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.