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B767 crew had a GPWS 'terrain terrain' warning triggered by heavy precipitation at 6000 ft over the ocean in sct class east.
| Attributes | |
| ACN | 503231 |
| Time | |
| Date | 200103 |
| Day | Mon |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | navaid : lax.vortac |
| State Reference | CA |
| Altitude | msl single value : 6000 |
| Environment | |
| Flight Conditions | IMC |
| Weather Elements | Turbulence Rain other |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | tracon : sct.tracon |
| Operator | common carrier : air carrier |
| Make Model Name | B767 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | ils localizer & glide slope : 6l other |
| Flight Phase | descent : approach |
| Route In Use | arrival : on vectors |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : commercial pilot : instrument pilot : multi engine |
| ASRS Report | 503231 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | aircraft equipment problem : critical inflight encounter : turbulence inflight encounter : weather inflight encounter other other anomaly other |
| Independent Detector | aircraft equipment : gpws other flight crewa other flight crewb |
| Resolutory Action | controller : issued new clearance controller : provided flight assist flight crew : took evasive action none taken : detected after the fact other |
| Consequence | other other |
| Supplementary | |
| Problem Areas | Weather FAA Aircraft |
| Primary Problem | Aircraft |
Narrative:
We were level at 6000 ft during our arrival into lax, being vectored to final for the 6L ILS. The radar was showing some areas of moderate to heavy precipitation between our position and lax. While passing through these areas we began to get decreasing radio altimeter indications at both crew positions. In one case the indication was low enough to generate a terrain warning 'terrain-terrain pull-up-pull up.' although we believed ourselves to still be over the ocean, we responded to the terrain warning, climbing up to approximately 9000 ft. We informed socal of our action, they said no way were we close to any terrain. At nearly the same time we passed through a pocket of severe turbulence. Socal said that due to our high altitude they would have to break us out and bring us around again. During the escape and recovery period of turbulence we might have exceeded the flaps 5 limiting speed. We told the controller that if he took us around again we would likely pass through the same area of heavy precipitation and turbulence, and we could not accept that. We were vectored in closer to the airport and then given a small box pattern keeping us east of the trouble spots. We proceeded to an uneventful landing. We wrote up the severe turbulence encounter, the possible flap overspeed, and the erroneous radio altimeter readings and terrain warnings. Are these normal indications for this aircraft in heavy precipitation, or was there a malfunction. It was very distracting in night IMC/turbulence to get a terrain warning.
Original NASA ASRS Text
Title: B767 CREW HAD A GPWS 'TERRAIN TERRAIN' WARNING TRIGGERED BY HEAVY PRECIPITATION AT 6000 FT OVER THE OCEAN IN SCT CLASS E.
Narrative: WE WERE LEVEL AT 6000 FT DURING OUR ARR INTO LAX, BEING VECTORED TO FINAL FOR THE 6L ILS. THE RADAR WAS SHOWING SOME AREAS OF MODERATE TO HEAVY PRECIP BTWN OUR POS AND LAX. WHILE PASSING THROUGH THESE AREAS WE BEGAN TO GET DECREASING RADIO ALTIMETER INDICATIONS AT BOTH CREW POSITIONS. IN ONE CASE THE INDICATION WAS LOW ENOUGH TO GENERATE A TERRAIN WARNING 'TERRAIN-TERRAIN PULL-UP-PULL UP.' ALTHOUGH WE BELIEVED OURSELVES TO STILL BE OVER THE OCEAN, WE RESPONDED TO THE TERRAIN WARNING, CLBING UP TO APPROX 9000 FT. WE INFORMED SOCAL OF OUR ACTION, THEY SAID NO WAY WERE WE CLOSE TO ANY TERRAIN. AT NEARLY THE SAME TIME WE PASSED THROUGH A POCKET OF SEVERE TURBULENCE. SOCAL SAID THAT DUE TO OUR HIGH ALTITUDE THEY WOULD HAVE TO BREAK US OUT AND BRING US AROUND AGAIN. DURING THE ESCAPE AND RECOVERY PERIOD OF TURBULENCE WE MIGHT HAVE EXCEEDED THE FLAPS 5 LIMITING SPEED. WE TOLD THE CTLR THAT IF HE TOOK US AROUND AGAIN WE WOULD LIKELY PASS THROUGH THE SAME AREA OF HEAVY PRECIP AND TURBULENCE, AND WE COULD NOT ACCEPT THAT. WE WERE VECTORED IN CLOSER TO THE ARPT AND THEN GIVEN A SMALL BOX PATTERN KEEPING US E OF THE TROUBLE SPOTS. WE PROCEEDED TO AN UNEVENTFUL LNDG. WE WROTE UP THE SEVERE TURBULENCE ENCOUNTER, THE POSSIBLE FLAP OVERSPEED, AND THE ERRONEOUS RADIO ALTIMETER READINGS AND TERRAIN WARNINGS. ARE THESE NORMAL INDICATIONS FOR THIS ACFT IN HEAVY PRECIP, OR WAS THERE A MALFUNCTION. IT WAS VERY DISTRACTING IN NIGHT IMC/TURB TO GET A TERRAIN WARNING.
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.