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From: bl@hplabsb.UUCP (Bruce T. Lowerre)
Newsgroups: net.aviation
Subject: Re: Out to dry on the glideslope
Message-ID: <3321@hplabsb.UUCP>
Date: Wed, 26-Feb-86 20:01:29 EST
Article-I.D.: hplabsb.3321
Posted: Wed Feb 26 20:01:29 1986
Date-Received: Sat, 1-Mar-86 04:49:10 EST
References: <2473@pixar.pixar> <474@gcc-milo.ARPA>
Organization: Hewlett Packard Labs, Palo Alto CA
Lines: 35

> In article <2473@pixar.pixar> good@pixar (Never tell your copilot "Cheer up" during the takeoff roll.) writes:
> >	I assume that most of you are aware of the 152 which tangled with
> >the power lines on final at Ontario the other night.  For those who don't
> >know anything about it, nobody was hurt...
> >	Directional radio, such as localizers, glideslopes, etc, have false
> >"lobes" on either side of the real beam.  There can be several such lobes.
> >Evidently the 152 in question, while on an night IFR training flight, was
> >flying one of the lobes underneath the GS on approach.  Thus they could have
> >had the needle nailed to the bullseye and still tangled with the power line.
> 
> I'm just a low time VFR pilot (so I could be wrong), but isn't the usual
> procedure to intercept the localizer before following the glideslope down?
> Isn't it impossible to get on such "false lobes" for both? (this may be
> obvious given that they ended up "hanging out" ;-) )
> 
> IFR old salts - what's the story here?

The localizer does not have false side lobes but does have a back course.
The glide slope does have side lobes (actually above and below the true
glide path).  It works on a different principle than the localizer.  The
side lobe phenomenon is (or at least should be) well known to IFR pilots.
If the accident was caused by tracking a side lobe, then the pilot made a
procedural error in his initial approach.  One must maintain a specified
altitude until established on the localizer course and outside of the final
approach fix (usually the outer marker).  This altitude places the aircraft
below the glide path.  The glide path is then intercepted as the plane flies
into it, and the descent is initiated.  It's almost inconceivable that the
plane could have intercepted a side lobe below the glide path unless he
was 20 miles or more from the runway when he intercepted the localizer.  A
cross check on altitude is the glide slope altitude at the final approach
fix which is published on the approach plate.  If he descends below this
altitude before reaching the final approcah fix, then he should know that
something is wrong.

Bruce T. Lowerre CFI