On October 17, 2019, a Saab 2000 airplane, operated by Peninsula Aviation Services Inc. d.b.a. PenAir flight 3296, overran the end of runway 13 at Unalaska Airport (DUT), Unalaska, Alaska. The flight crew executed a go-around during the first approach to runway 13; the airplane then entered the traffic pattern for a second landing attempt on the same runway. Shortly before landing, the flight crew learned that the wind at midfield was from 300° at 24 knots, indicating that a significant tailwind would be present during the landing. Because an airplane requires more runway length to decelerate and stop when a tailwind is present during landing, a landing in the opposite direction (on runway 31) would have favored the wind at the time. However, the flight crew continued with the plan to land on runway 13.
Our postaccident calculations showed that, when the airplane touched down on the runway, the tailwind was 15 knots. The captain reported after the accident that the initial braking action after touchdown was normal but that, as the airplane traveled down the runway, the airplane had “zero braking” despite the application of maximum brakes. The airplane subsequently overran the end of the runway and the adjacent 300-ft runway safety area (RSA), which was designed to reduce airplane damage during an overrun, and came to rest beyond the airport property. The airplane was substantially damaged during the runway overrun; as a result, of the 3 crewmembers and 39 passengers aboard, 1 passenger sustained fatal injuries, and 1 passenger sustained serious injuries. Eight passengers sustained minor injuries, most of which occurred during the evacuation, and the remaining 32 occupants were not injured.
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The the probable cause of this accident was the landing gear manufacturer’s incorrect wiring of the wheel speed transducer harnesses on the left MLG during overhaul. The incorrect wiring caused the antiskid 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. Contributing to the accident were (1) Saab’s design of the wheel speed transducer wire harnesses, which did not consider and protect against human error during maintenance; (2) the FAA’s lack of consideration of the RSA dimensions at DUT during the authorization process that allowed the Saab 2000 to operate at the airport; and (3) the flight crewmembers’ inappropriate decision, due to their plan continuation bias, to land on a runway with a reported tailwind that exceeded the airplane manufacturer’s limit. 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.
As a result of this investigation, we recommended that the FAA and the European Union Aviation Safety Agency review system safety assessments for landing gear systems on currently certificated transport-category airplanes to determine whether the assessments evaluated and mitigated human error that could lead to cross-wiring of antiskid brake system components, including the wheel speed transducers, and then require transport-category airplane manufacturers without such assessments to implement mitigations. We also recommended that the FAA and the European Union Aviation Safety Agency require system safety assessments addressing the landing gear antiskid system for the certification of future transport-category airplane designs; the certification should ensure that the system safety assessments evaluate and mitigate the potential for human error that can lead to a cross-wiring error. Further, we 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 European Union Aviation Safety Agency require organizations that design, manufacture, and maintain aircraft to establish a safety management system.
We also recommended that the FAA notify certificate management team personnel about the circumstances of this accident and emphasize the importance of detecting and mitigating the safety risks that can result when certificate holders experience significant organizational change, such as bankruptcy, acquisition, and merger, all of which PenAir was experiencing for more than 2 years before the accident. We further recommended that the FAA revise agency guidance to include a formalized transition procedure to be used during a changeover of certificate management team personnel responsible for overseeing a certificate holder that is undergoing significant organizational change to ensure that incoming personnel are fully aware of potential safety risks.
In addition, we recommended that the FAA include the runway design code for runways of intended use among the criteria assessed when authorizing a scheduled air carrier to operate its airplanes on a regular basis at an airport certificated under Title 14 Code of Federal Regulations Part 139.
