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B737-700 captain suggested his air carrier change priorities in VNAV software on descent profiles; from speed to altitude as the priority.
| Attributes | |
| ACN | 861415 |
| Time | |
| Date | 200911 |
| Environment | |
| Flight Conditions | Mixed |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737-700 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Descent |
| Flight Plan | IFR |
| Person 1 | |
| Function | Captain |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Last 90 Days 252 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy |
Narrative:
The purpose of this report is to call attention to an issue amongst our 737-700 fleet. The issue is in the VNAV software. The software appears to prioritize air speed instead of altitude. The issue is critical because ATC gives us a crossing restrictions; which become a legal obligation for compliance. ATC rarely cares about the speed; but the altitude is a hard violation if not complied with each time. Our software prioritizes speed to save fuel. I would guess; if allowed; the airplane would arrive high perhaps 40% of the time. This would be a violation for the pilots had they not 'pushed' the airplane over in vertical speed instead of VNAV path. I have talked to many of our pilots and head the same story from them. My suggestion is to correct the software to prioritize altitude vs speed.
Original NASA ASRS Text
Title: B737-700 Captain suggested his air carrier change priorities in VNAV software on descent profiles; from speed to altitude as the priority.
Narrative: The purpose of this report is to call attention to an issue amongst our 737-700 fleet. The issue is in the VNAV software. The software appears to prioritize air speed instead of altitude. The issue is critical because ATC gives us a crossing restrictions; which become a legal obligation for compliance. ATC rarely cares about the speed; but the altitude is a hard violation if not complied with each time. Our software prioritizes speed to save fuel. I would guess; if allowed; the airplane would arrive high perhaps 40% of the time. This would be a violation for the Pilots had they not 'pushed' the airplane over in vertical speed instead of VNAV path. I have talked to many of our Pilots and head the same story from them. My suggestion is to correct the software to prioritize altitude vs speed.
Data retrieved from NASA's ASRS site as of April 2012 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.