Sources close to the on-going investigation of US Airways Flight 1549 say that the Airbus A320's number one (left) engine continued to run at approximately 35% fan speed (N1) during the three-minute window between striking birds at 3,200ft and ditching in the Hudson River on 15 January.
Though limited, the left engine's speed would have been adequate to keep the aircraft's generators and hydraulic systems on-line, providing "normal" flight control laws and communications as well as giving pilots ability to deploy flaps and slats, elements that proved critical to performing a low-speed water landing. To maintain altitude on a single engine however, experts say the powerplant would have had to been running at 70% N1 or more.
Investigators planned to retrieve the left engine, which broke from the aircraft during the ditching, from the river bottom 23 January or 24 January to perform an inspection.
ATI affiliate Flight International has learned that the aircraft touched down at 125-130kt airspeed with flaps and slats both in the "2" position, or midpoint, position. An A320 normally lands at 120-125kt with fully deployed flaps and slats.
Officials have also confirmed that the A320's Hamilton Sundstrand-built ram air turbine (RAT) had deployed from its compartment near the root of the left wing during the event, and that the Honeywell auxiliary power unit in the tail had been operating. Though the RAT will deploy automatically when engine or electric power drops below a threshold, pilots can also manually deploy the propeller-driven emergency system. The device provides power to one of three hydraulic systems onboard which would have given pilots the ability to deploy slats but not flaps.
Sources tell Flight International that the first officer tried to relight the left engine during the descent, which averaged 1,000ft per minute, but that the engine did not respond other than to continue spinning at 35% N1. It's possible the pilots restarted the APU in order to have bleed air available to help restart the left engine as the A320's airspeed was relatively low.
Pilots review ditching procedures in textbooks during recurrent training but do not practice the events in simulators as there are no test-verified models available. Pilots do, however, practice double engine-out scenarios with a re-light afterward.
The National Transportation Safety Board (NTSB) has completed its interviews of the pilots, flight attendants and air traffic controllers and was working to wrap up its fact finding with passengers and a crew that two days earlier experienced a compressor stall on the accident aircraft. That event does not appear to be related to the 15 January accident.