Читать книгу Flight Theory and Aerodynamics - Joseph R. Badick - Страница 101

On 8 January 2003, Air Midwest Flight 5481 experienced a loss of pitch control on takeoff in Charlotte, NC and crashed, killing 2 crew members and 19 passengers. Several factors that led to this accident were topics addressed within this chapter and deserve application to the principles of aerodynamics and safety of flight. Due to the length of the NTSB accident report (NTSB/AAR‐04/01), only the factors that directly relate to this chapter will be discussed, and it is recommended that the reader review the entire accident report.

The Beech 1900D has a typical horizontal stabilizer with an elevator hinged to the back. Normal travel of the elevator allows for up to 20° airplane nose up (ANU) and up to 14° airplane nose down (AND). As we discussed in Section 3.1.1.2, the elevator allows the pilot to pitch the aircraft around the lateral axis. Figure 3.26 shows the Beech 1900D pitch control system, note the turnbuckles, aft bellcrank, and their connection to the elevator.

Due to improper maintenance on the turnbuckles within the pitch control system, the elevator was rigged improperly – (simplified for this discussion) not allowing for full elevator authority – and thus restricted downward elevator travel. The actual elevator position was restricted to 7° AND. In addition to the maintenance errors, a complicating factor was the weight and balance of the aircraft itself. Actual weight and balance calculations of the true weights (versus average weights) and position of all passengers and cargo proved the aircraft was also loaded overweight and with an aft center of gravity. As will be discussed later in the textbook the position of the center of gravity in accordance with the manufacturer’s guidelines is imperative to aircraft safety. The aft center of gravity in the accident aircraft exacerbated the maintenance error.

Figure 3.26 Beech 1900D pitch control system.

Source: Courtesy: National Transportation Safety Board.

As the aircraft departed the runway, the nose experienced a pitch upward. Due to the aforementioned maintenance error, the pilots only had 7° AND travel with the elevator, about one‐half of normal travel. This resulted in an increasing angle of attack and the flight crew was unable to recover. In this example, the flight crew was not at fault and could not have known about the maintenance error. Chapter 4 contains a more detailed discussion on the importance of understanding the principles of lift, and the consequences on safety of flight if these principles are not understood.