B737 flight crew reported a SPD LIM flap on The Captain's PFD in flight. The stick shaker on the Captain's control yoke began to activate repeatedly for 1 to 2 seconds at a time. The flight crew elected to perform an air turn back and precautionary landing at departure airport.
Synopsis
B737 flight crew reported a SPD LIM flap on The Captain's PFD in flight. The stick shaker on the Captain's control yoke began to activate repeatedly for 1 to 2 seconds at a time. The flight crew elected to perform an air turn back and precautionary landing at departure airport.
Narrative
On takeoff roll everything appeared to be working normally. CA's (PM) FD (Flight Director) pitch bar did not work from the beginning of climbout (simply was not there most of the time). Everything on FO's side seemed to be working normally and FO was PF (Pilot Flying). Also for about 95% of the flight the CA's speed tape had a 'SPD LIM' amber flag in the top left corner of the MFD (Multi-Function Flight Display). The CA's airspeed indicator closely matched the FO's and standby's airspeed the entire flight. During climbout we ran the Airspeed Unreadable checklist because we had SPD LIM failure flag on CA's side. We opted to not run the immediate action items because we determined that all airspeed indications on FO and standby were reliable and CA's airspeed exactly matched FO's side and the autopilot and autothrottles and FMS were all working normally.At roughly FL335 the stick shaker went off only on the captain's control column for 1-2 seconds. This was an erroneous warning. The CA's red barber pole would fill the entire visible airspeed range shown on the MFD momentarily while the stick shaker on CA's side (this is what happens every time we had the stick shaker on CA's side activate). The instruments on the FO side worked normally at this time and for the entire flight. We asked for a level off at FL350 (we had been cleared to FL370 at a final altitude). We slowed to Mach.74 to give us more buffer between both stall and overspeed. We then asked for a decent to FL330 to give us even more buffer. The sticker shaker went off for 1-2 seconds roughly 6 times during our cruise phase. FO continued to be PF and we decided to keep the autopilot and auto throttles engaged while CA tried to communicate with company but that did not work. ATC tried several VHF and HF frequencies to help us talk to M/C (Maintenance Control). I was thinking we had plenty of gas and there was a small chance M/C could help me fix the problem. After finally communicating with M/C after a few minutes of trying to reach them with static and bad connections we had no way to fix the problem in the air so we requested priority handling and decided to return to ZZZ. Our only really concern was getting a stick shaker during the decent and approach but neither happened and the decent approach seemed perfectly normal other than CA's FD pitch bar was missing most of the decent and SPD LIM warning flag was there most of the time on only the CA's side.Prior to decent we had a master caution during recall that indicated we also had an Auto Slat Fail. We ran the checklist and determined it was a single stall management/yaw damper computer that had failed. The decent and approach was uneventful other than CA's FD pitch bar was missing most of the decent and SPD LIM warning flag was there most of the time on only the CA's side. FO was the PF and we had vectors to a 10 mile final. We landed at normal landing weight with plenty of fuel to spare. Fire crash and rescue was ready but we did not need assistance. Overall; the plane flew completely normal and this was almost a non event. We never came even close to stalling or overspending. Every stick shaker activation was erroneous. The problem was that the stick shaker activating randomly on the CA control column was a nuisance and we decided the safer; more conservative; choice was to return to ZZZ1 which is a familiar field with no mountains and Company Maintenance. I was concerned that if the problem degraded or we experienced another malfunction we would be putting ourselves in a more difficult situation so I decided that returning to ZZZ1 was the appropriate action. We wrote an ELB reports for the appropriate discrepancies. We went to a new airplane in ZZZ1 and got our passengers to ZZZ2 3 hours and 50 minutes late.
Second reporter narrative
On Takeoff as the pilot flying we departed using gusty takeoff procedures. On climb out due to busy ATC instructions and the work load of both pilots I put the autopilot on early at around 5;000-6;000 feet. Unknown to me the Captain then informed me that his flight director was not functioning correctly by not showing the horizontal bar. The FO's side flight director was functioning correctly. We continued our climb out at this point as there were no other adverse indications. We also noticed above the CA's speed tape; a SPD LIM amber flag appeared above the speed awareness tape on the left corner of the PFD (Primary Flight Display). At this point the CA started to trouble shoot the problem while I took the radios and continued flying. We noted that the FO's PFD and airspeed indications were functioning correctly and also the CA's airspeed matched the FO's. We discussed returning to ZZZ at this point also; but the CA; after running the appropriate checklist wanted to check with Maintenance Control to determine if there was a fix that he was not seeing before diverting back to ZZZ. Passing through FL335 the stick shaker went off on the CA's control column for a couple of seconds. The FO's side did not get the shaker. Were then asked ATC to descend back down to FL330. It was noted again that the airspeed on both sides was exactly the same through that event and the only reason the shaker went off on the CA's side was because of erroneous speed awareness tape with the red barber pole filling the entire airspeed range on the PFD momentarily; leading to the shaker. We again both noted that the actual airspeed on both sides was the same and the FO's side was completely normal and therefore; although distracting; a completely erroneous stick shaker. However; at this point; we made the decision to divert back to ZZZ. The stick shaker went off erroneously maybe 5-6 times on the CA's side during this time. The CA during this time was also trying to get a hold of M/C but without effective communications. We then turned back towards ZZZ and request priority. We asked to be cleared direct to ZZZ and to set up for about a 15 mile final for Runway XR. The rest of the flight was uneventful. After swapping aircraft we continued onto Honduras a few hours later.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.