After over thirty years of instructing, one constant in my observation has been
the inability of pilots, including myself, to accurately gauge clearance height
over approach obstacles. Self assessments by pilots after landing are typically
only either 'well clear' or 'a bit low maybe'. When asked for an estimate of
actual clearance, the one constant is a significant over estimate.
Any pilot/instructor/observer who berates someone for the sake of it in such a
situation does both the observed pilot and themselves a huge injustice.
Concerned pilots/instructors/observers will offer genuine feedback on a task
that is actually extremely difficult to carry out ie accurate clearance
assessment over approach obstacles. At every stage in my gliding I appreciated
such feedback and took it on board for subsequent approach planning, as did my
peers.
Rather than 50', use of the term 'one wingspan' or 'one and a half wingspans'
is useful. I'd always thought that the one wingspan term was simply a more
useful derivative of the 50' requirement...much easier to visualise. A good
technique for giving genuine feedback is the use of the 'box'. If the span of a
glider on approach is considered the upper (horizontal) side of a square box
shape then the vertical sides of the box to the ground will be the same length.
If the box appears a rectangle then the glider's clearance is less than a
wingspan.
Adequate clearance over approach obstacles is essential for two main reasons.
Firstly our ability to identify an over shoot is much great than that of an
undershoot. By the time we are well in an undershoot situation significant gain
of height is needed to clear obstacles at a time when we are rapidly losing the
ability to gain height. Secondly, if I had a choice of going through the far
fence at 10kts or hitting a fence/tree/power pole on approach at 60kts, i know
which one I'll choose every time.
There is wisdom in retaining at least some rules in gliding. Given the strict
rules that apply on the road the risk of an accident is still high due to poor
judgment by so many drivers. I'm still far more fearful that I'll die in a road
accident than in a gliding accident. I'd hate to think of the increased risks
I'd face if most of the road rules were abolished. Just my twenty cents worth.
Regards
Laurie Hoffman
________________________________
From: Alan Wilson <a...@ozemail.com.au>
To: 'Discussion of issues relating to Soaring in Australia.'
<aus-soaring@lists.internode.on.net>
Sent: Friday, 19 October 2012 7:16 AM
Subject: Re: [Aus-soaring] 50' obstacle clearance rule
Ah the 50' rule. It has been around for more years than stated and has
been a contributing factor in many a prang I bet. I know of one in the
early 70's where the glider pilot had a predilection and acceptance of the
50' rule, landed over that fictitious obstacle and could not fit into the
outlanding paddock [at Emu Plains]. There was an option of missing the
non-existent obstacle, clear the 4' fence, and land across the diagonal with
40% more landing run!
At the time I landed as close as I dared over a fence at Forbes airfield and
paced out my touchdown to be 220' from the fence. Critical in a short
outlanding, and worse if one adds and unnecessary 50' at 30:1!
My google-fu found " Douglas Bader, British WWII air ace). Rules are for the
guidance of wise men and the blind obedience of fools. (Solon, the Lawmaker
of Athens, d. 559BCE)" ... Some unnecessary rules have been around for
millennia.
It may come from an instructor who could gauge that clearance of a fence
because 50' is a soft conversion of a 15 meter wingspan. Sitting safely on
a chair at the pie cart the instructor can visualize that and use it to
berate the pilot who considered he had a short landing well under control.
But in any event is the rule necessary? We all know the advantages of not
hitting the far fence at 5 knots over going through the near fence at 50
knots. Those who don't are not around to tell!
So, clear all obstacles is the key, and land as safely as you can.
Finally, appreciate that the younger set probably have a good appreciation
of metrics, but may not relate to Knots and feet.
My 'two bobs' worth, but you can call it 20 cents.
Alan Wilson
Canberra
-----Original Message-----
From: aus-soaring-boun...@lists.internode.on.net
[mailto:aus-soaring-boun...@lists.internode.on.net] On Behalf Of Peter F
Bradshaw
Sent: Friday, 19 October, 2012 2:24 AM
To: Discussion of issues relating to Soaring in Australia.
Subject: Re: [Aus-soaring] 50' obstacle clearance rule
Hi;
Irrespective of whether it is 50' or not I find it hard to believe that the
figure is given in a system which people under 40 have no heuristic
knowledge of.
On Mon, 15 Oct 2012, Mark Newton wrote:
>
> Hi folks.
>
> My google-fu is failing me, but at least one of you can probably help.
>
> I've long accepted that the rule for obstacle clearance is 50'.
>
> However, the GFA instructor handbook describes it as a wingspan, and
> the B certificate oral exam calls 50' a "recommended" minimum, so I'm
> trying to go back to sources to find the origin of the rule.
>
> And I can't seem to find it written down anywhere.
>
> I'm beginning to suspect that my long-term acceptance of the 50'
> rule is wrong, and that the real limit is, shall we say, more
> "operationally fluid" than that.
>
> Wondering if the strict mention of 50' that I've seen at clubs all
> over Australia is actually more of a tradition, perhaps derived from a
> misunderstanding of certified light aircraft performance charts which
> give minimum takeoff distances including clearance of a 50'
> obstacle.
>
> Does anyone have a cite to the regulations?
>
> (while you're at it, providing a cite to a current GFA or non-exempted
> CASA regulation which states what GFA annual check entails, whether
> it's required to be signed out in a logbook, or whether an instructor
> is even required to be present, would help to settle a long-standing
> argument :)
>
> - mark
Cheers
--
Peter F Bradshaw: http://www.exadios.com (public keys available there).
Personal site: http://personal.exadios.com "I love truth, and the way the
government still uses it occasionally to
keep us guessing." - Sam Kekovich.
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