S.J.H. Veronneau
FAA Civil Aerospace Medical Institute
Oklahoma City, OK 73125-5066

W.R. Ercoline
KRUG Life Sciences

D.W. Yauch
Armstrong Laboratory/CFTF
Brooks AFB, TX 78235-5104

Introduction
Little recent attention has been placed on spatial disorientation (SD) aspects in commercial aviation although more than a dozen air transport crashes reported on many years ago were believed to be a result of the somatogravic illusion. This paper discusses the forces that create the somatogravic illusion when a pilot executes a takeoff or missed approach, and the investigation of the events leading to a fatal commercial accident involving this illusion.

Methods
Flight data from an air transport crash were reviewed by the authors and correlated with pilot control inputs. The individual gravitoinertial force vectors acting along the longitudinal axis (Gx) and the vertical axis (Gz) were summed to produce the net gravitoinertial force (G) acting on the pilots. Perceived angles of pitch were calculated and compared to actual pitch from the digital flight data recorder.

Results
The missed approach was conducted close to the decision height for the instrument landing system, shortly after encountering instrument meteorological conditions (IMC) in a severe windshear/microburst with very heavy rain. The longitudinal gravitoinertial force which helped produce the false pitch sensation was a combination of the acceleration of the jet for the aborted landing and adverse weather. A net change between the actual pitch and the perceived pitch varied from no difference during the 150' initial climb in the go-around to a maximum of 19 degrees seconds before ground impact. The nonflying pilot (PIC) ordered the flying pilot to lower the aircraft nose. During the missed approach attempt the aircraft entered a descent and impacted the ground. Prior to impact the plane came out of the precipitation and encountered trees in the flight path.

Conclusions
The somatogravic illusion should be thought of as a potential threat to any aircraft flight. In this mishap a loss of situational awareness is documented in just about every aspect of the approach and go-around. As a scenario for cockpit resource management training this mishap illustrates the need for aircrew to be aware of how SD can affect team members separately and how in IMC and during critical phases of flight it can interfere with crew coordination. SD demonstrations and training, if made part of pilot human factors training and refresher programs, could enhance crew coordination and better prepare pilots to cope with SD.