US Airways Flight 1549

Investigation

The partially submerged plane was towed downstream and moored to a pier near the World Financial Center in Lower Manhattan, roughly 4 miles (4 mi) from the ditching location. On January 17, the aircraft was taken by barge to New Jersey. The left engine, which had been detached from the aircraft by the ditching, was recovered from the riverbed on January 23.

The initial National Transportation Safety Board (NTSB) evaluation that the plane had lost thrust after a bird strike was confirmed by analysis of the cockpit voice and flight data recorders.

It was found in the investigation that two days before the accident, the aircraft had experienced a compressor stall on the right engine, but the engine had restarted and the flight was completed. A faulty temperature sensor was found to be the cause of the compressor stall. This sensor had been replaced and the inspection also verified the engine had not been damaged in that incident.

On January 21, the NTSB found evidence of damage from a soft-body impact in the right engine along with organic debris including a feather. The left engine also showed soft-body impacts, with "dents on both the spinner and inlet lip of the engine cowling. Five booster inlet guide vanes are fractured and eight outlet guide vanes are missing." Both engines, missing large portions of their housings, were sent to the manufacturer for examination. On January 31, the plane was moved to Kearny, New Jersey. The bird remains were later identified by DNA testing to be Canada geese, which typically weigh more than engines are designed to withstand ingesting.

Since the plane had been assembled in France, the European Aviation Safety Agency (EASA; the European counterpart of the FAA) and the Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA; the French counterpart of the NTSB) joined the investigation, with technical assistance from Airbus and GE Aviation/Snecma, respectively the manufacturers of the airframe and the engines.

The NTSB used flight simulators to test the possibility that the flight could have returned safely to LaGuardia or diverted to Teterboro; only seven of the thirteen simulated returns to La Guardia succeeded, and only one of the two to Teterboro. Furthermore, the NTSB report called these simulations unrealistic: "The immediate turn made by the pilots during the simulations did not reflect or account for real-world considerations, such as the time delay required to recognize the bird strike and decide on a course of action." A further simulation, in which a 35-second delay was inserted to allow for those, crashed. In testimony before the NTSB, Sullenberger maintained that there had been no time to bring the plane to any airport and that attempting to do so would likely have killed those onboard and more on the ground.

The Board ultimately ruled that Sullenberger had made the correct decision, reasoning that the checklist for dual-engine failure is designed for higher altitudes when pilots have more time to deal with the situation, and that while simulations showed that the plane might have just barely made it back to LaGuardia, those scenarios assumed an instant decision to do so, with no time allowed for assessing the situation.

On May 4, 2010, the NTSB issued its final report, which identified the probable cause as "the ingestion of large birds into each engine, which resulted in an almost total loss of thrust in both engines". The final report credited the outcome to four factors: good decision-making and teamwork by the cockpit crew (including decisions to immediately turn on the APU and to ditch in the Hudson); that the A320 is certified for extended overwater operation (and hence carried life vests and additional raft/slides, despite those not being required for that route); the performance of the flight crew during the evacuation; and the proximity of working vessels to the ditching site. Contributing factors were good visibility and fast response times from the ferry operators and emergency responders. The report made 34 recommendations, including that engines be tested for resistance to bird strikes at low speeds; development of checklists for dual-engine failures at low altitude, and changes to checklist design in general "to minimize the risk of flight crewmembers becoming stuck in an inappropriate checklist or portion of a checklist"; improved pilot training for water landings; provision of life vests on all flights regardless of route, and changes to the locations of vests and other emergency equipment; research into improved wildlife management, and technical innovations on aircraft, to reduce bird strikes; research into possible changes in passenger brace positions; and research into "methods of overcoming passengers' inattention" during preflight safety briefings.

Author and pilot William Langewiesche asserted that insufficient credit was given to the A320's fly-by-wire design, by which the pilot uses a side-stick to make control inputs to the flight control computers. The computers then impose adjustments and limits of their own to keep the plane stable, which the pilot cannot override even in an emergency. This design allowed the pilots of Flight 1549 to concentrate on engine restart and deciding the course, without the burden of manually adjusting the glidepath to reduce the plane's rate of descent. Sullenberger, however, said that these computer-imposed limits also prevented him from achieving the optimal landing flare for the ditching, which would have softened the impact.