After challenges from aviation safety investigators from Sweden and the U.K., the National Transportation Safety Board (NTSB) is standing by its conclusion on the probable cause of the PenAir runway overrun accident at the Unalaska airport (KDUT) in Dutch Harbor, Alaska.
According to the NTSB final report, the accident, which happened on October 17, 2019, was caused by the flight crew’s improper decision-making coupled with the failure of the aircraft’s braking system attributed to improper maintenance.
However, the Swedish Accident Investigation Authority (SHK) and U.K. Air Accidents Investigation Branch (AAIB) responded that the NTSB’s report “did not sufficiently emphasize the PenAir flight crew’s role in the accident sequence.”
The NTSB maintains the testimony of the SHK and AAIB was considered during the November hearing.
What Happened
On October 17, 2019, the Saab SA-2000, operated by PenAir as flight 3296, overran the runway during an attempt to land. The aircraft had been cleared for the RNAV 13 approach, but during the descent, the winds shifted and were now from the northwest.
The first attempt resulted in a go-around. When the airplane entered the traffic pattern for a second landing attempt, the flight crew learned the wind was from 300 degrees at 24 knots. The captain chose to continue the approach to Runway 13, rather than maneuvering to land on Runway 31, although it meant landing with a tailwind of at least 15 knots. During the investigation, the flight crew reported they were unconcerned about the reported winds.
The captain reported that the touchdown was normal, but when maximum braking was applied, there was “zero braking” action. The left tire was destroyed and the aircraft overran the runway and the adjacent 300-foot runway safety area off the end of the pavement. The turboprop crashed through a fence and came to rest on the rocky bank of Dutch Harbor. One person, 38-year-old David Oltman of Ellensburg, Washington, was killed when a piece of a propeller broke off during the crash and pierced the cabin. One person was seriously injured and eight more people suffered minor injuries during the evacuation of the aircraft.
Neither the flight crew nor the remaining 29 passengers were hurt.
The Original Report
During its investigation, the NTSB looked at the crew qualifications and the technical complexity of the airport itself. The runway is located at the base of a mountain and is flanked on both sides by water. The runway measures 4,500 feet by 100 feet and has a reputation for being a difficult operating environment. It was determined that the captain of the PenAir flight had not been properly vetted for that particular airport.
The report noted “the captain might not have fully understood the challenges associated with landing the Saab 2000 at Unalaska airport because he had not achieved the experience that the company-designated pilot-in-command airport qualification policy intended.”
The NTSB determined the flight crew’s decision to land with a tailwind was an example of continuation bias and was “intentional and inappropriate.”
The board went on to state: “The safety margin was further reduced because of PenAir’s failure to correctly apply its company-designated PIC airport qualification policy, which allowed the accident captain to operate at one of the most challenging airports in PenAir’s route system with limited experience at the airport and in the Saab 2000.”
The NTSB received testimony indicating the lack of braking action was caused by “incorrect wiring [that] caused the anti-skid system not to function as intended, resulting in the failure of the left outboard tire and a significant loss of the airplane’s braking ability, which led to the runway overrun.”
The NTSB stated the design of the braking system was partially to blame for the maintenance error, as it is complicated and confusing to maintain.
The NTSB also noted that when the FAA approved PenAir to fly in and out of the Unalaska airport with the Saab 2000, “they did not recognize that the safety area beyond the end of the runway did not conform to the recommended safety criteria for an airplane in that design category.”
A 2007 report published by ICAO noted that except under special conditions, the Runway Safety Area standard dimensions for runways used by aircraft with approach speeds of 121 knots or more are 500 feet wide and 1,000 feet long.
Recommendations
The meeting concluded with the NTSB issuing several recommendations to the FAA and the European Union Aviation Safety Agency (EASA), and to Saab to prevent further accidents.
These include:
- A review of safety assessments for landing gear systems on currently certificated transport-category airplanes to determine if more needs to be done to prevent the cross-wiring of components.
- Require transport-category airplane manufacturers without such assessments to implement the mitigations.
- Require system safety assessments addressing the landing gear anti-skid system for the certification of future transport-category airplane designs.
In addition, the NTSB recommended that Saab redesign the wheel-speed-transducer wire harnesses for the Saab 2000 to prevent the harnesses from being installed incorrectly during maintenance and overhaul, and that the FAA and the EASA require organizations that design, manufacture, and maintain aircraft to establish a safety management system.
The NTSB also noted that it’s possible that safety risks can result when certificate holders experience significant organizational change, such as bankruptcy, acquisition, and merger.
All three were experienced at PenAir more than two years before the accident. Citing this, the NTSB suggested that the FAA revise agency guidance to include a formalized procedure for these transitions to ensure that incoming personnel are fully aware of potential safety risks.
The NTSB also suggested that the FAA pay more attention to the runway design code for runways of intended use when authorizing a scheduled air carrier to operate its airplanes at specific airfields under Part 139 on airport operations.
