CS Knowledge Base

Investigators immediately examined the fragments of the engine. They stated that the explosion might have been powerful enough to propel fragments of the turbine with sufficient speed to penetrate the plane and damage the flight controls, which could explain why the plane suddenly pitched up and barrel-rolled immediately after the explosion. Five years before the crash of Flight 105, in Poland an Ilyushin Il-62 crashed into a moat after its number 2 engine exploded and damaged the plane's elevator and aileron. Immediately after the explosion, the plane nosedived to the ground.^[1]

The explosion was caused by a detached removable sleeve spacer inside the right engine. The detachment was caused by metal fatigue. Examination of the turbine fragments and their distribution during the explosion led to the conclusion that the ejection of the fragments didn't contribute to the crash, as the velocity of the fragments was substantially absorbed and decreased by the engine cowling. The NTSB noted that several parts of the engine could not be found; they concluded that, based on their calculation and distribution of the fragments on the ground, the unidentified parts were reduced to tiny, harmless bits.

The NTSB also stated that, although the explosion caused serious damage to the engine cowling, the cowlings were all latched. None blew outwards, which would have caused a massive drag force on the plane. This, in turn, could have affected the controllability of the plane. Small portions of the cowling did blow outwards, but the NTSB concluded that these parts caused very little drag force.^[1]

The NTSB later concluded that even if any turbine parts were ejected and somehow able to penetrate the plane, the impact would be small and no controls would be affected.^[1]

In the initial seconds after the explosion, Flight 105 swayed to the right and left. In response, Captain Martin used the rudder to counteract the plane's movements. The investigation concluded that the plane was easily controllable, and that it could have been stabilized without the rudder inputs. However, Martin then made a pitch input, raising the aircraft's nose. This served to significantly reduce the DC-9's speed, making a stall more likely. Martin also began banking the plane to the right, the opposite side to the failed engine, which sent Flight 105 into a rapid, rolling dive.^[1]

The investigators believe that Martin wrongly perceived the nature of the emergency. The right engine's explosion caused an immediate loss of engine thrust, leading the speed of the aircraft to decrease. This rapid deceleration may have caused Martin to think that the plane was pitching down, and so tried to counter it by pitching up. In reality, Flight 105 was not pitching down; rather, it continued climbing with wings level, and was initially in no danger of stalling. The investigators suggested that Martin may have experienced a somatogravic illusion, a form of spatial disorientation, at the outset of the emergency, and so lost full awareness of what the plane was doing.^[1]

The NTSB noted that Flight 105 banked so far to the right that the plane entered a state that investigators refer to as an "accelerated stall".^[1]

Seconds after the failure of the right engine, Captain Martin correctly applied right rudder to level the plane. However, as he seems to have been uncertain about the exact situation Flight 105 was in, he asked First Officer Weiss what was going on. The NTSB suggested that, as Weiss was senior to and had more experience than Martin, the captain may have thought that Weiss might be more knowledgeable than him in identifying the nature of the emergency. However, both pilots were still fairly inexperienced on the DC-9, having just over one thousand hours each on the type.^[1]

As per their training, first officers are expected to work with their captains to handle emergencies together. However, Weiss did not respond to any of Martin's questions, leaving Martin to, effectively, deal with the crisis alone. Based on the evidence from the CVR, investigators believe that Weiss actually heard Martin's queries, but, for unknown reasons, ignored them. He was not incapacitated, as he responded to ATC's call while Martin was asking him what the problem was. Weiss's failure to respond may have further confused Captain Martin as to the exact state of the aircraft, leading to the captain quickly becoming overwhelmed and unable to diagnose the situation correctly.^[1]

Exactly why Weiss didn't answer Martin could never be fully determined. Investigators suggested that Weiss may have been equally confused by the information on his instruments, and so could not answer effectively. It is also possible (if not likely) that Weiss had been influenced by an unwritten policy at Midwest Express, known as the "silent cockpit" rule. Under this policy, Midwest Express pilots were expected to keep their focus on the takeoff after 100 knots (190 km/h), making no unnecessary callouts, or even discussing the nature of an emergency, until they had reached an altitude of 800 ft (240 m). The emergency on board Flight 105 that day started at roughly 700 ft (210 m), meaning that the "silent cockpit" rule was still in effect. Investigators stated that the pilots should have begun talking to each other immediately after the explosion, since a low altitude emergency was extremely dangerous. If Weiss was indeed following the "silent cockpit" rule, it meant that the crew's ability to work together effectively had been compromised from the outset. According to investigators, the "silent cockpit" rule conflicted with FAA regulations, and so should never have been approved in the first place.^[1]

Regardless of the reason, the NTSB argued that Weiss should have assisted Martin in responding to and diagnosing the problem that had occurred on board Flight 105, as:^[1]

"The redundancy provided by the First Officer is one of the basic tenets of Cockpit Resource Management."

The NTSB concluded that this breakdown in crew communication and coordination was one of the primary causes of the accident.^[1]

The lack of experience of an FAA Principal Operations Inspector (POI) may have caused the silent cockpit philosophy to be approved by the FAA without proper examination. The philosophy was contrary to the approved practice by the FAA. If she had had more experience, she might have recognized that the concept had flaws, and that the airline was already teaching the concept to their employees.^[1]

The NTSB believed that the POI who worked with Midwest Express did not perform her duties at an adequate level. As per the final report:^[1]

"The safety board believes that the FAA oversight of Midwest Express procedures and training during certification and ongoing day-to-day activity in the carrier's first 2 years of operation was less than optimum and probably suffered as a direct result of the inexperience of the POI. The POI testified that she devoted only 20 percent of her worktime to Midwest Express, her only FAR 121 scheduled passenger airline, and that she was still obligated to perform routine general aviation rules. The Board noted that the POI had no previous FAR 121 air carrier experience, that she was not rated in a turbojet of the category and class used by the airline, and that she had not rated received any formal training in the DC-9 airplane used by the certificate holder for which she was responsible. In fact, she had no turbojet pilot experience. Neither did the POI have available for consultation or assistance air carrier inspectors assigned to other offices to fulfill her responsibilities. Apparently, she had become so dependent on other inspectors in surveilling Midwest Express that her own role was reduced primarily to administrative matters. The absence of first-hand knowledge of the carrier and her lack of experience in turbojet air carrier operations severely handicapped her ability to perform the quality of surveillance required to detect shortcomings of FAR 121 airline operation. The Safety Board believes that the experience level of the POI was inappropriate for her assignment as the POI of a new air carrier operating turbojet equipment. She even testified that she was not totally comfortable with the arrangement."