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B757-200 crew was required to descend the aircraft without clearance to keep the airspeed from getting too slow when encountering windshear at FL400.
| Attributes | |
| ACN | 553936 |
| Time | |
| Date | 200207 |
| Day | Mon |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| State Reference | AB |
| Altitude | msl bound lower : 39700 msl bound upper : 40000 |
| Environment | |
| Flight Conditions | VMC |
| Weather Elements | Turbulence Windshear |
| Light | Dusk |
| Aircraft 1 | |
| Controlling Facilities | artcc : czeg.artcc tower : dca.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B757-200 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level cruise : enroute altitude change |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 175 flight time total : 14000 flight time type : 8500 |
| ASRS Report | 553936 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter other non adherence : company policies non adherence : published procedure other anomaly other anomaly other |
| Independent Detector | other flight crewa other flight crewb |
| Resolutory Action | controller : issued new clearance flight crew : regained aircraft control flight crew : declared emergency other |
| Supplementary | |
| Problem Areas | Weather Flight Crew Human Performance Aircraft |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
I initiated an emergency descent out of FL400 because of decreasing airspeed and the inability of the aircraft to accelerate through a wind shift. Contributing factors: 1) aircraft was at FL400 to avoid clear air turbulence. 2) aircraft was near its maximum altitude (FL404). 3) first officer and I were discussing the aftermath of a medical emergency on board and were distraction from the instruments. 4) aircraft entered an abrupt wind shift from about 245 degrees, 49 KTS to about 190 degrees, 20 KTS. 5) aircraft mach decreased to .72 mach and would not accelerate. 6) we called edmonton center to get FL380, but there was no response from the controller. 7) I then declared an emergency 'in the blind' and started the aircraft down. At about FL397, edmonton center approved our descent to FL380 and said there was 'no problem.' mach and airspeed were back to normal at about FL395.
Original NASA ASRS Text
Title: B757-200 CREW WAS REQUIRED TO DSND THE ACFT WITHOUT CLRNC TO KEEP THE AIRSPD FROM GETTING TOO SLOW WHEN ENCOUNTERING WINDSHEAR AT FL400.
Narrative: I INITIATED AN EMER DSCNT OUT OF FL400 BECAUSE OF DECREASING AIRSPD AND THE INABILITY OF THE ACFT TO ACCELERATE THROUGH A WIND SHIFT. CONTRIBUTING FACTORS: 1) ACFT WAS AT FL400 TO AVOID CLR AIR TURB. 2) ACFT WAS NEAR ITS MAX ALT (FL404). 3) FO AND I WERE DISCUSSING THE AFTERMATH OF A MEDICAL EMER ON BOARD AND WERE DISTR FROM THE INSTS. 4) ACFT ENTERED AN ABRUPT WIND SHIFT FROM ABOUT 245 DEGS, 49 KTS TO ABOUT 190 DEGS, 20 KTS. 5) ACFT MACH DECREASED TO .72 MACH AND WOULD NOT ACCELERATE. 6) WE CALLED EDMONTON CTR TO GET FL380, BUT THERE WAS NO RESPONSE FROM THE CTLR. 7) I THEN DECLARED AN EMER 'IN THE BLIND' AND STARTED THE ACFT DOWN. AT ABOUT FL397, EDMONTON CTR APPROVED OUR DSCNT TO FL380 AND SAID THERE WAS 'NO PROB.' MACH AND AIRSPD WERE BACK TO NORMAL AT ABOUT FL395.
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.