Narrative:

During the climbout we entered the ragged overcast between 12;000 and 14;000. At 18;000 ft we adjusted all barometric settings to 29.92. Passing through FL190 while cleared to climb to final cruise altitude of FL340; the ambient weather conditions indicated icing conditions existed and we turned on all engine anti-ice and airfoil anti-ice. (Note: the air data heat switch had been on since before conducting the 'before engine start' checklist back at the gate). No ice accumulation was noted throughout the climb; or anytime during the event. The FMS indicated that we were able to climb to a max altitude of FL345; with optimum altitude of FL340. Our gross weight was 107.4 thousand pounds. While passing through FL325; the pilot not flying (first officer) noted his pli [pitch limit indicator] spontaneously dropping down nearly touching his pfd's pitch indicator. I verified that mine was doing similarly. No abnormal power nor pitch adjustments had been initiated prior to these indications; and the split between the overspeed and underspeed footers had been a nominal 15 KTS; but with the pli's suddenly moving down; the footers on both pfd's rapidly closed to nearly zero KTS. We asked ATC if we could stop our climb at FL320; and they approved. I clicked off the autopilot and we descended from FL325 to FL320 and just as we entered the slight gentle descent; the overspeed and underspeed red footers on both pfd's crossed/overlapped and both stick shakers activated continuously. Indicated airspeed/mach was approximately .74/285; speeds that we knew were comfortably in limits for our gross weight; and with no icing present. We were both scanning all other instruments and ead and FMS pages for other indications; but there were no other alerts; nor warnings; nor fault codes of any nature; anywhere. All cockpit switches were verified to be in their normal position; and all circuit breakers were verified to be in. The aircraft seemed to be flying and responding normally; but the pfd indications and stick shakers were very disconcerting. We asked to descend to FL300; and ATC approved. After entering the next gentle descent; we then asked to descend to FL280. I considered getting low/slow enough to be able to extend the slats to troubleshoot; and possibly eliminate the stall indications that did not correspond with our situation; and which presented themselves with no notice. During the descent to FL280 there were intermittently; periods of a 10-15 KT gap between the overspeed and underspeed footers. Then whenever the pilot not flying would hard tune a speed that was in the middle between the footers; the footers would both close up to closely approach the hard tuned bug; even though we had not changed any power; nor airspeed; yet. No matter where we moved the airspeed bug; the footers seemed to follow it. And; the stick shakers continued to shake. There were never any indications of unusual flight control positions; no unusual throttle positions; no unusual weather (actually; zero icing was present); no changes noted in the FMS weight/balance page data entries. Also; there were no unusual handling characteristics of the aircraft while hand-flying throughout the event. Just prior to level off at FL280 the pilot not flying noted his pli suddenly jumped up approximately 5 degrees anu from his pfd's pitch indicator; and his stick shaker stopped. My captain's pli was still 1-2 degree below my pitch indicator; but my stick shaker seemed to weaken. At FL280 we recycled the air data heat switch. Approximately 1-2 minutes later; which also just coincidentally; corresponded with our leaving IMC conditions and entering clear air; my stick shaker stopped and immediately the overspeed footers on both pfd's went up to 340 KTS; and the underspeed footers descended to well out of view. All indications were now back to normal. There were still zero FMS indications of any faults; and nothing had ever alerted on the ead. After the abnormal situation was no longer present; we exchanged a couple ACARS messages with dispatch and maintenance. I wanted let them know what we just experienced; and if they had any suggestions for us. I also wanted to know if they wanted us to continue to destination; or land/divert at some other facility. I then tried to use the cockpit phone; but it was inoperative (would only dial and continuously 'search' for a signal; and then would automatically disconnect). I then contacted dispatch via VHF phone patch; and they indicated that they preferred that we continue to destination if we were comfortable with the aircraft's condition. The remainder of the flight (cruise at FL280; descent; and approach) were completed uneventfully; and in VMC conditions.

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Original NASA ASRS Text

Title: B717 Captain experienced simultaneous overspeed and underspeed warnings with stick shaker at FL320. A slow descent is initiated and upon departing IMC systems return to normal. Although no probe heat faults were annunciated; ADC probe icing was suspected.

Narrative: During the climbout we entered the ragged overcast between 12;000 and 14;000. At 18;000 FT we adjusted all barometric settings to 29.92. Passing through FL190 while cleared to climb to final cruise altitude of FL340; the ambient weather conditions indicated icing conditions existed and we turned on all engine anti-ice and airfoil anti-ice. (Note: The Air Data Heat switch had been on since before conducting the 'Before Engine Start' checklist back at the gate). No ice accumulation was noted throughout the climb; or anytime during the event. The FMS indicated that we were able to climb to a max altitude of FL345; with optimum altitude of FL340. Our gross weight was 107.4 thousand LBS. While passing through FL325; the pilot not flying (First Officer) noted his PLI [Pitch Limit Indicator] spontaneously dropping down nearly touching his PFD's pitch indicator. I verified that mine was doing similarly. No abnormal power nor pitch adjustments had been initiated prior to these indications; and the split between the overspeed and underspeed footers had been a nominal 15 KTS; but with the PLI's suddenly moving down; the footers on both PFD's rapidly closed to nearly zero KTS. We asked ATC if we could stop our climb at FL320; and they approved. I clicked off the autopilot and we descended from FL325 to FL320 and just as we entered the slight gentle descent; the overspeed and underspeed red footers on both PFD's crossed/overlapped and both stick shakers activated continuously. Indicated airspeed/Mach was approximately .74/285; speeds that we knew were comfortably in limits for our gross weight; and with no icing present. We were both scanning all other instruments and EAD and FMS pages for other indications; but there were no other alerts; nor warnings; nor fault codes of any nature; anywhere. All cockpit switches were verified to be in their normal position; and all circuit breakers were verified to be in. The aircraft seemed to be flying and responding normally; but the PFD indications and stick shakers were very disconcerting. We asked to descend to FL300; and ATC approved. After entering the next gentle descent; we then asked to descend to FL280. I considered getting low/slow enough to be able to extend the slats to troubleshoot; and possibly eliminate the stall indications that did not correspond with our situation; and which presented themselves with no notice. During the descent to FL280 there were intermittently; periods of a 10-15 KT gap between the overspeed and underspeed footers. Then whenever the pilot not flying would hard tune a speed that was in the middle between the footers; the footers would both close up to closely approach the hard tuned bug; even though we had not changed any power; nor airspeed; yet. No matter where we moved the airspeed bug; the footers seemed to follow it. And; the stick shakers continued to shake. There were never any indications of unusual flight control positions; no unusual throttle positions; no unusual weather (actually; zero icing was present); no changes noted in the FMS Weight/Balance page data entries. Also; there were no unusual handling characteristics of the aircraft while hand-flying throughout the event. Just prior to level off at FL280 the pilot not flying noted his PLI suddenly jumped up approximately 5 degrees ANU from his PFD's pitch indicator; and his stick shaker stopped. My Captain's PLI was still 1-2 degree below my pitch indicator; but my stick shaker seemed to weaken. At FL280 we recycled the Air Data Heat switch. Approximately 1-2 minutes later; which also just coincidentally; corresponded with our leaving IMC conditions and entering clear air; my stick shaker stopped and immediately the overspeed footers on both PFD's went up to 340 KTS; and the underspeed footers descended to well out of view. All indications were now back to normal. There were still zero FMS indications of any faults; and nothing had ever alerted on the EAD. After the abnormal situation was no longer present; we exchanged a couple ACARS messages with Dispatch and Maintenance. I wanted let them know what we just experienced; and if they had any suggestions for us. I also wanted to know if they wanted us to continue to destination; or land/divert at some other facility. I then tried to use the cockpit phone; but it was inoperative (would only dial and continuously 'search' for a signal; and then would automatically disconnect). I then contacted Dispatch via VHF phone patch; and they indicated that they preferred that we continue to destination if we were comfortable with the aircraft's condition. The remainder of the flight (cruise at FL280; descent; and approach) were completed uneventfully; and in VMC conditions.

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.