What is the determining factor?

[randomair]

Hello,

I have an interview coming up, and i have recieved some feedback from someone that had one with the same company in the summer.

One of the questions that he told me confused me slightly so any help from any of you would be very helpfull:

'You get your weather at your destination and it's a RVR of 550m and a 100ft cloud base, what is the determining factor?

thanks in advance

[BOAC]

In which country is the operator licenced and what is the approach aid?

[Spitoon]

I'm but a mere controller but in the UK I think you'll find it'll be the RVR.

[randomair]

Thanks very much! Yea it is in the UK however they do not mention an approach aid!

You'll have to excuse me..im pretty low on experience as far as hours etc go, but why is it the RVR?

[Alaskan Timber]

The 100ft cloudbase I would say. For an ILS (assuming they have one) you need at least 550m and 200ft, at the planning stage (before departure). Depending on the airport and runway, these minima could be higher aswell. Depending on the airport and runway, the 100ft ceiling could be enough for a CAT II. If available a CAT III would be even better.

If the question states that you are airborne and preparing for approach, than at most airlines the limiting factor to be ALLOWED to start the approach is the RVR (if before the final approach fix).

I hope this is not to confusing for you, especially if you have no airline experience yet. I would stick to the first situation.

[seat 0A]

One small correction:

E.g.: for a Cat III aproach, you need Cat II minima,

That is not entirely true: for a cat3 approach, you need cat 1 visibility and cloudbase as alternate minima.

But you are correct in stating the RVR is the determining factor.

[P-T-Gamekeeper]

The original question was about weather minima at destination, not alternate, so the minima required are the actual minima on the approach plate.

The determining factor will be approach specific. For a catIII ILS it will be RVR, but as you go down the approaches, it will become more muddled.

For example, at my home base, ILS approach minima require a 200' cloudbase, but 800m vis, due to an offset approach. To circle, you need 2400m and 500' cloudbase.

At the interview, did they show an approach plate to see if you could work it out? If not, I would suggest it is an impossible question to answer without more information.

HTH

[vin2004]

Just a guess!

But would the "determining factor" be if the plane and the pilot are capable of making the approach and landing safetly (determined by the company the pilot works for)..

[Astra driver]

For most US operators RVR is the determining factor in order to start the approach (1800 ft min is typical), of course we must then have at least the approach lights in view at 200 ft to continue down to 100 ft for cat I, or we can go straight down to 100 ft for cat II and in both cases have the threshold in sight to land. Cat III of course, are governed by RVR alone.