<< >> NASA ASRS Report 1070645, March 2013

A B737-400 nose gear ground/air sense squat switch failed to the ground mode preventing aircraft pressurization and other systems from functioning so an emergency was declared and the flight returned to the departure airport.

Attributes
ACN	1070645
Time
Date	201303
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	Squat Switch
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Maintenance

Narrative:

Conducting initial operator experience as check airman; first officer [was] pilot flying. Repairs supposedly made from previous day. After departure: autothrottles locked in thr hold. TCAS failed. Mode control panel (MCP) would not allow movement of airspeed bug; engagement of VNAV or LNAV. Cabin began an uncontrollable climb. Manual pressurization made rate of climb worse. Stopped climb at FL180. [We] declared an emergency. Allowed the first officer to make an expedited decent to 10;000 ft after ATC clearance received. ACARS again would not allow diversion message to be sent. Informed flight attendants; company and passengers we were returning to the departure airport. First officer landed after level 1 automation visual approach. Landing was uneventful. Cabin altitude never exceeded 7;000 ft. Crew/passenger O2 not used.

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Original NASA ASRS Text

Title: A B737-400 nose gear ground/air sense squat switch failed to the ground mode preventing aircraft pressurization and other systems from functioning so an emergency was declared and the flight returned to the departure airport.

Narrative: Conducting initial operator experience as Check Airman; First Officer [was] pilot flying. Repairs supposedly made from previous day. After departure: Autothrottles locked in THR HOLD. TCAS failed. Mode Control Panel (MCP) would not allow movement of airspeed bug; engagement of VNAV or LNAV. Cabin began an uncontrollable climb. Manual pressurization made rate of climb worse. Stopped climb at FL180. [We] declared an emergency. Allowed the First Officer to make an expedited decent to 10;000 FT after ATC clearance received. ACARS again would not allow diversion message to be sent. Informed flight attendants; company and passengers we were returning to the departure airport. First Officer landed after level 1 automation visual approach. Landing was uneventful. Cabin altitude never exceeded 7;000 FT. Crew/passenger O2 not used.

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.