Re: 757 Autoland

From:         Steve Le-Vien <slevien@eggw.demon.co.uk>
Organization: Home
Date:         17 Dec 95 02:11:48 
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In message <airliners.1995.1930@ohare.Chicago.COM>  wrote:

[snip]

> Category	Decision Height  	RVR
>
> I		200 FT
> II		100 FT
> IIIA		50 FT
> IIIB		0 FT			VARIES 100 M - 300 M (REQUIRES FULL
> 							AUTHORITY RUDDER)
> IIIC		0			0 (REQUIRES TAXI GUIDANCE; NON EXISTENT?)

Not quite. A Cat IIIb approach can be flown with a zero cloudbase but
there is always a decision height. It is designated as 'below 50ft' and
is set by the operating company, approved by the relevant Flight Operations
Department. Typical IRVR minumum is 75 metres.

> [snip] They are also redundant
> and must meet a requirement that a standby will come on line within 3 seconds
> if the transmitting unit fails.

No, there must not be more than a *one* second break. During Low Vis
Procedures we run the ILS and airfield lighting on diesel generators
and have the mains available as an instantaneous back up. In fact,
strictly speaking, whether on generators or mains, the ILS is running
off baterries which are being constantly charged by whatever supply is
in use.

--
___________________________________________________________________
____
\  /  Steve Le-Vien                                 AFTN: EGGWZPZX
 ||   Air Traffic Services Manager            tel: +44 1582 395230
 ||   London Luton Airport, UK                fax: +44 1582 395381
 ||   slevien@eggw.demon.co.uk               My views, not LLA Ltd