Your original post stated that you cannot declare an emergency with a PAN call. Allowing you the benefit of the doubt in the deviation from clearance case, there is nothing in the PAN call definition which would exclude it from being used to declare an emergency in other situations.
Yes, the very definition of what a pan call is:
ICAO Annex 10 vol 2, 5.3.1.2
The radiotelephony distress signal MAYDAY and the radiotelephony urgency signal PAN PAN shall be used at the commencement of the first distress and urgency communication respectively.
Keyword "respectively":
distress signal MAYDAY = at the commencement of the first
distress communication
urgency signal PAN PAN = at the commencement of
urgency communication
So you can't "declare an emergency" (distress) using PAN PAN...
After all an engine failure on a twin does not necessarily mean you will have to deviate from a clearance. In that case the preceding arguments would not be relevant.
Yes, say you can stick with your departure route initially, no need for a MAYDAY call. But:
- Would you like vectors ahead of the arriving traffic?
- Can you give ATC "2000 fpm or greater", due to inbound traffic?
- Can you accept to join a hold for 45 mins until an approach slot is ready for you?
- Would you like to have fire brigade on standby (perhaps hot brakes due to approach speed)?
- Etc.
So basically you might not be able to accept a later request: "Please enter holding for the next 45 min", "unable", "are you declaring an emergency?", "ahhh, yes, MAYDAY, MAYDAY, MAYDAY". Of course you can postpone the mayday call, until necessary. I see it a courteous to ATC to give them advance warning. And in the end of the day, a firetruck would still be nice?
You want priority right?
An urgent messages doesn't give you any priority (in theory), though:
Not Long Now,
I am aware that UK handles it differently (non ICAO standard). And in practice, I am sure you will get priority in most parts of the world too, when combining a PAN+"technical problem" (no guaranties though). But it still doesn't make it
correct. If ATC will treat you as en emergency trafic anyway, why use the wrong call, when it can be done right? What is the big problem about calling MAYDAY?
My philosophy is:
If I wan't/need something out of the ordinary from ATC = MAYDAY
If I don't, I keep quiet.
For an engine failure, I for sure want full co-operation and HELP (m'aidez) from ATC.
P.s.
peekay4
Of course the mayday call should be done when things are under control, I am not suggesting you have to give a mayday call before deviating - thought that was obvious. But thereafter as soon as possible... anyway ATC will probably enquire if you forget, when you miss the turn on the SID for you company contingency procedure.