June 11, 2009

Bird strikes by aircraft, while statistically a rare occurrence, are a “worsening threat” to air travel, according to Federal Aviation Administration officials who testified Thursday before a panel investigating the Hudson River ditching of US Airways Flight 1549.

With the goose population in the United States increasing over the last 30 years, and with aviation growth of 1 to 2 percent annually, “the bird threat has been increasing,” Robert Ganley, an FAA engine standards manager, told a National Transportation Safety Board panel.

Thursday was the last of three days of NTSB hearings into Flight 1549’s crash-landing, which occurred Jan. 15 after a bird strike caused a loss of thrust in both of the Airbus A320’s jet engines.

All 155 passengers and crew survived after the plane hit a flock of Canada geese minutes after takeoff from LaGuardia Airport. The birds later were determined to be migratory fowl.

There is only one other known bird strike involving a civilian aircraft that caused a double engine failure, like what happened to Flight 1549, said Marc Bouthillier, an aerospace engineer with the FAA. It involved an Ethiopian jet in 1988, he said.

In that September 1988 incident, which was a crash-landing on the ground, birds were sucked into both engines of an Ethiopian Airlines jet soon after takeoff from Bahir Dar, causing the engines to catch fire and cease to function, according to a British Broadcasting Corp. report.

The pilot made an emergency crash-landing about 14 miles south of the airport, with the Boeing 737 skidding along the ground before it split in two and caught on fire, the BBC reported. At least 31 of 104 passengers on the plane were killed.

According to the BBC report, the Ethiopian Airlines jet struck birds at a height of about 300 feet. That is a much lower altitude than was the case of Flight 1549, which had reached an altitude of about 2,800 feet when it struck the flock of Canada geese.

As there have been so few such events over the course of “a billion hours of flight” worldwide since the FAA began tracking bird strikes, such double-engine failures are “extremely unlikely,” Bouthillier said Thursday.

Despite the rarity of occurrence, Flight 1549’s crash-landing is prompting the FAA to “re-evaluate whether the current rule still meets our safety objective,” Ganley testified.

The NTSB is investigating whether certification standards for jet engines that sustain bird strikes need to be changed. For engines that sustain strikes from what are termed “large flocking birds,” current standards require that a safe engine shutdown without fire or the expelling of debris is necessary, according to testimony.

The FAA standards do not require that the affected engines maintain thrust.

The NTSB board, which will issue a final report on the crash early next year, could consider recommending to the FAA that engine certification standards be changed, said Robert Sumwalt, NTSB member and presiding hearing officer.

“That’s a possible area we may be able to explore,” Sumwalt said Thursday.

However, changes to jet engine design to harden engines against bird strike is difficult because of added weight, Sumwalt said.

“You could probably build an engine that would withstand a 20-pound bird strike, but it probably wouldn’t fly an airplane,” he said.

The NTSB hearings, which included testimony from Capt. Chesley Sullenberger, Flight 1549’s pilot, and passenger Billy Campbell, concluded Thursday.