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An small transport government pilot turned off his mode C when he realized the encoder was generating the wrong altitude readout for ATC. He later realized that he should have waited for the controller to advise him to go to the standby position on the mode C.
| Attributes | |
| ACN | 396280 |
| Time | |
| Date | 199803 |
| Day | Wed |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | airport : ord |
| State Reference | IL |
| Altitude | msl bound lower : 16000 msl bound upper : 16000 |
| Environment | |
| Flight Conditions | Mixed |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zau |
| Operator | other |
| Make Model Name | Any Unknown or Unlisted Aircraft Manufacturer |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | government other |
| Function | flight crew : single pilot |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 50 flight time total : 10200 flight time type : 575 |
| ASRS Report | 396280 |
| Person 2 | |
| Affiliation | government : faa |
| Function | controller : radar |
| Qualification | controller : radar |
| Events | |
| Anomaly | aircraft equipment problem : less severe non adherence : far non adherence : clearance other anomaly other |
| Independent Detector | other controllera |
| Resolutory Action | none taken : anomaly accepted |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | Pilot Deviation |
Narrative:
En route to ord at 17000 ft MSL I was asked to verify my altitude and altimeter setting. I was then instructed by ZKC to stop altitude squawk because of an inaccurate mode C readout. I complied and continued to and landed at ord. Departing ord I selected my other encoder. After leveling off at 16000 ft MSL I requested an altitude check from center. They reported me as being at 13400 ft MSL. I acknowledged and advised them I would stop altitude squawk. I now realized that I should have left the mode C on until instructed by ATC to stop squawking mode C. But after the incident with the other encoder I assumed they would not want to view an erroneous reading and if wished me to continue squawking mode C they would have informed me to continue with mode C on. After landing at home base I reported the problem to maintenance and they are fixing the encoders.
Original NASA ASRS Text
Title: AN SMT GOV PLT TURNED OFF HIS MODE C WHEN HE REALIZED THE ENCODER WAS GENERATING THE WRONG ALT READOUT FOR ATC. HE LATER REALIZED THAT HE SHOULD HAVE WAITED FOR THE CTLR TO ADVISE HIM TO GO TO THE STANDBY POS ON THE MODE C.
Narrative: ENRTE TO ORD AT 17000 FT MSL I WAS ASKED TO VERIFY MY ALT AND ALTIMETER SETTING. I WAS THEN INSTRUCTED BY ZKC TO STOP ALT SQUAWK BECAUSE OF AN INACCURATE MODE C READOUT. I COMPLIED AND CONTINUED TO AND LANDED AT ORD. DEPARTING ORD I SELECTED MY OTHER ENCODER. AFTER LEVELING OFF AT 16000 FT MSL I REQUESTED AN ALT CHK FROM CTR. THEY RPTED ME AS BEING AT 13400 FT MSL. I ACKNOWLEDGED AND ADVISED THEM I WOULD STOP ALT SQUAWK. I NOW REALIZED THAT I SHOULD HAVE LEFT THE MODE C ON UNTIL INSTRUCTED BY ATC TO STOP SQUAWKING MODE C. BUT AFTER THE INCIDENT WITH THE OTHER ENCODER I ASSUMED THEY WOULD NOT WANT TO VIEW AN ERRONEOUS READING AND IF WISHED ME TO CONTINUE SQUAWKING MODE C THEY WOULD HAVE INFORMED ME TO CONTINUE WITH MODE C ON. AFTER LNDG AT HOME BASE I RPTED THE PROB TO MAINT AND THEY ARE FIXING THE ENCODERS.
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.