Investigation Summary
The accident occurred during the crew's second attempt to land at Unalaska. Despite a shifting wind that resulted in a tailwind exceeding the aircraft's limitations, the crew continued the approach to Runway 13. During the landing roll, the pilot applied heavy braking, but the anti-skid system failed to function correctly on the left main gear. This failure was traced back to a maintenance error where the wiring for the wheel speed sensors had been crossed during a previous repair. Because the sensors were swapped, the anti-skid system released brake pressure on the wrong wheel when it detected a skid, effectively disabling the braking capability on one side and preventing the aircraft from stopping within the available runway length.
Final Conclusions
The National Transportation Safety Board (NTSB) determined that the probable cause of this accident was the incorrect wiring of the wheel speed transducers on the left main landing gear axle during overhaul, which caused the antiskid system to function improperly. Contributing to the accident were the flight crew's decision to land with a tailwind that exceeded the airplane's maximum demonstrated limit and the Federal Aviation Administration's failure to ensure that the runway safety area at Unalaska Airport was safe for the Saab 2000. Additionally, the NTSB cited PenAir's failure to correctly apply its company-designated pilot-in-command (PIC) airport qualification policy, which allowed a captain with limited experience at the challenging airport and in the Saab 2000 to operate the flight.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Paul Wells, age 56. Had limited experience at Unalaska Airport.
First Officer
Justin Lunn, age 39.
Systems & Failure Modes
Anti-skid System
A system designed to prevent wheel lock-up during braking. In this case, crossed wiring caused the system to release pressure on the wrong wheel, leading to a total loss of effective braking on the left main gear.
Wheel Speed Sensors
Transducers that provide rotation data to the anti-skid computer. The wiring for these sensors was swapped during maintenance, providing the computer with inverted data.
Interesting Facts
- 01The aircraft was a Saab 2000, a high-speed turboprop.
- 02The anti-skid system wiring had been crossed during a maintenance task performed months prior.
- 03The tailwind at the time of landing was approximately 15 knots, exceeding the 10-knot limit for the aircraft type.
- 04During the overrun, the left propeller struck a 4-to-5-foot signal post and a road sign, causing the blades to shatter.
- 05A shattered propeller blade penetrated the fuselage and entered the passenger cabin, fatally injuring one passenger.
Safety Actions & Advisories
Maintenance Procedure Review
Source ↗The NTSB recommended that Saab redesign the wheel speed sensor connectors to make them physically impossible to cross-connect.
Airport Safety Area Improvements
Recommendations were made to the FAA to re-evaluate the Runway Safety Area (RSA) at Unalaska, which was shorter than standard requirements.