Statuts:	Enquête Officielle
Date:	01 DEC 1974
Heure:	19:26 EST
Type/Sous-type:	Boeing 727-251
Compagnie:	Northwest Orient Airlines
Immatriculation:	N274US
Numéro de série:	20296/777
Année de Fabrication:	1969-11-25 (5 years )
Moteurs:	3 Pratt & Whitney JT8D-7B
Equipage:	victimes: 3 / à bord: 3
Passagers:	victimes: 0 / à bord: 0
Total:	victimes: 3 / à bord: 3
Dégats de l'appareil:	Perte Totale
Conséquences:	Written off (damaged beyond repair)
Lieu de l'accident:	Stony Point, NY (Etats-Unis d'Amérique)
Phase de vol:	En vol (ENR)
Nature:	Convoyage
Aéroport de départ:	New York-John F. Kennedy International Airport, NY (JFK/KJFK), Etats-Unis d'Amérique
Aéroport de destination:	Buffalo-Greater Buffalo International Airport, NY (BUF/KBUF), Etats-Unis d'Amérique
Numéro de vol:	6231

Détails:
Flight NW6231 departed New York-JFK at 19:14 for a ferry flight to Buffalo and was cleared by departure control to climb to FL140. At 19:21 the flight was cleared to climb to FL310. The aircraft began to climb 2500fpm at an airspeed of 305 knots. As the aircraft climbed through FL160, both the airspeed and the rate of climb began to increase. Reaching FL230, the airspeed had reached 405 knots and the rate of climb had exceeded 6500fpm. The overspeed warning horn sounded a little later, followed 10 seconds later by a stickshaker stall warning. The aircraft then leveled at 24800 feet with a speed of 420 knots until it turned rapidly to the right, 13 seconds later. The airplane started to descend out of control, reaching a vertical acceleration of +5g until it struck the ground in a slightly nose down and right wing-down attitude. The aircraft had descended from 24000 feet to 1090 feet in 83 seconds.

PROBABLE CAUSE: "The loss of control of the aircraft because the flight crew failed to recognize and correct the aircraft's high-angle-of-attack, low-speed stall and its descending spiral. The stall was precipitated by the flight crew's improper reaction to erroneous airspeed and Mach indications which had resulted from a blockage of the pitot heads by atmospheric icing. Contrary to standard operational procedures, the flight crew had not activated the pitot head heaters."

Sources:
» Flight International 06.03.1975 (355)
» NTSB Safety Recommendations A-75-27
» NTSB-AAR-75-13