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A B737-300 flight crew fails to note an uncommanded climb during a descent, speed change procedure when the autoplt reverts to control wheel steering mode. Loss of separation with trailing traffic occurs.
| Attributes | |
| ACN | 464573 |
| Time | |
| Date | 200002 |
| Day | Mon |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| State Reference | TX |
| Altitude | msl bound lower : 20000 msl bound upper : 21200 |
| Environment | |
| Flight Conditions | VMC |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | artcc : zhu.artcc tower : dfw.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other |
| Flight Phase | descent : holding descent : intermediate altitude |
| Route In Use | arrival star : cugar six |
| Flight Plan | IFR |
| Aircraft 2 | |
| Controlling Facilities | artcc : zhu.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent : vacating altitude |
| Route In Use | arrival star : cugar six |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp pilot : flight engineer pilot : cfi |
| Experience | flight time last 90 days : 37 flight time total : 7000 flight time type : 37 |
| ASRS Report | 464573 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : published procedure other anomaly other anomaly other |
| Independent Detector | aircraft equipment : tcas other flight crewa other flight crewb |
| Resolutory Action | flight crew : regained aircraft control flight crew : returned to original clearance |
| Consequence | faa : reviewed incident with flight crew faa : investigated |
| Miss Distance | horizontal : 15000 vertical : 500 |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
Our aircraft was given holding at the arnne intersection. Cleared from holding at arnne to hold at cll, FL200. Aircraft was slowed to 225 KTS for holding. We entered the hold, not yet fully established in the hold when we were cleared direct to 'hoagi' maintain 320 KTS, cross hoagi at 10000 ft and 250 KTS. We were given a right turn to 'hoagi.' the autoplt was being programmed for the descent. Autoplt was in 'heading' roll mode and placed in 'level change' for pitch mode. Speed was in 'MCP speed' and 320 KTS was selected. The MCP altitude was set to 10000 ft for the hoagi restr. After descent was started for hoagi, PF was 'heads down' cleaning up the FMC for continuing the cugar 6 arrival. PNF was calling company with ETA changes, and advising the flight attendants. Next thing we see is our aircraft climb through FL210 with a TA from an aircraft behind us. The autoplt had gone into a different mode of 'control wheel steering pitch.' the uncommanded climb was arrested at approximately FL212 and a hand flown descent started. We believe that the mode change was caused by the large power change from flight at 225 KTS to 320 KTS and the removal of the 'hard' altitude of FL200 being changed to 10000 ft. ATC advised us of a 'possible traffic conflict' caused by our uncommanded deviation.
Original NASA ASRS Text
Title: A B737-300 FLC FAILS TO NOTE AN UNCOMMANDED CLB DURING A DSCNT, SPD CHANGE PROC WHEN THE AUTOPLT REVERTS TO CTL WHEEL STEERING MODE. LOSS OF SEPARATION WITH TRAILING TFC OCCURS.
Narrative: OUR ACFT WAS GIVEN HOLDING AT THE ARNNE INTXN. CLRED FROM HOLDING AT ARNNE TO HOLD AT CLL, FL200. ACFT WAS SLOWED TO 225 KTS FOR HOLDING. WE ENTERED THE HOLD, NOT YET FULLY ESTABLISHED IN THE HOLD WHEN WE WERE CLRED DIRECT TO 'HOAGI' MAINTAIN 320 KTS, CROSS HOAGI AT 10000 FT AND 250 KTS. WE WERE GIVEN A R TURN TO 'HOAGI.' THE AUTOPLT WAS BEING PROGRAMMED FOR THE DSCNT. AUTOPLT WAS IN 'HDG' ROLL MODE AND PLACED IN 'LEVEL CHANGE' FOR PITCH MODE. SPD WAS IN 'MCP SPD' AND 320 KTS WAS SELECTED. THE MCP ALT WAS SET TO 10000 FT FOR THE HOAGI RESTR. AFTER DSCNT WAS STARTED FOR HOAGI, PF WAS 'HEADS DOWN' CLEANING UP THE FMC FOR CONTINUING THE CUGAR 6 ARR. PNF WAS CALLING COMPANY WITH ETA CHANGES, AND ADVISING THE FLT ATTENDANTS. NEXT THING WE SEE IS OUR ACFT CLB THROUGH FL210 WITH A TA FROM AN ACFT BEHIND US. THE AUTOPLT HAD GONE INTO A DIFFERENT MODE OF 'CTL WHEEL STEERING PITCH.' THE UNCOMMANDED CLB WAS ARRESTED AT APPROX FL212 AND A HAND FLOWN DSCNT STARTED. WE BELIEVE THAT THE MODE CHANGE WAS CAUSED BY THE LARGE PWR CHANGE FROM FLT AT 225 KTS TO 320 KTS AND THE REMOVAL OF THE 'HARD' ALT OF FL200 BEING CHANGED TO 10000 FT. ATC ADVISED US OF A 'POSSIBLE TFC CONFLICT' CAUSED BY OUR UNCOMMANDED DEV.
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.