Only an SLF view.
Sorry for butting in guys but as the holder of a VHF radio licence for the marine band I would like to add my tuppenceworth. I was taught by the RNLI that:-
Mayday (3times) should be used to declare an emergency which endangers the vessel and/or its passengers/crew.
Pan Pan (3 times) should be used to indicate an urgent transmission, taking precedence over everything except Mayday calls to report a threat to life or major problem short of a threat to the entire hull. (Note it is NOT a Pan call - it is a Pan-Pan call)
ie,One of 2 engines out in flight is a threat to the hull therefore a Mayday (even if you can continue on one engine since loss of the remaining engine could be a bad thing! just ask Ryanair) a heart attack passenger is regretable but no threat to the hull therefore a Pan Pan call if you want to off load them at the nearest airport.
Of passing interest - until about the mid 80s a man overboard (marine style) was just a Pan Pan and not a Mayday since there was no threat to the hull!!

Interesting to hear it from a different (nautical) point of view. In fact, the SOP is generally that an engine fire would be a "Mayday" and an engine failure (such as a run down in cruise) would be a "Pan Pan". It isn't a hard and fast rule but even on a twin jet, you would give consideration to downgrading to a "Pan" if you'd put the fire out. As you say, "Pan Pan" would be for a lesser event (a heart attack being one), although in certain parts of the world you would still need to say the M-word if you wanted assistance.

Human Factor, sorry for trying to extrapolate from marine to air and I know what you mean about the need to use the M word to wake people up in some areas.
Since I was driving a lifeboat I had little need to initiate a Mayday other than for the radio examination, but it was always possible. The only time we could envisage using it was if the boat was inverted and the self righting failed, I am not sure the VHF would have worked with the antenae a meter or 2 underwater, but hey, we had good lifejackets and our mates at base waiting for our return,so no real danger!

marine vs aviation . . . . . . . . . !
 

So, when did you last hear "Man overboard" being yelled on a 757 ? !

Or is that the way they deal with the smokers nowadays ? ! . . .:ok:

So, when did you last hear "Man overboard" being yelled on a 757 ? !
Not 757 - It was on a Shorts Sunderland!! :)
And MOB is too good for smokers - let them drown - it is cheaper than the medical care they need later.:sad:

Having had a number of situations flying jets and twin props I would add that there are often grey areas which are not white or black.
Obviously if the Donkey goes bang it is a straight mayday situation.

I had an emergency sitauation in a citation flying from Biggin Hill to Majorca at night. climbing through FL240 over the channel The first indication was a slight burning smell. I was asked to contact the french controllers but requested I remain with London for a little longer as there may be a problem.

Smoke then started coming out of the air vents. Priority then was to go to the emergency checklist to try and contain the problem and work out a course of action.

There followed communication with ATC who asked about the nature of the problem and my desired intentions.

At no time did ATC refer to a possible Mayday but instead used the terminology of "declaring an emergency". In other occasions when there has been a problem some which have been rectified or worked around there has always been ongoing communication with ATC and never once have I heard ATC refer to "are you declaring a Mayday" but ALWAYS "are you declaring an emergency". So not even ATC seem that committed to the word Mayday.

In the above ATC Placed a precautionary emergency in place and gave me a direct to Biggin with a continuous descent.

Mayday goes back a long time and always brings to mind wartime films with some poor guys wing falling off his spitfire.
Usually the situation is not clear cut and develops to a situation where an emergency is declared and usually with some length of communication with ATC.

Pace

I wonder if this isn't done deliberately. If all of a sudden ATC would utter "mayday" while the comms have a bit of static on them, the aircraft involved might think it was a mayday from another aircraft and shut up.

Sort of the same thing as we have with departure/take-off. To avoid any confusion, the first time the word take-off is used is when ATC clears you for take-off. Until then everybody talks about a departure.

I've never had ATC "offer" me a SVFR clearance. I had to ask for it first. There are certain words and phrases that they should not use - I agree with the idea of the "departure/take off" comment.

I *believe* that ATC used the correct phraseology with "Are you declaring an emergency" - if you elect to answer in the affirmative then it's up to you to decide the level of attention.

Heard a Pan-Pan call go out in the USA recently, a helicopter had a bird strike in which the feathery critter came through the canopy and splattered against the pasengers and pilot.

The call *started* with "Pan-Pan" and ended with pilot intentions which were "I *am* landing on the threshold of your runway 06" (It wasn't a request).

Routine in UK for rotary winged aircraft wishing to fly in Class A airspace. Normally the only thing offered!

Interesting thread. (Not just for the OP which, if the 'Pilot' letter is true, just goes to show that there are indeed some real idiots out there.)

To complete the set, after Pan Pan and Mayday, I've often wondered - is the "Securité Securité Securité" call ever used in Aviation?

Can only speak for UK ops - securite, securite, securite is used by D&D to broadcast on 121.5 and 243.0 details of temporary airspace restrictions, for instance TDAs established for SAROPS, and other non-emergency (but obviously very important) activities which may affect flyers.

Getting attention is what is important.
 

The primary purpose of using MAYDAY, PAN or SECURITE, is to secure the
attention of all others on the r/t channel, in two respects.
1. You need to talk to those who may be able to help you.
2. You need everyone else to stay quiet while you talk to those who
can help you.

No other phraseology will achieve both purposes INSTANTLY.
No other phraseology will ENTITLE you to priority on the channel.
And it should work EVERYWHERE. It is called ' The International Code of Signals.'
'Houston, we have a problem' will not cut through the crap on a busy
r/t channel.

I'm not a pilot, but I was a Marine Radio Officer for some years, and to the best of my knowledge the rules are the same.

The three codes are only a broad indication of the severity of the problem.
A Mayday can be downgraded to a PAN, or cancelled, if appropriate..

To illustrate: While at anchor in Table Bay, Capetown, some years ago,
we had a fire in the Engine room. Fire bells went off, I went to the Bridge
to see whats up. The Captain was screaming ' Capetown Radio, Capetown
Radio, emergency XXXX on fire" etc on VHF Channel 16 (emergency and calling channel), and getting drowned out by everyone else on the busy
channel, thus no response.
A single call of SAYKURITAY, SAYKURITAY, silenced the channel instantly
and got the undivided attention of Capetown Radio.

That's the way it is supposed to work.

So if you want to be all girly and coy, by all means do so, but dont be
surprised if no-one appreciates your plight.

Shy - you suggesting that they make the first suggestion of SVFR - or they happily accept your request for it? Different thing.

ATC are not permitted to ask you if you want it - are they? You have to suggest it first.

The London Heathrow control zone is class A airspace and there are published helicopter routes to various places within that airspace. They are all SVFR routes. If you call for zone entry via a route the clearance you receive is normally something along the lines of "Cleared H3, Standard operating altitudes, Special VFR, report at XXX."

i.e. Pilot asks for a clearance to enter the zone, giving details of the required route. ATC read back clearance incuding the words "Special VFR", so I guess the protocol is that they offer (only) SVFR. It would be hightly unusual to ask for an IFR clearance unless previously written flight planned and impossible to get a VFR clearance in Class A. So SVFR it usually is but ATC instigate the actual words.

There are some differences between US and UK procedures here, for good reason.

In the US, SVFR is exclusively a poor weather procedure. If the weather were VMC you'd use a VFR clearance instead. Thus it's reasonable that controllers should not volunteer SVFR to avoid tempting less capable pilots into flying in marginal weather.

In the UK, some control zones are class A, and also no VFR is permitted at night (anywhere). In those cases an SVFR clearance is required, even in glorious VMC. Thus there's no corresponding prohibition on ATC volunteering SVFR.

I once had a rough runner on take off and was losing 500rpm a time. I just carried on a normal, did a climbing turn up to 800' to stay close to the airfield and gave a downwind call as usual; there was little else I could do..... I felt happier flying a normal circuit than trying to be clever and do a turn back or start finals early. Runway infront of you is always a good thing!

Didn't bother making a PAN call....

Your call under your circumstances, but it might (under other circs) be advisable so that ATC (if any) and other traffic (if any) knows your problem and to keep clear until you are safely on the ground, especially if you find yourself executing a non-standard or truncated circuit.

SD