Qantas has been reluctant to talk about one of its airliner types, the high wing Dash 8 turboprops, since the 16 January ditching of a US Airways A320 in the Hudson River.
This is because a Dash 8 will most likely float, wings level but cabin submerged, soon after even the most benign of water landings.
It’s just a fact of life for high-wing aircraft. The wings are a major source of buoyancy, especially if full of fuel which is lighter than water, on any airliner, and because the cabin is slung under the wings it will go under water. Quickly but not necessarily immediately.
Qantas would actually have a pretty good story to tell about high-wing ditchings, and perhaps its reluctance is driven by not wanting to frighten people by discussing how such an incident could end well, just like the US ditching.
We spoke to some people with experience in safety training in high wing turboprops. But let’s start with an authoritative source in the US who hasn’t been filtered through the PR process.
“The US Airways incident appears to have verified all of the assumptions and values required for all types of airliners to meet the ditching standards that are a part of certification,” he says.
“This provides us with complete confidence that the ditching behaviour of airplanes like the Dash 8 and ATRs (which have high wings) will not cause immediate injury to the occupants or make it impossible for them to escape.”
So how do they escape if the cabin is about to go under water?
“You are trained to release the life rafts and get people through the doors into the water so fast you wouldn’t know it,” says a former flight attendant familiar with the procedures.
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“The cabin will not be level, and this will lift one set of exits higher than the other. On flights to Lord Howe Island we had even fewer than normal seats and two of us, so the level of close supervision of passengers prior to ditching ensures everyone has vests on, shoes off, and knows that everything is going to happen quickly and knows they are going to be close to the rafts.”
There is also an escape hatch in the roof of the cockpit which would remain clear of the water until, inevitably, the turbo-prop sinks. It is treated as a certainty in a ditching that an airliner of any type will rapidly take on so much water that it sinks.
While the spokesperson for Qantas would not discuss the moments during which the Dash 8 cabin might resemble a semi-submersible coral viewing boat on the Great Barrier Reef, he did provide the following guidance:-
The DHC 8 is capable of making a emergency water landing under a wide range of ditching conditions.
The maximum acceleration imposed on the DHC 8 during ditching are within the design envelope of the aircraft and no major structural failure will occur.
The structural strength of the belly will be adequate to sustain the pressure of the ditching impact.
No significant leakage will result.
The buoyancy and trim calculations suggest the centre of gravity will move slightly aft in the water. This will keep the aircraft in stable equilibrium flotation.
It has been shown that doors, hatches and windows will either not be damaged during ditching or they will have no influence on the predicted ditching and subsequent floating behaviour of the DHC 8.