 |
37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
|
Medium large transport mode C indicating higher at ATC facility than in cockpit. Requested to turn off.
| Attributes | |
| ACN | 230164 |
| Time | |
| Date | 199212 |
| Day | Mon |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | atc facility : orw airport : pvd |
| State Reference | CT |
| Altitude | msl bound lower : 10000 msl bound upper : 11000 |
| Environment | |
| Flight Conditions | IMC |
| Light | Dusk |
| Aircraft 1 | |
| Controlling Facilities | tower : lga |
| Operator | common carrier : air carrier |
| Make Model Name | Medium Large Transport, Low Wing, 2 Turbojet Eng |
| Navigation In Use | Other |
| Flight Phase | descent other |
| Route In Use | enroute airway : pvd |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : instrument pilot : cfi pilot : atp pilot : flight engineer |
| Experience | flight time last 90 days : 210 flight time total : 5800 flight time type : 3000 |
| ASRS Report | 230164 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | aircraft equipment problem : less severe inflight encounter : weather other anomaly other |
| Independent Detector | other controllera |
| Resolutory Action | none taken : unable none taken : anomaly accepted |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | other |
Narrative:
I was the first officer on flight from dtw to pvd. Over wipor intersection at 11000 ft MSL our aircraft was experiencing moderate icing conditions. We reported this condition to ATC. The controller issued a descent and we complied. At an altitude of approximately 10000 ft the controller asked our altitude and stated that his equipment still showed our flight at 11000 ft. He asked us to try the #2 transponder, we complied. The #2 also indicated a higher than actual altitude. ATC then asked us to stop altitude squawk. We complied. While on the approach a new controller asked us to try the mode C again. We selected 1 of the xponders on and mode C. The controller indicated that the altitude was still higher than actual but was within tolerance now. On the ground, we entered a logbook write-up of the #1 and #2 mode C functions. Our next flight, pud to dtw, was dispatched with mode C inoperative. Maintenance control theorizes that the inaccurate reports were caused by the large accumulation of ice on the mode C antenna. Perhaps this is why it was more accurate at the lower, warmer, non icing altitudes.
Original NASA ASRS Text
Title: MLG MODE C INDICATING HIGHER AT ATC FACILITY THAN IN COCKPIT. REQUESTED TO TURN OFF.
Narrative: I WAS THE FO ON FLT FROM DTW TO PVD. OVER WIPOR INTXN AT 11000 FT MSL OUR ACFT WAS EXPERIENCING MODERATE ICING CONDITIONS. WE RPTED THIS CONDITION TO ATC. THE CTLR ISSUED A DSCNT AND WE COMPLIED. AT AN ALT OF APPROX 10000 FT THE CTLR ASKED OUR ALT AND STATED THAT HIS EQUIP STILL SHOWED OUR FLT AT 11000 FT. HE ASKED US TO TRY THE #2 XPONDER, WE COMPLIED. THE #2 ALSO INDICATED A HIGHER THAN ACTUAL ALT. ATC THEN ASKED US TO STOP ALT SQUAWK. WE COMPLIED. WHILE ON THE APCH A NEW CTLR ASKED US TO TRY THE MODE C AGAIN. WE SELECTED 1 OF THE XPONDERS ON AND MODE C. THE CTLR INDICATED THAT THE ALT WAS STILL HIGHER THAN ACTUAL BUT WAS WITHIN TOLERANCE NOW. ON THE GND, WE ENTERED A LOGBOOK WRITE-UP OF THE #1 AND #2 MODE C FUNCTIONS. OUR NEXT FLT, PUD TO DTW, WAS DISPATCHED WITH MODE C INOP. MAINT CTL THEORIZES THAT THE INACCURATE RPTS WERE CAUSED BY THE LARGE ACCUMULATION OF ICE ON THE MODE C ANTENNA. PERHAPS THIS IS WHY IT WAS MORE ACCURATE AT THE LOWER, WARMER, NON ICING ALTS.
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.