A Mechanic reports a company EMB-120 Flight crew declared an Emergency; landed heavy; at high speeds with flaps up; to controlled violent Pitch-up and Down movements of the aircraft. Mechanic suspects hardware bolt failures of the elevator hinges in flight; in icing conditions; are occuring.

Narrative

I was informed by our Maintenance Director that the 'elevator of an EMB-120 had come off in-flight'. I was not made aware of the day or time; only that the elevator had come off and an emergency landing was made successfully. My initial reaction was shock. My initial thought was a possible flutter situation since the right elevator was one I had worked on and a complete Static Balance was completed on the elevator before it was reinstalled on the aircraft. As it turned out; the elevator involved was the left elevator; and initial investigation has indicated that two bolts were missing and that the [left] elevator did not depart the aircraft; but did cause a serious inflight emergency. My only involvement with the hardware in question was to clean it; inspect it for corrosion; damage; and any defects or other reasons to replace it. I saw no reason to replace any of the bolts in question on either the right or left elevator hinges so I took no action to remove them. My inspection confirmed correct installment and safety of the hardware with reference to the Manufacturer's Illustrated Parts Catalog (IPC); that is; the pileup [stacking/ positioning of washers and spacers during bolt installation]. I was informed by the Director of Maintenance at the time; that the event had occurred. I am not certain what had occurred other than two of the outer hinge bolts in the vertical axis of the left elevator hinges are missing and the movement of the elevator in flight precipitated an emergency landing. When installing the elevators; no defects in this hardware or missing hardware was noted or observed. Subsequent RII Inspection of the aircraft upon completion of installation did not indicate any of this hardware involved to be missing or incorrectly installed. Suggest [that] a more direct; comprehensive form of supervision of all personnel on the floor is indicated; comprehensive training on aircraft type is needed; Mechanic work habits and Work Turnover Procedures need to be improved; and given the availability of modern technology; i.e. digital cameras; etc.; better documentation of work performed should be brought to use in a more comprehensive manner. This is especially true when primary flight controls and flight critical components are involved. I am absolutely certain that the work I performed on this aircraft involving the elevators was completed 100% correct; and that when this aircraft was released to flight I volunteered to fly on the initial test flight after a complete brief with the company pilot as to the scope and detail of the work done by myself and others. I am equally as certain that the hardware in question was in fact installed properly; that it was in an airworthy condition; that our company RII Inspector did in fact look at and inspect every phase of this effort; including the hardware in question; and that the cause of its missing from the aircraft is not due to any error on my part.