Icarus 53,
The original question posted by Clackarjack was:
Here's a question for you....
This issue has come up repeatedly, and as far as I can tell, colleagues are evenly split on the answer.
Assume you are flying from A to B, with preflight WX not indicating alt required, so we are landing with standard company FOD (2.4 for 737 / 2.0 for Ejet).
ATC broadcasts a Hazard Alert for B, with WX now below the alt minima.
Do you now need an alternate for B ??
I have tried not to be leading in this senario - I have a strong opinion on the answer (which I'll withhold for now), and have sought answers from CAR, CAO, CAAP, Vol 1, Jepps etc, but opinions are divided.
Thoughts?
The question was fairly simple - "Do you need to hold an alternate for B?"
There was no question regarding whether or not the PIC was required to obtain the wx in flight, (this was asked and answered later), but once the information was in the hands of the PIC, whether a legal requirement to hold an ALT now existed.
From the AIP references listed in this thread, the answer is YES IT DOES.
I'm not trying to antagonize you or be a smart @rse, but I would like to comment on your point about semantics.
I don't believe anyone is being semantic about it, and I don't feel that the AIP wording is semantic.
Some (myself included) suggest that alternates can only be "provided for" in the planning stage.
Let us assume for a second that you had full tanks and only needed 1/4 tanks for your trip. An ALT requirement is placed on destination whilst you are airborne. It is now possible to 'provide for an Alternate' because you have the fuel - no diversion necessary. So I'm not sure how you can say that you can only provide for a ALT in the planning stage. If you have the fuel or other airfield options, you can 'provide for and alternate' in flight.
Let us now say you have only the legal arrival fuel for destination, and the same ALT requirement is put on. Now you don't have the fuel, therefore you must divert, this diversion is not your destination, but an alternate airfield, therefore you have met the requirement to provide for an alternate - your diversion is your alternate.
If you are beyond PNR/PSD then you have no choice, declare an emergency if required and continue - autoland/ditch whatever, but this is now an emergency procedure and the ALT rules no longer apply (nor do many other for that matter!)
The point here is that at the planning stage you did not need to 'provide for an alternate' as no requirement was in force at the time, however, in-flight things changed which required an alternate. In two of the scenarios above, you could 'provide for an alternate' airborne, and in the last one, you could not (through no fault of yours) so were required to continue, and seek priority (declare an emergency) in order to basically say 'I can not comply with my legal requirements now'
I would hold to the view that once airborne, operational changes become matters of diversion planning. To refer to it as "providing for an alternate" ignores the many other options available to a crew, including autoland, ditching (we all know it's been discussed!), using up their reserves etc. Not saying they're good options, but they don't involve "alternates". As others suggest, it comes down to command decision, airmanship, whatever you want to call it - not a matter of obeying a legal requirement
As I have hopefully pointed out above, unless you are declaring an emergency, then you ARE required to obey "a legal requirement" and you can 'provide for an ALT airborne"
All the best