B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 398; Flight Crew Type 21000
Workload; Training / Qualification; Situational Awareness; Human-Machine Interface; Distraction; Confusion; Physiological - Other
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Flight Crew Became Reoriented; General Maintenance Action
Weather
The purpose of this report is to describe a turbulence encounter which initially produced a momentary MMO exceedence (less than .84 Mach); followed almost immediately by a rapid decrease in airspeed (to stick shaker activation) and subsequent altitude deviation of minus 300 FT from cleared flight level. I was the Captain and pilot flying; cruising at FL370 overhead a Southwestern City at the time of the turbulence encounter. My First Officer (pilot not flying) was busy running the radar and communicating with Center in an effort to avoid the widespread buildups along our route. With the passengers and flight attendants seated; we were deviating around the last ridge of buildups (in and out of IMC) when we observed a towering cumulus directly in our path that didn't appear on radar. As we entered the cloud; we encountered moderate turbulence resulting in an instantaneous MMO exceedence of several seconds. I immediately disengaged both the autopilot and autothrottles; and retarded thrust levers to idle. As we came out of clacker; I advanced the thrust levers steadily as the engines slowly re-spooled; and it appeared for a few moments that our airspeed was stabilizing. However; a few seconds later we experienced a rapid airspeed decrease accompanied by stick shaker; and I responded by advancing the thrust levers to emergency thrust and lowering the nose to keep the airspeed within the yellow maneuvering margin. By this time; we had descended to 36;700 FT; at which point my First Officer advised ATC of our turbulence encounter and altitude deviation. The entire event was of short duration from onset to recovery. Dispatch was notified via ACARS of the MMO exceedence and RVSM airspace deviation. Follow-up with the flight attendants revealed no injuries to passengers or crew. Upon landing and not receiving an ACARS exceedence message; I made an Info Only write-up appropriate for this level of MMO exceedence and notified both Dispatch and Maintenance Control. We over-relied on the radar in this case and underestimated the severity of turbulence associated with cloud tops that were not producing radar returns.
[Narrative #2 contained no additional information]
A B737-700 encountered moderate turbulence in a cloud top which resulted in an MMO exceedence followed by rapid airspeed decrease and a 300 FT altitude loss in order to maintain airspeed.