Understanding Air Safety in the Jet Age/Wildlife Encounters/Bird Strikes/Cactus 1549

A partially submerged Airbus A320 with front emergency slides deployed and people standing on its wings

On January 15, 2009, US Airways Flight 1549, an Airbus A320 on a flight from New York City's LaGuardia Airport to Charlotte, North Carolina, struck a flock of birds shortly after take-off, losing all engine power. Unable to reach any airport for an emergency landing, pilots Chesley Sullenberger and Jeffrey Skiles glided the plane to a ditching in the Hudson River off Midtown Manhattan. All 155 people on board were rescued by nearby boats, with a few serious injuries.

This water landing of a powerless jetliner became known as the Miracle on the Hudson and a National Transportation Safety Board official described it as "the most successful ditching in aviation history". The pilots and flight attendants were awarded the Master's Medal of the Guild of Air Pilots and Air Navigators in recognition of their "heroic and unique aviation achievement". But what went wrong to make this superb airmanship necessary?

Background

N106US, the aircraft involved in the accident, at LaGuardia eight years earlier, while operating for US Airways Shuttle.

US Airways Flight 1549 with call sign 'Cactus 1549' was scheduled to fly from New York City's LaGuardia Airport Charlotte Douglas International Airport. The aircraft was an Airbus A320-214 powered by two GE Aviation/Snecma-designed turbofan engines. Delivered in 1999, the plane, registered N106US, was one of 74 A320s then in service at US Airways. At the time of the accident, the aircraft was 9.6 years old. The captain and pilot in command, 57-year-old Chesley Sullenberger, was a former fighter pilot who had been an airline pilot since leaving the United States Air Force in 1980. He was also a qualified glider pilot which would stand him in good stead as the accident developed.

Accident

Takeoff and bird strike

The flight was cleared for take off to the northeast from LaGuardia's Runway 4 at 3:24:56 pm Eastern Standard Time. With Skiles in control, the crew made its first report after becoming airborne at 3:25:51 as being at 700 feet and climbing.

The Hudson River from above the Bronx, with Manhattan in the diagonal centre and New Jersey in the distance. The George Washington Bridge is at right, Central Park Reservoir at upper left, and Teterboro Airport at the right centre within the elbow of the Overpeck Creek.

Flight path flown (red). Alternative trajectories to Teterboro (dark blue) and back toward La Guardia (magenta) were simulated for the investigation.

At 3:27:11 during the climb, the plane struck a flock of Canada geese at an altitude of 2800 feet about 4.5 miles north-northwest of LaGuardia. The pilots' view was filled with the large birds; passengers and crew heard very loud bangs and saw flames from the engines, followed by silence and an odour of jet fuel. Realising that both engines had shut down, Sullenberger took control while Skiles worked the checklist for engine restart. With the engines stopped, the plane lost its primary source of electrical and hydraulic power for the flight control systems. However, an auxiliary power unit and a ram air turbine can provide backup hydraulic pressure and electrical power at certain speeds. Both backup systems began to operate as the plane descended onto the river. The aircraft slowed but continued to climb for a further 19 seconds then began a glide descent.

At 3:27:33, Sullenberger radioed a mayday call "... this is Cactus 15, hit birds. We've lost thrust on both engines. We're turning back towards LaGuardia". New York air traffic controller Patrick Harten told LaGuardia's air traffic control tower to hold all departures, and directed Sullenberger back to Runway 31. Sullenberger responded, "Unable".

Sullenberger asked controllers for landing options in New Jersey, mentioning Teterboro Airport. Permission was given for Teterboro's Runway 1. Sullenberger initially responded "Yes", but then: "We can't do it... We're gonna be in the Hudson".> The aircraft passed less than 900 feet above the George Washington Bridge. Sullenberger commanded over the cabin address system, "Brace for impact", and the flight attendants relayed the command to passengers. Meanwhile, air traffic controllers asked the Coast Guard to caution vessels in the Hudson and ask them to prepare to assist with rescue.

Ditching and evacuation

Coast Guard video of the water landing, and rescue

About ninety seconds later, at 3:31 pm, the plane made an unpowered ditching, descending southwards into the middle of the North River section of the Hudson tidal estuary roughly opposite West 50th Street. Flight attendants compared the ditching to a "hard landing" with "one impact, no bounce, then a gradual deceleration." The ebb tide began to take the plane southward.

Sullenberger opened the cockpit door and gave the order to evacuate. The crew began evacuating the passengers through the four overwing window exits and into an inflatable slide/raft deployed from the front right passenger door (the front left slide failed to operate, so the manual inflation handle was pulled). The evacuation was made more difficult by the fact that someone opened the rear left door, allowing more water to enter the plane. Water was also entering through a hole in the fuselage and through cargo doors that had come open, so as the water rose the attendant urged passengers to move forward by climbing over seats. The situation may have been improved if the pilots had activated the Airbus A320 system that closes valves and other openings in the fuselage, in order to slow flooding after a water landing. Sullenberger later said this would have made little difference since the water impact tore substantial holes in the fuselage. Sullenberger walked the cabin twice to confirm it was empty before himself abandoning the plane.

The air and water temperatures were about -7 Celsius and 5 Celsius respectively. Some evacuees waited for rescue knee-deep in water on the partially submerged slides, some wearing life vests. Others stood on the wings or, fearing an explosion, swam away from the plane. One passenger, after helping with the evacuation, found the wing so crowded that he jumped into the river and swam to a boat.

Rescue

The plane had ditched near boats, which facilitated rescue. Two NY Waterway ferries arrived within minutes and began taking people aboard; numerous other boats, including from the US Coast Guard, were quickly on scene as well. Sullenberger advised the ferry crews to rescue those on the wings first, as they were in more jeopardy than those on the slides, which detached to become life rafts. The last person was taken from the plane at 3:55 pm. About 140 New York City firefighters responded to nearby dock while other agencies provided medical help on the Weehawken side of the river, where most passengers were taken.

Investigation

The plane being recovered from the river during the night of January 17

The initial (NTSB) evaluation that the plane had lost thrust after a bird strike was confirmed by analysis of the cockpit voice and flight data recorders. On January 21, the NTSB found evidence of soft-body damage in the right engine along with organic debris including a feather. The left engine also evidenced soft body impact, 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. The bird remains were identified by DNA testing to be Canada geese, which typically weigh more than engines are designed to withstand ingesting.

Goose feather found in the left engine

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 auxiliary power unit and to ditch in the Hudson); the fact that the A320 is certified for extended overwater operation (and hence carried life vests and additional raft/slides) even though not 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. However, Sullenberger said that these computer-imposed limits also prevented him from achieving the optimum landing flare for the ditching, which would have softened the impact.

Conclusion

This isn't the first time a pilot who knows how to fly a glider has, potentially, increased the chances of surviving an accident. It's also an interesting insight into the benefits - or not - of automation. If everyone had died, maybe the A320's automation would have come in for criticism (like the later 737 MAX problems) for preventing the pilot doing what was needed. What we can say is that having a seasoned ex-military pilot is definitely a good thing because calm heads are more likely to save your life than someone panicking.