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B747 flight crew reported an inability to maintain M.85 after climbing to FL370 even though the FMC and flight plan indicated it as acceptable. The crew returned to FL350 and suspected the aircraft may have been substantially heavier than advertised.
| Attributes | |
| ACN | 1298894 |
| Time | |
| Date | 201509 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | KZAK.ARTCC |
| State Reference | HI |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B747 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Cruise |
| Flight Plan | IFR |
| Person 1 | |
| Function | Pilot Not Flying First Officer |
| Experience | Flight Crew Last 90 Days 218 Flight Crew Total 13722 Flight Crew Type 8885 |
| Person 2 | |
| Function | Pilot Not Flying Captain |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Last 90 Days 235 Flight Crew Total 8584 Flight Crew Type 5330 |
| Events | |
| Anomaly | Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Weight And Balance Deviation - Speed All Types |
Narrative:
Climbed aircraft from FL350 to FL370 using VNAV. Aircraft leveled off; .85M; shortly afterwards airspeed started to decrease; throttles advanced by auto-throttle; airspeed kept decreasing; manually fire walled throttles. At max EPR; airspeed kept decreasing; as airspeed dropped below min maneuver speed and continued to decrease; I disconnected autopilot and lowered the nose slightly below the horizon. Airspeed stabilized at max thrust and began to increase as we descended. Returned to FL370 at .85M. With autopilot on; aircraft still could not hold airspeed at max EPR. Requested a descent to FL350. Descended and had no problem at FL350. At the time the aircraft weight was 635.8 VNAV max alt 389; opt alt 358. Flt plan had us going up earlier but delayed an hour due to better winds at 350. Flight conditions were smooth; max deviation from assigned FL370 was 200 feet low; airspeed went 20 knots below min maneuver speed before recovering. At FL350 .85M EPR required to maintain airspeed appeared to be higher than normal for those conditions. 3 flight attendants reported minor injuries. They were in the middle of a crew change when the event occurred; moving about in the crew rest area.suspect the aircraft was much heavier than the weights given us at departure.
Original NASA ASRS Text
Title: B747 flight crew reported an inability to maintain M.85 after climbing to FL370 even though the FMC and flight plan indicated it as acceptable. The crew returned to FL350 and suspected the aircraft may have been substantially heavier than advertised.
Narrative: Climbed aircraft from FL350 to FL370 using VNAV. Aircraft leveled off; .85M; shortly afterwards airspeed started to decrease; throttles advanced by auto-throttle; airspeed kept decreasing; manually fire walled throttles. At max EPR; airspeed kept decreasing; as airspeed dropped below min maneuver speed and continued to decrease; I disconnected autopilot and lowered the nose slightly below the horizon. Airspeed stabilized at max thrust and began to increase as we descended. Returned to FL370 at .85M. With autopilot on; aircraft still could not hold airspeed at max EPR. Requested a descent to FL350. Descended and had no problem at FL350. At the time the aircraft weight was 635.8 VNAV max alt 389; opt alt 358. Flt plan had us going up earlier but delayed an hour due to better winds at 350. Flight conditions were smooth; max deviation from assigned FL370 was 200 feet low; airspeed went 20 knots below min maneuver speed before recovering. At FL350 .85M EPR required to maintain airspeed appeared to be higher than normal for those conditions. 3 flight attendants reported minor injuries. They were in the middle of a crew change when the event occurred; moving about in the crew rest area.Suspect the aircraft was much heavier than the weights given us at departure.
Data retrieved from NASA's ASRS site 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.