Investigation Summary
The flight originated in Seattle and made an intermediate stop in Yakima. During the stop at Yakima, the crew observed ice on the wings and manually cleared some of it, but the captain twice declined professional deicing services for the wings and tail. Upon departure for Pasco, the aircraft encountered further icing conditions. During the approach to Pasco, air traffic controllers provided vectors that placed the aircraft inside the outer marker while it was still significantly above the glideslope. To compensate, the crew initiated a rapid descent of 2,000 to 3,000 feet per minute at a 7-degree glidepath, more than double the standard angle. As the aircraft slowed to 110 knots to configure for landing, the combination of the steep pitch angle, low speed, and ice-contaminated tailplane led to an aerodynamic stall and a sudden nose-down pitch from which the crew could not recover.
Final Conclusions
The NTSB determined the probable cause was the flightcrew's decision to continue an unstabilized instrument landing system approach that led to a stall, most likely of the horizontal stabilizer, and loss of control at low altitude. Contributing factors included improper air traffic control vectors and the accumulation of airframe ice that degraded aerodynamic performance.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Barry W. Roberts, age 38.
First Officer
Douglas K. McInroe, age 25.
Systems & Failure Modes
Horizontal Stabilizer
The tail surface responsible for longitudinal stability; investigators believe ice on this surface caused a tailplane stall during the steep descent.
Instrument Landing System (ILS)
A precision approach system; the crew attempted to capture the ILS glideslope from an unstabilized, high-altitude position.
Deicing System
The aircraft encountered icing in flight, and the crew's failure to use ground deicing at Yakima left residual ice on the tail surfaces.
Interesting Facts
- 01The aircraft was not equipped with a Cockpit Voice Recorder (CVR) or Flight Data Recorder (FDR).
- 02The aircraft was not equipped with a Ground Proximity Warning System (GPWS).
- 03The captain declined deicing services at Yakima despite other departing flights utilizing them.
- 04The aircraft was flying at a 7-degree glidepath, more than twice the standard 3-degree ILS angle.
- 05The investigation concluded the horizontal stabilizer likely stalled due to ice and high descent rates.
- 06The aircraft was manufactured in October 1987, making it approximately two years old at the time of the accident.
Safety Actions & Advisories
NTSB Safety Recommendations
The NTSB issued recommendations A-92-59 through -65 and A-94-70 through -72 regarding icing procedures and pilot training for the Jetstream 31.