Investigation Summary
The flight was a late-night commuter service operating in deteriorating weather conditions, including light drizzle and an indefinite ceiling of 300 feet. The flight was originally scheduled as Flight 1788, but due to air traffic control delays in Boston, that flight was canceled. The crew was instead assigned to operate Flight 1808, with Auburn added as a 'flag stop' to accommodate passengers from the canceled service. During the approach, a Portland controller noticed the aircraft was east of the localizer course and issued a corrective left turn to heading 340. This instruction created a 60-degree intercept angle just one mile from the outer marker, a maneuver that violated standard radar-assisted arrival guidelines. The crew accepted the vector but overshot the localizer. Radar data indicated the aircraft was 30 knots too fast and 600 feet too high at the outer marker. In an attempt to salvage the approach, the crew descended steeply to capture the glide slope but allowed the aircraft to drop below the glide slope boundary. The Beechcraft 99 struck trees at an elevation of 345 feet MSL in a wings-level attitude, subsequently impacting the ground and coming to rest in a nearly inverted position. The lack of a Cockpit Voice Recorder (CVR) or Flight Data Recorder (FDR), which were not required for aircraft of this size at the time, prevented investigators from determining the exact nature of the crew's internal coordination or the specific altimeter settings used.
Final Conclusions
The NTSB concluded the probable cause was the captain's continuation of an unstabilized approach which resulted in a descent below the glide slope. Contributing factors included the radar controller's issuance and the captain's acceptance of a non-standard radar vector, resulting in an excessive intercept angle. The board also noted that excessive cockpit noise levels likely interfered with effective oral communication between the pilots. The final report is NTSB/AAR-86/06.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Instrument Landing System (ILS)
The precision approach system the crew was using to navigate to Runway 4 in low visibility; the aircraft failed to stabilize on the localizer and glide slope.
Ground Proximity Warning System (GPWS)
The aircraft was not equipped with GPWS; the NTSB estimated such a system would have provided 10 to 17 seconds of warning before impact.
Cockpit Voice Recorder (CVR)
Absent on this aircraft; its absence hindered investigators' ability to understand crew coordination and communication issues.
Interesting Facts
- 01One of the passengers was Samantha Smith, a famous 13-year-old American goodwill ambassador to the Soviet Union.
- 02The aircraft was not equipped with a Cockpit Voice Recorder or Flight Data Recorder as it was below the FAA weight threshold for mandatory installation.
- 03The Beechcraft 99 lacked a crew interphone system, forcing pilots to use hand signals or shout over engine noise.
- 04The crash occurred 440 feet to the right of the extended runway centerline.
- 05The controller's 60-degree intercept vector was issued when the aircraft was only one mile from the outer marker.
Safety Actions & Advisories
GPWS Mandate for Commuters
The NTSB recommended amending 14 CFR 135.153 to require Ground Proximity Warning Systems on all multiengine, turbine-powered airplanes certificated to carry 10 or more passengers.
Flight Recorder Requirements
The NTSB recommended that aircraft for hire capable of carrying six or more passengers be equipped with flight recorders.
Cockpit Noise Standards
The NTSB urged the FAA to establish maximum cockpit noise levels and require interphone systems to ensure adequate crew communication.