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Overspeeding in 737-300

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PostPosted: Sun Mar 02, 2008 12:45 pm    Post subject: Overspeeding in 737-300 Reply with quote

VMO/MMO is the airplane maximum certified operating speed and should not be intentionally exceeded. Airplanes have been flight tested beyond VMO/MMO to ensure smooth pilot inputs will return the airplane safely to the normal flight envelope.

During cruise the typical causes of overspeed events are windshear encounters or high altitude wave activity. Some windshears and wave activity speed changes are beyond the capability of the autothrottle system to prevent short term overspeeds. When correcting an overspeed during cruise at high altitude, avoid reducing thrust to idle which results in slow engine acceleration back to cruise thrust and may result in overcontrolling the airspeed or a loss of altitude. If autothrottle corrections are not satisfactory, temporarily deploying partial speed brakes can assist in reducing speed and avoiding the need for idle thrust.

During descents at or near VMO/MMO, most overspeeds are encountered after the autopilot initiates capture of the VNAV path from above or during a level-off when the speedbrakes were required to maintain the path. In these cases, if the speedbrakes are retracted during the level-off, the airplane can momentarily overspeed. During descents using speedbrakes near VMO/MMO, delay retraction of the speedbrakes until after VNAV path or altitude capture is complete. Crews routinely climbing or descending in windshear conditions may wish to consider a 5 to 10 knot reduction in climb or descent speeds to reduce overspeed occurrences. This will have a minimal effect on fuel consumption and total trip time.

During climb or descent, if VNAV or LVL CHG pitch control is not correcting the overspeed satisfactorily, switching to the V/S mode temporarily may be helpful in controlling speed. In the V/S mode, the selected vertical speed can be adjusted slightly to increase the pitch attitude to help correct the overspeed. As soon as the speed is below VMO/MMO, VNAV or LVL CHG may be re-selected.

Anytime VMO/MMO is exceeded, the maximum airspeed should be noted in the flight log.
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