Loss of aircraft control in a cessna citation-750.

Attributes
ACN	311863
Time
Date	199507
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : pxr
State Reference	AZ
Altitude	msl bound lower : 23100 msl bound upper : 30000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zab
Operator	general aviation : corporate
Make Model Name	Experimental
Operating Under FAR Part	Part 91
Navigation In Use	Other Other
Flight Phase	cruise other other other
Route In Use	enroute : direct enroute other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : commercial pilot : cfi pilot : atp pilot : instrument
Experience	flight time last 90 days : 80 flight time total : 2000 flight time type : 200
ASRS Report	311863
Person 2
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : declared emergency flight crew : overcame equipment problem flight crew : regained aircraft control other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

During autoplt developmental flight test a simulated pitch trim runaway was injected. Desired result was autoplt monitor's trip off autoplt or crew could disconnect runaway. However during this test pitch trim ran full nose down and crew was unable to recover until FL231. Declared an emergency (due to exceeding vmo by 10 percent) and landed at dvt without incident. Problem resolution lies in how we conduct test relative to injection point and disconnect methodologies. Corrected! Callback conversation with reporter revealed the following information: reporter stated that the aircraft was a cessna citation-750, not as yet certified and therefore classified as 'experimental.' the purpose of the test was to check the automatic trip function of the autoplt when it senses a pitch trim runaway. This pitch trim anomaly was 'introduced' by the engineer sitting in the aft cabin, through his keyboard and computer. When the severe nose down signal was sent, the aircraft pitched over violently, throwing that engineer against his seat belt and impacting the keyboard. That motion, unfortunately, sent a 'locked' signal to the trim disconnect/transfer system. The crew spent their time in the ensuing descent attempting to get to the secondary trim system via a guarded switch on the console. The design of the autoplt sensing system is supposed to have the autoplt detect this runaway signal to the #1 system and automatic transfer the autoplt to the #2 system. The 'keyboard lock' shut out this transfer which, it can be noted, was rather late in performing its designed function. Reporter stated that there was a software problem. The aircraft now has a 'kill' switch in the cockpit to prevent a 'locked' signal from overriding any automatic-transfer or disconnect signals by the pilots.

Original NASA ASRS Text

Title: LOSS OF ACFT CTL IN A CESSNA CITATION-750.

Narrative: DURING AUTOPLT DEVELOPMENTAL FLT TEST A SIMULATED PITCH TRIM RUNAWAY WAS INJECTED. DESIRED RESULT WAS AUTOPLT MONITOR'S TRIP OFF AUTOPLT OR CREW COULD DISCONNECT RUNAWAY. HOWEVER DURING THIS TEST PITCH TRIM RAN FULL NOSE DOWN AND CREW WAS UNABLE TO RECOVER UNTIL FL231. DECLARED AN EMER (DUE TO EXCEEDING VMO BY 10 PERCENT) AND LANDED AT DVT WITHOUT INCIDENT. PROB RESOLUTION LIES IN HOW WE CONDUCT TEST RELATIVE TO INJECTION POINT AND DISCONNECT METHODOLOGIES. CORRECTED! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE ACFT WAS A CESSNA CITATION-750, NOT AS YET CERTIFIED AND THEREFORE CLASSIFIED AS 'EXPERIMENTAL.' THE PURPOSE OF THE TEST WAS TO CHK THE AUTO TRIP FUNCTION OF THE AUTOPLT WHEN IT SENSES A PITCH TRIM RUNAWAY. THIS PITCH TRIM ANOMALY WAS 'INTRODUCED' BY THE ENGINEER SITTING IN THE AFT CABIN, THROUGH HIS KEYBOARD AND COMPUTER. WHEN THE SEVERE NOSE DOWN SIGNAL WAS SENT, THE ACFT PITCHED OVER VIOLENTLY, THROWING THAT ENGINEER AGAINST HIS SEAT BELT AND IMPACTING THE KEYBOARD. THAT MOTION, UNFORTUNATELY, SENT A 'LOCKED' SIGNAL TO THE TRIM DISCONNECT/TRANSFER SYS. THE CREW SPENT THEIR TIME IN THE ENSUING DSCNT ATTEMPTING TO GET TO THE SECONDARY TRIM SYS VIA A GUARDED SWITCH ON THE CONSOLE. THE DESIGN OF THE AUTOPLT SENSING SYS IS SUPPOSED TO HAVE THE AUTOPLT DETECT THIS RUNAWAY SIGNAL TO THE #1 SYS AND AUTO TRANSFER THE AUTOPLT TO THE #2 SYS. THE 'KEYBOARD LOCK' SHUT OUT THIS TRANSFER WHICH, IT CAN BE NOTED, WAS RATHER LATE IN PERFORMING ITS DESIGNED FUNCTION. RPTR STATED THAT THERE WAS A SOFTWARE PROB. THE ACFT NOW HAS A 'KILL' SWITCH IN THE COCKPIT TO PREVENT A 'LOCKED' SIGNAL FROM OVERRIDING ANY AUTO-TRANSFER OR DISCONNECT SIGNALS BY THE PLTS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.