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Advanced cockpit large transport received radio altimeter activated voice warning of minimums 100' before aircraft reached minimum altitude.
| Attributes | |
| ACN | 97683 |
| Time | |
| Date | 198811 |
| Day | Sat |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | airport : san |
| State Reference | CA |
| Altitude | agl bound lower : 450 agl bound upper : 450 |
| Environment | |
| Flight Conditions | IMC |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | tower : san |
| Operator | common carrier : air carrier |
| Make Model Name | Large Transport, Low Wing, 2 Turbojet Eng |
| Navigation In Use | Other Other |
| Flight Phase | descent : approach |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 170 flight time total : 16000 |
| ASRS Report | 97683 |
| Events | |
| Anomaly | aircraft equipment problem : less severe other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified |
| Resolutory Action | none taken : unable |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Airport |
| Air Traffic Incident | other |
Narrative:
DH on ILS 9 is 350' MSL and 336' ht above ground (radio altitude). At 450' MSL a rapid decrease occurred in the radio altimeter. On the large transport this initiated a minimums warning prior to reaching minimums. There is something on the ground at this point on approach that is causing the radio altimeter to read approximately 100' in error. This situation caused 2 aircraft to initiate a premature go around. 2 other pilots told of having this same problem. A note should be made that the radio altimeter is unusable and the minimums adjusted accordingly. Callback conversation with reporter revealed the following: reporter is not familiar with san and thinks flight crews should be reminded that radio altimeter readings do fluctuate at low altitude on this approach. Says an air carrier ahead of him made an unnecessary go around reacting to a voice warning that aircraft was at minimum altitude for approach. Reporter will ask company to put a reminder in their company newsletter about the potential false warning.
Original NASA ASRS Text
Title: ADVANCED COCKPIT LGT RECEIVED RADIO ALTIMETER ACTIVATED VOICE WARNING OF MINIMUMS 100' BEFORE ACFT REACHED MINIMUM ALT.
Narrative: DH ON ILS 9 IS 350' MSL AND 336' HT ABOVE GND (RADIO ALT). AT 450' MSL A RAPID DECREASE OCCURRED IN THE RADIO ALTIMETER. ON THE LGT THIS INITIATED A MINIMUMS WARNING PRIOR TO REACHING MINIMUMS. THERE IS SOMETHING ON THE GND AT THIS POINT ON APCH THAT IS CAUSING THE RADIO ALTIMETER TO READ APPROX 100' IN ERROR. THIS SITUATION CAUSED 2 ACFT TO INITIATE A PREMATURE GO AROUND. 2 OTHER PLTS TOLD OF HAVING THIS SAME PROB. A NOTE SHOULD BE MADE THAT THE RADIO ALTIMETER IS UNUSABLE AND THE MINIMUMS ADJUSTED ACCORDINGLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR IS NOT FAMILIAR WITH SAN AND THINKS FLT CREWS SHOULD BE REMINDED THAT RADIO ALTIMETER READINGS DO FLUCTUATE AT LOW ALT ON THIS APCH. SAYS AN ACR AHEAD OF HIM MADE AN UNNECESSARY GO AROUND REACTING TO A VOICE WARNING THAT ACFT WAS AT MINIMUM ALT FOR APCH. RPTR WILL ASK COMPANY TO PUT A REMINDER IN THEIR COMPANY NEWSLETTER ABOUT THE POTENTIAL FALSE WARNING.
Data retrieved from NASA's ASRS site as of August 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.