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Learjet 35 flight crew were observed by ARTCC radar controller below assigned cruising altitude to which the flight crew responded that they were having autoplt problems after returning to assigned.
| Attributes | |
| ACN | 542766 |
| Time | |
| Date | 200204 |
| Day | Mon |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | navaid : gqo.vortac |
| State Reference | TN |
| Altitude | msl single value : 37000 |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : ztl.artcc |
| Operator | other |
| Make Model Name | Learjet 35 |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | government : faa |
| Function | controller : radar controller : supervisor controller : handoff position |
| Qualification | controller : radar |
| Experience | controller limited radar : 20 controller non radar : 20 controller radar : 20 controller supervisory : 0.25 controller time certified in position1 : 19 controller time certified in position2 : 6 |
| ASRS Report | 542766 |
| Person 2 | |
| Affiliation | government : military |
| Function | flight crew : captain oversight : pic |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance |
| Independent Detector | atc equipment other atc equipment : radar aircraft equipment other aircraft equipment : auto plt other controllera |
| Resolutory Action | controller : issued alert flight crew : overrode automation flight crew : returned to assigned altitude |
| Consequence | faa : reviewed incident with flight crew |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance |
| Primary Problem | Aircraft |
| Air Traffic Incident | Pilot Deviation |
Narrative:
Aircraft reported on frequency level at FL370, and mode C was indicating FL370 at that time. (Note: for aircraft in level flight at their assigned cruise altitude, center radar will not display a deviation of less than 250 ft above or below that altitude.) a few mins after the pilot checked in, I noticed the mode C reporting FL367 instead of FL370. This is not uncommon -- our radar often displays an incorrect altitude for 5-12 seconds for a number of reasons which have nothing to do with the aircraft's actual altitude. In this case, there were no aircraft in immediate confliction, so I elected to not check with the pilot right away since erroneous (but brief) mode C readouts are common. After a couple more radar sweeps, I observed the readout at FL366, and I advised the pilot that 'mode C indicates 400 ft low, maintain FL370.' the pilot advised that they appeared to have had a problem with the autoplt, and they were climbing back to FL370. There was no loss of separation. The nearest aircraft was still almost 2 mins away at FL350 when the mode C again indicated FL370.
Original NASA ASRS Text
Title: LEARJET 35 FLC WERE OBSERVED BY ARTCC RADAR CTLR BELOW ASSIGNED CRUISING ALT TO WHICH THE FLC RESPONDED THAT THEY WERE HAVING AUTOPLT PROBS AFTER RETURNING TO ASSIGNED.
Narrative: ACFT RPTED ON FREQ LEVEL AT FL370, AND MODE C WAS INDICATING FL370 AT THAT TIME. (NOTE: FOR ACFT IN LEVEL FLT AT THEIR ASSIGNED CRUISE ALT, CTR RADAR WILL NOT DISPLAY A DEV OF LESS THAN 250 FT ABOVE OR BELOW THAT ALT.) A FEW MINS AFTER THE PLT CHKED IN, I NOTICED THE MODE C RPTING FL367 INSTEAD OF FL370. THIS IS NOT UNCOMMON -- OUR RADAR OFTEN DISPLAYS AN INCORRECT ALT FOR 5-12 SECONDS FOR A NUMBER OF REASONS WHICH HAVE NOTHING TO DO WITH THE ACFT'S ACTUAL ALT. IN THIS CASE, THERE WERE NO ACFT IN IMMEDIATE CONFLICTION, SO I ELECTED TO NOT CHK WITH THE PLT RIGHT AWAY SINCE ERRONEOUS (BUT BRIEF) MODE C READOUTS ARE COMMON. AFTER A COUPLE MORE RADAR SWEEPS, I OBSERVED THE READOUT AT FL366, AND I ADVISED THE PLT THAT 'MODE C INDICATES 400 FT LOW, MAINTAIN FL370.' THE PLT ADVISED THAT THEY APPEARED TO HAVE HAD A PROB WITH THE AUTOPLT, AND THEY WERE CLBING BACK TO FL370. THERE WAS NO LOSS OF SEPARATION. THE NEAREST ACFT WAS STILL ALMOST 2 MINS AWAY AT FL350 WHEN THE MODE C AGAIN INDICATED FL370.
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.