B737-800 flight crew reported they received an Airspeed Disagree warning followed by other instruments failing so they returned to the departure airport and made an overweight landing.
Synopsis
B737-800 flight crew reported they received an Airspeed Disagree warning followed by other instruments failing so they returned to the departure airport and made an overweight landing.
Narrative
On climb at approximately 16;000 ft. I saw an amber flash on the Primary Flight Display (PFD) but didn't see what it was. I assumed it was the altimeter reminder to go to STD; but noticed we were below 18000 ft. As we approached 18000 ft. and went to standard; the 'AS DISAGREE' illuminated with approximately 8 kts. variance between my PFD and the First Officer's (FO). I continued to fly while I asked the FO to get out the checklist. We ran the QRC and followed up with the QRH and continued the climb while running the initial checklist. As we climbed; the disparity grew greater eventually close to 20 kts. At that point the engine instruments went to '-' s and I told ATC we were returning ZZZ. I briefed the Flight Attendants; Dispatch; ATC and the passengers. I opted to [request priority handling] so we wouldn't have to fly the STAR back in and because it would be an overweight landing. I got a bit task saturated on final. As we were configuring on final; we were gear down and flaps 25 by about 2;000 ft.; but I was late getting fully configured to flaps 30 at approximately 800 ft. due to talking to ATC about our intentions and ZZZ command procedures.It was a very benign event initially but got more intense as we were procedurally directed to turn off the autothrottles and as we continued to climb briefly. Then got distracted and slightly late configuring to final flaps below 1000 ft. In retrospect; I should have let the FO fly since he had the correct info displayed; instead of just making his flight director the master and using that.
Second reporter narrative
Uneventful up this event. During out climbout on the ZZZZZ 3 SID; at approximately 16;000 ft.; I noticed an amber light on the Primary Flight Display (PFD). Knowing it was coming close to our transition altitude; I assumed without verifying that it was our altimeter reminder to set STD. Shortly after; I noticed that we weren't at 18000 ft. and the amber light had momentarily extinguished. When it came back on; realized it was the IAS Disagree light. I was the pilot monitoring so I immediately looked at all three airspeed sources and the Captain and I quickly noticed that his IAS was the one at fault and was showing about 8 kts. faster. I pulled out the QRC and QRH and ran the Airspeed Unreliable checklist and confirmed with the IAS disagree checklist which directed me to the Airspeed Unreliable checklist. The Captain elected to fly while I did the checklists and facilitated the return to ZZZ with ATC. As we continued the climb while working the checklist and our game plan; the error with the IAS grew to as much as 20 kts. When that happened; we also lost some of our engine instruments. This solidified that we needed to return much sooner and elected for an overweight landing rather than burn down fuel. The Captain continued to fly and I ran the QRH and coordinated the [priority] return. As we descended; the IAS and the engine instruments returned to normal indications. The rest of the descent and landing was uneventful. After landing; we precautionary went to a holding pad to have safety vehicles view the aircraft and the brakes to ensure no hot bakes situations existed before returning to the gate. Gave the plane to maintenance and debriefed them. I am not aware of any causal factors that we played a roll in. The event was very benign and only got worse the higher we climbed as we were already running the checklist. After we saw it getting worse; we immediately coordinated for our return and ATC approved a decent which helped alleviate the deviations. After the flight; the Captain and I debriefed the event and both agreed that a transfer of the aircraft to the FO with the good displays would have been a better decision; inline with current SOP. Otherwise; since it was mechanical; there wasn't anything we could do to prevent this from happening again.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.