Miracle on the Hudson prompts safety review

 - May 27, 2010, 10:34 AM

Although the outcome of US Airways Flight 1549 could not have been much better, the accident nevertheless prompted the National Transportation Safety Board to issue 33 recommendations to U.S. and European aviation authorities and the U.S. Department of Agriculture.

All of the 150 passengers and five crewmembers survived the Jan. 15, 2009, accident in which a US Airways Airbus A320 bound for Charlotte, N.C., was ditched into the Hudson River after striking a flock of geese shortly after departing La Guardia Airport (LGA). One flight attendant and four passengers suffered serious injuries.

“I believe the safety recommendations that have come out of this investigation have an extra- ordinary origin–a very serious accident in which everyone survived,” said NTSB chairman Deborah Hersman. “Even in an accident where everyone survives, there are lessons learned and areas that could use improvement.”

In addition to the decisions and actions of the flight crewmembers, overwater safety equipment that was not required to be on board Flight 1549, which became known as the Miracle on the Hudson, likely saved lives that might otherwise have been lost to drowning, the NTSB said. Had the aircraft not been equipped with forward slide/rafts, many of the 64 occupants of those rafts would likely have been submerged in the 41-degree water, potentially causing a phenomenon called “cold shock,” which can lead to drowning in as little as five minutes.

The accident flight had the additional safety equipment available only because the particular aircraft operated that day happened to be certified for extended overwater operations, even though current FAA regulations did not require the flight from New York to Charlotte to be so equipped.

Good visibility, calm water and proximity of passenger ferries, which rescued everyone on Flight 1549 within 20 minutes, were other post-accident factors the Safety Board credited for the survival of all aboard the aircraft.

After a 15-month investigation, the NTSB determined early last month that the probable cause of this accident was the ingestion of large birds into each engine, which resulted in an almost total loss of thrust in both engines and the subsequent ditching on the Hudson.

In addressing the hazards that birds pose to aircraft of all sizes, the report noted that most birdstrikes occur within 500 feet of the ground while Flight 1549 struck geese at 2,700 feet. Investigators said that this difference demonstrates that birdstrike hazards to commercial aircraft are not limited to any predictable circumstance.

The accident birdstrike occurred at a distance and altitude beyond the range of LGA’s wildlife hazard responsibilities and, therefore, would not have been mitigated by LGA’s wildlife management practices. “This accident was not a typical birdstrike event,” the Board said. “Therefore, this accident demonstrates that a birdstrike does not need to be typical to be hazardous.”

In addition, the largest bird used in certification testing for the CFM56 engines was four pounds, while the engines on the accident airplane encountered eight-pound Canada geese, significantly heavier than certification requirements.

The NTSB recommended that both the FAA and the European Aviation Safety Agency reevaluate the current bird-ingestion certification regulations, specifically large flocking bird certification test standards to determine whether they should apply to engines with an inlet area of less than 3,875 sq in and include a requirement for engine core ingestion.

Substantial damage to the A320 airframe was caused by the high-energy impact at the aft fuselage and the ensuing forward motion of the airplane through the water, which rendered two aft slide/rafts unavailable.

Contributing to the severity of the fuselage damage were the FAA’s approval of ditching certification without determining whether pilots could attain the ditching parameters without engine thrust, the lack of industry flight crew training and guidance on ditching techniques and the captain’s resulting difficulty maintaining his intended airspeed on final approach due to the task saturation resulting from the emergency situation.

“The captain’s difficulty maintaining his intended airspeed during the final approach resulted in high angles-of-attack, which contributed to the difficulties in flaring the airplane, the high descent rate at touchdown and the fuselage damage,” the report said, adding that he was saddled with a high workload, stress and task distraction.

Despite being unable to complete the “engine dual failure checklist,” the captain started the auxiliary power unit, which improved the outcome of the ditching by ensuring that a primary source of electrical power was available to the airplane and that the airplane’s fly-by-wire system remained in normal law and maintained the flight envelope protections, one of which protects against a stall.

While Flight 1549 was a regularly scheduled Part 121 airline operation, several of the Safety Board’s recommendations to the FAA were extended to cover Part 25 transport-category aircraft operated under Part 135 and Part 91 Subpart K.

Among these are:
•    Require manufacturers of Part 25-certified aircraft to develop a checklist and procedure for a dual engine failure occurring at low altitude.
•    Develop and validate guidelines for emergency and abnormal checklist design and development.
•    In initial and recurrent ground and simulator training, require a dual-engine-failure exercise at a low altitude designed to improve pilots’ skills in critical thinking, task shedding, decision making and workload management skills.

The Board is considering adding Part 23 aircraft to the recommendation. The NTSB also recommended that the U.S. Department of Agriculture develop and implement,
in conjunction with the FAA, innovative technologies that can be installed on aircraft that would reduce the likelihood of a birdstrike.

In its report, the safety agency noted that although no technological, regulatory or operational changes related to wildlife mitigation–including the use of avian radar–could be made that would lessen the probability of a similar birdstrike event from occurring, considerable research is being conducted in this area. Research on the use of aircraft systems such as pulsating lights, lasers and weather radar might lead to effective methods of deterring birds from entering aircraft flight paths and, therefore, reduce the likelihood of a birdstrike.