AOPA questions NTSB probable cause in Hudson midair

September 15, 2010

In a rare move Sept. 14, members of the National Transportation Safety Board overruled the recommendation of their expert staff and cited the probable cause of the midair collision over the Hudson River on Aug. 8, 2009, as “the inherent limitations of the see-and-avoid concept, which made it difficult for the airplane pilot to see the helicopter until the final seconds before the collision.”

Nine people died in the midair collision between a Piper PA-32R-300 and a Eurocopter AS350BA tour helicopter over the Hudson River. The original proposed probable cause focused on procedural failures based on a readback/hearback error and the frequency handoff between Teterboro Tower and Newark Approach. See and avoid, specifically the difficulty of picking out the helicopter that was nearly stationary against a complex background relative to the Piper pilot, was listed as a contributing factor. The board made the limitations of see and avoid first in its determination, which included the controller’s distraction from his duties as a second cause. AOPA questioned the board’s decision to emphasize this over procedural issues.

Accident investigators described the breakdown of each layer of defense in the accident: a delayed radio handoff, an uncorrected readback error that led the Piper into congested airspace without communication, the repeated aural “traffic” alerts that the pilots may have viewed as “nuisance alerts,” and finally the Piper pilot’s view of the helicopter as a “a tiny object against the background of Manhattan buildings.” NTSB staff submitted a probable cause citing the controller’s distraction for setting the stage for the tragedy, but the board overrode the recommendation.

“There are certainly limitations to see and avoid, but that is the basis of our VFR system. It can be augmented by traffic avoidance equipment. Today's GA and even air carrier TCAS equipment is not well suited to the reality of extremely high density traffic. Until that is developed at reasonable cost, we should look at procedural solutions, which is exactly what was undertaken by the FAA-industry working group,” said AOPA Air Safety Foundation President Bruce Landsberg.

The Piper tracked south from Teterboro and turned left toward the Hudson River upon instructions from the tower, explained Bob Gretz, investigator in charge. The electronic handoff to Newark tower was completed, but the Teterboro controller, distracted by a personal phone call, missed two opportunities to hand off radio communications. When he assigned the pilot a frequency, he did not hear the incorrect readback because of a simultaneous transmission from Newark tower asking him to issue the frequency change and assign the Piper a heading. He did not ask the pilot to repeat the frequency.

Investigators showed an animation of the Piper’s route of flight with the ATC transcript overlaid. As the seconds ticked by, the words “PERSONAL PHONE CALL” were fixed at the top of the screen to illustrate the duration of the nonpertinent call, which staff said distracted the controller from his primary duties.

“He’s lost in the hertz,” the Newark controller said after the Piper did not establish contact. In the moments that followed the Piper pilot was not in contact with any controllers who could clear him into Class B airspace or issue traffic advisories. He may have been searching for the appropriate frequency as the helicopter grew in his windscreen—or he may have thought initially that he was still receiving traffic advisories from ATC.

The aviation community took action immediately after the crash to address the procedural problems that contributed to the accident. The FAA convened a working group of industry organizations immediately after the collision and soon after implemented safety recommendations that formalized best practices in the area and modified the airspace. AOPA participated in the working group and advocated for continued access to the airspace, and the AOPA Air Safety Foundation reached out to help pilots become more familiar with the area and implement safety procedures in their flights. The board praised the industry response in the hearing.

NTSB Chairman Deborah A.P. Hersman said many of the board’s preliminary recommendations have already been implemented because of collaboration between the FAA and industry groups. “While there is still a lot of work to be done, the good news is that many important changes have already taken place,” she said.

Hersman described the accident chain that led to the midair as a “merger of missteps.” The Piper pilot had never intended to enter the Hudson River Class B exclusion zone, NTSB staff said, and because of communication errors and inattention on the controller’s part he did so without radio contact with either air traffic control or the common traffic advisory frequency. As the two aircraft converged, neither pilot responded properly to multiple traffic information service (TIS) alerts. The Piper was not visible to the Eurocopter pilot for the final 32 seconds, and the helicopter appeared to the airplane pilot as a small, stationary object on the complex background of the Manhattan skyline. By the time the helicopter was clearly visible, the pilot had only seconds to react.

Both aircraft were equipped with TIS displays that should have provided traffic alerts to the pilots. Staff recreated what the displays might have looked like in the final seconds: The Piper would have had three traffic alerts on his screen regarding traffic in the corridor, and the Eurocopter would have had two. The pilots may have failed to take action on these alerts because they viewed them as “nuisance alerts,” products of a busy section of airspace.

The board cited both pilots’ ineffective use of available information from TIS to maintain traffic awareness, along with inadequate FAA procedures for the transfer of communication near the Hudson Class B exclusion and inadequate vertical separation in the exclusion zone, as contributing factors in the crash. The investigation also raised the question of why the Eurocopter was flying at 1,100 feet—higher than the 1,000 feet specified by the tour operator.

The board also issued recommendations to further improve the safety of the Hudson River airspace, which is now a special flight rules area. The FAA implemented eight safety recommendations from the government-industry working group just months after the crash.

The FAA has an online training course,  New York City Special Flight Rules Area (SFRA), to familiarize pilots with the requirements for flying within the corridor and the SFRA. The course includes a simulation of how a flight in the exclusion is conducted, along with the visual reporting points and audio examples of position reporting calls. (To receive FAA Wings credit, log in to the FAA’s website to take the course.) There is also a quiz to test your understanding of the information and a kneeboard summary of requirements for the exclusion.