What Numbers are used for Marginal VMC, or Special VFR?

We often hear pilots seeking a Special VFR clearance to get out of secondary airports under VFR flight rules. It is of interest to know just how degraded are the 'VMC' in flight visibility, and cloud base numbers - before ATC call a stop to it?  Is it done anymore?

The recent helicopter accident in Los Angeles suggests that the FAA controllers have a very liberal interpretation of what constitutes VMC, and what is allowable for a SVFR clearance. Presumably both pilot and helicopter were IFR capable, but had reason to stay below the fog/cloud layer.

I've recently noted on windy.com that their 'actuals' for a given location may contain the letters MVFR, which I take to be numbers lower than those considered to be VMC. Are these decided by a meteorologist, or computer derived?

happy days,

We often hear pilots seeking a Special VFR clearance to get out of secondary airports under VFR flight rules. It is of interest to know just how degraded are the 'VMC' in flight visibility, and cloud base numbers - before ATC call a stop to it? 

 

In Australia, Special VFR is 1600m visibility and clear of cloud.

However, it's not ATC's job to call a stop to it. Visibility is the pilot's responsibility. ATC's job is to make sure you don't run into IFR or other special VFR aircraft.

I've been told atc in Australia are very reluctant to handout special vfr clearance.

Not sure how true.....

I'm also following the helicòpter crash.  Did he only have special vfr for the class D, then went normal vfr once clear?

I think you have slightly muddled 2 concepts, Weather conditions and VFR minimum conditions.

The USA use 4 levels of weather description. From worst to best they are LIFR>>IFR>>MVFR>>VFR

The definitions are given in the FAA AIM as:

1. LIFR (Low IFR).Ceiling less than 500 feet and/or visibility less than 1 mile.

2. IFR.Ceiling 500 to less than 1,000 feet and/or visibility 1 to less than 3 miles.

3. MVFR (Marginal VFR).Ceiling 1,000 to 3,000 feet and/or visibility 3 to 5 miles inclusive.

4. VFR. Ceiling greater than 3,000 feet and visibility greater than 5 miles; includes sky clear.

If you look at something like sjyvector(https://skyvector.com/) or foreflight (Ozrunways equivilient) then they color code an airports conditions from Pink>>Red>>Blue>> Green. It gives you a very quick overview of the conditions at an area or along your route. It is also useful for setting personal minimum above the legal minimums. While it is legal to fly in MVFR conditions as a VFR pilot many people choose not to. 

A special VFR Clarence is a clearance given by ATC that allows a VFR pilot to fly in conditions that are below the normal VFR minimums of 91.155. For instance in class D airspace the normal VFR minimums are 3 Statute mile visability, and distances from cloud of 500 feet below, 1000 above and 2,000 feet horizontal, In class G airspace below 1'200 feet AGL the requirements are 1 statute mile and clear of cloud.

Now if you wanted to take off from an airport where the ceiling was 1300 feet. If you were at a non-towered airport you could takeoff, climb to 1'000 feet and depart on your way. If the airport had a control tower and was class D you wouldn't be able to climb to 1000 feet and fly off.   A special VFR clearance allows you to operate where the viability is 1 statute mile and you are clear of cloud, essentially the same as the class G airspace requirements. 

The above is all based on the USA rules and regulations. The Australian rules are similar but with some subtle changes.

I've been told atc in Australia are very reluctant to handout special vfr clearance.

 

Not sure how true.....

 

Hi

i got SVFR out of Moorabbin a couple of years ago. Coastal fog/smog and low cloud in the basin.

Tower sent a light twin to check out and let me go when it returned. VIS about 2km. Base about 1000 south rising to 1200 north.

He asked me what height I wanted. I said I was happy with 1200 and He cleared me SHEPP via Coldstream.. Weather improved considerably as I tracked NE over suburbs and was able to navigate Glenburn Gap to head home. Clear skies north of GBR.

I can understand them not being TOO eager. They will wear the "result" if it goes wrong. Nev

I personally haven't done SVFR in Australia but in the USA ATC can't offer it but can give it if requested by the pilot. It's a deliberate policy to discourage it. That being said there are times when it is useful to depart a control zone when the weather directly at the airport is poor but along your light path is good and improving. 

The special VFR we used to get into Sydney( KS ) from the north ( Coastal) was at a  level that the big stuff doing a circling approach would be on their minimum. I guess that's fair enough. We were informed that IF we mucked it up all bets are off. ( Not over the radio. )  The Aero Club at Newcastle  made THAT very clear. It was a dispensation they wished to preserve.  Nev

I've been told atc in Australia are very reluctant to handout special vfr clearance.

 

Not sure how true.....

 

I've only used it twice, with no problems. Once was into Essendon, controller advised "Special VFR is available" before I could request it.

I've only used it twice, with no problems. Once was into Essendon, controller advised "Special VFR is available" before I could request it.

 

Thankyou. Good to know....

SVFR in Bankstown is rather usual, I met it several times in 2 years. Clouds 1500 and/or unsufficient visibility (as their robot reports and it is officialy included in atis) and thats it - tower has no choice, SVFR or flight will be illegal. They just cover their backs, supposing everybody can fly without problems in real conditions.

There is obviously a big difference between SVFR when the cloud clearance does not meet the rules for the particular airspace, and SVFR when horizontal visibility doesn't meet VFR minimums.

Just looking at my last post, it could be read a couple of ways.

What I meant was, given the conditions I was about to request Special VFR anyway but tower beat me to it.

Controllers can't offer it, you have to request it. But as antonts points out, they can see that you're not VFR so if you don't request it they'll advise it is available, just to keep everyone legal!

I was going into Wagga this morning and reversed track at 7 miles due smoke and poor vis.

I could hear two heavies doing missed approaches and decided it wasn’t worth it.

Kaz

I was going into Wagga this morning and reversed track at 7 miles due smoke and poor vis.

 

I could hear two heavies doing missed approaches and decided it wasn’t worth it.

 

Kaz

Smart move; smoke can be weird; one minute it's just smokey and you can see forever, next minute there's no forward vision.

Yes Turbs...I was watching my height to remain visual with ground versus height of the hills on the way in. Some of the hills rise 1000’ above the plains. A particularly heavy patch rolled towards me and that made the decision easy.

I think both the heavies made it in after I left ...I was back on Area...but I wasn’t prepared to have another attempt. I had nav lights and landing light on to make myself a little more visible.

It was a bit bumpy in the smoke and under the inversion it caused. Good flying conditions once I could climb back to 4500’ towards YWG with 10 KN tailwind.

Way back last century I was working in the electronic media, on the day the pointy end fell off an oil tanker off the W.A. coast.

This link has the details.

Aust. Maritime Safety Authority

As the report says,

.......the proposed evacuation was being delayed by bad weather and fog, which was seriously hampering the helicopters.

Perth's 3 commercial TV stations were within a few hundred metres of each other in Tuart Hill and Dianella. The fog that day was pretty bad, it was nearly 30 years ago (faaarrrkk am I that old????) and I thought that the fog would prevent us flying. My recollection is that visibility was less than 200 metres, and that's being generous. Extremely generous.

But the helicopter pilot said, "Get your gear organised, we're off."

Me, "What about the fog??? And isn't the Jetranger only VFR?"

Pilot, " Yep, but we have Special VFR clearance."

So we take off, and after about 1 and a half seconds, can't see diddly squat.

I realise the turn indicator is not level, obviously without visual reference the body can't feel the turn, don't want to distract the pilot, but don't want to die either, so I decide the safe course of action is to point to it, he nods. (Later I explained my thinking to him, and he was happy).

Anyway, we finally break out of the fog and can see the A.B.C. transmitter tower at Hammersley, just above the fog. The tower is 180 metres high, sitting about 24 metres ASL, which means the top of the fog was about 650 ft ASL.

Sepcial VFR. The VFR you have when you can't see a thing.

CASA & Special VFR for helicopters

Anyway, for some pictures of what really happened here's a Youtube link taken from inside the Channel 7 AS 350 Squirrel. No I wasn't working for Channel 7.

I have used both "Special VFR" and "Helicopter VFR" on many occasions. If you are flying coastal or in an area you know it's not tooo bad. If you are in a new area it can be a bit challenging, especially if you are planning on crossing ridgelines or there are towers power lines around. Clear of cloud can be a very subjective process. Oh and just a tip, make sure you know speeds for best maneuvering and know how to safely perform a min radius turn!!!