Cessna Aircraft Company U206A, VH-OWA

It was likely that, in lowering the right wing while passing the
airstrip and golf course, the pilot 'slipped' the aircraft in order
to counter the aircraft tendency to turn. However, the period of
any uncoordinated flight could not be determined. Although the
quantity of fuel in the selected tank exceeded the '1/4 tanks or
less' quoted in the Owner's Manual caution about uncoordinated
flight, there was still a risk of fuel starvation and engine
stoppage with 1/3 tank capacity. Given the absence of any evidence
of pre-accident aircraft defects or engine mis-handling, it is
possible that the engine failure was due to uncovering of the right
fuel tank outlets and introduction of air into the fuel system.

While the previous power loss event was of interest to the
investigation the lack of specific information about that event
meant that a link with the engine failure could not be
established.

The pilot's response to the engine failure was based on a
generic procedure that was inconsistent with the in-flight engine
restarting procedures produced by the aircraft manufacturer.
Although the investigation could not determine the status of the
auxiliary fuel pump wiring, the information available indicated
that the LO function of the fuel pump was capable of producing
significant fuel flow. It was likely that sustained use of the
auxiliary fuel pump, instead of the momentary use specified by the
engine manufacturer, provided fuel flow that exceeded the engine's
requirements and prevented a restart. Had the pilot referred to the
fuel flow gauge, he could have ascertained the amount of fuel being
supplied to the engine, and responded accordingly. The pilot's lack
of awareness of the manufacturer's procedures could be attributed
in part to the absence of the applicable placard and procedure card
in the aircraft and the absence of training in type-specific
emergency procedures.

The pilot delayed the search for a specific landing site until
the aircraft had descended to about 750 ft, because he was
initially focussing on restarting the engine. This was primarily
due to the pilot's perception that the engine failure was similar
to the previous engine power loss event and his expectation that
the engine would eventually restart. Although the pilot managed to
reach a clear area, an earlier diversion to a specific landing area
after the engine failure would have reduced the risk of a forced
landing in a less favourable location.

The tailwind during the glide approach, and the limited amount
of flap extension had a positive effect on the aircraft's glide
range. However, those two factors contributed to a relatively
higher touchdown speed, which increased the risk of aircraft damage
and occupant injury. Due to the prevailing wind conditions and the
track to the landing area, a tailwind during landing was
unavoidable. The spring-loaded flap switch combined with high pilot
workload made it difficult for the pilot to further extend flap in
the late stage of the approach.

On 4 June 2004, the pilot of a Cessna Aircraft Company U206A
planned to conduct a private flight from Lakeside Airpark to
Proserpine aerodrome and return, a total distance of 40 km. The
pilot was the only occupant on the flight to Proserpine which he
described as uneventful. Three passengers boarded at Proserpine for
the return flight via Laguna Whitsunday Resort, a diversion for
sightseeing that added a few minutes flight time.

The pilot described the pre-flight engine run-ups and takeoff at
Proserpine as normal and said that he was operating on the right
fuel tank as he climbed the aircraft to 1,500 ft above mean sea
level. About 4 minutes after departure, the aircraft flew parallel
to the resort's airstrip construction site, and then passed the
golf course and marina. The pilot reported that, for short periods
of less than a minute he had banked the right wing 30 degrees down
to optimise the view for his passengers, but he could not recall
the extent to which opposite rudder¹ was applied during those times.
Shortly after passing the marina, when the aircraft was flying
straight and level and was over water at about 1,200 ft, the engine
failed.

The pilot selected the right half (coloured yellow) of the
auxiliary fuel pump switch to LO and changed the fuel selector
position from the right to left tank. There was no response from
the engine so he changed the position of the fuel selector a number
of times and selected the left half (coloured red) of the fuel pump
switch to HI for short periods.

Figure 1: VH-OWA auxiliary fuel pump switch
(centre).

The pilot reported that he didn't refer to the fuel flow gauge,
but was convinced that fuel wasn't being supplied to the engine. By
this stage the altimeter was indicating 750 ft and he began
searching for a specific landing area. The pilot glided the
aircraft in a north-westerly direction towards a flat area between
the marina and the resort golf course. The wind was from the
south-east at about 10 kts. He continued with his attempts to
restart the engine and managed to transmit a Mayday late in the
approach. Flap was not extended beyond 5 degrees and the pilot
reported that he was too busy during the final stage of the
approach to hold the spring-loaded flap control switch down.

The stall warning activated just before the aircraft landed
heavily on a flat area about 20 m before a 1.4 m high embankment.
The propeller dug into the bank and the aircraft overturned,
resulting in substantial damage. Witnesses and resort staff
attended the scene and helped the pilot and passengers out of the
aircraft. Emergency services attended from Proserpine and treated
the four occupants, who were seriously injured.

The pilot reported that he was not manipulating any engine
controls or switches immediately prior to the engine failure and
that there were no prior indications of the failure. An extensive
examination of the aircraft including the fuel system, ignition
system and engine did not reveal any contaminants or defects that
would have contributed to the engine failure. The aircraft's fuel
tanks contained approximately 50L of fuel per side, which was about
1/3 of each tank's capacity. Laboratory testing of samples from
both tanks identified the fuel as aviation gasoline (AVGAS) and did
not identify any characteristics that would have contributed to the
engine failure.

The Owner's Manual stated that when selected to LO, the
auxiliary fuel pump would only operate when the starter was
engaged. However, the pilot advised that when priming the engine
prior to starter engagement, the auxiliary fuel pump selected to LO
consistently produced at least a 12 gal/hr fuel flow. While this
indicated that the aircraft's auxiliary fuel pump wiring did not
conform to the manufacturer's specifications, damage to the
aircraft prevented an assessment of the pump output and exactly how
the fuel pump switch was wired.

A Civil Aviation Safety Authority airworthiness directive (AD),
issued by the then Australian Civil Aviation Authority in 1979,
mandated action in accordance with a service information letter
issued by the aircraft manufacturer. The service letter specified
provision of a fuel flow stabilisation placard and associated
procedure card in that aircraft model. Although the aircraft
logbooks indicated compliance in 1985 with the requirements of the
AD, neither the placard, nor the procedure card that included
in-flight engine restarting procedures, was in the aircraft. The
restart procedures specified that the auxiliary fuel pump be
selected to ON or HI until the indicated fuel flow was in the green
arc, then it should be selected off. The pilot reported that he was
not aware of the requirement for the placard and procedure card,
nor was he aware of the type-specific in-flight engine restarting
procedures. The copy of the owner's manual that was in the aircraft
did not include any emergency procedures.

The pilot related that about 8 months prior to the accident the
aircraft had sustained a significant power loss while cruising
straight and level at 6,500 ft in calm conditions. He had applied
the same engine restart procedure that he used during the accident
sequence and after a series of engine power fluctuations eventually
accomplished a sustained restart at about 3,000 ft. The pilot
believed that there had been a vacuum or blockage and the only way
he got the engine to run satisfactorily was to rotate the fuel
selector between the left and right tanks using a small amount of
boost. There was no reason identified for that power loss and the
aircraft operated normally for a further 70 hrs. During that time,
a periodic inspection was carried out and no aircraft defects that
could have contributed to the power loss were identified.

The owner's manual included the following caution in the
description of the fuel system.

... with 1/4 tanks or less, prolonged uncoordinated
flight such as slips or skids can uncover the fuel tank outlets,
causing fuel starvation and engine stoppage. Therefore, with low
fuel reserves, do not allow the airplane to remain in uncoordinated
flight for periods in excess of 1 minute.

The ATSB recently completed an investigation into an engine
failure resulting from fuel starvation that involved a similar
aircraft type (Cessna 207, ATSB report 200403210). That
investigation found that the in-flight engine restart procedures
published by the manufacturer were not followed, but the engine
restarted after a significant height loss of about 700 ft.

¹ Application
of rudder in the opposite direction to a lowered wing inhibits the
development of a turn, resulting in a slip that can allow flight on
a straight track. An aircraft that is slipped is considered to be
in uncoordinated flight.