 |
37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
|
B747-400 captain attempted to descend using aircraft automation. When reprogrammed to comply with a new clearance, descent was delayed excessively.
| Attributes | |
| ACN | 410940 |
| Time | |
| Date | 199808 |
| Day | Wed |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : eck |
| State Reference | MI |
| Altitude | msl bound lower : 29000 msl bound upper : 29600 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zob tower : sjt |
| Operator | common carrier : air carrier |
| Make Model Name | B747-400 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other Other |
| Flight Phase | descent other |
| Flight Plan | IFR |
| Aircraft 2 | |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | other : unknown |
| Flight Phase | cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : instrument pilot : atp |
| Experience | flight time last 90 days : 15 flight time total : 18000 flight time type : 300 |
| ASRS Report | 410940 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : commercial pilot : instrument |
| Events | |
| Anomaly | aircraft equipment problem : critical altitude deviation : undershoot conflict : airborne less severe |
| Independent Detector | other controllera |
| Resolutory Action | flight crew : returned to intended course or assigned course other |
| Consequence | Other |
| Miss Distance | horizontal : 30000 vertical : 1400 |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | Pilot Deviation |
Narrative:
My aircraft was given a crossing restr of a point about 30 mi east of eck VOR to be at or below FL290 then pilot discretion to FL240. A descent from FL390 was started. The FMC was reprogrammed at about FL300 for a cruise altitude of FL290 so that a new top of descent had to be figured so as to start down in time to cross the polak intersection at 12000 ft. The FMC leveled the aircraft off at about FL296 while it computed a new top of descent point (approximately 30 seconds). That 30 second period was long enough for an aircraft to get within 2000 ft of our aircraft (he was at FL310). ATC warned us to descend the other 600 ft immediately, which we did. I don't believe a violation was filed but it taught me a good lesson in using the FMC.
Original NASA ASRS Text
Title: B747-400 CAPT ATTEMPTED TO DSND USING ACFT AUTOMATION. WHEN REPROGRAMMED TO COMPLY WITH A NEW CLRNC, DSCNT WAS DELAYED EXCESSIVELY.
Narrative: MY ACFT WAS GIVEN A XING RESTR OF A POINT ABOUT 30 MI E OF ECK VOR TO BE AT OR BELOW FL290 THEN PLT DISCRETION TO FL240. A DSCNT FROM FL390 WAS STARTED. THE FMC WAS REPROGRAMMED AT ABOUT FL300 FOR A CRUISE ALT OF FL290 SO THAT A NEW TOP OF DSCNT HAD TO BE FIGURED SO AS TO START DOWN IN TIME TO CROSS THE POLAK INTXN AT 12000 FT. THE FMC LEVELED THE ACFT OFF AT ABOUT FL296 WHILE IT COMPUTED A NEW TOP OF DSCNT POINT (APPROX 30 SECONDS). THAT 30 SECOND PERIOD WAS LONG ENOUGH FOR AN ACFT TO GET WITHIN 2000 FT OF OUR ACFT (HE WAS AT FL310). ATC WARNED US TO DSND THE OTHER 600 FT IMMEDIATELY, WHICH WE DID. I DON'T BELIEVE A VIOLATION WAS FILED BUT IT TAUGHT ME A GOOD LESSON IN USING THE FMC.
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.