This article is reprinted courtesy of the
Transport Canada Aviation Safety Letter.
It appeared in the ASL issue 4/2003 on page 11
COPA Corner:
Why Do a
Walk Around?
by Adam Hunt,
Canadian Owners and Pilots Association (COPA)
I recently received a question from some low time pilots. They
reported several instances where experienced pilots have jumped
into their plane and flown away without doing a pre-flight
inspection. They wondered if pre-flights are something worth
doing, or if they are just exercises for student pilots?
Of course most
of the time the aircraft has sat, untouched, since its last
flight. But an oil leak may have developed, or someone may have
done some "hangar rash" to the plane. In some cases, a thief may
have siphoned out all the fuel, except a few litres. That could be
a surprise on take-off. Pilots have taken off with external
control locks in place, or with concrete blocks tied to the tail.
It is very important to do a complete pre-flight inspection before
every flight.
One of the
most important times to do a careful pre-flight inspection is when
the aircraft has been through maintenance or when it has just been
reassembled after being transported. This story shows just how
wrong things can go, for lack of a pre-flight inspection. The
worst thing is that the same accident has been repeated more than
once, always with the same fatal results.
Even though
this story involves a particular aircraft type, the Pterodactyl
Ascender ultralight aircraft, the lesson learned is universal.
These cartop transportable aircraft are often kept at home and
then assembled prior to flight at the airport. There were original
manufacturer's investigations following up the official
investigations of several early 1980s accidents where a leading
edge spar failed in flight, with no other aircraft components
failing. In all cases the results were fatal.
The official investigations listed these accidents as "Undetermined,"
but the follow-up factory investigations found the answers. In
each case the spar failed just outboard of the inboard spar sleeve
junction, where the inner set of rigging cables joins the spar.
The spar failed upwards and twisted as it failed, giving a very
distinctive signature to the failure.
These spar failures all had the same signatures and the same
causes - the inboard compression strut had failed to do its job.
Each wing has two compression struts. The compression struts are
designed to keep the front and rear tubular spars apart and also
to take the wing's inter-spar compressional forces. Without the
inboard compression strut in place, both spars will move together
until one breaks. The rear spar is prevented from moving forward
by the hang cage centering cable, so the front spar is the one
that fails.
There are several reasons why the compression strut can fail to do
its job. The compression strut mounting brackets, the bolts or the
compression strut itself could fail. There are no recorded
instances of the failure of any of these parts. In all accidents
investigated, the parts mentioned above were undamaged. The most
likely reason for these accidents is that the compression strut
was not secured during assembly of the aircraft.
Pterodactyl Ascender ultralights are designed for quick
disassembly and reassembly and the compression strut is provided
in two parts, joined by a sliding bolt lock. If the two
compression strut parts are not connected during assembly, or the
bolt lock is not slid into place, the result will be a spar
failure in flight. The requirement to check this item is clearly
outlined in the Pterodactyl Builder's Manual.
|
Empty Weight: |
254 lbs. |
| Gross Weight: |
535 lbs. |
| Wing Span: |
33 ft. |
| Wing Area: |
173 sq. ft. |
| Engine:
|
430 Cuyuna |
| Cruise Speed: |
55 mph. |
| Stall Speed: |
25 mph. |
| VNE: |
85 mph. |
| Construction: |
bolt together tube and dacron fabric |
| Building time: |
100 hrs. |
The Pterodactyl wing sail is
provided with four zippers for just this pre-flight item.
The key defence against these kinds of spar failures is a good
pre-flight inspection. Special care should be taken to inspect
these after the aircraft has been reassembled or has undergone
maintenance affecting the compression strut area.
Your aircraft doesn't have to have "quick disconnect" style
compression struts to have critical pre-flight inspection items.
All aircraft have items related to control locks, tie-downs, fuel,
oil and other fluids plus many damage-sensitive, structural and
control-related areas that must be inspected before each flight.
Do you really need a pre-flight inspection before you fly any type
of aircraft? You bet your life you do!
From ASL 4/2003 Page 11
