NTSB issues 'urgent' advice for Hawker jet stall tests

Along with the two fatal accidents, another incident and two related events prompted the NTSB to call attention to gaps investigators identified in documentation, procedures, and the criteria for qualifying pilots to conduct these test flights. Ice and other wing irregularities, including bent vortex generators, caused stalls before stick pusher and simultaneously with stick shaker activation. Lack of pilot training and experience requirements that led to improper remedial action was found to be causal in one of the fatal accidents, while another investigation is ongoing.

The NTSB’s guidance to Textron Aviation, current holder of the Hawker type certificate, recommended a review of the aircraft documentation provided to pilots on all airplanes on the A3EU type certificate. Updated guidance should, according to the agency, include the effects of wing deformities or contamination on stall behavior, including that tiny changes in wing shape can have dramatic effect, allowing stalls to commence before there's any indication from the aircraft, and include an abrupt roll. The NTSB recommends that any pilot conducting such a flight be trained on proper recovery procedures, beginning with sufficient altitude.

The NTSB also recommended Textron develop for the Hawker 700, 800, 800XP, 850XP, and 900XP a “clear and thorough” stall test plan; define manufacturer-authorized training and experience requirements to qualify pilots to conduct stall training; and review all other airplanes on the type certificate model for similar issues.

In one of the accidents involving a Hawker 900XP, N900VA, near Westwater, Utah, in February 2024, the stick shaker and stick pusher failed to activate before a stall. The aircraft stalled as the stick shaker activated and before the stick pusher engaged. The late response by the stall protection system was “likely due to wing performance degradation from structural ice that accumulated as the airplane entered the clouds during part of its climb,” the NTSB wrote.

According to the final report, after the airplane entered a stall, it abruptly rolled to the right. The flight crew responded with full left-wing-down aileron control input, full power, and full aft (airplane-nose-up pitch) elevator control input, which aggravated the aerodynamic stall and spin. The accident killed both crewmembers on board.

The NTSB found that although the aircraft manual references “unacceptable stall characteristics,” which includes that a stall may occur before stick shaker or stick pusher activation or an uncommanded roll that exceeds 20 degrees and cannot be limited by a pilot’s aileron control input, current documentation for pilots does “not provide clear information or recovery procedures beyond a statement that the elevator control must be moved forward.”

A more recent accident in October involved a Hawker 800XP airplane, XA-JMR, that crashed during a stall test flight near Bath Township, Michigan, killing the pilot, co-pilot, and a company maintenance representative on board. The NTSB wrote in its guidance that, although the investigation is ongoing, the “descent profile and other aspects of the flight are similar to those identified” in the Utah accident.

The NTSB guidance also cited a 2006 investigation of an accident involving a Corporate Jets Limited BAE 125-800A—another of 51 unique airplane models on the type rating. Six crewmembers were injured during a stall test flight when the airplane entered a stall without the expected stick shaker and stick pusher activation and rolled uncommanded through 360 degrees. Ice contamination on the wings, the NTSB wrote, resulted in the airplane’s adverse stall behavior.

The NTSB referenced two other stall test flight events where deformed vortex generators caused stalls without stick shaker or stick pusher activation and uncommanded rolls, though neither of these events resulted in damage or injuries.