On November 30, 1994, a Piper PA-31T1 (registration N22CN) was involved in an aviation accident near Brockway, MT. Investigators recorded the probable cause as: a loss of control for undetermined reasons. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
An airplane cruising at FL220 at night experienced altitude fluctuations up to 500 feet above, then descended and lost transponder contact. It broke up in flight; the right elevator separated in negative overload, wings separated, and empennage separated before wings. A preimpact fire occurred. The initiating event could not be determined.
Flight History
The airplane was level at flight level 220 (FL220) during night conditions when the Salt Lake Center controller observed vertical fluctuations in altitude of up to 500 feet above the assigned altitude. Immediately thereafter, the aircraft began a descent and its transponder targets were lost. A trajectory study showed the aircraft descending in a tight right turn.
Wreckage Examination
Examination of the wreckage revealed that the right elevator had separated in negative overload, and both wings had also separated under negative loads. The distribution of wreckage indicated that the empennage and its associated control surfaces separated from the aircraft before the wings separated. A preimpact fire was witnessed, and the main fuselage was destroyed by an intense postcrash fire.
Conclusion
The initiating event that led to the altitude divergence and descending turn could not be determined from the available evidence.