page_title: Downeast Flight 46
section_title: Aircraft operation and maintenance
hierarchical_section_title: Downeast Flight 46 / Aircraft operation and maintenance
caption_attribution_description: English: &#160;United States of America, Chicago, Meigs Field. Air Illinois de Havilland Canada DHC-6 200 Twin Otter N659MA, c/n 229, delivered to Miami Aviation in 1969-05-02. Delivered to Air Illinois in February 1971. Delivered to Newcal Aviation Inc. in March 1978. Registered N68DE in 1988-03-17 and cancelled in 2009-04-23.
context_page_description: Downeast Airlines Flight 46 was a scheduled airline service in the United States from Boston's Logan International Airport to Rockland, Maine operated by Downeast Airlines. On May 30, 1979 a de Havilland Canada DHC-6 Twin Otter operating the flight crashed during a nonprecision approach to Rockland's Knox County Regional Airport. All but one of the 18 people on board were killed. The cause of the accident was controlled flight into terrain after the failure of the flightcrew to stop the aircraft's descent below the minimum descent altitude for the nonprecision approach at Knox County airport. The investigation into the accident looked into the airline's corporate culture as a contributing factor to the crash; this was the first time an investigation took this approach to an air crash.
  The crash of Flight 46 is currently the deadliest to have occurred in the state of Maine. At the time of the crash, the crew had descended the Twin Otter below the minimum descent altitude in order to see the runway in heavy fog.
context_section_description: The aircraft involved in the accident, a twin-engine turboprop, was known to have a right engine that ran hotter and used more fuel in flight than the left engine. In addition to the high fuel flow and oil temperature in the right engine, the aircraft had poor cockpit lighting at night. Observation flights by the National Transportation Safety Board (NTSB) investigators found that errors in flap settings due to poor lighting were common on Twin Otters during night flights. The area around the flap control overhead was not illuminated; and the flap position indicator on the windscreen center post was poorly illuminated to the point of being barely visible. Some of the lights in the engine gauges had been incorrectly replaced with red, instead of white bulbs, making the gauges hard to see. Pilots had requested the maintenance crew standardize on one color of light bulb, but this had not been done at the time of the accident. Among Downeast pilots, there was discussion of the first officer's altimeter sticking and indicating as much as a 100 ft (30m) difference in altitude compared to the pilot's altimeter during descent and ascent. There was no formal record of the altimeter problem in the aircraft's logbooks, but investigators were told that it had been checked during an inspection in the past with no defects found.
caption: The aircraft involved in the crash pictured in 1973, then operated by Air Illinois
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