Cessna Aircraft Company A185F, VH-SLC

The pilot made an inappropriate power reduction before terrain
clearance was assured.
Turbulence and downdrafts in the lee of the headland
significantly degraded the aircraft's climb performance.

The combination of near maximum takeoff weight, and the
reduction of engine power to 81% soon after takeoff, meant that the
aircraft had marginal climb performance when it encountered the
turbulence and associated downdrafts. By not using the full takeoff
distance available the pilot placed the aircraft on a climb profile
that reduced terrain clearance and increased the risk of exposure
to strong downdrafts.

The pilot's judgement may have been influenced by previous
flights where different wind directions and lower wind strengths
combined to give more favourable takeoff conditions. Additionally,
the detrimental effect of an early power reduction would not have
been as perceptible on training flights conducted at lower aircraft
weights where the aircraft's climb performance would have been far
greater. Although turbulence in the lee of the headland may have
been present on previous occasions, the pilot had not encountered
any significant downdraft activity. Consequently he was unprepared
for conditions of that severity.

Although the pilot turned left to avoid the elevated terrain
when the aircraft descended in the turbulence, it was likely that
the flight path placed the aircraft into even stronger downdraft
activity. Without the immediate application of a higher power
setting, the aircraft did not have sufficient performance margin to
continue the climb or maintain altitude.

From the point where the pilot attempted to land the aircraft
there was insufficient water distance remaining on which to land
and stop the aircraft normally. The aircraft contacted the beach at
a speed that was fast enough, when combined with the high centre of
gravity of the aircraft type, to cause it to overturn.

The pilot of the Cessna 185 Floatplane, with five passengers on
board, was making a water departure for a charter flight. The pilot
positioned the floatplane for a takeoff into a north easterly wind
of 15 kts that was gusting to over 20 kts. The takeoff path was
over a sand spit, approximately 50 ft above the water level. To the
north, and left of the takeoff path, was a steep, rocky headland
that rose to a height of approximately 300 ft above mean sea
level.

The pilot reported that he had selected 20 degrees of flap and
applied maximum power for takeoff. The aircraft became airborne
after a short run and the pilot climbed it at an indicated airspeed
(IAS) of 70 kts. At about 200 ft the pilot reduced engine power to
25 inches of manifold pressure and 2,500 RPM. The pilot reported
that just after he reduced power, the aircraft encountered
turbulence and started to descend rapidly. He turned the aircraft
left, away from the spit, with the intention of regaining altitude
over the water before he attempted to cross the spit. However, the
aircraft continued to descend, and the pilot decided to land
straight ahead. The aircraft contacted the water and bounced, then
ran aground on the beach and overturned.

The pilot reported that he exited through a window and
instructed the passengers to evacuate quickly, as there was a
possibility of fire. The passengers reported that they were
entangled in their seat belts and had difficulty releasing the
buckles. A small child was being held by a passenger and another
passenger was temporarily restrained by clothing that became caught
on the right control yoke.

The load chart for the flight showed that the aircraft was 31 kg
below its maximum takeoff weight. The pilot commenced the takeoff
with a takeoff distance of approximately 1,100 m, which exceeded
the minimum takeoff distance of 1,000 m stipulated by the
aircraft's flight manual. However, this takeoff distance was less
than the 1,300 m pilots were directed to use by the operator's
Authorised Landing Area (ALA) register. The pilot reported that he
had not used the full length available as previous takeoffs that
day, from the same point in lighter winds, had been uneventful. He
considered that the increased headwind component would have
improved the takeoff performance and climb gradient of the
aircraft.

The ALA register also stated that a north-easterly wind required
a climb over the spit to avoid turbulence in the lee of the
adjacent headland. Another warning in the operator's ALA survey
report cautioned "Dumping will be encountered on the lee side of
the headland especially in the north easterly winds".

A fact sheet on mountain wave turbulence that accompanied a
recent ATSB report (Occurrence 200104092) involving mechanical
turbulence stated, in part:

"Flowing air near the ground is forced up the windward side of
any elevated barrier and then sinks down the leeward side. Air
flowing at speeds greater than 20 kts produces seriously turbulent
air and significant downdrafts on the leeward side."

That situation was referred to as "dumping" in the operator's
ALA survey sheet. The pilot reported that he hadn't encountered
severe "dumping" during any previous takeoffs.

The fact sheet also stated, in part:

"In addition to generating turbulence that has demonstrated
sufficient ferocity to significantly damage aircraft or lead to
loss of aircraft control, the more prevailing danger to aircraft in
the lower levels in Australia seems to be the effect on a
aircraft's climb rate. General aviation aircraft rarely have
performance capability sufficient to enable the pilot to overcome
the effects of a severe downdraft generated by a mountain wave, or
the turbulence or windshear generated by a rotor."

The Cessna 185 Pilot's Operating Handbook (POH) procedures for
both normal takeoff and short field takeoff recommend that once
clear of any obstacles, the pilot retract the wing flaps and select
full throttle and 2,700 RPM. Operations manual data produced by the
operator listed the climb power setting as 25 inches manifold
pressure and 2,700 RPM, with a footnote that the information be
used as a guide only and that the user refer to the POH and Flight
Manual. The aircraft's flight manual did not provide guidance on
takeoff procedure or associated power settings. The climb power
setting of 25 inches manifold pressure and 2,500 RPM, selected by
the pilot when the aircraft reached approximately 200 ft, delivered
only 81 per cent of the available power.

The pilot reported that he had been encouraged by the operator
to reduce power as soon as possible after takeoff as a noise
reduction technique. The Chief Pilot stated that a power reduction
early in the climb was demonstrated during training to reduce the
noise impact and to reduce engine wear. The Chief Pilot also stated
that, during training it was emphasised that power reductions
should only be made when clear of obstacles and when terrain had
been cleared. It was also stressed that when required, full power
should be used, at the pilot's discretion.