Can you convert from VIS to approx cieling?

[meatlover]

Sorry for the dump ques, but for example if an airfield has 2500 meters VIS.
That's about 1.4 NM.
Can we assume we will be visual with the runway at about 450 feet using the 300 feet/NM rule?

[Gulfstreamaviator]

VIS has no relation to Cloud base..... Glf

[meatlover]

Glf,

Thanks for reply.
If you had a failure where the FO lost his PFF and ND after departure.
Visibility at airfield you took off from was 2500 M.
CAV at your home base about 1.20 hours away.
What do you do?

No land amber or land ASAP. But ONLY one set of screens amongst other minor failures.

[BOAC]

On a day with no cloud below 450' and remembering that approach lights will complicate this, yes, it is a guide, but if the cloudbase is 300'??

No understand your last question. I would go home. Who needs screens?

[darkroomsource]

I've seen airports with 5 miles vis but only 200' cloud base often enough to say that cloud base is more important than visibility for this decision.

1.2 hours is a fair bit away, is there another airfield closer?
What are you flying?
What is there for a backup of the FO's screens?
What is there for a backup of the primary screens?
What do the company docs say about this situation?

[Natstrackalpha]

Sorry for the dump ques, but for example if an airfield has 2500 meters VIS.
That's about 1.4 NM.
Can we assume we will be visual with the runway at about 450 feet using the 300 feet/NM rule?
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No.


Its kind of silly really. Because 2500metres in mist or precip or smoke has no bearing on your IMC you are in and therefore your cloudbase (ceiling!) too/either.

Either you can see the runway or you cannot. If you cannot then you won`t until you get below the cloudbase - if the mist is part of even thicker fog somewhere close by then you might see :mad: all until touchdown or minimums, also due to other IMC stuff around too - known as fog when it hits the deck.

Often you can see V V looking down but never slant range, often you can fly over a runway with low fog to look down directly (less shallow) and you will quite often see nothing.

You can take off on a gin clear day and be in fog at 200 feet, where did that come from you may ask?

You can approach and the world says come on in all is lovely and yet you are still not visual by 1,000 which is not cool when the glideslope has just packed up.

See whadda mean?

In other words, 2500 metres (whatever) on the ground has no bearing or relation to what is going on in the air, in the air.

You can work out a glidepath if you want based on speed RoD time and all the rest of it but, the resultant outcome cannot be determined.

You wont see if there is stuff between you and the ground or you are in stuff. There is nothing concrete or dynamic to determine when you will be visual - except a cloudbase, below the cloudbase does not mean you are out of the :mad: and can see!