An MD88 airline crew overshot their assigned altitude during a descent, in part, due to a runaway cr...

Attributes
ACN	435262
Time
Date	199904
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : flm.vor
State Reference	KY
Altitude	msl bound lower : 21600 msl bound upper : 22000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid.artcc
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	other vortac
Flight Phase	descent : intermediate altitude
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 160 flight time total : 8000 flight time type : 1920
ASRS Report	435262
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : far non adherence : clearance
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : returned to original clearance
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were given a crossing restr of 20 mi south of flm VOR at FL220. We started descent at 30 mi south of flm. The captain was flying with the aircraft on autoplt. Descending through FL230 for FL220 the aircraft started pitching down more instead of pitching up. I warned the captain to be prepared to manually level off. The captain tried to level off smoothly but in doing so the aircraft momentarily descended 400 ft low to FL216. During the later phase of the leveloff we noticed that the secondary trim was stuck engaged and slowly running away in the nose down position. This gave the captain great difficulty in the leveloff until the problem was recognized and we switched to primary (faster) trim. We wrote up the problem for maintenance and continued uneventfully to dayton. ZID did not mention or question the momentary altitude deviation to us. No traffic conflicts were noted visually or on TCASII. Callback conversation with reporter revealed the following information: the first officer said that he has enough experience in the MD88 to know that he should be prepared to take action to insure that altitudes are captured by the autoplt. During this incident, the first officer thinks that he was listening to the ATIS or doing something else when he noticed that the descent rate seemed excessive for the amount of altitude remaining before their assigned leveloff altitude. He suggested that the captain manually level off, but instead he initially attempted to use the autoplt pitch control wheel. At this time, the flight crew noticed that the autoplt trim was still moving in the nose down direction. The captain then disconnected the autoplt and used the main electric trim and control wheel displacement to climb back to their assigned altitude. The cruise trim circuit was disconnected according to the checklist and the proper entry was made in the maintenance log. The first officer said that he was unable to follow up on the maintenance action because they changed aircraft and he has not flown that aircraft since.

Original NASA ASRS Text

Title: AN MD88 AIRLINE CREW OVERSHOT THEIR ASSIGNED ALT DURING A DSCNT, IN PART, DUE TO A RUNAWAY CRUISE TRIM NOSE DOWN.

Narrative: WE WERE GIVEN A XING RESTR OF 20 MI S OF FLM VOR AT FL220. WE STARTED DSCNT AT 30 MI S OF FLM. THE CAPT WAS FLYING WITH THE ACFT ON AUTOPLT. DSNDING THROUGH FL230 FOR FL220 THE ACFT STARTED PITCHING DOWN MORE INSTEAD OF PITCHING UP. I WARNED THE CAPT TO BE PREPARED TO MANUALLY LEVEL OFF. THE CAPT TRIED TO LEVEL OFF SMOOTHLY BUT IN DOING SO THE ACFT MOMENTARILY DSNDED 400 FT LOW TO FL216. DURING THE LATER PHASE OF THE LEVELOFF WE NOTICED THAT THE SECONDARY TRIM WAS STUCK ENGAGED AND SLOWLY RUNNING AWAY IN THE NOSE DOWN POS. THIS GAVE THE CAPT GREAT DIFFICULTY IN THE LEVELOFF UNTIL THE PROB WAS RECOGNIZED AND WE SWITCHED TO PRIMARY (FASTER) TRIM. WE WROTE UP THE PROB FOR MAINT AND CONTINUED UNEVENTFULLY TO DAYTON. ZID DID NOT MENTION OR QUESTION THE MOMENTARY ALTDEV TO US. NO TFC CONFLICTS WERE NOTED VISUALLY OR ON TCASII. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FO SAID THAT HE HAS ENOUGH EXPERIENCE IN THE MD88 TO KNOW THAT HE SHOULD BE PREPARED TO TAKE ACTION TO INSURE THAT ALTS ARE CAPTURED BY THE AUTOPLT. DURING THIS INCIDENT, THE FO THINKS THAT HE WAS LISTENING TO THE ATIS OR DOING SOMETHING ELSE WHEN HE NOTICED THAT THE DSCNT RATE SEEMED EXCESSIVE FOR THE AMOUNT OF ALT REMAINING BEFORE THEIR ASSIGNED LEVELOFF ALT. HE SUGGESTED THAT THE CAPT MANUALLY LEVEL OFF, BUT INSTEAD HE INITIALLY ATTEMPTED TO USE THE AUTOPLT PITCH CTL WHEEL. AT THIS TIME, THE FLC NOTICED THAT THE AUTOPLT TRIM WAS STILL MOVING IN THE NOSE DOWN DIRECTION. THE CAPT THEN DISCONNECTED THE AUTOPLT AND USED THE MAIN ELECTRIC TRIM AND CTL WHEEL DISPLACEMENT TO CLB BACK TO THEIR ASSIGNED ALT. THE CRUISE TRIM CIRCUIT WAS DISCONNECTED ACCORDING TO THE CHKLIST AND THE PROPER ENTRY WAS MADE IN THE MAINT LOG. THE FO SAID THAT HE WAS UNABLE TO FOLLOW UP ON THE MAINT ACTION BECAUSE THEY CHANGED ACFT AND HE HAS NOT FLOWN THAT ACFT SINCE.

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.

An MD88 airline crew overshot their assigned altitude during a descent, in part, due to a runaway cruise trim nose down.