There are several cases of successful aircraft landing in water. Most famous recently is the US Airways incident in 2009, where an Airbus A320 successfully splashed down in the Hudson River after a twin engine failure on takeoff from La Guardia. In such situations, it is obviously important to make the aircraft as airtight as possible. Airbus aircraft have an automated feature to help achieve this goal.
Airbus’ ditching switch
All aircraft will have a set of procedures on what to do in the event of a ditching. Some aircraft, including many types of Airbuses, automate some of these procedures with a single switch – which we refer to here as a “ditching switch”. This is discussed in useful detail in an Airliners.net article.
The switch is present on the Airbus A320 family aircraft as well as the Airbus A330 and A340. We don’t believe it’s available on the A350 or A380. If you know different, share it in the comments.
The switch is located on an overhead panel in the cockpit, in the same set of controls as the cabin pressurization.
The switch automates several actions aimed at preparing the aircraft for ditching and making it as watertight as possible. This should slow the flooding of the aircraft by closing all open inlets, valves, etc. below the waterline and help the aircraft stay afloat longer. Based on pilot feedback, these actions include shutting down the following:
- The relief valve,
- The emergency dynamic air intake (it forces air into the cabin in the event of air conditioning failure or for smoke extraction)
- Avionics ventilation intake and exhaust valves
- Flow control valves pack
- Luggage compartment isolation valves
The actions should help the aircraft stay afloat after splashdown (this is the landing of US1549 in the Hudson River). Photo: Getty Images
Similar procedures on Boeing aircraft
It does not appear that Boeing aircraft have such a ditching switch. Some McDonnell Douglas aircraft, including the MD-11, do, however. Instead, Boeing aircraft have a set of procedures for performing similar actions included in the ditching checklist. Most valve actions and closures can be accomplished with separate switches.
It should, of course, be just as good for a well-trained pilot. In the event of a forced landing, the pilots will rigorously follow a checklist. However, an emergency ditching can be sudden and hasty, and any aircraft feature that speeds this up can only be a good thing.
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Will the switch keep the plane afloat?
It’s an interesting question – and of course, every ditching scenario is different. Sealing the inlets should definitely help keep the plane afloat longer, but not indefinitely. FAA regulations (regulation 14 CFR 25.801 for anyone wanting a full examination) state that the plane must remain afloat long enough to allow occupants to evacuate the plane. The regulations state:
“It must be demonstrated that, under reasonably probable water conditions, the float time and aircraft trim will allow occupants to exit the aircraft and enter the life rafts.”
In terms of testing, there is no need to directly test a new aircraft in ditching conditions. Instead, models can be used – and these tests can be referenced on similar aircraft (such as earlier model tests for the A300 in the case of A320 certification).
As a recent example, during the US Airways 1549 ditching in 2009, using the A320’s ditching switch would likely be out of order. The accident report does not state whether the pilot pressed the button, but the impact with the water caused damage to the fuselage that would allow water ingress in any case. Nevertheless, the aircraft remained afloat long after its evacuation.
Do you know more about these ditching switches, their functions and any other type of aircraft equipped with them? Feel free to share this in the comments.
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