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Flight crew of a B727 descended off altitude prior to the assigned fix resulting in a GPWS terrain warning due to missetting the VOR/DME captain and first officer display switches. They returned to assigned altitude at once upon recognizing their error.
| Attributes | |
| ACN | 410049 |
| Time | |
| Date | 199808 |
| Day | Mon |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | airport : mzt |
| State Reference | FO |
| Altitude | msl bound lower : 6000 msl bound upper : 8000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : mzt tracon : msp |
| Operator | common carrier : air carrier |
| Make Model Name | B727 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : commercial pilot : flight engineer pilot : instrument pilot : atp |
| Experience | flight time last 90 days : 150 flight time total : 13000 flight time type : 11500 |
| ASRS Report | 410049 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp pilot : instrument pilot : flight engineer pilot : commercial |
| Experience | flight time last 90 days : 205 flight time total : 8000 flight time type : 450 |
| ASRS Report | 410060 |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other |
| Independent Detector | other flight crewa |
| Resolutory Action | flight crew : returned to intended course or assigned course |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
Approach cleared us to descend to 8000 ft, until 22 DME, then to 6000 ft. Captain had mzt on VOR, corin on GPS. First officer had mzt on VOR, corin on GPS. GPS/VOR switch was in VOR on captain and GPS on first officer. This had the effect of having captain DME window reading mzt DME and both GPS CDU's and first officer DME reading distance to corin. At 22 DME (as read on first officer DME, descent to 6000 ft was started -- first officer was PF). Because of visual conditions we determined that we were going low, realized the mistake and climbed back to 8000 ft until the mzt 22 DME fix. Although we got a terrain warning, the radar altimeter never moved off the stops. Human performance: clearly the most important factor in this situation was reading the wrong DME to mzt. The nature of the instrument switching system made this easy to do.
Original NASA ASRS Text
Title: FLC OF A B727 DSNDED OFF ALT PRIOR TO THE ASSIGNED FIX RESULTING IN A GPWS TERRAIN WARNING DUE TO MISSETTING THE VOR/DME CAPT AND FO DISPLAY SWITCHES. THEY RETURNED TO ASSIGNED ALT AT ONCE UPON RECOGNIZING THEIR ERROR.
Narrative: APCH CLRED US TO DSND TO 8000 FT, UNTIL 22 DME, THEN TO 6000 FT. CAPT HAD MZT ON VOR, CORIN ON GPS. FO HAD MZT ON VOR, CORIN ON GPS. GPS/VOR SWITCH WAS IN VOR ON CAPT AND GPS ON FO. THIS HAD THE EFFECT OF HAVING CAPT DME WINDOW READING MZT DME AND BOTH GPS CDU'S AND FO DME READING DISTANCE TO CORIN. AT 22 DME (AS READ ON FO DME, DSCNT TO 6000 FT WAS STARTED -- FO WAS PF). BECAUSE OF VISUAL CONDITIONS WE DETERMINED THAT WE WERE GOING LOW, REALIZED THE MISTAKE AND CLBED BACK TO 8000 FT UNTIL THE MZT 22 DME FIX. ALTHOUGH WE GOT A TERRAIN WARNING, THE RADAR ALTIMETER NEVER MOVED OFF THE STOPS. HUMAN PERFORMANCE: CLRLY THE MOST IMPORTANT FACTOR IN THIS SIT WAS READING THE WRONG DME TO MZT. THE NATURE OF THE INST SWITCHING SYS MADE THIS EASY TO DO.
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.