B737-700 flight crew experiences airspeed and altitude anomalies on the captain's displays during cl...

Narrative:

I was PF flying in IMC conditions; night during climbout on last leg of pairing for day. Pm in left seat questioned IAS and relayed that he was seeing IAS rollback; altitude fluctuate on pfd display and matched in HUD. PF had associated IAS and altitude disagree annunciations matched on bottom of pfd. Both FMC/CDU screens became degraded. Flight director and map displays were normal. Ex: winds aloft data both on IRS and on FMC were not accurate with report info from PIREPS as relayed by ATC. No master caution illuminated. No cbs popped. Pm discovered eec [in] alt mode on overhead; depressed recall then engine light noted. PF sought VMC conditions with ATC and maintained aircraft control and ATC comms. Pm performed QRH checklist; comms with dispatch and maintenance via phone patch as VHF comm frequencies on release weren't satisfactory. Dispatch recommended ZZZ (close by) and later [continue to destination]. Crew chose to maintain VMC above undercast with good ambient lighting all the way to destination reported with straight-in long runway and VMC conditions. Fuel log with dispatch; IAS and altitude cross checks with ATC were performed while troubleshooting malfunctioning systems. Landed uneventfully at destination; maintained VMC entire portion of leg. System operated normally on descent after descent checklist completion. Air data computer failure of this nature not common. Never experienced kind of indications without associated master caution prior to this event. Felt risk of descending into IMC conditions or congested airport environment with degraded flight instruments could have become compounded further with any more malfunctions of pfd instruments PF was monitoring. Both PF and pm had never been exposed to a similar malfunction in training. Exposing this scenario would be valuable. We discussed [previous] pitot static aircraft problems where PF used HUD as only info available to maintain aircraft control and situational awareness. Pm pfd erroneous indications matched in HUD and eec soft alt mode switchover.

Original NASA ASRS Text

Title: B737-700 flight crew experiences airspeed and altitude anomalies on the Captain's displays during climb. Crew elects to maintain an intermediate altitude in VMC and continue to destination also VMC. During descent the Captain's instruments return to normal.

Narrative: I was PF flying in IMC conditions; night during climbout on last leg of pairing for day. PM in left seat questioned IAS and relayed that he was seeing IAS rollback; altitude fluctuate on PFD display and matched in HUD. PF had associated IAS and ALT disagree annunciations matched on bottom of PFD. Both FMC/CDU screens became degraded. Flight Director and map displays were normal. Ex: winds aloft data both on IRS and on FMC were not accurate with report info from PIREPS as relayed by ATC. No Master Caution illuminated. No CBs popped. PM discovered EEC [in] alt mode on overhead; depressed recall then engine light noted. PF sought VMC conditions with ATC and maintained aircraft control and ATC comms. PM performed QRH checklist; comms with Dispatch and Maintenance via phone patch as VHF comm frequencies on release weren't satisfactory. Dispatch recommended ZZZ (close by) and later [continue to destination]. Crew chose to maintain VMC above undercast with good ambient lighting all the way to destination reported with straight-in long runway and VMC conditions. Fuel log with Dispatch; IAS and ALT cross checks with ATC were performed while troubleshooting malfunctioning systems. Landed uneventfully at destination; maintained VMC entire portion of leg. System operated normally on descent after Descent Checklist completion. Air data computer failure of this nature not common. Never experienced kind of indications without associated Master Caution prior to this event. Felt risk of descending into IMC conditions or congested airport environment with degraded flight instruments could have become compounded further with any more malfunctions of PFD instruments PF was monitoring. Both PF and PM had never been exposed to a similar malfunction in training. Exposing this scenario would be valuable. We discussed [previous] pitot static aircraft problems where PF used HUD as only info available to maintain aircraft control and situational awareness. PM PFD erroneous indications matched in HUD and EEC soft alt mode switchover.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1130775
Time
Date	201311
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Climb
Component
Aircraft Component	Air Data Computer
Person 1
Function	First Officer Pilot Flying
Experience	Flight Crew Last 90 Days 232
Person 2
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 222 Flight Crew Type 14000
Events
Anomaly	Aircraft Equipment Problem Critical

B737-700 flight crew experiences airspeed and altitude anomalies on the captain's displays during climb. Crew elects to maintain an intermediate altitude in VMC and continue to destination also VMC. During descent the captain's instruments return to normal.