CE414 pilot reports landing gear collapse as the aircraft is taxiing onto the runway for takeoff.

Attributes
ACN	734023
Time
Date	200705
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : hya.airport
State Reference	MA
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Chancellor 414A & C414
Operating Under FAR Part	Part 91
Flight Phase	ground : taxi
Flight Plan	VFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : atp
Experience	flight time total : 12000 flight time type : 250
ASRS Report	734023
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : unable
Consequence	other other
Supplementary
Problem Areas	Maintenance Human Performance Aircraft
Primary Problem	Aircraft

Narrative:

After a normal preflight and run-up I taxied to runway 24 for departure. After being cleared for takeoff; I began to taxi onto the runway; at which time the left landing gear collapsed and the left wing of the aircraft struck the ground; as did the left propeller. After the gear collapsed; all 3 landing gear indicators were indicating that the gear were still down and locked; suggesting some kind of mechanical failure of the landing gear system. I notified the control tower who contacted the FAA and massachusetts aeronautics commission; as well as local emergency personnel. Callback conversation with reporter revealed the following information: the CE414 landing gear is hydraulically actuated with the pump running when the gear is selected down. The pump stops running when a micro switch; on each gear; closes as the gear locks down. One switch had failed closed on the last landing; allowing the pump to stop running prior to that gear reaching the locked position. The gear held as long as no side loads were imposed on that gear. Side loads were imposed as the aircraft was taxied into position. Post flight revealed that both main landing gear actuators had significant quantities of water in them and was responsible for the micro switch failure. The right actuator was so corroded as to be not repairable.

Original NASA ASRS Text

Title: CE414 PILOT REPORTS LANDING GEAR COLLAPSE AS THE ACFT IS TAXIING ONTO THE RWY FOR TKOF.

Narrative: AFTER A NORMAL PREFLT AND RUN-UP I TAXIED TO RWY 24 FOR DEP. AFTER BEING CLRED FOR TKOF; I BEGAN TO TAXI ONTO THE RWY; AT WHICH TIME THE L LNDG GEAR COLLAPSED AND THE L WING OF THE ACFT STRUCK THE GND; AS DID THE L PROP. AFTER THE GEAR COLLAPSED; ALL 3 LNDG GEAR INDICATORS WERE INDICATING THAT THE GEAR WERE STILL DOWN AND LOCKED; SUGGESTING SOME KIND OF MECHANICAL FAILURE OF THE LNDG GEAR SYS. I NOTIFIED THE CTL TWR WHO CONTACTED THE FAA AND MASSACHUSETTS AERONAUTICS COMMISSION; AS WELL AS LCL EMER PERSONNEL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CE414 LANDING GEAR IS HYDRAULICALLY ACTUATED WITH THE PUMP RUNNING WHEN THE GEAR IS SELECTED DOWN. THE PUMP STOPS RUNNING WHEN A MICRO SWITCH; ON EACH GEAR; CLOSES AS THE GEAR LOCKS DOWN. ONE SWITCH HAD FAILED CLOSED ON THE LAST LANDING; ALLOWING THE PUMP TO STOP RUNNING PRIOR TO THAT GEAR REACHING THE LOCKED POSITION. THE GEAR HELD AS LONG AS NO SIDE LOADS WERE IMPOSED ON THAT GEAR. SIDE LOADS WERE IMPOSED AS THE ACFT WAS TAXIED INTO POSITION. POST FLIGHT REVEALED THAT BOTH MAIN LANDING GEAR ACTUATORS HAD SIGNIFICANT QUANTITIES OF WATER IN THEM AND WAS RESPONSIBLE FOR THE MICRO SWITCH FAILURE. THE RIGHT ACTUATOR WAS SO CORRODED AS TO BE NOT REPAIRABLE.

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.