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B737-400 first officer inadvertently descended early on a localizer approach outside the final approach fix due to momentarily setting his navigation reference to a VOR frequency and when returning, the DME momentarily hang up on the wrong distance.
| Attributes | |
| ACN | 535016 |
| Time | |
| Date | 200201 |
| Day | Mon |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | airport : lga.airport |
| State Reference | NY |
| Altitude | msl single value : 1600 |
| Environment | |
| Flight Conditions | IMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tower : lga.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B737-400 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | ils localizer only : 31 other |
| Route In Use | approach : instrument non precision arrival : on vectors |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 60 flight time total : 14000 flight time type : 6000 |
| ASRS Report | 535016 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp pilot : cfi pilot : flight engineer |
| Experience | flight time last 90 days : 150 flight time total : 15500 flight time type : 3500 |
| ASRS Report | 534415 |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : published procedure |
| Independent Detector | aircraft equipment other aircraft equipment : dme distance other flight crewa other flight crewb |
| Resolutory Action | flight crew : returned to assigned altitude other |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
First officer flying localizer runway 31 approach to lga with raw data localizer frequency and course set in. Captain was in FMC navigation mode. On base leg, first officer temporarily switched to lga VOR frequency for bearing/DME reference and returned to localizer frequency. Due to some anomaly DME hung up at 5 DME resulting in captain's early callout of FAF and a slightly early descent below FAF altitude. We were unsure exactly how early and when we positively reestablished our DME, we were within parameters. An uneventful descent to minimums was made and normal landing. First officer's decision to switch frequencys was bad at critical base leg position. Possible equipment malfunction contributed. DME was written up at destination for a thorough check. Unknown results. Better xchk with FMC data would have helped.
Original NASA ASRS Text
Title: B737-400 FO INADVERTENTLY DSNDED EARLY ON A LOC APCH OUTSIDE THE FINAL APCH FIX DUE TO MOMENTARILY SETTING HIS NAV REF TO A VOR FREQ AND WHEN RETURNING, THE DME MOMENTARILY HANG UP ON THE WRONG DISTANCE.
Narrative: FO FLYING LOC RWY 31 APCH TO LGA WITH RAW DATA LOC FREQ AND COURSE SET IN. CAPT WAS IN FMC NAV MODE. ON BASE LEG, FO TEMPORARILY SWITCHED TO LGA VOR FREQ FOR BEARING/DME REF AND RETURNED TO LOC FREQ. DUE TO SOME ANOMALY DME HUNG UP AT 5 DME RESULTING IN CAPT'S EARLY CALLOUT OF FAF AND A SLIGHTLY EARLY DSCNT BELOW FAF ALT. WE WERE UNSURE EXACTLY HOW EARLY AND WHEN WE POSITIVELY REESTABLISHED OUR DME, WE WERE WITHIN PARAMETERS. AN UNEVENTFUL DSCNT TO MINIMUMS WAS MADE AND NORMAL LNDG. FO'S DECISION TO SWITCH FREQS WAS BAD AT CRITICAL BASE LEG POS. POSSIBLE EQUIP MALFUNCTION CONTRIBUTED. DME WAS WRITTEN UP AT DEST FOR A THOROUGH CHK. UNKNOWN RESULTS. BETTER XCHK WITH FMC DATA WOULD HAVE HELPED.
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.