Not every airliner is certified to land on water. The regulation that covers it opens with a conditional: “If certification with ditching provisions is requested.” Ditching approval is something a manufacturer asks for, not something every aeroplane has.
What follows comes from 14 CFR 25.801, the certification rule for ditching, and 14 CFR 121.339, which sets the equipment an airliner must carry over water.
Ditching certification is optional, and that is the first surprise
An aeroplane only has to meet 25.801 if the manufacturer asks for ditching provisions. When they do, the aircraft must also satisfy the rules on emergency exits above the waterline, on liferafts, and on emergency lighting.
The core requirement is written in plain terms. Every practicable design measure must be taken to minimise the chance that, in an emergency landing on water, the aircraft behaves in a way that injures occupants immediately or traps them inside.
Note what that does not say. It does not promise the aeroplane will float, stay upright, or remain intact. It requires the manufacturer to have taken every practicable step, and to have proven what the aircraft will probably do.
How the behaviour is proven, and why it is “probable”
The rule requires the probable behaviour in a water landing to be investigated either by model tests or by comparison with aircraft of similar configuration whose ditching characteristics are already known. Nobody ditches a real airliner to find out.
The regulation names what has to be accounted for: scoops, flaps, projections, and anything else likely to affect how the airframe behaves hydrodynamically. These are the parts that catch water and decide whether the aircraft skips, digs in or breaks up.
There is also a quiet structural requirement at the end. Unless the investigation already accounts for external doors and windows collapsing, those doors and windows must be designed to withstand the probable maximum local pressures. Someone has to have calculated what the water will do to them.
Floating long enough is the actual standard
The test is not whether the aircraft floats. It is whether, under reasonably probable water conditions, flotation time and trim allow the occupants to get out and into the liferafts.
Two details make that honest rather than optimistic:
- If flotation is shown by buoyancy and trim calculation rather than testing, appropriate allowances must be made for probable structural damage and leakage. The sums have to assume the aeroplane is already broken.
- Fuel tanks with jettisoning provisions that could reasonably be expected to survive a ditching without leaking may be counted as buoyancy volume. Empty tanks are part of what holds the aircraft up.
Trim matters as much as time. An aircraft floating nose down with the exits underwater has satisfied nothing, however long it stays on the surface.
What the aircraft must carry over water
For extended overwater operations, 121.339 lists the equipment precisely.
- A life preserver for every occupant, each with an approved survivor locator light.
- Enough liferafts for everyone, each with a locator light.
- At least one pyrotechnic signalling device per raft.
- An approved survival type emergency locator transmitter.
- A survival kit attached to each raft, equipped appropriately for the route being flown.
The raft requirement contains the detail most people miss. Unless there are excess rafts, the buoyancy and seating capacity beyond the rafts’ rated capacity must accommodate everyone in the event of a loss of one raft of the largest rated capacity. The fleet of rafts has to work with the biggest one missing, because in a real ditching one may be unusable or simply float away.
The line that is designed to let go
The equipment rule, 14 CFR 25.1415, contains the single best piece of thinking in the whole subject.
Each raft must have a trailing line, and a static line designed to hold the raft near the airplane but to release it if the airplane becomes totally submerged.
Both failure modes are accounted for in one sentence. A raft that is not tethered drifts away from the people still climbing out. A raft that is tethered too well gets pulled under with the aircraft. The answer is a line that holds, then deliberately fails at exactly the moment holding becomes lethal.
The same section closes the loop on certification. An aeroplane not certificated for ditching, and without approved life preservers, must still carry an approved flotation means for every occupant, within easy reach of each seated occupant and readily removable from the aircraft. Optional certification does not mean nothing in the cabin.
Reachable without preparation
The rule anticipates that a ditching may arrive with no warning. The rafts, life preservers and the survival ELT must be easily accessible in the event of a ditching without appreciable time for preparatory procedures, installed in conspicuously marked, approved locations.
That is the regulation acknowledging the realistic case. Not the briefed, planned descent to a calm sea, but the one where the crew have seconds and the cabin has to work anyway.
Frequently asked questions
Are all airliners certified for ditching?
No. Ditching provisions are certified only if the manufacturer requests them. An aircraft without that certification has not been shown to meet 25.801, though it still carries the overwater equipment required for its operations.
Will a plane float after landing on water?
The standard is not indefinite flotation. It is that flotation time and trim allow occupants to leave and reach the liferafts, under reasonably probable water conditions, with allowances made for structural damage and leakage.
Why are there more liferaft places than passengers?
Because the rules assume one raft will be lost. Unless excess rafts are carried, the remaining capacity must still accommodate everyone after losing the largest raft.
What is in the survival kit on a liferaft?
The regulation does not fix a universal list. It requires a survival kit appropriately equipped for the route being flown, which is why a North Atlantic kit differs from a tropical one.
Do empty fuel tanks help a plane float?
Yes, and the rule says so. Fuel tanks with jettisoning provisions that could reasonably survive a ditching without leaking may be counted as buoyancy volume in the calculations.
Sources
The certification requirements, the model test provision, the flotation and trim standard, the fuel tank buoyancy allowance and the door and window pressure rule are from 14 CFR 25.801. The equipment list, the lost raft provision, the accessibility requirement and the survival kit rule are from 14 CFR 121.339. Both were read from the current edition on 12 October 2026. These are US rules; other regulators set their own ditching and overwater requirements.
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