US investigators have concluded that an AirNow Embraer EMB-110 freighter crashed as a result of a minimum control-speed roll, after the pilot attempted a single-engined go-around at Dillant-Hopkins airport, New Hampshire in 2005.

The US National Transportation Safety Board (NTSB) says the pilot, who was killed in the crash, made an "improper decision" to attempt the missed approach, adding that he was trying to divert, at night, to an airport with low ceilings and visibility when better conditions were present elsewhere.

For reasons that remain unknown, the right-hand Pratt & Whitney Canada PT6A engine had either lost power or been shut down by the pilot during the January 13, 2005, flight from Bangor, Maine to AirNow's base at Bennington, Vermont.

Although Bennington had night visual meteorological conditions, and there was no evidence of malfunction in the remaining engine, the pilot chose instead to follow an instrument approach to the closer Dillant-Hopkins airport - despite its having a 100ft (30m) cloud ceiling, fog and less than 1.6km (0.9nm) visibility.

"The pilot did not advise or seek assistance from air traffic control or the [operating] company," says the NTSB. "When the aircraft broke out of the clouds, it was not stable."

Although the pilot aborted the descent to Runway 02, he applied maximum power to the left engine. This combination of high power, slow airspeed and full flaps induced a minimum control-speed roll - a phenomenon whereby, at low speed, the flight controls cannot counter the roll generated by asymmetric thrust.

In its inquiry the NTSB says: "No determination could be made as to why the right engine was inoperative, and there were no mechanical or fuel-related anomalies found that would have precluded normal operation."