An emergency landing is a prioritized landing made by an aircraft in response to an emergency containing an imminent or ongoing threat to the safety of:
1- Operation of the aircraft.
2- A passenger /crew on board (such as a medical emergency).
It is usually a forced diversion to the nearest or most suitable airport or airbase, in which air traffic control must prioritize and give way immediately upon the declaration of the emergency.
Of course, during aircraft design, they take into consideration the redundancy for all vital systems, for example almost all commercial aircraft has 3 hydraulic systems with 3 or more independent pressure pump source with independent feed and return pipes , also the hydraulic pump types redundancy ,you can find EDP (Engine Driven Pump) and electrical pump as redundancy in same hydraulic system , in some hydraulic systems designs you can find PTU (Power Transfer Unit) to pressurize hydraulic system from other hydraulic system as redundancy
What are Emergency Landing Causes?
There are many causes for emergency landing, for example and not limited to:
- Emergency medical for any of human been on board.
- Engine failures.
- Major failure in any system may affect directly / indirectly on aircraft safety (hydraulic system, pneumatic system, fuel system…)
- Structure damage (like what may happen as a result of bird strike or lightning strike).
- Tire burst.
- Partial or complete failure in cabin pressure.
- Smoke or fire (after proper action to fir extinguish and eliminate the smoke)
What are the Types of Emergency Landing?
- Forced landing: the aircraft is forced to make a landing due to technical problems. Landing as soon as possible is a priority, no matter where, since a major system failure has occurred or is imminent. It is caused by the failure of or damage to vital systems such as engines, hydraulics, or landing gear, and so a landing must be attempted where a runway is needed but none is available. The pilot is essentially trying to get the aircraft on the ground in a way which minimizes the possibility of injury or death to the people aboard. This means that the forced landing may even occur when the aircraft is still flyable, in order to prevent a crash or ditching situation.
- Precautionary landing: may result from a planned landing at a location about which information is limited, from unanticipated changes during the flight, or from abnormal or even emergency situations. This may be as a result of problems with the aircraft, or a medical or police emergency. The sooner a pilot locates and inspects a potential landing site, the less the chance of additional limitations being imposed by worsening aircraft conditions, deteriorating weather, or other factors.
- Ditching: is the same as a forced landing, only on water. After the disabled aircraft contacts the surface of the water, the aircraft will most likely sink if it is not designed to float, although it may float for hours, depending on damage.
The FAA does not require commercial pilots to train to ditch but airline cabin personnel must train on the evacuation process. In addition, the FAA implemented rules under which circumstances (kind of operator, number of passengers, weight, route) an aircraft has to carry emergency equipment including floating devices such as life jackets and life rafts.
Some aircraft are designed with the possibility of a water landing in mind. Airbus aircraft, for example, feature a "ditching button" which, if pressed, closes valves and openings underneath the aircraft, including the outflow valve, the air inlet for the emergency RAT, the avionics inlet, the extract valve, and the flow control valve. It is meant to slow flooding in a water landing
How often Emergency Landing happen?
The good news is that large aircrafts have multiple engines and redundant systems, so emergency landings are extremely rare for them, but even that some notable ones have occurred.
As a result of neat aviation accident investigations and corrective / preventive actions taken by the authorities in form of AD’s issuance, the traveling by airplane are the safest traveling method today.
As 2016 statistics, there were only 185 emergency landings total in the domestic U.S. out of an estimated 9.7 million flights — all of which concluded without incident. That's a nerves-alleviating 0.00002 % chance of having an emergency landing.
Who is responsible for aviation accident investigations?
“The State of Occurrence shall institute an investigation into the circumstances of the accident and be responsible for the conduct of the investigation, but it may delegate the whole or any part of the conducting of such investigation to another State by mutual arrangement and consent. In any event the State of Occurrence shall use every means to facilitate the investigation.” ICAO annex 13- CHAPTER 5. INVESTIGATION RESPONSIBILITY FOR INSTITUTING AND CONDUCTING THE INVESTIGATION
Of course, you will find more details in above reference as it may differ according to circumstances like the accident / incident locations.