Amateur built aircraft - Smythe Model S Sidewinder

The investigation established that the aircraft performed a barrel roll or similar manoeuvre to the right, followed immediately by a series of flick rolls or a spin to the left. (A barrel roll is a manoeuvre where the nose of the aircraft is made to travel around a spiral path which is some distance from the axis of the roll. A flick roll is a manoeuvre where the aircraft is induced into a stall at a higher than normal speed and the aircraft rotates or rolls rapidly about its longitudinal axis. A spin is characterised by the same rotational movement but the axis of a spin is usually vertical.) The investigation could not establish any reason for the manoeuvre. During the course of the roll, the engine noise was heard to cease, and this was most probably due to fuel starvation. The investigation established that the centre of gravity may have been near the aft limit and this would have accentuated the uncontrolled manoeuvre and reduced the chances of recovery by the pilot. During the recovery from the rolling manoeuvre, the aircraft then stalled and rolled rapidly left two or three times before ground impact.

The engine was estimated to have been running for approximately 50 minutes before the accident. As a result, the fuel quantity remaining may have been insufficient to allow continued fuel supply to the engine when the aircraft was banked steeply, and may have caused the engine to cease operating due to fuel starvation.

The homebuilt aircraft had been completed over a period of about
22 years and was in flying condition. The aircraft, known as the
Smyth Model S Sidewinder, was designed in the USA in 1958. The
designer was aiming to produce a sporting monoplane that was
reasonably easy to build, easy to fly, stressed to 9g for
aerobatics, and economical in operation. The first flight of this
aircraft type was made on 21 February 1969 and it received the
Outstanding Design Award at the 17th Experimental Aircraft
Association Fly-in that year. Plans became available to amateur
constructors and in 1973 the plans for the accident aircraft were
purchased by the owner.

By 1978, the fuselage construction was well advanced and the
initial inspection was carried out. The project proceeded slowly
and in 1985 the owner moved from NSW to live in Qld. The aircraft
was nearing completion in 1994 when the owner made an application
to the then Civil Aviation Authority (CAA) to reserve the
registration VH-LKV. The aircraft was a first of type in Australia,
and the necessary certification processes were incomplete. At the
time of the accident, the aircraft was unregistered and did not
have a certificate of airworthiness or a permit to fly. However,
the pilot on the accident flight had flown the aircraft some weeks
earlier on its first flight.

It had not been the intention of the owner to fly the aircraft
on the day of the accident. The pilot arrived at the aerodrome and
found the owner and his friend working on the aircraft. After some
discussion, the pilot suggested to the owner that they should take
the aircraft for a flight. The owner initially declined the offer
but the pilot persuaded him to accede to the suggestion.
Subsequently, the pilot added 20 L of fuel to the main fuel tank,
which had contained about 6 L of residual fuel. The pilot then
assisted the owner and his friend to replace panels and cowling and
to prepare the aircraft for flight.

The weather was fine with a light south-easterly wind. Witnesses
observed the aircraft taking off from runway 06. After takeoff, the
aircraft initially flew low down the runway with a tail-down
attitude, and then began a shallow climb. A flight of about 30
minutes was conducted, during which the pilot demonstrated some of
the handling characteristics to the owner. The pilot also carried
out circuits and landings during this period. The aircraft was then
landed and taxied back to the hangar. While the engine was running
and the owner was getting out of the aircraft, the pilot motioned
to the owner's friend to come over to the aircraft. The friend
indicated to another person he was with at the time, that he did
not wish to go flying as he would be late getting home. However, he
boarded the aircraft and the pilot taxied out for another
takeoff.

The aircraft became airborne, again from runway 06, and headed
north-east for about 2 km before turning left and heading back
towards the aerodrome. When the aircraft was over the aerodrome at
about 1,000 ft, witnesses saw the aircraft descend in a shallow
dive and then perform what appeared to be a steeply banked
manoeuvre or barrel roll to the right. One witness said he
remembered seeing the belly of the aircraft faced towards him.
Another witness said the aircraft rolled completely over in what
appeared to be a controlled manoeuvre. During this manoeuvre, a
third witness heard the engine noise increase and then completely
cease. The aircraft recovered to a level attitude but immediately
flick-rolled to the left and adopted a steep nose-down attitude.
The aircraft continued to flick-roll or spin and struck the ground.
The aircraft was descending almost vertically at impact with a
30-degree nose-down attitude. There was no fire and the impact was
not surviveable.

Aircraft particulars

This was the first aircraft of its type to be constructed in
Australia. Another builder in WA had commenced construction of a
Sidewinder at about the same time, but the project was not
completed. The aircraft was powered by a Lycoming Model 0-290-D2B
engine which had a take-off power rating of 140 h.p. at 2800 r.p.m.
The aircraft was designed with a fixed tricycle landing gear but
the subject aircraft had been fitted with retractable gear. The
gear was not retracted on the accident flight because the alternate
gear extension system was not operative. The main fuel tank had a
capacity of 65 L. The two wing tanks each had a capacity of 49 L,
and were empty on the accident flight. The fuel consumption quoted
by the engine specifications was 6.5 US gal or 24.6 L/h for
economical cruise. Fuel consumption for the pre-accident flights
could not be determined but would have been significantly higher
than the economical cruise consumption because of the nature of the
flights.

The aircraft was fitted with fully functioning dual controls and
side-by-side seating for two persons. The constructor's manual
quoted a stalling speed of 48 kts and a maximum speed (Vne) of 174
kts. The flight characteristics of this aircraft were unknown as a
flight test schedule had not been carried out. The empty weight of
the aircraft was approximately 477.5 kg but a final weighing of the
aircraft had not been carried out as was required for certification
of type. The aircraft had been test flown in December 1996 by the
accident pilot. After that flight, the pilot had expressed his
dissatisfaction with the aircraft's stalling characteristics, and
said that he would not fly it again. It was discovered that the
aircraft had 26 L of fuel in the left wing tank and no fuel in the
right tank. This may have affected the stalling
characteristics.

Damage to aircraft

The aircraft impacted the ground whilst rotating to the right
with a nose-down attitude of approximately 30 degrees. The cockpit
area was destroyed by the impact. The engine was embedded in the
ground to a depth of about 0.5 m. One propeller blade was sheared
off and fragmented by impact. The fractured surface indicated no
powered rotational movement at the time of impact. The remaining
propeller blade was intact and undamaged. The cockpit structure and
floor had been compressed forward against the rear of the engine.
The force of impact against the rear of the engine had fractured
the engine gear housing. The throttle was found in the fully open
position, the mixture fully rich and carburettor heat control in
the cold position. However, the position of the cockpit controls
before impact could not be positively determined due to the extent
of damage. The main fuselage fuel tank had disintegrated and there
was no evidence of fuel at the accident site immediately after the
accident.

Wreckage examination

Examination of the airframe did not reveal any failure or defect
which might have contributed to the accident. The engine exhaust
pipe was metallurgically tested and was at less than operating
temperature at impact. The engine was bulk stripped and no defects
or failures were discovered other than those caused by impact
damage. The retractable landing gear was in the extended position
at impact. During the investigation the possibility of propeller or
spinner failure was considered, but there was no evidence to
support this hypothesis. The possibility of a bird strike was also
considered, but again there was no evidence found during the
wreckage examination to support this theory.

Weight and balance

The aircraft had been weighed on 10 January 1994 to determine
the empty weight and centre of gravity. A final weighing was
required after fitting of the radio and other equipment but this
had not been carried out. The actual weight and balance at the time
of the accident could not be determined. However, based on the
initial weight and balance determination, the aircraft was within
the weight and balance envelope and the centre of gravity near the
prescribed aft limit. The summary showed that with two persons on
board and no fuel, the centre of gravity was 0.55 inches forward of
the aft limit.

Personnel information

The pilot was the holder of a senior commercial pilot licence
(aeroplane) and was qualified and endorsed on the aircraft
category. He had flown the aircraft on one other occasion some
three weeks before the accident, but otherwise had no experience on
the particular aircraft type. He was, however, widely experienced
with over 38 years as a flying instructor, airline pilot and
general aviation pilot. He had previously test flown a home-built
aircraft for the passenger on the accident flight. The passenger
held a student pilot licence and had accumulated about 267 hours
aeronautical experience.

Medical information

The pilot was medically fit and qualified to perform the flight.
He had a current class one medical certification status. There was
no evidence found to indicate that there were any physiological or
medical factors which may have contributed to the accident. The
passenger was medically fit and held a valid medical certificate
for his licence category.

Meteorological conditions

Witnesses reported conditions at the time of the accident as
fine with a light easterly breeze. There was an insignificant
amount of high-level cloud and the temperature was 24 degrees
C.

Communications

The aircraft was fitted with a VHF radio. The Caboolture
aerodrome is outside controlled airspace but within the
Caloundra/Redcliffe Common Traffic Avisory Frequency area. The
frequency is used for inter-aircraft and advisory communication and
is not recorded. There was no other known flying activity in the
vicinity of Caboolture aerodrome at the time of the accident, and
it is not known if there were any transmissions made from the
aircraft immediately before the accident.

Aerodrome information

The Caboolture aerodrome is unlicensed. The grass runways are
06/24 and 12/30, and are 900 m and 1,350 m in length respectively.
The aerodrome is 40 ft above sea level. The aircraft impacted the
aerodrome on the southern side the runway 06 flight strip near the
north-eastern end of the runway.