the simplest way there is to work back from yr legal fuel res on landing to where you are now (holding for Eg). The "commitment" decision is pilot based & actioned on.
So if yr in that hold as you mention for the instructed 20 mins then theoretically you can only stay there for 10 mins if you want to land with yr fixed res intact.
The 'SLAM' or any other Ldg min's for Eg higher Min's due other rwy's not avail or navaids out etc are academic really, the above applies for all.
The recent MIA Ldg's where an interesting scenario we can all learn from
Wmk2
Last edited by Wally Mk2; 19th Aug 2013 at 23:47.