<< >> NASA ASRS Report 679516, November 2005

B737-400 on climb out at 16000 ft had the left main landing gear extend uncommanded. Returned to departure airport.

Attributes
ACN	679516
Time
Date	200511
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 16000
Environment
Flight Conditions	VMC
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Flight Phase	climbout : initial
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	679516
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : l main gear pos ind other flight crewa other flight crewb
Resolutory Action	flight crew : diverted to alternate flight crew : landed as precaution other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

On climb out through 16000 ft; left main gear extended. Discussed with maintenance control and dispatch. Decision made to return to ZZZ. Uneventful landing and taxi to gate. Callback conversation with reporter revealed the following information: the reporter stated no noise or vibration was felt in the airframe when the left main landing gear extended. The only effect noted was the airplane was out of trim and the main gear indication. The initial maintenance finding of the uncommanded extension was the failure of the uplock mechanism. The mode of failure of the uplock mechanism being mechanical or hydraulic is unknown.

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Original NASA ASRS Text

Title: B737-400 ON CLBOUT AT 16000 FT HAD THE L MAIN LNDG GEAR EXTEND UNCOMMANDED. RETURNED TO DEP ARPT.

Narrative: ON CLBOUT THROUGH 16000 FT; L MAIN GEAR EXTENDED. DISCUSSED WITH MAINT CTL AND DISPATCH. DECISION MADE TO RETURN TO ZZZ. UNEVENTFUL LNDG AND TAXI TO GATE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED NO NOISE OR VIBRATION WAS FELT IN THE AIRFRAME WHEN THE L MAIN LNDG GEAR EXTENDED. THE ONLY EFFECT NOTED WAS THE AIRPLANE WAS OUT OF TRIM AND THE MAIN GEAR INDICATION. THE INITIAL MAINT FINDING OF THE UNCOMMANDED EXTENSION WAS THE FAILURE OF THE UPLOCK MECHANISM. THE MODE OF FAILURE OF THE UPLOCK MECHANISM BEING MECHANICAL OR HYD IS UNKNOWN.

Data retrieved from NASA's ASRS site as of January 2009 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.