Re: Korean Air 801 crashed on approach to Guam

Date:         08 Aug 97 05:41:22 
From:         k_ish <kenish@ix.netcom..com>
Organization: Netcom
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jf mezei wrote:
>
> Karl Swartz wrote:
> > to the crash, which occurred at 2:35 am local time in heavy rain.
> > NTSB chairman James Hall said the glide slope portion of the ILS was
> > not functioning.
>
> Could someone put this missing glide slope in perspective ?
>
> Just how important is it to a landing in darkness with little or no
> visibility ? What other instruments/information would have been
> available to the pilot to help him stay on track to the runway ?

An Instrument Landing System (ILS) has two radio beams projecting from
the runway up the approach profile.  The localizer indicates whether the
aircraft is left or right of the extended runway centerline.  The glide
slope slopes down (usually at a 3 degree angle) to the runway.  An
instrument in the cockpit merges these two (the simplest ones use
crosshairs) and by keeping the needles centered, you know you are
descending properly to the runway.  This type of approach is called an
ILS approach.

If the glide slope component of the ILS is inoperative then the approach
is called a Localizer approach.  It is quite common (especially for
general aviation airports) to have a localizer and no glide slope.  In a
localizer approach, you begin the approach at an "initial approach fix"
(IAF).  Your distance to the runway is determined by one or more
methods:  1)  Time from IAF  2) Distance Measuring Equipment (DME) which
indicates distance to the runway  3) A set of ground radio beacons
called the outer, middle, and inner markers.  In all 3 cases, at certain
distances from the IAF or runway, you can then descend to a lower
altitude in a stairstep fashion.

> Is it plausible that the missing glide slope would have resulted in the
> plane being much lower than it should have been in its approach ?

The glide slope had been out of service for a month, and hundreds of
aircraft landed uneventfully.  In some footage, you can see a flat,
circular dirt area with a white antenna in the center.  This is the
middle marker beacon!  Just wild speculation on my part; possibly the
pilot confused the middle marker for the inner marker...a profound
blunder if this is what happened.  The altitude over the middle marker
at Guam is 2100 feet according to a commercial pilot friend.

> How common is it for the glide slope to be inoperational for airports
> that handle 747s on a daily basis ? Is this a no-brainer for pilots when
> it is missing, or does this require a lot more attention ?

All approaches and landings require a lot of attention!  As a pilot,
believing *any* aspect of a flight is a "no brainer" can leave you very
dead!  Nonetheless, the inoperative glide slope should not have posed
any unusual challenge, IMHO.

Hope this helps put things in perspective.

Ken Ishiguro