At 1735 eastern summer time on 20 January 2005, a Cessna Aircraft Company A185F floatplane, registered VH-SBH, with one pilot and three passengers on board was taking off on a water departure for a charter flight from Rose Bay aircraft landing area (ALA) to Palm Beach, NSW. Shortly after becoming airborne, the aircraft rolled 45 degrees to the left causing the left wing to strike the water. The aircraft became inverted and was substantially damaged. The four occupants escaped with minor injuries.
The pilot had positioned the floatplane to the eastern side of the ALA, approximately 200 m from the shoreline and to the west of a headland, to achieve more favourable sea conditions for a takeoff to the north-north-west. The pilot reported that the wind direction was 010 degrees M at a speed of 20 kts. The intended take-off path ran approximately parallel to the headland in a direction of 350 degrees M.
The pilot reported selecting 20 degrees of flap for the takeoff. As the aircraft was about to leave the surface, he selected 30 degrees of flap. This technique was used to help get the aircraft off the surface of the water quickly in difficult sea and/or weather conditions. He also reported that the aircraft took longer than he expected to reach take-off speed. The aircraft became airborne at 45 to 50 kts and he then selected 20 degrees of flap. At approximately 30 ft above the water, the aircraft commenced an uncommanded left roll that he was able to correct with full right aileron input. The aircraft then commenced a second uncommanded left roll that he was unable to correct with control inputs. The pilot, passengers and witnesses, all reported that the aircraft rolled more than 45 degrees to the left before the left wing struck the water.
The floatplane came to rest inverted and shortly after the cabin became submerged. The pilot reported that he had completed Helicopter Underwater Escape Training (HUET) previously, and that he thought that assisted him to exit the cabin quickly through the pilot's door, located on the left of the cabin. The passenger in the copilot's seat, located on the right of the cabin, was momentarily disorientated, but managed to undo his seat belt while the passenger in the middle row was attempting to locate and undo his seatbelt. The rear seat passenger was able to swim towards the front passenger and reported kicking open a door with her foot before pushing the front passenger out of the aircraft. She then returned to the middle row passenger and unfastened his seat belt buckle before pushing him out of the aircraft and then exiting the submerged cabin herself. One passenger reported that he was initially disoriented after the aircraft entered the water. In addition, given the rapid nature of the event and the need to exit the inverted cabin quickly, the passengers did not retrieve the life jackets which were stowed underneath their seats. It was likely that all passengers exited the floatplane via the pilot's door, because the co-pilot's door was still locked closed when the aircraft was recovered.
The floatplane stayed inverted with its floats remaining buoyant. After exiting the aircraft, the passengers were picked up by a passing boat. The pilot remained with the aircraft and secured it to a boat.
The load chart for the flight showed that the aircraft was within weight and balance limitations. The pilot was appropriately licensed and endorsed for the operation and was experienced in floatplane operations in Sydney Harbour. The aircraft was capable of normal operations before flight and there were no known maintenance issues.
A Bureau of Meteorology (BoM) report of the weather in Sydney Harbour at the time of the accident, showed that the prevailing wind around the time of the accident was from the north-east, averaging 26 to 29 kts, with gusts reaching 37 kts. The report also suggested that:
…in considering the wind shear that would have been experienced by a plane taking off from Rose Bay, the sheltering effect of the surrounding topography, especially the shielding of Rose Bay from north easterlies by the southern headland of Sydney Harbour, needs to be taken into account. It is conceivable that in passing from the relatively sheltered inshore waters of Rose Bay to a more exposed location, either through ascent or forward motion or both, that significant wind shear may have been experienced.
The pilot advised that he used a number of cues to determine the wind velocity, particularly the orientation of moored boats and flags, the BoM forecast and the water conditions.
Mountain waves and their turbulence can occur downwind of any obstacle, including an isolated hill a few hundred feet high. If the wind at the altitude of the top of the obstacle is 20 kts or more, there will be noticeable wave turbulence and significant downdrafts. This turbulence will be greatest in the rotor zone in the lee of the obstacle and will be at a maximum at about the same altitude as the top of the obstacle.1
The company ALA register notation for Rose Bay warned that 'Dumping will be encountered in winds over 20 kts from the North East, South and West'. The significant downdrafts described in the previous paragraph are what the operator's ALA register referred to as 'dumping'.
A fact sheet on mountain wave turbulence that accompanied Australian Transport Safety Bureau (ATSB) report BO/200104092 into an accident involving mechanical turbulence stated in part that:
In addition to generating turbulence that has demonstrated sufficient ferocity to significantly damage aircraft or lead to loss of control, the more prevailing danger to aircraft in the lower levels in Australia seems to be the effect on an aircraft's climb rate. General Aviation aircraft rarely have the performance capability sufficient to enable the pilot to overcome the effects of a severe downdraft generated by a mountain wave, or the turbulence or the windshear2 generated by the rotor.
The Pilots Operating Handbook (POH) for the Cessna 185 indicated that the stalling speed in a 20 degree flap configuration, at a mid-range centre of gravity, was 55 kts. The POH also indicated a maximum demonstrated crosswind velocity for takeoff and landing of 13 kts. The investigation determined that the crosswind for the accident flight would have been between 19 and 24 kts.
In December 2001, the ATSB investigated an accident involving a floatplane in Tasmania where the occupants had insufficient time to don life jackets before exiting the aircraft (see ATSB report BO/200105932). That accident investigation highlighted that regulations governing the use of life jackets, do not reflect the operational realities of exiting from an inverted submerged cabin.
Civil Aviation Order (CAO) 20.11 part 5.1.4 stated that:
Amphibious aircraft when operating on water, helicopters equipped with fixed flotation equipment when operating on water, and all seaplanes and flying boats on all flights shall be equipped with:
(a) 1 life jacket for each occupant; and
(b) an additional number of life jackets (equal to at least one-fifth of the total number of occupants) in a readily accessible position near the exits.
CAO 20.11part 5.1.4 stated that:
Life jackets shall be so stowed in the aircraft that 1 life jacket is readily accessible to each occupant and, in the case of passengers, within easy reach of their seats.
CAO 20.11 part 5.1.8 stated that:
Where life jackets are required to be carried in accordance with paragraph 5.1.4 each occupant of a single engine aircraft shall wear a life jacket during flight over water when the aircraft is operated beyond gliding distance from land or water, as appropriate, suitable for an emergency landing. However, occupants need not wear life jackets when the aircraft is taking-off or landing at an aerodrome in accordance with a normal navigational procedure for departing from or arriving at that aerodrome, and occupants of aeroplanes need not wear life jackets during flight above 2 000 feet above the water.
Federal Aviation Administration Advisory Circular (AC) 91-69A contained recommendations and revised information for the safe operation of seaplanes. The AC stated that:
Life jackets in sealed pouches can be awkward to remove and don in a flooded aircraft. When a survivor attempts to put on a jacket in the water, it may be difficult to find and fasten its straps and hooks. It would take considerable effort to accomplish the combined maneuver [sic] of pulling a lifejacket over one's head while in the water trying to stay afloat. If a life preserver is not worn before flight, it is practically impossible for a survivor with an injured arm, for example, to don the life preserver in time for it to be effective for survival. Wearing an uninflated TSO C13f life preserver at all times in the seaplane and inflating it only after exiting the seaplane would seem to be the best protection.
Furthermore, the AC stated that after a seaplane accident:
and especially while submerged inverted in water, the passengers are likely to become disoriented and panic.
It also stated that:
Maneuvring [sic] while holding flotation devices can also be disorienting because it occupies the hands, making swimming or treading water difficult.
Additionally the AC stated in Section 1.b. (1)
For-hire operators must use FAA-approved PFD's. A PFD should be worn by each occupant while on the seaplane.
1. Modern Airmanship, Eighth Edition, Van Nostrand Reinhold Company, New York, 1999.
2. A change of wind velocity with distance along an axis at right angles to wind direction, specified vertically or horizontally. Recognised as an extremely dangerous phenomenon because encountered chiefly at low altitude (in squall or local frontal systems) in approach configuration at speed where it makes sudden and potentially disastrous difference to airspeed and thus lift.
