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While in level cruise at FL350, the mode C of an HS125-700A transmits a false altitude reading of FL365 which causes another aircraft at FL370 to execute an evasive action climb. A problem for the crew is cited by the controller at ZDV, co.
| Attributes | |
| ACN | 585936 |
| Time | |
| Date | 200306 |
| Day | Thu |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : zdv.artcc |
| State Reference | CO |
| Altitude | msl bound lower : 35000 msl bound upper : 37000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zdv.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | HS 125 Series 700 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Aircraft 2 | |
| Controlling Facilities | artcc : zdv.artcc |
| Make Model Name | Any Unknown or Unlisted Aircraft Manufacturer |
| Flight Phase | cruise : enroute altitude change cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : multi engine pilot : cfi pilot : atp |
| Experience | flight time last 90 days : 100 flight time total : 5000 flight time type : 1200 |
| ASRS Report | 585936 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | aircraft equipment problem : less severe non adherence : published procedure other anomaly other |
| Independent Detector | atc equipment other atc equipment : radar mode c other controllera |
| Resolutory Action | controller : issued advisory |
| Consequence | faa : investigated faa : reviewed incident with flight crew other |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance Aircraft ATC Human Performance |
| Primary Problem | Aircraft |
| Air Traffic Incident | other |
Narrative:
On a flight from pnc (ponca city, ok) to jac (jackson hole) we were level at FL350. Center asked 'are you descending to FL350?' we replied 'we are level at FL350.' no definite response from center just an 'oh' or some such. About 5-10 mins later we heard center ask an aircraft what he was doing. 'I'm responding to an RA' said the aircraft. Center told him there weren't any aircraft nearby, and that a faulty mode 'C' from another aircraft had caused his false RA. A min or two later, center called us and said our mode 'C' had glitched from FL350 to FL365 and back again. The other aircraft had responded to our glitch. He asked us to turn off altitude reporting, which we did. He said that he was going to have to write this up. Maintenance found and repaired the mode 'C' problem. The mode 'C' has operated properly during the last 5 flts.
Original NASA ASRS Text
Title: WHILE IN LEVEL CRUISE AT FL350, THE MODE C OF AN HS125-700A XMITS A FALSE ALT READING OF FL365 WHICH CAUSES ANOTHER ACFT AT FL370 TO EXECUTE AN EVASIVE ACTION CLB. A PROB FOR THE CREW IS CITED BY THE CTLR AT ZDV, CO.
Narrative: ON A FLT FROM PNC (PONCA CITY, OK) TO JAC (JACKSON HOLE) WE WERE LEVEL AT FL350. CTR ASKED 'ARE YOU DSNDING TO FL350?' WE REPLIED 'WE ARE LEVEL AT FL350.' NO DEFINITE RESPONSE FROM CTR JUST AN 'OH' OR SOME SUCH. ABOUT 5-10 MINS LATER WE HEARD CTR ASK AN ACFT WHAT HE WAS DOING. 'I'M RESPONDING TO AN RA' SAID THE ACFT. CTR TOLD HIM THERE WEREN'T ANY ACFT NEARBY, AND THAT A FAULTY MODE 'C' FROM ANOTHER ACFT HAD CAUSED HIS FALSE RA. A MIN OR TWO LATER, CTR CALLED US AND SAID OUR MODE 'C' HAD GLITCHED FROM FL350 TO FL365 AND BACK AGAIN. THE OTHER ACFT HAD RESPONDED TO OUR GLITCH. HE ASKED US TO TURN OFF ALT RPTING, WHICH WE DID. HE SAID THAT HE WAS GOING TO HAVE TO WRITE THIS UP. MAINT FOUND AND REPAIRED THE MODE 'C' PROB. THE MODE 'C' HAS OPERATED PROPERLY DURING THE LAST 5 FLTS.
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.