Investigation Summary
Flight 946 was a scheduled passenger service from Boston to Lebanon, New Hampshire, and Montpelier, Vermont. After a routine flight at 8,000 feet, the crew was cleared for an instrument approach to Lebanon. Instead of following the published full instrument approach procedure, the crew executed an abbreviated maneuver, making a right turn and then a left turn to intercept the inbound radial to the Lebanon VOR. This interception occurred approximately 8 to 10 miles northeast of the station at an altitude of 4,500 feet. The crew then began a descent that should have leveled off at 2,800 feet, the minimum altitude for that segment. However, the aircraft continued descending until it impacted Moose Mountain at 2,237 feet. All 10 survivors were seated in the rear of the aircraft, which remained relatively intact while the forward section was destroyed by impact and a post-crash fire that burned for 18 hours. Rescue efforts were severely hampered by the remote, steep terrain, freezing temperatures, and rain.
Final Conclusions
The National Transportation Safety Board (NTSB) concluded that the probable cause was the premature initiation of a descent toward the Minimum Descent Altitude. This was triggered by navigational instrument indications of an impending station passage caused by course roughness (signal interference) in the area. The board noted that the crew's ability to accurately determine their position was compromised because they had performed a nonstandard approach and lacked supplemental navigational aids. The NTSB report (AAR-70-07) was finalized in April 1970.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
John A. Rapsis, age 52. Had been with Northeast Airlines since 1957.
First Officer
John C. O'Neil, age 29. Hired in 1967.
Systems & Failure Modes
VOR (VHF Omnidirectional Range)
The primary navigational aid used for the approach. Investigators found that 'course roughness' or signal fluctuations near the station likely gave the pilots a false indication that they were closer to the airport than they actually were.
Flight Data Recorder (FDR)
A device that recorded flight parameters; it survived the impact and fire, allowing investigators to determine the aircraft's altitude and heading during the final descent.
Interesting Facts
- 01The aircraft crashed 57 feet below the 2,290-foot summit of Moose Mountain.
- 02The cockpit voice recorder was recovered but was too badly damaged to provide any usable data.
- 03The flight data recorder was recovered and provided information used to reconstruct the flight path.
- 04Seventeen people initially survived the impact, but seven died from their injuries before they could be rescued.
- 05The New Hampshire Aeronautics Commission had previously requested an Instrument Landing System (ILS) for Lebanon, which had not been installed at the time of the crash.
- 06Notable fatalities included historian J. P. Nettl, author of a biography on Rosa Luxemburg; his wife was among the survivors.
- 07Fatalities included four employees of the National Life Insurance Company returning from a business trip.
- 08Six passengers were en route to a Head Start conference at Goddard College; four of them were killed in the crash.
- 09Other victims included a former reporter for the Barre Times and a U.S. Navy member traveling home for the weekend.
Safety Actions & Advisories
Navigation System Review
The crash led to safety recommendations regarding the reliability of VOR navigation signals in mountainous terrain and the risks associated with non-standard instrument approaches.
Known Controversies & Unanswered Questions
Lack of Instrument Landing System (ILS)
Reference ↗The New Hampshire Aeronautics Commission publicly criticized the FAA for failing to install an ILS at Lebanon Municipal Airport despite repeated warnings, arguing that such a system would have provided the vertical guidance necessary to prevent the crash.