Approved for Ditching

The fifth anniversary of the Sully and Jeff splash down in the Hudson River reminded me of a little know fact. Did you know that most transport category airplanes are approved for ditching?

The idea that a normal landplane could be certified for a water landing had never crossed my mind. On the surface—pun intended—it sounds both impossible and ridiculous.

I became aware of the rather new aspect of the certification standards about 25 years ago when a couple of newly approved business jets had little flip-up panels at the bottom of the cabin entry door. After closing the door you raised the panel. When I asked what the heck that thing was for I was told that it would keep the water out to meet the ditching approval requirements.

I asked if the manufacturer had actually splashed one of the prototype jets down to see if that door panel or any other feature of the airplane worked in a water landing. The answer is, of course, no. Earning ditching certification is entirely an analytical process.

The rules that define acceptable ditching are in FAR 25.801. In general, the aim of the rule is to have some assurance that the airplane will remain afloat long enough for all passengers to exit in the same 90 second time limit required for emergency exit on the ground. A manufacturer must show that passengers won’t be immediately injured by the water landing.

The analysis of a ditching outcome must use whatever experience resulted from ditching of similar airplanes in the past. For example, if the engines are wing mounted, how did a similar configuration fare during an actual ditching. There haven’t been many ditchings so there isn’t a lot of historical data available. And every ditching has occurred in a wide range of water surface conditions which has everything to do with how a ditching would work out.

Cabin volume and empty space in the wings that won’t immediately flood with water provide a guess at the buoyancy of the airplane once it stops in the water. Windows and door openings must be strong enough to survive the ditching and at least initially be above the expected water line.

The only actual testing of a design uses models. The placement of engines, flap position, scoops that may let in water and other “projections” must be considered during the model testing.

When I first saw the video of the Airbus touching down on the Hudson, how it held together, and how it floated with at least the forward door sills above the water line I remembered my skepticism about the ditching rules. The certification procedures worked. Sully and Skiles did a great job with the approach and landing, but still, the Airbus behaved pretty much as expected.

Of course, the Hudson River is nothing like the open ocean that could have huge swells and waves traveling over or even across the swells. The Hudson on that day was as close to a real life test tank as you could hope for.

There is no equivalent certification standard for ditching light airplanes, which makes sense. Paying passengers deserve every possible safety consideration but for those of us who fly for our own reasons we get to make our own decisions and guesses on how a ditching, or any forced landing of any kind for that matter, will turn out.

The actual powerless approach of the Airbus and splash down were not exactly what the ditching certification predicted. The aft doors were under water which was not expected. And there wasn’t time for the pilots to complete every emergency checklist item because the situation involved several different lists including total loss of thrust and ditching. But the ditching worked. I have to take back the snarky things I said and wrote about the whole concept of approving an airplane for ditching. And the ditching certification procedures will be improved as a result of the Miracle on the Hudson, but batting one for one is a good start.

 

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10 Responses to Approved for Ditching

  1. Bill Tomlinson says:

    So there you are, flying over the sea, minding your own business, when it all goes quiet. But wait! Your aircraft is not approved for ditching!!

    So you’ll just have to wait up there in the sky until somebody comes to rescue you.

    Isn’t bureaucracy marvelous?

  2. Yes it is. I wonder what an LSA with it’s mandatory fixed gear would look like after a ditching.

  3. Keith Walker says:

    As a retired Aircraft Certification Engineer with Transport Canada I was delighted to see Mac McClellan’s article Approved for Ditching on FAR 25.803. For the certification of our Challenger jet, models were used for ditching tests.
    There is a big subject here in Certification which I would like to say, EXPOSE to the aircraft community, ie namely certification to the Design Standards which are often looked upon as merely Govt bureaucracy and rules . The FARS both 23 and 25 and others really show how to design an aircraft safely and are extremely knowledgeable and in many cases information used from of accidents and incidents. They are not perfect but as seen from the present discussion, just ditching and passenger exit can and has saved many lives.
    I have thought of writing a book to show how important and wide reaching these Design standards are and would like EAA to open up this subject with articles.
    I would be ready to help with such articles. Keith Walker. k.j.wlk@rogers.com

    • Mac says:

      You are so right, Keith. It has been forever true that we learn from our mistakes, often very costly ones, in aviation. As imperfect as they are, the ditching standards no doubt played an important role in the outcome of the Hudson splashdown.
      And I’m happy to say similar lessons have and continue to be learned in the homebuilt world.
      Bests,
      Mac Mc

      • Keith Walker says:

        Mac. Thanks for your prompt reply and concurrence but no comments on my suggestion to Expose the FAR requirements further to the aviation community by writing articles on them. I have also worked in the OEM’s for many years(Boeing 707,727,737,Chinook- Canadair/Bombardier aircraft) as well as Govt Certification and when I moved over to Govt was greatly enlightened too see how much the Govt was contributing to aircraft design and safety with the FAR’s etc. The EAA seems to be interested in keeping friendly with the FAA, probably good politics but I would like to see more appreciation and respect of the Govt effort. Note the 90 second rule was very effective in the A330 crash in Toronto which had the doors closed on one side due to fire and no lives lost and few injuries. Guess most people only see the Govt from the outside and not many from the inside. I have dealt with the FAA many times and always found them to be courteous and knowledgeable people.
        Keith Walker. PEng and also hold a PPL.

    • Bill Tomlinson says:

      Nothing to do with ditching, but something else I should like to see implemented is a long-time suggestion from BALPA [British Airline Pilots Association], which is that airliner doors should be fitted with explosive bolts so that the pilot can blow them off if he sees an impact coming. All too often people die because doors are jammed by impact damage.

      It happened to a friend of mine, in a C206. He was going into a “difficult” bush strip, with a line of trees next to the runway. He wasn’t happy with his approach, so inaugurated a go-round – right decision – but drifted sideways and clipped the top of the trees. This caused the 206 to make a very heavy landing, heavy enough to rip the landing gear off.

      And, crucially, to buckle the door-frames. As he and his passengers struggled to open the doors, the nearly-full fuel tanks caught fire. When I went to his funeral I knew the coffin contained only sandbags.

      Ever since I have made a point of unlatching the doors before touch-down at any questionable strip.

  4. Douglas says:

    You say the “The aft doors were under water which was not expected. ” I thought the aft doors of an Airbus are not supposed to be used in a water landing? I had assumed that was because they did expect them to be under water. If I remember correctly a passenger opened the rear door in a panic and the crew tried to close it again?

  5. Pingback: Ditching Certification | High Altitude Flying Club

  6. Keith Walker says:

    The FAR’s address safety. FAR 25 for Transport aircraft have highest level of safety naturally as passenger aircraft. FAR 23 much lower level of safety as few passengers carried . Money has lot to do with level of safety chosen. Keith Walker

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