Date: 201811
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Aircraft: B737-400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Initial Climb; Takeoff / Launch
Airspace: Class D ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Autothrottle/Speed Control
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Time Pressure; Situational Awareness
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Speed All Types
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Took Evasive Action; Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During takeoff; [I] noticed First Officer did not call 80 knots. At that time; the auto-throttles disconnected and the First Officer announced that there was an airspeed disagreement. [It was] concluded that Captain's airspeed was correct and continued the takeoff. During initial climb; the stick shaker activated and I flew the aircraft using pitch and power indications. We notified ATC that we had a malfunction and returned immediately to the airport. Completed all checklists and set up for landing RWY XXL at ZZZ and landed without incident.Aircraft equipment failure of pitot static or air data computer.


Second narrative: I was the Pilot Monitoring and First Officer. During my preflight; I did not notice any damage to any of the pitot tubes. Due to the location of the pitot tubes; I cannot look down them to check for blockages; but I did not notice any obvious signs of damage or blockage. We prepared for the flight normally and taxied out for takeoff. During the takeoff roll; as Pilot Monitoring; it was my job to set the thrust. The autothrottles didn't quite get the thrust setting to the desired takeoff thrust setting; so I spent a few seconds tweaking the thrust setting and verifying the N1 gauges and the FMC. Once the thrust was set; I called 'Thrust set;' and my eyes went to my airspeed tape. It indicated about 60 KIAS and was rising in what initially appeared to be a normal fashion. At that time; the Captain called '80 knots' and simultaneously the auto throttle disconnected. When this happened; my eyes went to the flashing red autothrottle light; then to the autothrottle switch; then to the N1 gauges. The N1 gauges still indicated normal takeoff thrust; so I reached up and tried to reset the autothrottle switch. (Sometimes the autothrottle will be inadvertently disconnected and can be reset.) The autothrottle switch would not reset and when my eyes went back to my airspeed tape; it indicated that we were not yet to V1; but the Captain called V1. That is when I looked at his airspeed indicator and realized that our two airspeed indicators did not match; which is why he had been beating me to the calls. Mine was indicating about 30 knots less than the Captain's. I quickly looked at the standby airspeed indicator and it matched the Captain's. I said 'your airspeed is correct;' and we rotated normally and climbed out; as we were already at too high of a speed to reject. As our angle of attack increased on the climbout; the difference between our two airspeed indicators got much worse. While his was increasing as we accelerated in the climb; mine was decreasing as we pitched up; and at one point mine was indicating at least 50-60 knots less than his; and the stick shaker activated. I cross-checked with the standby again; and it still matched the Captain's; and was confirmed by our current flight conditions; pitch and power settings. I reiterated 'your airspeed is correct' and the Captain continued hand flying. We retracted the flaps on schedule and I contacted Departure and advised that we would need to return to ZZZ. ATC asked if we were declaring; and after a short discussion with the Captain; we decided that since we had positive control of the aircraft and we did not need emergency services that we would not declare. In hindsight; I should've used the phrase PAN-PAN to relay that we had an urgent situation that required priority; but wasn't an emergency. ATC understood what we needed though; and they provided us vectors back to the ILS XXL immediately. When we were in level flight; my airspeed came back up to within 30 knots of the Captain's. We completed all checklists and came back around and landed without incident. (We were well under max landing weight.) I noticed that throughout the event; my analog airspeed indicator and my digital airspeed tape both matched; and were both lower than the Captain's analog and digital indicators as well as the standby. I also noticed that except for the climb-out with the higher angle of attack; my airspeed indicators behaved somewhat normally; increasing as we accelerated and decreasing when we decelerated which made the problem hard to identify at first; but they were consistently indicating much slower than the others. Upon landing I conducted a post-flight inspection; and again noticed no irregularities in the areas of the pitot tubes. Ops; [Dispatch] and MX were all notified. The cause of this event was the erroneous airspeed indications on the First Officer side. There are many things that could cause this including a pitot tube blockage; a leak in the pitot static system; or a bad ADC.If it is determined that a partial blockage was to blame; then I would suggest that we have maintenance personnel install pitot tube covers during long layovers. I wish I could've recognized the problem early enough to do a low speed reject; but that didn't happen. When we did recognize the problem; I think we handled it very well. I wish I could've been a little clearer in my communications with ATC; but ATC handled the situation very well too.


Synopsis: B737 flight crew reported an airspeed disagreement on takeoff roll and activation of the stick shaker on climbout.