Re: landing in fog

From:         dpw@dircon.co.uk (Daniel Wilder)
Organization: Direct Connection (Call 0181 297 2200 for info)
Date:         04 Dec 95 01:14:51 
References:   1
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On 29 Nov 95 01:36:19 , susanle@ix.netcom.com (Susan Leibowitz )
wrote:

>I'm curious...a friend of mine was coming into LA on an L-1011.. It was
>on one of those very foggy days.  They tried to land three times and
>then gave up and landed in Las Vegas.
>
>The rumor on the plane was that the pilot wasn't fog certified.  Does
>that make sense?
>
>And why wouldn't they've been able to use instruments to land?
>

Susan,

There is no such thing as a fog certificate.

However, when the weather is bad, the pilots will fly an instrument
approach using a ground based radio aid for lateral and longitudinal
guidance. A typical device would be an Instrument Landing System
(ILS).

There are several types of ILS broken down into categories. Different
categories allow the aircraft to fly lower before having to commence
the  "go-around" and hence have a better chance of making visual
contact with the runway. The category minimums are as follows :

CAT I (1) - Down to 200ft with a runway visual range (RVR) of 600m
(sometimes reduced to 550m with high intensity centreline lighting).

CAT II (2) - Down to 100ft with a RVR of 300m.

CATIIIA (3A) - Down to 0ft with a RVR of 200m
CATIIIB (3B) - Down to 0ft with a RVR of 100m
CATIIIC (3C) - Down to 0ft with a RVR of 0m

CATIIIC has not been used commercially as the visibility would not
allow the aircraft to taxi to its parking stand.

However, it doesn't end here. The category that a particular airport
has depends on the type of ground transmitters it uses, the runway
lighting available and other factors. I would assume (although this is
just a guess) that LAX would be CATIII.

There is more. Just because an airport may have a certain category of
ILS, not all aircraft are capable/certified to fly that category.
Almost all transport aircraft will be able to fly CATI. However, to
fly CAT II and III, the aircraft has to have additional hardware such
as radio altimeter, dual autopilots (in CAT III case), ILS deviation
warning systems etc.

Finally, the pilots themselves may not be certified to fly below a
certain category. All commercial instrument rated pilots will be able
to fly CAT I, however, further training is required to fly CAT II &
III. The pilot then has to be in current practice if he/she wishes to
use them.

The above relates to the UK, and as far as I am aware, the
International Civil Aviation Organisation. Minimas/rules may differ in
the US.

Regards,

Daniel.

---
Daniel Wilder
dpw@dircon.co.uk