US National Transportation Safety Board (NSTB) member Robert Sumwalt says it is possible that investigators may never determine the exact number of Canadian geese struck by US Airways Flight 1549 before it crash landed into the Hudson River near New York City on 15 January.
Former US Airways pilot Sumwalt made that assessment today during a hearing of the US House aviation subcommittee.
The Captain of the US Airways Airbus A320 Chelsey Sullenberger told members of the committee birds completely covered the view of the outside window.
Sumwalt of NTSB says information obtained from the A320's flight data recorder shows the aircraft struck birds at 2,750ft msl roughly 1.5 minutes after takeoff. The elapsed time from the birdstrikes to touchdown in the water was 3.5 minutes.
"Most often, bird ingestion causes no loss of thrust or a partial power loss," says Sumwalt. "Even in the case of US Airways flight 1549, which did lose thrust in the left engine, the right engine did not fail completely." However, Sumwalt explains the power from that engine was insufficient to keep the A320 airborne.
FAA data suggests striking birds at that altitude is somewhat uncommon as agency associate administrator for aviation safety Margaret Gilligan says that roughly 73% of bird strikes occur at altitudes up to 500ft.
Both Sullenberger and Skiles say striking smaller birds is not particularly unusual but the captain notes the Hudson situation was atypical, and the associated risks need to be adequately assessed.
Sullenberger suggested to committee members that the industry should think about re-evaluating engine certification standards for birdstrikes.
In his testimony to the committee Sumwalt says that current test standards for the CFM56-5 engines similar to those powering the Airbus A320 is one 2-1/2lb bird directed at the core of the engine followed by five 1-1/2lb birds with a maximum allowable 25% thrust.
"The fact that the accident engines exceeded even today's standard and still failed is of great concern to the safety board," says Sumwalt.
In November 2007 FAA altered its certification standard future engines, raising the weight of the bird to 8lbs, says the board member. NTSB during the comment period to change the standard told FAA its proposed weight was too low.
"We did not specify a minimum weight, but we did note that the weight should be increased to represent birds as large as the Canada Goose, which can up to 24 pounds," Sumwalt explains. "Thereby representing a more realistic threat to airplanes.