The B737 crew had different indications on their flights directors and fmas; and a steady warning ho...

Narrative:

After takeoff with gear up; captains flight director (FD) and flight management annunciations (FMA) showed different indications than what was depicted on first officer instruments. The crew climbed to 10;000 feet per the departure SID. A steady warning horn sounded at level off. There were no amber caution lights; or master caution lights. There was no QRH checklist that addressed the steady warning horn. The crew elected to return to departure airport suspecting a possible landing gear sensing switch. There was no adverse cautions or lights except the steady warning horn. The crew landed 5;000 lbs over max landing weight at approximately 150 feet per minute vertical speed. After rollout the pseu light illuminated (light only active on ground.) the aircraft was taken out of service by maintenance. A built-in test equipment (bite) check of the proximity switch electronic unit (pseu) showed the aircraft electronics had calculated that the flight never climbed above 200 feet AGL. The crew climbed to 10;000 feet indicated before assessing the cause of the steady warning horn. The bite check determined a huge difference in actual altitude versus computed altitude. The steady warning horn was indicating erroneously an altitude deviation. The crew flew the aircraft normally to a landing. After gear down; flaps 15; the warning horn stopped sounding.

Original NASA ASRS Text

Title: The B737 crew had different indications on their flights directors and FMAs; and a steady warning horn sounded at level off. The crew returned to the departure airport; and Maintenance discovered a faulty Proximity Switch Electronic Unit (PSEU).

Narrative: After takeoff with gear up; Captains Flight Director (FD) and Flight Management Annunciations (FMA) showed different indications than what was depicted on First Officer instruments. The crew climbed to 10;000 feet per the departure SID. A steady warning horn sounded at level off. There were no Amber Caution lights; or Master Caution lights. There was no QRH checklist that addressed the steady warning horn. The crew elected to return to departure airport suspecting a possible landing gear sensing switch. There was no adverse cautions or lights except the steady warning horn. The crew landed 5;000 lbs over max landing weight at approximately 150 feet per minute vertical speed. After rollout the PSEU light illuminated (light only active on ground.) The aircraft was taken out of service by Maintenance. A Built-in Test Equipment (BITE) check of the Proximity Switch Electronic Unit (PSEU) showed the aircraft electronics had calculated that the flight never climbed above 200 feet AGL. The crew climbed to 10;000 feet indicated before assessing the cause of the steady warning horn. The BITE check determined a huge difference in actual altitude versus computed altitude. The steady warning horn was indicating erroneously an altitude deviation. The crew flew the aircraft normally to a landing. After gear down; flaps 15; the warning horn stopped sounding.

Data retrieved from NASA's ASRS site 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	1324877
Time
Date	201601
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	Central Warning/Master Caution
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 161.15 Flight Crew Total 22693 Flight Crew Type 1605.98
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy

The B737 crew had different indications on their flights directors and fmas; and a steady warning horn sounded at level off. The crew returned to the departure airport; and maintenance discovered a faulty proximity switch electronic unit (pseu).