Ditching switch on Airbus A320

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Chesley Burnett “Sully” Sullenberger III was hailed as an aviation hero Friday, the day after he guided a US Airways jetliner carrying 155 passengers and crew to safety when its engines failed shortly after taking off from New York’s LaGuardia Airport.

A320 has a design feature known as a “ditching switch” that seals underside of the jet in the event of a water landing — to make the aircraft more buoyant. The pilots never activated it. Instructions to do so are at the end of a three-page check list for a twin-engine failure. The co-pilot, Skiles, did not have time to finish the check list in the roughly three minutes from bird impact to water touchdown.

It is possible that the passengers would have had more time to exit the plane had the “ditching switch” been activated.

Why can’t the plane’s software automatically activate the “ditching switch” when it senses that a belly landing is imminent? This can be done using inputs from the radio altimeter, landing gear position, speed, attitude (pitch) etc. This will remove one item from the checklist.

Typically when a plane lands belly up (i.e without extending the landing gear), there are 3 reasons:

  1. The pilots are unable to confirm that all the wheels down and locked and so decide to land belly up on the runway — as this is a better option than to land and have the landing gear collapse. They have plenty of time to make the decision to land belly up and so will be able to go thru the checklist for this scenario.
  2. The pilot forgets to lower the landing gear and lands belly up. There is a saying in the aviation community: “There are 2 kinds of pilots, those who have landed a plane belly up and those who will”. Nevertheless, this typically happens in small planes which are less automated, that require only a single pilot and where the pilot has less than a couple of hundred hours of experience.
  3. Ditching — which means landing on water. If you land on water with the gears down, the plane will most likely tumble. So, pilots of retractable gear planes will elect to land on water belly up.

It won’t matter if the ditching switch is in activated in the case where the plane lands belly-up on a concrete runway (case #1). The plane will anyway require quite a bit of repair before it is brought back to service.

About Babu Srinivasan

My interests are in computer security, cryptography, functional programming and general aviation. I occasionally write articles on these and other topics in my blog.

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